FAA-8083-31 amt_airframe_vol1

300 Wire size 26 24 22 20 18 16 14 12 10 Temperature difference (wire rating minus the ambient °C) 200 1 NOT TO BE USED AS SINGLE WIRE 11 100 90 80 70 60 50 40 30 5 6 7 8 9 10 20 30 40 50 60 70 80 90 100 4 Wire size 8 300 64 2 1 1/0 2/0 3/0 4/0 Temperature difference (wire rating minus the ambient °C) 200 100 90 80 70 60 50 40 30 50 60 70 80 90 100 200 300 400 500 600 700 800 900 1000 40 Current Amperes Figure 9-117. Single copper wire in free air. 9-73

Current derating factor 1.00 Bundle loading percent 20 40 60 80 100 0.90 0.80 3 5 7 9 11 13 15 17 19 21 23 25 27 29 31 33 35 37 39 41 0.70 0.60 Number of wires in bundle 0.50 0.40 0.30 0.20 0.10 0 1 Figure 9-118. Bundle derating curve. 1.00 0.95 Current derating factor 0.90 0.85 0.80 0.75 0.70 10 20 30 40 50 60 70 80 90 100 0 Altitude (x1,000 feet) Figure 9-119. Altitude derating curve. 9-74

current should not exceed 55.2 A, size 22 wire should not Step 4—Refer to the altitude derating curve of Figure 9-119, carry more than 7.2 amps and size 20 wire should not carry look for sea level and 20,000 feet (on the horizontal axis) more than 9.6 amps. since these are the conditions at which the load is carried. The wire must be derated by a factor of 1.0 and 0.91, respectively. Step 6—Determine the actual circuit current for each wire in Step 5—Derate the size 12 in a bundle ratings by multiplying the bundle and for the whole bundle. If the values calculated 29.2 amps at sea level and 25.4 amps at 20,000 feet by 1.0 in step 5 are exceeded, select the next larger size wire and and 0.91, respectively to obtain 29.2 amps and 23.1 amps. repeat the calculations. The total bundle capacity at sea level and 25 °C ambient temperature is 29.2 × 12=350.4 amps. At 20,000 feet and Example 2 60 °C ambient temperature, the bundle capacity is 23.1 × Assume a harness (open or braided), consisting of 12 size 12=277.2 amps. Each size 12 wire can carry 29.2 amps at 12, 200 °C rated copper wires, is operated in an ambient sea level, 25 °C ambient temperature or 23.1 amps at 20,000 temperature of 25 °C at sea level and 60 °C at a 20,000- feet and 60 °C ambient temperature. foot altitude. All 12 wires are operated at or near their maximum capacity. Step 1—Refer to the single wire in free air curve in Step 6—Determine the actual circuit current for each wire Figure 9-117, determine the temperature difference of the in the bundle and for the bundle. If the values calculated wire to determine free air ratings. Since the wire is in ambient in Step 5 are exceeded, select the next larger size wire and temperature of 25 °C and 60 °C and is rated at 200 °C, the repeat the calculations. temperature differences are 200 °C – 25 °C = 175 °C and 200 °C – 60 °C = 140 °C, respectively. Follow the 175 °C Allowable Voltage Drop and the 140 °C temperature difference lines on Figure 9-116 until each intersects wire size line. The free air ratings of size The voltage drop in the main power wires from the generation 12 are 68 amps and 59 amps, respectively. source or the battery to the bus should not exceed 2 percent of the regulated voltage when the generator is carrying rated Step 2—Refer to the bundling derating curves in Figure 9-120. current or the battery is being discharged at the 5-minute rate. The 100 percent curve is selected because we know all 12 The tabulation shown in Figure 9-121 defines the maximum wires are carrying full load. Find 12 (on the horizontal acceptable voltage drop in the load circuits between the bus axis) since there are 12 wires in the bundle and determine and the utilization equipment ground. a derating factor of 0.43 (on the vertical axis) from the 100 percent curve. Nominal system Allowable voltage Intermittent voltage drop during operation Wire Continuous duty current Max. size (amp) wires in bundles, groups, resistance 14 continuous operation 1 ohms/1000feet 28 2 #8 or harnesses or conduits 115 0.5 8 #6 200 1 14 #4 Wire conductor temperature rating 4 #2 7 #1 #0 @ 105 °C @ 150 °C @ 20 °C Figure 9-121. Tabulation chart (allowable voltage drop between #00 bus and utilization equipment ground). #000 30 45 1.093 #0000 40 61 0.641 The resistance of the current return path through the aircraft structure is generally considered negligible. However, this 54 82 0.427 is based on the assumption that adequate bonding to the structure or a special electric current return path has been 76 113 0.268 provided that is capable of carrying the required electric current with a negligible voltage drop. To determine circuit 90 133 0.214 resistance, check the voltage drop across the circuit. If the voltage drop does not exceed the limit established by the 102 153 0.169 aircraft or product manufacturer, the resistance value for the circuit may be considered satisfactory. When checking a 117 178 0.133 circuit, the input voltage should be maintained at a constant value. Figures 9-122 and 9-123 show formulas that may be 138 209 0.109 used to determine electrical resistance in wires and some typical examples. 163 248 0.085 Figure 9-120. Current-carrying capacity and resistance of aluminum wire. Step 3—Derate the size #12 free air ratings by multiplying 68 amps and 61 amps by 0.43 to get 29.2 amps and 25.4 amps, respectively. 9-75

Voltage Run Circuit Wire Check calculated To meet the two requirements for selecting the correct wire drop lengths current size voltage drop (VD) size using Figure 9-116, the following must be known: (amps) from = (resistance/feet) (feet) chart (length) (current) 1. The wire length in feet. No. 6 1 107 20 No. 4 VD = (0.00044 ohms/feet) 2. The number of amperes of current to be carried. No. 12 0.5 90 20 No. 14 (107 x 20) = 0.942 3. The allowable voltage drop permitted. 4 88 20 VD = (0.00028 ohms/feet) 4. The required continuous or intermittent current. 7 100 20 (90 x 20) = 0.504 5. The estimated or measured conductor temperature. VD = (0.00202 ohms/feet) 6. Is the wire to be installed in conduit and/or bundle? (88 x 20) = 3.60 7. Is the wire to be installed as a single wire in free air? VD = (0.00306 ohms/feet) Example A. Find the wire size in Figure 9-116 using the following known (100 x 20) = 6.12 information: Figure 9-122. Determining required tin-plated copper wire size 1. The wire run is 50 feet long, including the ground and checking voltage drop. wire. Maximum Wire Circuit Maximum Check calculated 2. Current load is 20 amps. Voltage size current wire run voltage drop (VD) (amps) length = (resistance/feet) 3. The voltage source is 28 volts from bus to equipment. drop (feet) (length) (current) 4. The circuit has continuous operation. 1 No. 10 20 39 VD = (0.00126 ohms/feet) 0.5 --- 19.5 5. Estimated conductor temperature is 20 °C or less. The 4 --- 156 (39 x 20) = 0.98 scale on the left of the chart represents maximum wire 7 --- 273 length in feet to prevent an excessive voltage drop for VD = (0.00126 ohms/feet) a specified voltage source system (e.g., 14V, 28V, 115V, 200V). This voltage is identified at the top of (19.5 x 20) = 0.366 scale and the corresponding voltage drop limit for continuous operation at the bottom. The scale (slant VD = (0.00126 ohms/feet) lines) on top of the chart represents amperes. The scale at the bottom of the chart represents wire gauge. (156 x 20) = 3.93 VD = (0.00126 ohms/feet) (273 x 20) = 6.88 Figure 9-123. Determining maximum tin-plated copper wire length and checking voltage drop. The following formula can be used to check the voltage Step 1—From the left scale, find the wire length 50 feet under drop. The resistance/ft can be found in Figures 9-122 and the 28V source column. 9-123 for the wire size. Calculated Voltage drop (VD) = resistance/ft × length × Step 2—Follow the corresponding horizontal line to the right current until it intersects the slanted line for the 20-amp load. Electric Wire Chart Instructions Step 3—At this point, drop vertically to the bottom of the chart. The value falls between No. 8 and No. 10. Select To select the correct size of electrical wire, two major the next larger size wire to the right, in this case No. 8. requirements must be met: This is the smallest size wire that can be used without exceeding the voltage drop limit expressed at the bottom of 1. The wire size should be sufficient to prevent an the left scale. This example is plotted on the wire chart in excessive voltage drop while carrying the required Figure 9-116. Use Figure 9-116 (top) for continuous flow current over the required distance. [Figure 9-121] and Figure 9-116 (bottom) for intermittent flow. 2. The size should be sufficient to prevent overheating of Example B. the wire carrying the required current. (See Maximum Find the wire size in Figure 9-116 using the following known Operating Temperature earlier in this chapter for information: computing current carrying capacity methods.) 1. The wire run is 200 feet long, including the ground wire. 9-76

2. Current load is 10 amps. identified. Wires 3 to 7 inches in length should be identified approximately at the center. Added identification marker 3. The voltage source is 115 volts from bus to equipment. sleeves should be located so that ties, clamps, or supporting devices need not be removed to read the identification. The 4. The circuit has intermittent operation. wire identification code must be printed to read horizontally (from left to right) or vertically (from top to bottom). The Step 1—From the left scale, find the wire length of 200 feet two methods of marking wire or cable are as follows: under the 115V source column. 1. Direct marking is accomplished by printing the cable’s Step 2—Follow the corresponding horizontal line to the right outer covering. [Figure 9-124B] until it intersects the slanted line for the 10 amp load. 2. Indirect marking is accomplished by printing a heat- Step 3—At this point, drop vertically to the bottom of the shrinkable sleeve and installing the printed sleeve on chart. The value falls between No. 16 and No. 14. Select the the wire or cables outer covering. Indirectly-marked next larger size wire to the right—in this case, No. 14. This is wire or cable should be identified with printed the smallest size wire that can be used without exceeding the sleeves at each end and at intervals not longer than voltage drop limit expressed at the bottom of the left scale. 6 feet. [Figure 9-125] The individual wires inside a cable should be identified within 3 inches of their Wire Identification termination. [Figure 9-124A] The proper identification of electrical wires and cables with their circuits and voltages is necessary to provide Types of Wire Markings safety of operation, safety to maintenance personnel, and The preferred method is to mark directly on the wire without ease of maintenance. All wire used on aircraft must have causing insulation degradation. Teflon-coated wires, shielded its type identification imprinted along its length. It is wiring, multiconductor cable, and thermocouple wires common practice to follow this part number with the five usually require special sleeves to carry identification marks. digit/letter Commercial and Government Entity (CAGE) There are some special wire marking machines available that code identifying the wire manufacturer. You can identify can be used to stamp directly on the type wires mentioned the performance capabilities of existing installed wire you above. Whatever method of marking is used, the marking need to replace, and avoid the inadvertent use of a lower should be legible and the color should contrast with the wire performance and unsuitable replacement wire. insulation or sleeve. Placement of Identification Markings Several different methods can be used to mark directly on the wire: hot stamp marking, ink jet printers, and laser jet Identification markings should be placed at each end of the printers. [Figure 9-126] The hot stamp method can damage wire and at 15-inch maximum intervals along the length the insulation of a newer type of wire that utilizes thin of the wire. Wires less than 3 inches in length need not be 3 inches max White lue hite e W Blu B Orange 15 inches max 3 inches H215A20 Orange H215A20 WHITE H217A20 ORANGE H246A20 BLUE 9-77 3 inches max 3 inches max A. Multiple wires in a sleeve 3 inches 15 inches 15 inches H215A20 H215A20 B. Single wire without sleeve Figure 9-124. Wire markings for single wire without sleeve.

3 inches 6 ft 3 inches used as part of a cable, the identification sleeve should specify 6 ft which color is associated with each wire identification code. H215A20 H215A20 Identification sleeves are normally used for identifying the H215A20 following types of wire or cable: unjacketed shielded wire, thermocouple wire, coaxial cable, multiconductor cable, Figure 9-125. Spacing of printed identification marks (indirect and high temperature wire. In most cases, identification tape marking). can be used in place of sleeving. For sleeving exposed to high temperatures (over 400 °F), materials, such as silicone fiberglass, should be used. Polyolefin sleeving should be used in areas where resistance to solvent and synthetic hydraulic fluids is necessary. Sleeves may be secured in place with cable ties or by heat shrinking. The identification sleeving for various sizes of wire is shown in Figure 9-128. Wire size Sleeving size AN # AL # No. Nominal ID (inch) Figure 9-126. Laser wire printer. 24 8 12 0.085 22 6 11 0.095 insulators. Fracture of the insulation wall and penetration to 20 4 10 0.106 the conductor of these materials by the stamping dies have 18 2 0.118 occurred. Later in service, when these openings have been 16 1 9 0.113 wetted by various fluids or moisture, serious arcing and 14 0 8 0.148 surface tracking have damaged wire bundles. 12 00 7 0.166 10 000 6 0.208 Identification sleeves can be used if the direct marking on 8 0000 4 0.263 the wire is not possible. [Figure 9-127] 6 2 0.330 4 0 0.375 2 3/8 inch 0.500 1 1/2 inch 0.500 0 1/2 inch 0.625 00 5/8 inch 0.625 000 5/8 inch 0.750 0000 3/4 inch 0.750 3/4 inch Figure 9-128. Recommended size of identification sleeving. Wire Installation and Routing Open Wiring Interconnecting wire is used in point-to-point open harnesses, normally in the interior or pressurized fuselage, with each wire providing enough insulation to resist damage from handling and service exposure. Electrical wiring is often installed in aircraft without special enclosing means. This practice is known as open wiring and offers the advantages of ease of maintenance and reduced weight. Figure 9-127. Alternate method of identifying wire bundles. Wire Groups and Bundles and Routing Flexible sleeving, either clear or opaque, is satisfactory for Wires are often installed in bundles to create a more organized general use. When color-coded or striped component wire is installation. These wire bundles are often called wire harnesses. Wire harnesses are often made in the factory or 9-78

electrical shop on a jig board so that the wire bundles could be Slack in Wire Bundles preformed to fit into the aircraft. [Figure 9-129] As a result, each harness for a particular aircraft installation is identical Wiring should be installed with sufficient slack so that in shape and length. The wiring harness could be covered by bundles and individual wires are not under tension. Wires a shielding (metal braid) to avoid EMI. Grouping or bundling connected to movable or shock-mounted equipment should certain wires, such as electrically unprotected power wiring have sufficient length to allow full travel without tension and wiring going to duplicate vital equipment, should be on the bundle. Wiring at terminal lugs or connectors should avoided. Wire bundles should generally be less than 75 wires, have sufficient slack to allow two reterminations without or 11⁄2 to 2 inches in diameter where practicable. When several replacement of wires. This slack should be in addition to wires are grouped at junction boxes, terminal blocks, panels, the drip loop and the allowance for movable equipment. etc., identity of the groups within a bundle can be retained. Normally, wire groups or bundles should not exceed 1⁄2 inch deflection between support points. [Figure 9-130] This measurement may be exceeded if there is no possibility of the wire group or bundle touching a surface that may cause abrasion. Sufficient slack should be provided at each end to permit replacement of terminals and ease of maintenance; prevent mechanical strain on the wires, cables, junctions, and supports; permit free movement of shock- and vibration- mounted equipment; and allow shifting of equipment, as necessary, to perform alignment, servicing, tuning, removal of dust covers, and changing of internal components while installed in aircraft. Twisting Wires When specified on the engineering drawing, or when accomplished as a local practice, parallel wires must sometimes be twisted. The following are the most common examples: 1. Wiring in the vicinity of magnetic compass or flux valve 2. Three-phase distribution wiring 3. Certain other wires (usually radio wiring) as specified on engineering drawings Figure 9-129. Cable harness jig board. Twist the wires so they lie snugly against each other, making approximately the number of twists per foot as shown in Figure 9-131. Always check wire insulation for damage after twisting. If the insulation is torn or frayed, replace the wire. 1/2\" maximum with normal hand pressure Figure 9-130. Slack between supports of a cable harness. 9-79

Gauge # 22 20 18 16 14 12 10 8 6 4 potted termination device, to splice multiple wires to a single wire, or to adjust the wire sizes so that they are compatible 2 Wires 10 10 9 8 7 1/2 7 6 1/2 6 5 4 with the contact crimp barrel sizes. 3 Wires 10 10 8 1/2 7 6 1/2 6 5 1/2 5 4 3 Bend Radii Figure 9-131. Recommended number of wire twists per foot. The minimum radius of bends in wire groups or bundles must Spliced Connections In Wire Bundles not be less than 10 times the outside diameter of the largest Splicing is permitted on wiring as long as it does not affect wire or cable, except that at the terminal strips where wires the reliability and the electromechanical characteristics of break out at terminations or reverse direction in a bundle. the wiring. Splicing of power wires, coaxial cables, multiplex Where the wire is suitably supported, the radius may be bus, and large-gauge wire must have approved data. Splicing three times the diameter of the wire or cable. Where it is of electrical wire should be kept to a minimum and avoided not practical to install wiring or cables within the radius entirely in locations subject to extreme vibrations. Splicing requirements, the bend should be enclosed in insulating of individual wires in a group or bundle should have tubing. The radius for thermocouple wire should be done in engineering approval, and the splice(s) should be located accordance with the manufacturer’s recommendation and to allow periodic inspection. shall be sufficient to avoid excess losses or damage to the cable. Ensure that RF cables (e.g., coaxial and triaxial) are Many types of aircraft splice connector are available for bent at a radius of no less than six times the outside diameter use when splicing individual wires. Use of a self-insulated of the cable. splice connector is preferred; however, a non-insulated splice connector may be used provided the splice is covered with Protection Against Chafing plastic sleeving that is secured at both ends. Environmentally sealed splices that conform to MIL-T-7928 provide a reliable Wires and wire groups should be protected against chafing or means of splicing in SWAMP areas. However, a non- abrasion in those locations where contact with sharp surfaces insulated splice connector may be used, provided the splice is or other wires would damage the insulation, or chafing could covered with dual-wall shrink sleeving of a suitable material. occur against the airframe or other components. Damage to the insulation can cause short circuits, malfunction, or There should be no more than one splice in any one wire inadvertent operation of equipment. segment between any two connectors or other disconnect points. Exceptions include when attaching to the spare pigtail Protection Against High Temperature lead of a potted connector, when splicing multiple wires to a single wire, when adjusting wire size to fit connector contact Wiring must be routed away from high-temperature crimp barrel size, and when required to make an approved equipment and lines to prevent deterioration of insulation. repair. Wires must be rated so the conductor temperature remains within the wire specification maximum when the ambient Splices in bundles must be staggered to minimize any temperature and heat rise related to current-carrying capacity increase in the size of the bundle, preventing the bundle from are taken into account. The residual heating effects caused by fitting into its designated space or causing congestion that exposure to sunlight when aircraft are parked for extended adversely affects maintenance. [Figure 9-132] periods should also be taken into account. Wires, such as those used in fire detection, fire extinguishing, fuel shutoff, Splices should not be used within 12 inches of a termination and fly-by-wire flight control systems that must operate device, except when attaching to the pigtail spare lead of a during and after a fire, must be selected from types that are qualified to provide circuit integrity after exposure to fire for Figure 9-132. Staggered splices in wire bundle. 9-80

a specified period. Wire insulation deteriorates rapidly when Wires, or groups of wires, should enter a junction box, or subjected to high temperatures. terminate at a piece of equipment in an upward direction where practicable. Ensure that a trap, or drip loop, is provided Separate wires from high-temperature equipment, such as to prevent fluids or condensation from running into wire or resistors, exhaust stacks, heating ducts, to prevent insulation cable ends that slope downward toward a connector, terminal breakdown. Insulate wires that must run through hot areas block, panel, or junction block. A drip loop is an area where with a high-temperature insulation material, such as fiberglass the wire(s) are made to travel downward and then up to the or PTFE. Avoid high-temperature areas when using cables connector. [Figure 9-134] Fluids and moisture will flow with soft plastic insulation, such as polyethylene, because along the wires to the bottom of the loop and be trapped there these materials are subject to deterioration and deformation to drip or evaporate without affecting electrical conductivity at elevated temperatures. Many coaxial cables have this type in the wire, junction, or connected device. of insulation. Protection Against Solvents and Fluids Figure 9-134. Drip loop. An arcing fault between an electrical wire and a metallic Where wires must be routed downwards to a junction box flammable fluid line may puncture the line and result in a fire. or electrical unit and a drip loop is not possible, the entrance Every effort must be made to avoid this hazard by physical should be sealed according to manufacturer’s specifications separation of the wire from lines and equipment containing to prevent moisture from entering the box/unit. Wires and oxygen, oil, fuel, hydraulic fluid, or alcohol. Wiring must cables installed in bilges and other locations where fluids be routed above these lines and equipment with a minimum collect must be routed as far from the lowest point as possible separation of 6 inches or more whenever possible. When such or otherwise be provided with a moisture-proof covering. an arrangement is not practicable, wiring must be routed so that it does not run parallel to the fluid lines. A minimum of 2 inches must be maintained between wiring and such lines and equipment, except when the wiring is positively clamped to maintain at least 1⁄2-inch separation, or when it must be connected directly to the fluid-carrying equipment. Install clamps as shown in Figure 9-133. These clamps should not be used as a means of supporting the wire bundle. Additional clamps should be installed to support the wire bundle and the clamps fastened to the same structure used to support the fluid line(s) to prevent relative motion. Protection of Wires in Wheel Well Areas Wires located on landing gear and in the wheel well area can be exposed to many hazardous conditions if not suitably protected. Where wire bundles pass flex points, there must not be any strain on attachments or excessive slack when parts are fully extended or retracted. The wiring and protective tubing must be inspected frequently and replaced at the first sign of wear. Figure 9-133. Positive separation of wire and fluid lines and Wires should be routed so that fluids drain away from the wire clamps. connectors. When this is not practicable, connectors must be potted. Wiring which must be routed in wheel wells or other external areas must be given extra protection in the form of harness jacketing and connector strain relief. Conduits or flexible sleeving used to protect wiring must be equipped with drain holes to prevent entrapment of moisture. 9-81

The technician should check during inspections that wires Dangerous angles and cables are adequately protected in wheel wells and other areas where they may be exposed to damage from impact of 45° max 45° max rocks, ice, mud, etc. (If rerouting of wires or cables is not practical, protective jacketing may be installed). This type of installation must be held to a minimum. Clamp Installation Wires and wire bundles must be supported by clamps or plastic cable straps. [Figure 9-135] Clamps and other primary support devices must be constructed of materials that are compatible with their installation and environment, in terms of temperature, fluid resistance, exposure to ultraviolet (UV) light, and wire bundle mechanical loads. They should be spaced at intervals not exceeding 24 inches. Clamps on wire bundles should be selected so that they have a snug fit without pinching wires [Figures 9-136 through 9-138] Safe angles Figure 9-135. Wire clamps. Figure 9-136. Safe angle for cable clamps. Caution: The use of metal clamps on coaxial RF cables may Clamps on wire bundles should not allow the bundle to cause problems, if clamp fit is such that RF cable’s original move through the clamp when a slight axial pull is applied. cross section is distorted. Clamps on RF cables must fit without crushing and must be snug enough to prevent the cable from moving freely through the clamp, but may allow the cable to slide through the clamp when a light axial pull is applied. The cable or wire bundle may be wrapped with one or more turns of electrical tape when required to achieve this fit. Plastic clamps or cable ties must not be used where their failure could result in interference with movable controls, wire bundle contact with movable equipment, or chafing damage to essential or unprotected wiring. They must not be used on vertical runs where inadvertent slack migration could result in chafing or other damage. Clamps must be installed with their attachment hardware positioned above them, wherever practicable, so that they are unlikely to rotate as the result of wire bundle weight or wire bundle chafing. [Figure 9-136] Cable clamps Bolt Split lockwasher Plain washer Plain washers Self-locking nut Nut Lockwasher external teeth Figure 9-137. Typical mounting hardware for MS-21919 cable clamps. 9-82

Cable clamps Angle bracket Correct Wire is pinched in clamp “Angle” member “Z” member Figure 9-138. Installing cable clamp to structure. Clamps lined with nonmetallic material should be used to ducts, or conduits. The supporting devices should be of a support the wire bundle along the run. Tying may be used suitable size and type, with the wires and cables held securely between clamps, but should not be considered as a substitute in place without damage to the insulation. for adequate clamping. Adhesive tapes are subject to age deterioration and, therefore, are not acceptable as a clamping Use metal stand-offs to maintain clearance between wires and means. [Figure 9-137] structure. Tape or tubing is not acceptable as an alternative to stand-offs for maintaining clearance. Install phenolic blocks, The back of the clamp, whenever practical, should be rested plastic liners, or rubber grommets in holes, bulkheads, floors, against a structural member. [Figure 9-138] Stand-offs or structural members where it is impossible to install off- should be used to maintain clearance between the wires and angle clamps to maintain wiring separation. In such cases, the structure. Clamps must be installed in such a manner additional protection in the form of plastic or insulating tape that the electrical wires do not come in contact with other may be used. parts of the aircraft when subjected to vibration. Sufficient slack should be left between the last clamp and the electrical Properly secure clamp retaining bolts so the movement of equipment to prevent strain at the terminal and to minimize wires and cables is restricted to the span between the points adverse effects on shock-mounted equipment. Where wires of support and not on soldered or mechanical connections at or wire bundles pass through bulkheads or other structural terminal posts or connectors. members, a grommet or suitable clamp should be provided to prevent abrasion. Movable Controls Wiring Precautions Clamping of wires routed near movable flight controls When a wire bundle is clamped into position, if there is less must be attached with steel hardware and must be spaced than 3⁄8-inch of clearance between the bulkhead cutout and so that failure of a single attachment point cannot result in the wire bundle, a suitable grommet should be installed as interference with controls. The minimum separation between indicated in Figure 9-139. The grommet may be cut at a 45° wiring and movable controls must be at least 1⁄2 inch when angle to facilitate installation, provided it is cemented in place the bundle is displaced by light hand pressure in the direction and the slot is located at the top of the cutout. of the controls. Wire and Cable Clamp Inspection Conduit Inspect wire and cable clamps for proper tightness. Where Conduit is manufactured in metallic and nonmetallic cables pass through structure or bulkheads, inspect for proper materials and in both rigid and flexible forms. Primarily, clamping and grommets. Inspect for sufficient slack between its purpose is for mechanical protection of cables or wires. the last clamp and the electronic equipment to prevent strain Conduit size should be selected for a specific wire bundle at the cable terminals and to minimize adverse effects on application to allow for ease in maintenance, and possible shock-mounted equipment. Wires and cables are supported future circuit expansion, by specifying the conduit inner by suitable clamps, grommets, or other devices at intervals of diameter (ID) about 25 percent larger than the maximum not more than 24 inches, except when contained in troughs, diameter of the wire bundle. [Figure 9-140] 9-83

Clearance 3/8\" minimum Wires less than 3/8\" from hole edge Grommet Cable clamp MS21919 Angle bracket with two point fastening A. Cushion clamp at bulkhead hole B. Cushion clamp at bulkhead hole with MS35489 grommet Cable clamp MS21919 Angle bracket with two point fastening C. Cushion clamp at bulkhead hole with MS21266 grommet Figure 9-139. Clamping at a bulkhead hole. Conduit problems can be avoided by following these guidelines: Figure 9-140. Flexible conduit. 9-84 • Do not locate conduit where passengers or maintenance personnel might use it as a handhold or footstep. • Provide drain holes at the lowest point in a conduit run. Drilling burrs should be carefully removed. • Support conduit to prevent chafing against structure and to avoid stressing its end fittings. Rigid Conduit Damaged conduit sections should be repaired to preclude injury to the wires or wire bundle that may consume as much as 80 percent of the tube area. Minimum acceptable tube bend

radii for rigid conduit are shown in Figure 9-141. Kinked or Nominal ID of Minimum bending wrinkled bends in rigid conduits are not recommended and conduit (inches) radius inside (inches) should be replaced. Tubing bends that have been flattened into an ellipse and have a minor diameter of less than 75 3/16 21/4 percent of the nominal tubing diameter should be replaced, 1/4 23/4 because the tube area has been reduced by at least 10 percent. 3/8 33/4 Tubing that has been formed and cut to final length should be 1/2 33/4 deburred to prevent wire insulation damage. When installing 5/8 33/4 replacement tube sections with fittings at both ends, care 3/4 41/4 should be taken to eliminate mechanical strain. 1 53/4 8 Nominal tube OD (inches) Minimum bend radius (inches) 11/4 11/2 81/4 1/8 3/8 13/4 9 3/16 7/16 2 1/4 9/16 93/4 3/8 15/16 21/2 10 1/2 11/4 5/8 11/2 Figure 9-142. Minimum bending radii for flexible aluminum or 3/4 13/4 brass conduit. 1 3 each circuit’s shielding requirement called out for in the 11/4 33/4 engineering documentation. A wire is normally shielded 11/2 5 when it is anticipated that the circuit can be affected by 13/4 another circuit in the wire harness. When the wires come 2 7 close together, they can couple enough interference to cause a detrimental upset to attached circuitry. This effect is often 8 called crosstalk. Wires must come close enough for their fields to interact, and they must be in an operating mode Figure 9-141. Minimum bend radii for rigid conduit. that produces the crosstalk effect. However, the potential for crosstalk is real, and the only way to prevent crosstalk is to Flexible Conduit shield the wire. [Figure 9-143] Flexible aluminum conduit conforming to specification Two wires in free air may MIL-C-6136 is available in two types: Type I, bare flexible couple capacitively, conduit, and Type II, rubber-covered flexible conduit. Flexible resulting in crosstalk. brass conduit conforming to specification MIL-C-7931 is available and normally used instead of flexible aluminum A charge on the 1st wire where necessary to minimize radio interference. Also induces an opposite available is a plastic flexible tubing. (Reference MIL-T- charge on the 2nd wire. 8191A.) Flexible conduit may be used where it is impractical to use rigid conduit, such as areas that have motion between +− conduit ends or where complex bends are necessary. Figure 9-143. Crosstalk. The use of transparent adhesive tape is recommended when cutting flexible tubing with a hacksaw to minimize fraying Bonding and Grounding of the braid. The tape should be centered over the cutting reference mark with the saw cutting through the tape. After One of the more important factors in the design and cutting the flexible conduit, the transparent tape should be maintenance of aircraft electrical systems is proper bonding removed, the frayed braid ends trimmed, burrs removed from and grounding. Inadequate bonding or grounding can lead to inside the conduit, and coupling nut and ferrule installed. unreliable operation of systems, EMI, electrostatic discharge Minimum acceptable bending radii for flexible conduit are damage to sensitive electronics, personnel shock hazard, or shown in Figure 9-142. damage from lightning strike. Wire Shielding In conventional wiring systems, circuits are shielded individually, in pairs, triples, or quads depending on 9-85

Grounding wiring (e.g., circuit breaker panel) and routing the power wire and its ground return in a twisted pair. Special care Grounding is the process of electrically connecting should be exercised to ensure replacement on ground return conductive objects to either a conductive structure or some leads. The use of numbered insulated wire leads instead of other conductive return path for the purpose of safely bare grounding jumpers may aid in this respect. In general, completing either a normal or fault circuit. [Figure 9-144] equipment items should have an external ground connection, If wires carrying return currents from different types of even when internally grounded. Direct connections to a sources, such as signals of DC and AC generators, are magnesium structure must not be used for ground return connected to the same ground point or have a common because they may create a fire hazard. connection in the return paths, an interaction of the currents occurs. Mixing return currents from various sources should Power ground connections for generators, transformer be avoided because noise is coupled from one source to rectifiers, batteries, external power receptacles, and other another and can be a major problem for digital systems. To heavy-current loads must be attached to individual grounding minimize the interaction between various return currents, brackets that are attached to aircraft structure with a proper different types of ground should be identified and used. As metal-to-metal bonding attachment. This attachment and the a minimum, the design should use three ground types: (1) surrounding structure must provide adequate conductivity AC returns, (2) DC returns, and (3) all others. to accommodate normal and fault currents of the system without creating excessive voltage drop or damage to the structure. At least three fasteners, located in a triangular or rectangular pattern, must be used to secure such brackets in order to minimize susceptibility to loosening under vibration. If the structure is fabricated of a material, such as carbon fiber composite (CFC), that has a higher resistivity than aluminum or copper, it is necessary to provide an alternative ground path(s) for power return current. Special attention should be considered for composite aircraft. Figure 9-144. Ground wires. Power return or fault current ground connections within flammable vapor areas must be avoided. If they must be For distributed power systems, the power return point for an made, make sure these connections do not arc, spark, or alternative power source would be separated. For example, overheat under all possible current flow or mechanical in a two-AC generator (one on the right side and the other on failure conditions, including induced lightning currents. the left side) system, if the right AC generator were supplying Criteria for inspection and maintenance to ensure continued backup power to equipment located in the left side, (left airworthiness throughout the expected life of the aircraft equipment rack) the backup AC ground return should be should be established. Power return fault currents are labeled “AC Right.” The return currents for the left generator normally the highest currents flowing in a structure. These can should be connected to a ground point labeled “AC Left.” be the full generator current capacity. If full generator fault current flows through a localized region of the carbon fiber The design of the ground return circuit should be given as structure, major heating and failure can occur. CFC and other much attention as the other leads of a circuit. A requirement similar low-resistive materials must not be used in power for proper ground connections is that they maintain an return paths. Additional voltage drops in the return path impedance that is essentially constant. Ground return circuits can cause voltage regulation problems. Likewise, repeated should have a current rating and voltage drop adequate localized material heating by current surges can cause for satisfactory operation of the connected electrical and material degradation. Both problems may occur without electronic equipment. EMI problems that can be caused by a warning and cause no repeatable failures or anomalies. system’s power wire can be reduced substantially by locating the associated ground return near the origin of the power The use of common ground connections for more than one circuit or function should be avoided except where it can be shown that related malfunctions that could affect more than one circuit do not result in a hazardous condition. Even when the loss of multiple systems does not, in itself, create a hazard, the effect of such failure can be quite distracting to the crew. 9-86

Bonding Bonding is the electrical connecting of two or more conducting objects not otherwise adequately connected. The following bonding requirements must be considered: Figure 9-145. Bonding jumpers. • Equipment bonding—low-impedance paths to • Bonding connections—to ensure a low-resistance aircraft structure are normally required for electronic connection, nonconducting finishes, such as paint equipment to provide radio frequency return circuits and anodizing films, should be removed from the and for most electrical equipment to facilitate reduction attachment surface to be contacted by the bonding in EMI. The cases of components that produce terminal. Electrical wiring should not be grounded electromagnetic energy should be grounded to structure. directly to magnesium parts. To ensure proper operation of electronic equipment, it is particularly important to conform the system’s • Corrosion protection—one of the more frequent installation specification when interconnections, causes of failures in electrical system bonding and bonding, and grounding are being accomplished. grounding is corrosion. The areas around completed connections should be post-finished quickly with a • Metallic surface bonding—all conducting objects suitable finish coating. on the exterior of the airframe must be electrically connected to the airframe through mechanical joints, • Corrosion prevention—electrolytic action may conductive hinges, or bond straps capable of conducting rapidly corrode a bonding connection if suitable static charges and lightning strikes. Exceptions may be precautions are not taken. Aluminum alloy jumpers necessary for some objects, such as antenna elements, are recommended for most cases; however, copper whose function requires them to be electrically isolated jumpers should be used to bond together parts made from the airframe. Such items should be provided with of stainless steel, cadmium plated steel, copper, an alternative means to conduct static charges and/or brass, or bronze. Where contact between dissimilar lightning currents, as appropriate. metals cannot be avoided, the choice of jumper and hardware should be such that corrosion is minimized; • Static bonds—all isolated conducting parts inside the part likely to corrode should be the jumper or and outside the aircraft, having an area greater than 3 associated hardware. square inches and a linear dimension over 3 inches, that are subjected to appreciable electrostatic charging • Bonding jumper attachment—the use of solder to due to precipitation, fluid, or air in motion, should attach bonding jumpers should be avoided. Tubular have a mechanically secure electrical connection to the members should be bonded by means of clamps to aircraft structure of sufficient conductivity to dissipate which the jumper is attached. Proper choice of clamp possible static charges. A resistance of less than 1 ohm material should minimize the probability of corrosion. when clean and dry generally ensures such dissipation on larger objects. Higher resistances are permissible • Ground return connection—when bonding jumpers in connecting smaller objects to airframe structure. carry substantial ground return current, the current rating of the jumper should be determined to be Testing of Bonds and Grounds adequate, and a negligible voltage drop is produced. [Figure 9-146] The resistance of all bond and ground connections should be tested after connections are made before re-finishing. The resistance of each connection should normally not exceed 0.003 ohm. A high quality test instrument, an AN/USM-21A or equivalent, is required to accurately measure the very low resistance values. Bonding Jumper Installation Bonding jumpers should be made as short as practicable, and installed in such a manner that the resistance of each connection does not exceed .003 ohm. The jumper should not interfere with the operation of movable aircraft elements, such as surface controls, nor should normal movement of these elements result in damage to the bonding jumper. [Figure 9-145] 9-87

Screw or bolt Washer A Washer B Structure Terminal (limit to 4) Lockwasher Washer C Locknut Aluminum Terminal and Jumper Structure Screw or bolt and nut plate Locknut Washer A Washer B Washer C Aluminum alloys Cadmium-plated Cadmium-plated Cadmium-plated None Cadmium-plated steel steel or aluminum steel or aluminum steel Magnesium alloys Cadmium-plated Cadmium-plated Magnesium-alloy None or Cadmium-plated steel steel magnesium alloy steel or aluminum Cadmium-plated Cadmium-plated Cadmium-plated Cadmium-plated Cadmium-plated Cadmium-plated steel or aluminum steel steel steel steel steel Cadmium-plated Cadmium-plated steel or aluminum Corrosion-resisting Corrosion-resisting steel or Cadmium-plated Corrosion-resisting steel Cadmium-plated steel steel steel steel Cadmium-plated steel Tinned Copper Terminal and Jumper Aluminum alloys2 Aluminum alloys Cadmium-plated Cadmium-plated Cadmium-plated steel steel steel Magnesium alloys1 Cadmium-plated Cadmium-plated Cadmium-plated Cadmium-plated none Cadmium-plated steel steel steel steel none steel Corrosion-resisting Corrosion-resisting steel or Cadmium-plated Corrosion-resisting Cadmium-plated steel cadmium-plated steel steel steel steel 1Avoid connecting copper to magnesium. 2Use washers with a conductive finish treated to prevent corrosion, such as AN960JD10L. Figure 9-146. Bolt and nut bonding or grounding to flat surface. Lacing and Tying Wire Bundles Ties, lacing, and straps are used to secure wire groups or bundles to provide ease of maintenance, inspection, and installation. Straps may not be used in areas of SWAMP, such as wheel wells, near wing flaps, or wing folds. They may not be used in high vibration areas where failure of the strap would permit wiring to move against parts that could damage the insulation and foul mechanical linkages or other moving mechanical parts. They also may not be used where they could be exposed to UV light, unless the straps are resistant to such exposure. [Figure 9-147] The single cord-lacing method and tying tape may be used Figure 9-147. Wire lacing. for wire groups of bundles 1 inch in diameter or less. The recommended knot for starting the single cord-lacing method is a clove hitch secured by a double-looped overhand knot. 9-88

[Figure 9-148, step A] Use the double cordlacing method on Tying wire bundles 1 inch in diameter or larger. When using the double cord-lacing method, employ a bowline-on-a-bight as Use wire group or bundle ties where the supports for the the starting knot. [Figure 9-149, step A] wire are more than 12 inches apart. A tie consists of a clove hitch around the wire group or bundle, secured by a square knot. [Figure 9-150] Step A—Starting knot Pull here until tight before finishing knot Cord crosses under loop Step C—part II Starting knot tightened Final knot Step B—Intermediate half hitches Step C—part I First part of final knot tightened Trim to 3/8\" minimum Figure 9-148. Single cord lacing method. Starting knot tightened Step C—Final knot Step A—Starting knot bowline-on-a-bight Step B—Intermediate half hitches Figure 9-149. Double cord lacing. 9-89

Wrap cord twice over bundle Clove hitch and square knot Figure 9-150. Tying. Wire Termination Stripping Wire Before wire can be assembled to connectors, terminals, splices, etc., the insulation must be stripped from connecting ends to expose the bare conductor. Copper wire can be stripped in a number of ways depending on the size and insulation. Aluminum wire must be stripped using extreme care, since Figure 9-151. Wire strippers. individual strands break very easily after being nicked. The following general precautions are recommended when following general procedures describe the steps for stripping stripping any type of wire: wire with a hand stripper. 1. When using any type of wire stripper, hold the wire 1. Insert wire into exact center of correct cutting slot so that it is perpendicular to cutting blades. for wire size to be stripped. Each slot is marked with wire size. 2. Adjust automatic stripping tools carefully; follow the manufacturer’s instructions to avoid nicking, cutting, 2. Close handles together as far as they will go. or otherwise damaging strands. This is especially important for aluminum wires and for copper wires 3. Release handles, allowing wire holder to return to the smaller than No. 10. Examine stripped wires for open position. damage. Cut off and restrip (if length is sufficient), or reject and replace any wires having more than the 4. Remove stripped wire. allowable number of nicked or broken strands listed in the manufacturer’s instructions. Terminals are attached to the ends of electrical wires to facilitate connection of the wires to terminal strips or items 3. Make sure insulation is clean-cut with no frayed or of equipment. [Figure 9-152] The tensile strength of the ragged edges. Trim, if necessary. wire-to-terminal joint should be at least equivalent to the tensile strength of the wire itself, and its resistance negligible 4. Make sure all insulation is removed from stripped area. relative to the normal resistance of the wire. Some types of wire are supplied with a transparent layer of insulation between the conductor and the The following should be considered in the selection of wire primary insulation. If this is present, remove it. terminals: current rating, wire size (gauge) and insulation diameter, conductor material compatibility, stud size, 5. When using hand-plier strippers to remove lengths of insulation material compatibility, application environment, insulation longer than 3⁄4 inch, it is easier to accomplish and solder versus solderless. in two or more operations. 6. Retwist copper strands by hand or with pliers, if necessary, to restore natural lay and tightness of strands. A pair of handheld wire strippers is shown in Figure 9-151. This tool is commonly used to strip most types of wire. The 9-90

surfaces and not by the stud itself. Defective studs should be replaced with studs of the same size and material since terminal strip studs of the smaller sizes may shear due to overtightening the nut. The replacement stud should be securely mounted in the terminal strip and the terminal securing nut should be tight. Terminal strips should be mounted in such a manner that loose metallic objects cannot fall across the terminals or studs. It is good practice to provide at least one spare stud for future circuit expansion or in case a stud is broken. Figure 9-152. Ring-tongue terminals. Terminal strips that provide connection of radio and electronic systems to the aircraft electrical system should Preinsulated crimp-type ring-tongue terminals are preferred. be inspected for loose connections, metallic objects that The strength, size, and supporting means of studs and may have fallen across the terminal strip, dirt and grease binding posts, as well as the wire size, may be considered accumulation, etc. These conditions can cause arcing, which when determining the number of terminals to be attached may result in a fire or system failures. to any one post. In high-temperature applications, the terminal temperature rating must be greater than the ambient Terminal Lugs temperature plus current related temperature rise. Use of Wire terminal lugs should be used to connect wiring to terminal nickel-plated terminals and of uninsulated terminals with block studs or equipment terminal studs. No more than four high-temperature insulating sleeves should be considered. terminal lugs, or three terminal lugs and a bus bar, should be Terminal blocks should be provided with adequate electrical connected to any one stud. The total number of terminal lugs clearance or insulation strips between mounting hardware per stud includes a common bus bar joining adjacent studs. and conductive parts. Four terminal lugs plus a common bus bar are not permitted on one stud. Terminal lugs should be selected with a stud Terminal Strips hole diameter that matches the diameter of the stud. However, Wires are usually joined at terminal strips. [Figure 9-153] A when the terminal lugs attached to a stud vary in diameter, terminal strip fitted with barriers may be used to prevent the the greatest diameter should be placed on the bottom and the terminals on adjacent studs from contacting each other. Studs smallest diameter on top. Tightening terminal connections should be anchored against rotation. When more than four should not deform the terminal lugs or the studs. Terminal lugs terminals are to be connected together, a small metal bus should be positioned so that bending of the terminal lug is not should be mounted across two or more adjacent studs. In all required to remove the fastening screw or nut, and movement cases, the current should be carried by the terminal contact of the terminal lugs tends to tighten the connection. Copper Wire Terminals Solderless crimp-style, copper wire, terminal lugs may be used which conform to MIL-T-7928. Spacers or washers should not be used between the tongues of terminal lugs. [Figure 9-154] Insulation grip Barrel Manufacturer’s Tongue mark XX 22-1B Wire insulation Stripped wire Range of wire sizes Color-coded insulation Figure 9-153. Terminal strip. Figure 9-154. Wire terminal. 9-91

Aluminum Wire Terminals The aluminum terminal lugs should be crimped to aluminum wire only. The tongue of the aluminum terminal lugs, or the total number of tongues of aluminum terminal lugs when stacked, should be sandwiched between two flat washers when terminated on terminal studs. Spacers or washers should not be used between the tongues of terminal lugs. Special attention should be given to aluminum wire and cable installations to guard against conditions that would result in excessive voltage drop and high resistance at junctions that may ultimately lead to failure of the junction. Examples of such conditions are improper installation of terminals and washers, improper torsion (torquing of nuts), and inadequate terminal contact areas. Pre-Insulated Splices Figure 9-156. Crimping pliers. Pre-insulated terminal lugs and splices must be installed using be replaced as soon as possible with permanent repairs. a high-quality crimping tool. Such tools are provided with Since some manufacturers prohibit splicing, the applicable positioners for the wire size and are adjusted for each wire manufacturer’s instructions should always be consulted. size. It is essential that the crimp depth be appropriate for each wire size. If the crimp is too deep, it may break or cut Junction Boxes individual strands. If the crimp is not deep enough, it may not Junction boxes are used for collecting, organizing, and be tight enough to retain the wire in the terminal or connector. distributing circuits to the appropriate harnesses that are Crimps that are not tight enough are also susceptible to high attached to the equipment. [Figure 9-157] Junction boxes are resistance due to corrosion buildup between the crimped also used to conveniently house miscellaneous components, terminal and the wire. [Figure 9-155] such as relays and diodes. Junction boxes that are used in high-temperature areas should be made of stainless steel. Figure 9-155. Terminal splices. Crimping Tools Hand, portable, and stationary power tools are available for crimping terminal lugs. These tools crimp the barrel to the conductor, and simultaneously form the insulation support to the wire insulation. [Figure 9-156] Emergency Splicing Repairs Figure 9-157. Junction boxes. Broken wires can be repaired by means of crimped splices, by using terminal lugs from which the tongue has been cut off, or by soldering together and potting broken strands. These repairs are applicable to copper wire. Damaged aluminum wire must not be temporarily spliced. These repairs are for temporary emergency use only and should 9-92

Replacement junction boxes should be fabricated using the same material as the original or from a fire-resistant, nonabsorbent material, such as aluminum, or an acceptable plastic material. Where fireproofing is necessary, a stainless steel junction box is recommended. Rigid construction prevents oil-canning of the box sides that could result in internal short circuits. In all cases, drain holes should be provided in the lowest portion of the box. Cases of electrical power equipment must be insulated from metallic structure to avoid ground fault related fires. The junction box arrangement should permit easy access to Figure 9-158. Electrical connectors. any installed items of equipment, terminals, and wires. Where marginal clearances are unavoidable, an insulating material reliability to the aircraft. For the installation of any particular should be inserted between current carrying parts and any connector assembly, the specification of the manufacturer or grounded surface. It is not good practice to mount equipment the appropriate governing agency must be followed. on the covers or doors of junction boxes, since inspection for internal clearance is impossible when the door or cover is in the closed position. Junction boxes should be securely mounted to the aircraft Types of Connector structure in such a manner that the contents are readily accessible for inspection. When possible, the open side Connectors must be identified by an original identification should face downward or at an angle so that loose metallic number derived from MIL Specification (MS) or OEM objects, such as washers or nuts, tend to fall out of the junction specification. Figure 9-159 provides information about MS box rather than wedge between terminals. style connectors. Junction box layouts should take into consideration the Environment-resistant connectors are used in applications necessity for adequate wiring space and possible future where they are probably subjected to fluids, vibration, heat, additions. Electrical wire bundles should be laced or clamped mechanical shock, corrosive elements, etc. Firewall class inside the box so that cables do not touch other components, connectors incorporating these same features should, in prevent ready access, or obscure markings or labels. Cables addition, be able to prevent the penetration of the fire through at entrance openings should be protected against chafing by the aircraft firewall connector opening and continue to using grommets or other suitable means. function without failure for a specified period of time when exposed to fire. Hermetic connectors provide a pressure AN/MS Connectors seal for maintaining pressurized areas. When EMI/RFI Connectors (plugs and receptacles) facilitate maintenance protection is required, special attention should be given to when frequent disconnection is required. There is a multitude the termination of individual and overall shields. Backshell of types of connectors. The connector types that use crimped adapters designed for shield termination, connectors with contacts are generally used on aircraft. Some of the more conductive finishes, and EMI grounding fingers are available common types are the round cannon type, the rectangular, for this purpose. and the module blocks. Environmentally resistant connectors should be used in applications subject to fluids, vibration, Rectangular connectors are typically used in applications heat, mechanical shock, and/or corrosive elements. where a very large number of circuits are accommodated in a single mated pair. [Figure 9-160] They are available with a When HIRF/lightning protection is required, special attention great variety of contacts, which can include a mix of standard, should be given to the terminations of individual or overall coaxial, and large power types. Coupling is accomplished by shields. The number and complexity of wiring systems various means. Smaller types are secured with screws which have resulted in an increased use of electrical connectors. hold their flanges together. Larger ones have integral guide [Figure 9-158] The proper choice and application of pins that ensure correct alignment, or jackscrews that both connectors is a significant part of the aircraft wiring system. align and lock the connectors. Rack and panel connectors Connectors must be kept to a minimum, selected, and use integral or rack-mounted pins for alignment and box installed to provide the maximum degree of safety and mounting hardware for couplings. 9-93

MS27480 E 10 A6 PB POLARIZATION MIL SPECIFICATION CONTACT STYLE CLASS INSERT ARRANGEMENT FINISH SHELL SIZE MS27484 Straight plug, EMI grounding MS27472 Wall mount receptacle MS27497 Wall receptacle, back panel mounting MS27473 Straight plug MS27499 Box mounting receptacle MS27474 Jam nut receptacle MS27500 90° Plug (note 1) MS27475 Hermetic wall mount receptacle MS27503 Hermetic solder mount receptacle (note 1) MS27476 Hermetic box mount receptacle MS27504 Box mount receptacle (note 1) MS27477 Hermetic jam nut receptacle MS27508 Box mount receptacle, back panel mounting MS27478 Hermetic solder mount receptacle MS27513 Box mount receptacle, long grommet MS27479 Wall mount receptacle (note 1) MS27664 Wall mount receptacle, back panel mounting MS27480 Straight plug(note 1) MS27481 Jam nut receptacle (note 1) (note 1) MS27482 Hermetic wall mount receptacle (note 1) MS27667 Thru-bulkhead receptacle MS27483 Hermetic jam nut receptacle (note 1) NOTE Supersedes B Olive drab cadmium plate over suitable underplate 1. Active (conductive), –65 °C to 175 °C MS27472 MS27479 C Anodic (nonconductive), –65 °C to + 175 °C MS27473 MS27480 D Fused tin, carbon steel(conductive), –65 °C to +150 °C MS27474 MS27481 E Corrosion resistant steel (cres), passivated MS27475 MS27482 MS27477 MS27483 (conductive), –65 °C to +200 °C MS27473 with MS27507 elbow MS27500 F Electroless nickel coating (conductive), –65 °C to MS27478 MS27503 MS27499 MS27504 +200 °C MS27497 MS27664 N Hermetic seal or environment resisting cres CLASS (conductive plating), –65 °C to +200 °C E Environment-resisting box and thru-bulkhead mounting CONTACT STYLE A Without pin contacts types only (see class T) B Without socket contacts P Potting—includes potting form and short rear grommet C Feed through T Environment-resisting wall and jam-nut mounting P Pin contact—including hermetics with solder cups S Socket contacts—including hermetics with solder cups receptacle and plug types: thread and teeth for X Pin contacts with eyelet (hermetic) accessory attachment Z Socket contacts with eyelet (hermetic) Y Hermetically sealed POLARIZATION A, B Normal—no letter required FINISH C, or D A Silver to light iridescent yellow color cadmium plate over nickel (conductive) –65 °C to +150 °C (inactive for new design) Figure 9-159. MS connector information sheet. Module blocks are types of junctions that accept crimped Standardized modules are available with wire end grommet contacts similar to those on connectors. Some use internal seals for environmental applications and are track mounted. busing to provide a variety of circuit arrangements. They Function module blocks are used to provide an easily are useful where a number of wires are connected for power wired package for environment-resistant mounting of small or signal distribution. When used as grounding modules, resistors, diodes, filters, and suppression networks. In-line they save and reduce hardware installation on the aircraft. 9-94

Wire Installation Into the Connector Wires that perform the same function in redundant systems must be routed through separate connectors. On systems critical to flight safety, system operation wiring should be routed through separate connectors from the wiring used for system failure warning. It is also good practice to route a system’s indication wiring in separate connectors from its failure warning circuits to the extent practicable. These steps can reduce an aircraft’s susceptibility to incidents that might result from connector failures. Figure 9-160. Rectangular connectors. Adjacent Locations terminal junctions are sometimes used in lieu of a connector Mating of adjacent connectors should not be possible. In order when only a few wires are terminated and when the ability to to ensure this, adjacent connector pairs must be different in disconnect the wires is desired. The in-line terminal junction shell size, coupling means, insert arrangement, or keying is environment resistant. The terminal junction splice is arrangement. When such means are impractical, wires should small and may be tied to the surface of a wire bundle when be routed and clamped so that incorrectly mated pairs cannot approved by the OEM. reach each other. Reliance on markings or color stripes is not recommended as they are likely to deteriorate with age. [Figure 9-161] Voltage and Current Rating Figure 9-161. Connector arrangement to avoid wrong connection. Selected connectors must be rated for continuous operation under the maximum combination of ambient temperature and circuit current load. Hermetic connectors and connectors used in circuit applications involving high-inrush currents should be derated. It is good engineering practice to conduct preliminary testing in any situation where the connector is to operate with most or all of its contacts at maximum rated current load. When wiring is operating with a high conductor temperature near its rated temperature, connector contact sizes should be suitably rated for the circuit load. This may require an increase in wire size. Voltage derating is required when connectors are used at high altitude in nonpressurized areas. Spare Contacts for Future Wiring Sealing To accommodate future wiring additions, spare contacts are Connectors must be of a type that excludes moisture entry normally provided. Locating the unwired contacts along through the use of peripheral and interfacial seal that are the outer part of the connector facilitates future access. A compressed when the connector is mated. Moisture entry good practice is to provide two spares on connectors with through the rear of the connector must be avoided by 25 or fewer contacts; 4 spares on connectors with 26 to correctly matching the wire’s outside diameter with the 100 contacts; and 6 spares on connectors with more than connector’s rear grommet sealing range. It is recommended 100 contacts. Spare contacts are not normally provided on that no more than one wire be terminated in any crimp style receptacles of components that are unlikely to have added contact. The use of heat-shrinkable tubing to build up the wiring. Connectors must have all available contact cavities wire diameter, or the application of potting to the wire entry filled with wired or unwired contacts. Unwired contacts area as additional means of providing a rear compatibility should be provided with a plastic grommet sealing plug. with the rear grommet is recommended. These extra means 9-95

have inherent penalties and should be considered only where other means cannot be used. Unwired spare contacts should have a correctly sized plastic plug installed. Drainage Connectors must be installed in a manner that ensures moisture and fluids drain out of and not into the connector when unmated. Wiring must be routed so that moisture accumulated on the bundle drains away from connectors. When connectors must be mounted in a vertical position, as through a shelf or floor, the connectors must be potted or environmentally sealed. In this situation, it is better to have the receptacle faced downward so that it is less susceptible to collecting moisture when unmated. Wire Support Figure 9-163. Coaxial cables. A rear accessory back shell must be used on connectors that damage can occur when clamped too tightly, or when they are are not enclosed. Connectors with very small size wiring, or bent sharply (normally at or near connectors). Damage can subject to frequent maintenance activity, or located in high- also be incurred during unrelated maintenance actions around vibration areas must be provided with a strain-relief-type back the coaxial cable. Coaxial cable can be severely damaged on shell. The wire bundle should be protected from mechanical the inside without any evidence of damage on the outside. damage with suitable cushion material where it is secured Coaxial cables with solid center conductors should not be by the clamp. Connectors that are potted or have molded used. Stranded center coaxial cables can be used as a direct rear adapters do not normally use a separate strain relief replacement for solid center coaxial. [Figure 9-164] accessory. Strain relief clamps should not impart tension on Coaxial cable precautions include: wires between the clamp and contact. [Figure 9-162] • Never kink coaxial cable. • Never drop anything on coaxial cable. • Never step on coaxial cable. • Never bend coaxial cable sharply. • Never loop coaxial cable tighter than the allowable bend radius. • Never pull on coaxial cable except in a straight line. • Never use coaxial cable for a handle, lean on it, or hang things on it (or any other wire). Figure 9-162. Backshells with strain relief. Wire Inspection Aircraft service imposes severe environmental condition on Sufficient wire length must be provided at connectors to electrical wire. To ensure satisfactory service, inspect wire ensure a proper drip loop and that there is no strain on annually for abrasions, defective insulation, condition of termination after a complete replacement of the connector terminations, and potential corrosion. Grounding connections and its contacts. for power, distribution equipment, and electromagnetic shielding must be given particular attention to ensure that Coaxial Cable electrical bonding resistance has not been significantly All wiring needs to be protected from damage. However, increased by the loosening of connections or corrosion. coaxial and triaxial cables are particularly vulnerable to certain types of damage. Personnel should exercise care while Electrical System Components handling or working around coaxial. [Figure 9-163] Coaxial Switches Switches are devices that open and close circuits. They consist of one or more pair of contacts. The current in the circuit flows when the contacts are closed. Switches with 9-96

Plug Straight receptacle Flange mount receptacle Plug BNC series connectors Flange mount receptacle Straight receptacle Plug TNC series connectors Flange mount receptacle Straight receptacle Plug N series connectors Flange mount receptacle Straight receptacle C series connectors Figure 9-164. Coaxial cable connectors. momentary contacts actuate the circuit temporarily, and they so that the on position is reached by an upward or forward return to the normal position with an internal spring when movement of the toggle. When the switch controls movable the switch is released. Switches with continuous contacts aircraft elements, such as landing gear or flaps, the toggle remain in position when activated. Hazardous errors in should move in the same direction as the desired motion. switch operation can be avoided by logical and consistent Inadvertent operation of a switch can be prevented by installation. Two-position on/off switches should be mounted mounting a suitable guard over the switch. [Figure 9-165] 9-97

Figure 9-166 is used for selecting the proper nominal switch rating when the continuous load current is known. This selection is essentially a derating to obtain reasonable switch efficiency and service life. Nominal system Type of load Derating factor voltage (DC) 28V Lamp 8 28V Inductive 4 28V Resistive 2 28V 3 12V Motor 5 12V Lamp 2 12V Inductive 1 12V Resistive 2 Motor Figure 9-166. Derating table for switches. Type of Switches Single-pole single-throw (SPST)—opens and closes a single circuit. Pole indicates the number of separate circuits that can be activated, and throw indicates the number of current paths. Figure 9-165. Switch guard. Double-pole single-throw (DPST)—turn two circuits on and off with one lever. A specifically designed switch should be used in all circuits where a switch malfunction would be hazardous. Such Single-pole double-throw (SPDT)—route circuit current to switches are of rugged construction and have sufficient either of two paths. The switch is ON in both positions. For contact capacity to break, make, and carry continuously example, switch turns on red lamp in one position and turns the connected load current. Snap action design is generally on green lamp in the other position. preferred to obtain rapid opening and closing of contacts regardless of the speed of the operating toggle or plunger, Double-pole double-throw (DPDT)—activates two separate thereby minimizing contact arcing. The nominal current circuits at the same time. rating of the conventional aircraft switch is usually stamped on the switch housing. This rating represents the continuous Double-throw switches—have either two or three positions. current rating with the contacts closed. Switches should be derated from their nominal current rating for the following Two position switch—pole always connected to one of the types of circuits: two throws. Three-position switches have a center OFF position that disconnects the pole from both throws. 1. High rush-in circuits—contain incandescent lamps that can draw an initial current 15 times greater than Spring loaded switches—available in two types: 1) normally the continuous current. Contact burning or welding open (NO) and 2) normally closed (NC). The contacts of may occur when the switch is closed. the NO switch are disconnected in the normal position and become closed when the switch is activated. The switch 2. Inductive circuits—magnetic energy stored in solenoid returns to the normal position when the applied force to coils or relays is released and appears as an arc when the switch is released. The contacts of the NC switch are the control switch is opened. connected in the normal position and become open when the switch is activated. The switch returns to the normal position 3. Motors—DC motors draw several times their rated when the applied force to the switch is released. current during starting, and magnetic energy stored in their armature and field coils is released when the Toggle and Rocker Switches control switch is opened. Toggle and rocker switches control most of aircraft’s electrical components. [Figure 9-167] Aircraft that are 9-98

Figure 9-168. A micro switch. to switch motors and other electrical equipment on and off and to protect them from overheating. A solenoid is a special type of relay that has a moving core. The electromagnet core in a relay is fixed. Solenoids are mostly used as mechanical actuators but can also be used for switching large currents. Relays are only used to switch currents. Figure 9-167. Toggle and rocker switches. Solenoids outfitted with a glass cockpit often use push buttons to control Solenoids are used as switching devices where a weight electrical components. reduction can be achieved or electrical controls can be simplified. The foregoing discussion of switch ratings is generally applicable to solenoid contact ratings. Solenoids have a movable core/armature that is usually made of steel or iron, and the coil is wrapped around the armature. The solenoid has an electromagnetic tube and the armature moves in and out of the tube. [Figure 9-169] Rotary Switches Rotary switches are activated by twisting a knob or shaft and are commonly found on radio control panels. Rotary switches are utilized for controlling more than two circuits. Precision (Micro) Switches Figure 9-169. Solenoid. Micro switches require very little pressure to activate. These types of switches are spring loaded, once the pressure is Relays removed, the contacts return to the normal position. These The two main types of relays are electromechanical and types of switches are typically single pole double throw solid state. Electromechanical relays have a fixed core and (SPDT) or double pole double throw (DPDT) and have three a moving plate with contacts on it, while solid-state relays contacts: normally open, normally closed, and common. work similar to transistors and have no moving parts. Current Micro switches are used to detect position or to limit travel flowing through the coil of an electromechanical relay creates of moving parts, such as landing gear, flaps, spoilers, etc. a magnetic field that attracts a lever and changes the switch [Figure 9-168] contacts. The coil current can be on or off so relays have two switch positions, and they are double throw switches. Relays and Solenoids (Electromagnetic Switches) Relays are used to control the flow of large currents using a small current. A low-power DC circuit is used to activate the relay and control the flow of large AC currents. They are used 9-99

Residual magnetism is a common problem and the contacts Wire AN Circuit breaker Fuse amperage may stay closed or are opened by a slight amount of residual gauge copper amperage magnetism. A relay is an electrically operated switch and 5 5 is therefore subject to dropout under low system voltage 22 7.5 5 conditions. Relays allow one circuit to switch a second circuit 20 10 10 that can be completely separate from the first. For example, 18 15 10 a low voltage DC battery circuit can use a relay to switch 16 20 15 a 110-volt three-phase AC circuit. There is no electrical 14 30 20 connection inside the relay between the two circuits; the link 12 40 30 is magnetic and mechanical. [Figure 9-170] 10 50 50 80 70 8 100 70 6 125 100 4 150 2 150 1 0 Figure 9-171. Wired and circuit protection chart. Figure 9-170. Relay. Current Limiting Devices Figure 9-172. A fuse. Conductors should be protected with circuit breakers or fuses located as close as possible to the electrical power source of the fuse the metal strip heats up and breaks. As a result of bus. Normally, the manufacturer of the electrical equipment this, the flow of current in the circuit stops. specifies the fuse or circuit breaker to be used when installing equipment. The circuit breaker or fuse should open the circuit There are two basic types of fuses: fast acting and slow before the conductor emits smoke. To accomplish this, the blow. The fast-acting type opens very quickly when their time current characteristic of the protection device must fall particular current rating is exceeded. This is important for below that of the associated conductor. Circuit protector electric devices that can quickly be destroyed when too much characteristics should be matched to obtain the maximum current flows through them for even a very small amount utilization of the connected equipment. Figure 9-171 shows a of time. Slow blow fuses have a coiled construction inside. chart used in selecting the circuit breaker and fuse protection They are designed to open only on a continued overload, for copper conductors. This limited chart is applicable to a such as a short circuit. specific set of ambient temperatures and wire bundle sizes and is presented as typical only. It is important to consult such Circuit Breakers guides before selecting a conductor for a specific purpose. A circuit breaker is an automatically operated electrical For example, a wire run individually in the open air may be switch designed to protect an electrical circuit from damage protected by the circuit breaker of the next higher rating to caused by an overload or short circuit. Its basic function that shown on the chart. is to detect a fault condition and immediately discontinue electrical flow. Unlike a fuse that operates once and then has Fuses to be replaced, a circuit breaker can be reset to resume normal operation. All resettable circuit breakers should open the A fuse is placed in series with the voltage source and all circuit in which they are installed regardless of the position of current must flow through it. [Figure 9-172] The fuse consists the operating control when an overload or circuit fault exists. of a strip of metal that is enclosed in a glass or plastic housing. Such circuit breakers are referred to as trip-free. Automatic The metal strip has a low melting point and is usually made reset circuit breakers automatically reset themselves. They of lead, tin, or copper. When the current exceeds the capacity 9-100

should not be used as circuit protection devices in aircraft. Position Lights When a circuit breaker trips, the electrical circuit should be checked and the fault removed before the circuit breaker Aircraft operating at night must be equipped with position is reset. Sometimes circuit breakers trip for no apparent lights that meet the minimum requirements specified by Title reason, and the circuit breaker can be reset one time. If the 14 of the Code of Federal Regulations. A set of position circuit breaker trips again, there exists a circuit fault and the lights consist of one red, one green, and one white light. technician must troubleshoot the circuit before resetting the [Figures 9-174 and 9-175] circuit breaker. [Figure 9-173] Figure 9-174. A left wing tip position light (red) and a white strobe light. Figure 9-173. Circuit breaker panel. Some new aircraft designs use a digital circuit protection architecture. This system monitors the amperage through a particular circuit. When the maximum amperage for that circuit is reached, the power is rerouted away from the circuit. This system reduces the use of mechanical circuit breakers. The advantages are weight savings and the reduction of mechanical parts. Aircraft Lighting Systems Figure 9-175. A right wing tip position light, also known as a navigation light. Aircraft lighting systems provide illumination for both exterior and interior use. Lights on the exterior provide illumination On some types of installations, a switch in the cockpit for such operations as landing at night, inspection of icing provides for steady or flashing operation of the position conditions, and safety from midair collision. Interior lighting lights. On many aircraft, each light unit contains a single lamp provides illumination for instruments, cockpits, cabins, and mounted on the surface of the aircraft. Other types of position other sections occupied by crewmembers and passengers. light units contain two lamps and are often streamlined into Certain special lights, such as indicator and warning lights, the surface of the aircraft structure. The green light unit is indicate the operation status of equipment. always mounted at the extreme tip of the right wing. The red unit is mounted in a similar position on the left wing. The Exterior Lights Position, anticollision, landing, and taxi lights are common examples of aircraft exterior lights. Some lights are required for night operations. Other types of exterior lights, such as wing inspection lights, are of great benefit for specialized flying operations. 9-101

white unit is usually located on the vertical stabilizer in a of the aircraft. Figure 9-177 shows a typical anticollision position where it is clearly visible through a wide angle from light installation in a vertical stabilizer. the rear of the aircraft. Figure 9-176 illustrates a schematic diagram of a position light circuit. Position lights are also known as navigation lights. There are, of course, many variations in the position light circuits used on different aircraft. All circuits are protected by fuses or circuit breakers, and many circuits include flashing and dimming equipment. Small aircraft are usually equipped with a simplified control switch and circuitry. In some cases, one control knob or switch is used to turn on several sets of lights; for example, one type utilizes a control knob, the first movement of which turns on the position lights and the instrument panel lights. Further rotation of the control knob increases the intensity of only the panel lights. A flasher unit is seldom included in the position light circuitry of very light aircraft but is used in small twin-engine aircraft. Traditional position lights use incandescent light bulbs. LED lights have been introduced on modern aircraft because of their good visibility, high reliability, and low power consumption. Anticollision Lights Figure 9-177. Anticollision lights. An anticollision light system may consist of one or more lights. They are rotating beam lights that are usually installed on top of the fuselage or tail in such a location that the light does not affect the vision of the crewmember or detract from the visibility of the position lights. Large transport type aircraft use an anticollision light on top and one on the bottom L168A20 WG Nav light PWR 20 G DS104/XDS104 STA Ground 20 R Nav light A223 panel assembly 124.6 subpanel, L INBD J282 P282 25-53-02 H L168B20 W159 91-29 5A L168D20 P238 J238 Red C DS103/XDS103 CB121 I Blk Tail nav light NAV LIGHT I L170A20N WG P239 J239 GS129 33-47 STA L168F20 124.6 Nav light PWR 20 R DS104/XDS104 J281 P281 Ground 20 L Nav light H L168G20 91-28 Figure 9-176. Navigation light system schematic. 9-102

An anticollision light unit usually consists of one or two Taxi lights are designed to provide illumination on the ground rotating lights operated by an electric motor. The light may be while taxiing or towing the aircraft to or from a runway, taxi fixed but mounted under rotating mirrors inside a protruding strip, or in the hangar area. [Figure 9-179] Taxi lights are red glass housing. The mirrors rotate in an arc, and the not designed to provide the degree of illumination necessary resulting flash rate is between 40 and 100 cycles per minute. for landing lights. On aircraft with tricycle landing gear, Newer aircraft designs use a LED type of anticollision light. either single or multiple taxi lights are often mounted on The anticollision light is a safety light to warn other aircraft, the non‑steerable part of the nose landing gear. They are especially in congested areas. positioned at an oblique angle to the center line of the aircraft to provide illumination directly in front of the aircraft and A white strobe light is a second type of anti-collision light also some illumination to the right and left of the aircraft’s that is also common. Usually mounted at the wing tips and, path. On some aircraft, the dual taxi lights are supplemented possibly, at empennage extremities, strobe lights produce by wingtip clearance lights controlled by the same circuitry. an extremely bright intermittent flash of white light that Taxi lights are also mounted in the recessed areas of the wing is highly visible. The light is produced by a high voltage leading edge, often in the same area with a fixed landing light. discharge of a capacitor. A dedicated power pack houses the capacitor and supplies voltage to a sealed xenon-filled tube. The xenon ionizes with a flash when the voltage is applied. A strobe light is shown in Figure 9-174. Landing and Taxi Lights Landing lights are installed in aircraft to illuminate runways during night landings. These lights are very powerful and are directed by a parabolic reflector at an angle providing a maximum range of illumination. Landing lights of smaller aircraft are usually located midway in the leading edge of each wing or streamlined into the aircraft surface. Landing lights for larger transport category aircraft are usually located in the leading edge of the wing close to the fuselage. Each light may be controlled by a relay, or it may be connected directly into the electric circuit. On some aircraft, the landing light is mounted in the same area with a taxi light. [Figure 9-178] A sealed beam, halogen, or high intensity xenon discharge lamp is used. Figure 9-178. Landing lights. Figure 9-179. Taxi lights. 9-103

Many small aircraft are not equipped with any type of taxi Interior Lights light, but rely on the intermittent use of a landing light to Aircraft are equipped with interior lights to illuminate the illuminate taxiing operations. Still other aircraft utilize cabin. [Figure 9-181] Often white and red light settings are a dimming resistor in the landing light circuit to provide provided. Commercial aircraft have a lighting systems that reduced illumination for taxiing. A typical circuit for taxi illuminates the main cabin, an independent lighting system lights is shown in Figure 9-180. so that passengers can read when the cabin lights are off, and an emergency lighting system on the floor of the aircraft to Some large aircraft are equipped with alternate taxi lights aid passengers of the aircraft during an emergency. located on the lower surface of the aircraft, aft of the nose radome. These lights, operated by a separate switch from the main taxi lights, illuminate the area immediately in front of and below the aircraft nose. Wing Inspection Lights Figure 9-181. Interior cockpit and cabin light system. Some aircraft are equipped with wing inspection lights to illuminate the leading edge of the wings to permit observation of icing and general condition of these areas in flight. These lights permit visual detection of ice formation on wing leading edges while flying at night. They are usually controlled through a relay by an on/off toggle switch in the cockpit. Some wing inspection light systems may include or be supplemented by additional lights, sometimes called nacelle lights, that illuminate adjacent areas, such a cowl flaps or the landing gear. These are normally the same type of lights and can be controlled by the same circuits. TB102 24-53-02 2 W159 5 L178A16 15A 4 CB121 TAXI LIGHT C L176B18 L178A16 10A L177A18N CB178 R LANDING DS110 CR127 CR217 LIGHT XDS110 CR126 RIGHT LANDING LIGHT C L178B16 54 S104-4-20 L179A16N 6 DS106 XDS106 32-61 24-53-01 TAXI LIGHT S104 NOSE GEAR UP LOCK SWITCH W119 C L173B18 3 L173A18 10A L174A18N CB177 L LANDING DS109 LIGHT XDS109 LEFT LANDING A223 PANEL ASSY - SUBPANEL, LIGHT L INBOARD L30A22 31-51-04 1 32-61 Figure 9-180. Taxi light circuit. 9-104

Maintenance and Inspection of Lighting Systems Inspection of an aircraft’s lighting system normally includes checking the condition and security of all visible wiring, connections, terminals, fuses, and switches. A continuity light or meter can be used in making these checks, since the cause of many troubles can often be located by systematically testing each circuit for continuity. 9-105

9-106

Glossary Aborted takeoff. A takeoff that is terminated prematurely Aerodynamic drag. The total resistance to the movement of when it is determined that some condition exists that makes an object through the air. Aerodynamic drag is composed of takeoff or further flight dangerous. both induced drag and parasite drag. See induced drag and parasite drag. Absolute pressure. Pressure measured from zero pressure or a vacuum. Aerodynamic lift. The force produced by air moving over a specially shaped surface called an airfoil. Aerodynamic Absolute pressure regulator. A valve used in a pneumatic lift acts in a direction perpendicular to the direction the air system at the pump inlet to regulate the compressor inlet is moving. air pressure to prevent excessive speed variation and/or overspeeding of the compressor. Aeroelastic tailoring. The design of an aerodynamic surface whose strength and stiffness are matched to the aerodynamic Absolute zero. The point at which all molecular motion loads that will be imposed upon it. ceases. Absolute zero is –460 °F and –273 °C. Aeronautical Radio Incorporated (ARINC). A corporation Accumulator. A hydraulic component that consists of two whose principal stockholders are the airlines. Its function is compartments separated by a movable component, such as to operate certain communication links between airliners a piston, diaphragm, or bladder. One compartment is filled in flight and the airline ground facilities. ARINC also sets with compressed air or nitrogen, and the other is filled with standards for communication equipment used by the airlines. hydraulic fluid and is connected into the system pressure manifold. An accumulator allows an incompressible fluid to be Aging. A change in the characteristics of a material with time. stored under pressure by the force produced by a compressible Certain aluminum alloys do not have their full strength when fluid. Its primary purposes are to act as a shock absorber in the they are first removed from the quench bath after they have system, and to provide a source of additional hydraulic power been heat-treated, but they gain this strength after a few days when heavy demands are placed on the system. by the natural process of aging. Actuator. A fluid power device that changes fluid pressure Agonic line. A line drawn on an aeronautical chart along into mechanical motion. which there is no angular difference between the magnetic and geographic north poles. ADC. Air data computer. Air carrier. An organization or person involved in ADF. Automatic direction finder. the business of transporting people or cargo by air for compensation or hire. ADI. Attitude director indicator. Air-cycle cooling system. A system for cooling the air in Advancing blade. The blade on a helicopter rotor whose the cabin of a turbojet-powered aircraft. Compressor bleed tip is moving in the same direction the helicopter is moving. air passes through two heat exchangers where it gives up some of its heat; then, it drives an expansion turbine where Adverse yaw. A condition of flight at the beginning of a it loses still more of its heat energy as the turbine drives a turn in which the nose of an airplane momentarily yaws in compressor. When the air leaves the turbine, it expands and the opposite direction from the direction in which the turn its pressure and temperature are both low. is to be made. G-1

Aircraft communication addressing and reporting system Ambient pressure. The pressure of the air surrounding a (ACARS). A two-way communication link between an person or an object. airliner in flight and the airline’s main ground facilities. Data is collected in the aircraft by digital sensors and is transmitted Ambient temperature. The temperature of the air to the ground facilities. Replies from the ground may be surrounding a person or an object. printed out so the appropriate flight crewmember can have a hard copy of the response. American wire gauge. The system of measurement of wire size used in aircraft electrical systems. Airfoil. Any surface designed to obtain a useful reaction, or lift, from air passing over it. Amphibian. An airplane with landing gear that allows it to operate from both water and land surfaces. Airspeed indicator. A flight instrument that measures the pressure differential between the pitot, or ram, air pressure, Amplifier. An electronic circuit in which a small change in and the static pressure of the air surrounding the aircraft. voltage or current controls a much larger change in voltage This differential pressure is shown in units of miles per hour, or current. knots, or kilometers per hour. Analog electronics. Electronics in which values change in Airworthiness Alert. A notice sent by the FAA to certain a linear fashion. Output values vary in direct relationship to interested maintenance personnel identifying problems changes of input values. with aircraft that have been gathered from Malfunction and Defect Reports. These problems are being studied at the time Analog-type indicator. An electrical meter that indicates the Airworthiness Alert is issued but have not been fully values by the amount a pointer moves across a graduated evaluated by the time the material went to press. numerical scale. Airworthiness Directive (AD note). A notice sent out by the Aneroid. The sensitive component in an altimeter or FAA to the registered owner of an aircraft notifying him or barometer that measures the absolute pressure of the air. The her of an unsafe condition that has been found on the aircraft. aneroid is a sealed, flat capsule made of thin corrugated disks Compliance with AD notes is mandatory. of metal soldered together and evacuated by pumping all of the air out of it. Evacuating the aneroid allows it to expand Alclad. A registered trade name for clad aluminum alloy. or collapse as the air pressure on the outside changes. Alodine. The registered trade name for a popular conversion Angle of attack. The acute angle formed between the chord coating chemical used to produce a hard, airtight, oxide film line of an airfoil and the direction of the air that strikes the on aluminum alloy for corrosion protection. airfoil. Alphanumeric symbols. Symbols made up of all of the Angle of attack indicator. An instrument that measures the letters in our alphabet, numerals, punctuation marks, and angle between the local airflow around the direction detector certain other special symbols. and the fuselage reference plane. Alternator. An electrical generator that produces alternating Angle of incidence. The acute angle formed between the current. The popular DC alternator used on light aircraft chord line of an airfoil and the longitudinal axis of the aircraft produces three-phase AC in its stator windings. This AC is on which it is mounted. changed into DC by a six-diode, solid-state rectifier before it leaves the alternator. Annual rings. The rings that appear in the end of a log cut from a tree. The number of annual rings per inch gives an Altimeter setting. The barometric pressure at a given indication of the strength of the wood. The more rings there location corrected to mean (average) sea level. are and the closer they are together, the stronger the wood. The pattern of alternating light and dark rings is caused by Altitude engine. A reciprocating engine whose rated sea-level the seasonal variations in the growth rate of the tree. A tree takeoff power can be produced to an established higher altitude. grows quickly in the spring and produces the light-colored, less dense rings. The slower growth during the summer, or Alumel. An alloy of nickel, aluminum, manganese, and latter part of the growing season, produces the dark-colored, silicon that is the negative element in a thermocouple used denser rings. to measure exhaust gas temperature. G-2

Annunciator panel. A panel of warning lights in plain sight Aspect ratio. The ratio of the length, or span, of an airplane of the pilot. These lights are identified by the name of the wing to its width, or chord. For a nonrectangular wing, the system they represent and are usually covered with colored lenses to show the meaning of the condition they announce. aspect ratio is found by dividing the square of the span of the wing by its area. Aspect Ratio = span2 ÷ area. Anodizing. The electrolytic process in which a hard, airtight, Asymmetrical airfoil. An airfoil section that is not the same oxide film is deposited on aluminum alloy for corrosion on both sides of the chord line. protection. Asymmetrical lift. A condition of uneven lift produced by Antenna. A special device used with electronic the rotor when a helicopter is in forward flight. Asymmetrical communication and navigation systems to radiate and receive lift is caused by the difference between the airspeed of the electromagnetic energy. advancing blade and that of the retreating blade. Anti-icer system. A system that prevents the formation of Attenuate. To weaken, or lessen the intensity of, an activity. ice on an aircraft structure. Attitude indicator. A gyroscopic flight instrument that gives Anti-icing additive. A chemical added to the turbine-engine the pilot an indication of the attitude of the aircraft relative to fuel used in some aircraft. This additive mixes with water that its pitch and roll axes. The attitude indicator in an autopilot condenses from the fuel and lowers its freezing temperature is in the sensing system that detects deviation from a level- so it will not freeze and block the fuel filters. It also acts as flight attitude. a biocidal agent and prevents the formation of microbial contamination in the tanks. Augmenter tube. A long, stainless steel tube around the discharge of the exhaust pipes of a reciprocating engine. Antidrag wire. A structural wire inside a Pratt truss airplane Exhaust gases flow through the augmenter tube and produce wing between the spars. Antidrag wires run from the rear spar a low pressure that pulls additional cooling air through the inboard, to the front spar at the next bay outboard. Antidrag engine compartment. Heat may be taken from the augmenter wires oppose the forces that try to pull the wing forward. tubes and directed through the leading edges of the wings for thermal anti-icing. Antiservo tab. A tab installed on the trailing edge of a stabilator to make it less sensitive. The tab automatically Autoclave. A pressure vessel inside of which air can be moves in the same direction as the stabilator to produce an heated to a high temperature and pressure raised to a high aerodynamic force that tries to bring the surface back to a value. Autoclaves are used in the composite manufacturing streamline position. This tab is also called an antibalance tab. industry to apply heat and pressure for curing resins. Antiskid brake system. An electrohydraulic system in an Autogiro. A heavier-than-air rotor-wing aircraft sustained airplane’s power brake system that senses the deceleration rate in the air by rotors turned by aerodynamic forces rather than of every main landing gear wheel. If any wheel decelerates by engine power. When the name Autogiro is spelled with too rapidly, indicating an impending skid, pressure to that a capital A, it refers to a specific series of machines built by bake is released and the wheel stops decelerating. Pressure Juan de la Cierva or his successors. is then reapplied at a slightly lower value. Autoignition system. A system on a turbine engine that Antitear strip. Strips of aircraft fabric laid under the automatically energizes the igniters to provide a relight if reinforcing tape before the fabric is stitched to an aircraft wing. the engine should flame out. Arbor press. A press with either a mechanically or Automatic adjuster. A subsystem in an aircraft disk brake hydraulically operated ram used in a maintenance shop for that compensates for disk or lining wear. Each time the brakes a variety of pressing functions. are applied, the automatic adjuster is reset for zero clearance, and when the brakes are released, the clearance between the Arcing. Sparking between a commutator and brush or disks or the disk and lining is returned to a preset value. A between switch contacts that is caused by induced current malfunctioning automatic adjuster in a multiple-disk brake when a circuit is broken. can cause sluggish and jerky operation. Area. The number of square units in a surface. G-3

Automatic flight control system (AFCS). The full system Backup ring. A flat leather or Teflon ring installed in the of automatic flight control that includes the autopilot, flight groove in which an O-ring or T-seal is placed. The backup director, horizontal situation indicator, air data sensors, and ring is on the side of the seal away from the pressure, and it other avionics inputs. prevents the pressure extruding the seal between the piston and the cylinder wall. Automatic pilot (autopilot). An automatic flight control device that controls an aircraft about one or more of its three Balance cable. A cable in the aileron system of an airplane axes. The primary purpose of an autopilot is to relieve the that connects to one side of each aileron. When the control pilot of the control of the aircraft during long periods of flight. wheel is rotated, a cable from the cockpit pulls one aileron autorotation. Descent of a helicopter without the use of engine down and relaxes the cable going to the other aileron. The power. An aerodynamic force causes the rotors to rotate. balance cable pulls the other aileron up. Autosyn system. A synchro system used in remote indicating Balance panel. A flat panel hinged to the leading edge of instruments. The rotors in an Autosyn system are two-pole some ailerons that produces a force which assists the pilot electromagnets, and the stators are delta-connected, three-phase, in holding the ailerons deflected. The balance panel divides distributed-pole windings in the stator housings. The rotors in a chamber ahead of the aileron in such a way that when the the transmitters and indicators are connected in parallel and aileron is deflected downward, for example, air flowing are excited with 26-volt, 400-Hz AC. The rotor in the indicator over its top surface produces a low pressure that acts on the follows the movement of the rotor in the transmitter. balance panel and causes it to apply an upward force to the aileron leading edge. Auxiliary power unit (APU). A small turbine or reciprocating engine that drives a generator, hydraulic pump, and air pump. Balance tab. An adjustable tab mounted on the trailing edge The APU is installed in the aircraft and is used to supply of a control surface to produce a force that aids the pilot in electrical power, compressed air, and hydraulic pressure moving the surface. The tab is automatically actuated in such when the main engines are not running. a way it moves in the direction opposite to the direction the control surface on which it is mounted moves. Aviation snips. Compound-action hand shears used for cutting sheet metal. Aviation snips come in sets of three. One Balanced actuator. A linear hydraulic or pneumatic actuator pair cuts to the left, one pair cuts to the right, and the third that has the same area on each side of the piston. pair of snips cuts straight. Banana oil. Nitrocellulose dissolved in amyl acetate, so Aviator’s oxygen. Oxygen that has had almost all of the named because it smells like bananas. water and water vapor removed from it. Bank (verb). The act of rotating an aircraft about its Avionics. The branch of technology that deals with the longitudinal axis. design, production, installation, use, and servicing of electronic equipment mounted in aircraft. Barometric scale. A small window in the dial of a sensitive altimeter in which the pilot sets the barometric pressure level Azimuth. A horizontal angular distance, measured clockwise from which the altitude shown on the altimeter is measured. from a fixed reference direction to an object. This window is sometimes called the “Kollsman” window. base. The electrode of a bipolar transistor between the emitter Back course. The reciprocal of the localizer course for an and the collector. Varying a small flow of electrons moving ILS (Instrument Landing System). When flying a back-course into or out of the base controls a much larger flow of electron approach, the aircraft approaches the instrument runway from between the emitter and the collector. the end on which the localizer antennas are installed. Base. The electrode of a bipolar transistor between the emitter Backhand welding. Welding in which the torch is pointed and the collector. Varying a small flow of electrons moving away from the direction the weld is progressing. into or out of the base controls a much larger flow of electrons between the emitter and the collector. Backplate (brake component). A floating plate on which the wheel cylinder and the brake shoes attach on an energizing- Bead (tire component). The high-strength carbon-steel wire type brake. bundles that give an aircraft tire its strength and stiffness where it mounts on the wheel. G-4

Bead seat area. The flat surface on the inside of the rim of Black box. A term used for any portion of an electrical or an aircraft wheel on which the bead of the tire seats. electronic system that can be removed as a unit. A black box does not have to be a physical box. Bearing strength (sheet metal characteristic). The amount of pull needed to cause a piece of sheet metal to tear at the Bladder-type fuel cell. A plastic-impregnated fabric bag points at which it is held together with rivets. The bearing supported in a portion of an aircraft structure so that it forms strength of a material is affected by both its thickness and a cell in which fuel is carried. the diameter of the rivet. Bleeder. A material such as glass cloth or mat that is placed Beehive spring. A hardened-steel, coil-spring retainer used over a composite lay-up to absorb the excess resin forced out to hold a rivet set in a pneumatic rivet gun. This spring gets of the ply fibers when pressure is applied. its name from its shape. It screws onto the end of the rivet gun and allows the set to move back and forth, but prevents Bleeding dope. Dope whose pigments are soluble in the it being driven from the gun. solvents or thinners used in the finishing system. The color will bleed up through the finished coats. Bend allowance. The amount of material actually used to make a bend in a piece of sheet metal. Bend allowance Bleeding of brakes. The maintenance procedure of removing depends upon the thickness of the metal and the radius of air entrapped in hydraulic fluid in the brakes. Fluid is bled the bend, and is normally found in a bend allowance chart. from the brake system until fluid with no bubbles flows out. Bend radius. The radius of the inside of a bend. Blimp. A cigar-shaped, nonrigid lighter-than-air flying machine. Bend tangent line. A line made in a sheet metal layout that Blush. A defect in a lacquer or dope finish caused by moisture indicates the point at which the bend starts. condensing on the surface before the finish dries. If the humidity of the air is high, the evaporation of the solvents Bernoulli’s principle. The basic principle that explains cools the air enough to cause the moisture to condense. The the relation between kinetic energy and potential energy in water condensed from the air mixes with the lacquer or dope fluids that are in motion. When the total energy in a column and forms a dull, porous, chalky-looking finish called blush. of moving fluid remains constant, any increase in the kinetic A blushed finish is neither attractive nor protective. energy of the fluid (its velocity) results in a corresponding decrease in its potential energy (its pressure). Bonding. The process of electrically connecting all isolated components to the aircraft structure. Bonding provides a Bezel. The rim that holds the glass cover in the case of an path for return current from electrical components, and a aircraft instrument. low-impedance path to ground to minimize static electrical charges. Shock-mounted components have bonding braids Bias-cut surface tape. A fabric tape in which the threads connected across the shock mounts. run at an angle of 45° to the length of the tape. Bias-cut tape may be stretched around a compound curve such as a wing Boost pump. An electrically driven centrifugal pump tip bow without wrinkling. mounted in the bottom of the fuel tanks in large aircraft. Boost pumps provide a positive flow of fuel under pressure to the Bilge area. A low portion in an aircraft structure in which engine for starting and serve as an emergency backup in the water and contaminants collect. The area under the cabin event an engine-driven pump should fail. They are also used floorboards is normally called the bilge. to transfer fuel from one tank to another and to pump fuel overboard when it is being dumped. Boost pumps prevent Bipolar transistor. A solid-state component in which the vapor locks by holding pressure on the fuel in the line to the flow of current between its emitter and collector is controlled engine-driven pump. Centrifugal boost pumps have a small by a much smaller flow of current into or out of its base. agitator propeller on top of the impeller to force vapors from Bipolar transistors may be of either the NPN or PNP type. the fuel before it leaves the tank. BITE. Built-in test equipment. Blade track. The condition of a helicopter rotor in which each blade follows the exact same path as the blade ahead of it. G-5

Boundary layer. The layer of air that flows next to an Bus. A point within an electrical system from which the aerodynamic surface. Because of the design of the surface individual circuits get their power. and local surface roughness, the boundary layer often has a random flow pattern, sometimes even flowing in a direction Buttock line. A line used to locate a position to the right or opposite to the direction of flight. A turbulent boundary layer left of the center line of an aircraft structure. causes a great deal of aerodynamic drag. Butyl. Trade name for a synthetic rubber product made by the Bourdon tube. A pressure-indicating mechanism used in polymerization of isobutylene. Butyl withstands such potent most oil pressure and hydraulic pressure gages. It consists of chemicals as phosphate ester-base (Skydrol) hydraulic fluids. a sealed, curved tube with an elliptical cross section. Pressure inside the tube tries to straighten it, and as it straightens, Cage (verb). To lock the gimbals of a gyroscopic instrument it moves a pointer across a calibrated dial. Bourdon-tube so it will not be damaged by abrupt flight maneuvers or pressure gauges are used to measure temperature by rough handling. measuring the vapor pressure in a sealed container of a volatile liquid, such as methyl chloride, whose vapor pressure Calendar month. A measurement of time used by the FAA varies directly with its temperature. for inspection and certification purposes. One calendar month from a given day extends from that day until midnight of the Brazing. A method of thermally joining metal parts by last day of that month. wetting the surface with a molten nonferrous alloy. When the molten material cools and solidifies, it holds the pieces Calender (fabric treatment). To pass fabric through a series together. Brazing materials melt at a temperature higher than of heated rollers to give it a smooth shiny surface. 800 °F, but lower than the melting temperature of the metal on which they are used. Calibrated airspeed (CAS). Indicated airspeed corrected for position error. See position error. British thermal unit (BTU). The amount of heat energy needed to raise the temperature of one pound of pure water 1 °F. Calorie. The amount of heat energy needed to raise the temperature of one gram of pure water 1 °C. Bucking bar. A heavy steel bar with smooth, hardened surfaces, or faces. The bucking bar is held against the end Canted rate gyro. A rate gyro whose gimbal axis is tilted of the rivet shank when it is driven with a pneumatic rivet so it can sense rotation of the aircraft about its roll axis as gun, and the shop head is formed against the bucking bar. well as its yaw axis. Buffeting. Turbulent movement of the air over an Camber (wheel alignment). The amount the wheels of an aerodynamic surface. aircraft are tilted, or inclined, from the vertical. If the top of the wheel tilts outward, the camber is positive. If the top of Bulb angle. An L-shaped metal extrusion having an enlarged, the wheel tilts inward, the camber is negative. rounded edge that resembles a bulb on one of its legs. Canard. A horizontal control surface mounted ahead of the Bulkhead. A structural partition that divides the fuselage of wing to provide longitudinal stability and control. an aircraft into compartments, or bays. Cantilever wing. A wing that is supported by its internal Bungee shock cord. A cushioning material used with the structure and requires no external supports. The wing spars nonshock absorbing landing gears installed on older aircraft. are built in such a way that they carry all the bending and Bungee cord is made up of many small rubber bands encased torsional loads. in a loose-woven cotton braid. Cap strip. The main top and bottom members of a wing rib. Burnish (verb). To smooth the surface of metal that has been The cap strips give the rib its aerodynamic shape. damaged by a deep scratch or gouge. The metal piled up at the edge of the damage is pushed back into the damage with a smooth, hard steel burnishing tool. Burr. A sharp rough edge of a piece of metal left when the metal was sheared, punched, or drilled. G-6

Capacitance-type fuel quantity measuring system. A Cavitation. A condition that exist in a hydraulic pump when popular type of electronic fuel quantity indicating system there is not enough pressure in the reservoir to force fluid to that has no moving parts in the fuel tank. The tank units are the inlet of the pump. The pump picks up air instead of fluid. cylindrical capacitors, called probes, mounted across the tank, from top to bottom. The dielectric between the plates CDI. Course deviation indicator. of the probes is either fuel or the air above the fuel, and the capacitance of the probe varies with the amount of fuel in CDU. Control display unit. the tank. The indicator is a servo-type instrument driven by the amplified output of a capacitance bridge. Center of gravity. The location on an aircraft about which the force of gravity is concentrated. Capillary tube. A soft copper tube with a small inside diameter. The capillary tube used with vapor-pressure Center of lift. The location of the chord line of an airfoil at thermometer connects the temperature sensing bulb to the which all the lift forces produced by the airfoil are considered Bourdon tube. The capillary tube is protected from physical to be concentrated. damage by enclosing it in a braided metal wire jacket. Center of pressure. The point on the chord line of an airfoil Carbon monoxide detector. A packet of chemical crystals where all of the aerodynamic forces are considered to be mounted in the aircraft cockpit or cabin where they are easily concentrated. visible. The crystals change their color from yellow to green when they are exposed to carbon monoxide. Centering cam. A cam in the nose-gear shock strut that causes the piston to center when the strut fully extends. Carbon-pile voltage regulator. A type of voltage regulator When the aircraft takes off and the strut extends, the wheel is used with high-output DC generators. Field current is straightened in its fore-and-aft position so it can be retracted controlled by varying the resistance of a stack of thin carbon into the wheel well. disks. This resistance is varied by controlling the amount the stack is compressed by a spring whose force is opposed by Charging stand (air conditioning service equipment). the pull of an electromagnet. The electromagnet’s strength A handy and compact arrangement of air conditioning is proportional to the generator’s output voltage. servicing equipment. A charging stand contains a vacuum pump, a manifold gauge set, and a method of measuring and Carburizing flame. An oxyacetylene flame produced by dispensing the refrigerant. an excess of acetylene. This flame is identified by a feather around the inner cone. A carburizing flame is also called a Chatter. A type of rapid vibration of a hydraulic pump reducing flame. caused by the pump taking in some air along with the hydraulic fluid. Carcass (tire component). The layers of rubberized fabric that make up the body of an aircraft tire. Check (wood defect). Longitudinal cracks that extend across a log’s annual rings. Case pressure. A low pressure that is maintained inside the case of a hydraulic pump. If a seal becomes damaged, Check valve. A hydraulic or pneumatic system component hydraulic fluid will be forced out of the pump rather than that allows full flow of fluid in one direction but blocks all allowing air to be drawn into the pump. flow in the opposite direction. Cathode-ray tube (CRT). A display tube used for Chemical oxygen candle system. An oxygen system used oscilloscopes and computer video displays. An electron gun for emergency or backup use. Solid blocks of material that emits a stream of electrons that is attracted to a positively release oxygen when they are burned are carried in special charged inner surface of the face of the tube. Acceleration and fireproof fixtures. When oxygen is needed, the candles are focusing grids speed the movement of the electrons and shape ignited with an integral igniter, and oxygen flows into the the beam into a pinpoint size. Electrostatic or electromagnetic tubing leading to the masks. forces caused by deflection plates or coils move the beam over the face of the tube. The inside surface of the face of the tube is treated with a phosphor material that emits light when the beam of electrons strikes it. G-7

Chevron seal. A form of one-way seal used in some fluid- Closed-center selector valve. A type of flow-control valve power actuators. A chevron seal is made of a resilient material used to direct pressurized fluid into one side of an actuator, whose cross section is in the shape of the letter V. The pressure and at the same time, direct the return fluid from the other being sealed must be applied to the open side of the V. side of the actuator to the fluid reservoir. Closed-center selector valves are connected in parallel between the pressure Chromel. An alloy of nickel and chromium used as the manifold and the return manifold. positive element in a thermocouple for measuring exhaust gas temperature. Coaxial. Rotating about the same axis. Coaxial rotors of a helicopter are mounted on concentric shafts in such a way Circle. A closed plane figure with every point an equal that they turn in opposite directions to cancel torque. distance from the center. A circle has the greatest area for its circumference of any enclosed shape. Coaxial cable. A special type of electrical cable that consists of a central conductor held rigidly in the center of a braided Circuit breaker. An electrical component that automatically outer conductor. Coaxial cable, commonly called coax, is used opens a circuit any time excessive current flows through it. for attaching radio receivers and transmitters to their antenna. A circuit breaker may be reset to restore the circuit after the fault causing the excessive current has been corrected. Coefficient of drag. A dimensionless number used in the formula for determining induced drag as it relates to the Clad aluminum. A sheet of aluminum alloy that has a angle of attack. coating of pure aluminum rolled on one or both of its surfaces for corrosion protection. Coefficient of lift. A dimensionless number relating to the angle of attack used in the formula for determining Clamp-on ammeter. An electrical instrument used to measure aerodynamic lift. current without opening the circuit through which it is flowing. The jaws of the ammeter are opened, slipped over the current- Coin dimpling. A process of preparing a hole in sheet metal carrying wire, and then clamped shut. Current flowing through for flush riveting. A coining die is pressed into the rivet hole to the wire produces a magnetic field which induces a voltage form a sharp-edged depression into which the rivet head fits. in the ammeter that is proportional to the amount of current. Collective pitch control. The helicopter control that changes Cleco fastener. A patented spring-type fastener used to the pitch of all of the rotor blades at the same time. Movement hold metal sheets in position until they can be permanently of the collective pitch control increases or decreases the lift riveted together. produced by the entire rotor disk. Close-quarter iron. A small hand-held iron with an Collodion. Cellulose nitrate used as a film base for certain accurately calibrated thermostat. This iron is used for heat- aircraft dopes. shrinking polyester fabrics in areas that would be difficult to work with a large iron. Combustion heater. A type of cabin heater used in some aircraft. Gasoline from the aircraft fuel tanks is burned in Closed angle. An angle formed in sheet metal that has been the heater. bent more than 90°. Compass fluid. A highly refined, water-clear petroleum Closed assembly time. The time elapsing between the product similar to kerosene. Compass fluid is used to dampen assembly of glued joints and the application of pressure. the oscillations of magnetic compasses. Closed-center hydraulic system. A hydraulic system in Compass rose. A location on an airport where an aircraft can which the selector valves are installed in parallel with each be taken to have its compasses “swung.” Lines are painted on other. When no unit is actuated, fluid circulates from the the rose to mark the magnetic directions in 30° increments. pump back to the reservoir without flowing through any of the selector valves. G-8

Compass swinging. A maintenance procedure that minimizes Compression strut. A heavy structural member, often in deviation error in a magnetic compass. The aircraft is aligned on the form of a steel tube, used to hold the spars of a Pratt a compass rose, and the compensating magnets in the compass truss airplane wing apart. A compression strut opposes the case are adjusted so the compass card indicates the direction compressive loads between the spars arising from the tensile marked on the rose. After the deviation error is minimized on all loads produced by the drag and antidrug wires. headings, a compass correction card is completed and mounted on the instrument panel next to the compass. Compression wood. A defect in wood that causes it to have a high specific gravity and the appearance of an excessive Compensated fuel pump. A vane-type, engine-driven growth of summerwood. In most species, there is little fuel pump that has a diaphragm connected to the pressure difference between the color of the springwood and the regulating valve. The chamber above the diaphragm is vented summerwood. Any material containing compression wood to the carburetor upper deck where it senses the pressure is unsuited for aircraft structural use and must be rejected. of the air as it enters the engine. The diaphragm allows the fuel pump to compensate for altitude changes and keeps the Compressor (air conditioning system component). carburetor inlet fuel pressure a constant amount higher than The component in a vapor-cycle cooling system in which the carburetor inlet air pressure. the low-pressure refrigerant vapors, after they leave the evaporator, are compressed to increase both their temperature Compensator port (brake system component). A small and pressure before they pass into the condenser. Some hole between a hydraulic brake master cylinder and the compressors are driven by electric motors, others by reservoir. When the brakes are released, this port is uncovered hydraulic motors and, in the case of most light airplanes, are and the fluid in the master cylinder is vented to the reservoir. belt driven from the engine. When the brake is applied, the master-cylinder piston covers the compensator port and allows pressure in the line to the Concave surface. A surface that is curved inward. The outer brake to build up and apply the brakes. When the brake is edges are higher than the center. released, the piston uncovers the compensator port. If any fluid has been lost from the brake, the reservoir will refill the Condenser (air conditioning system component). The master cylinder. A restricted compensator port will cause component in a vapor-cycle cooling system in which the the brakes to drag or will cause them to be slow to release. heat taken from the aircraft cabin is given up to the ambient air outside the aircraft. Composite. Something made up of different materials combined in such a way that the characteristics of the Conductor (electrical). A material that allows electrons to resulting material are different from those of any of the move freely from one atom to another within the material. components. Coning angle. The angle formed between the plane of Compound curve. A curve formed in more than one plane. rotation of a helicopter rotor blade when it is producing lift The surface of a sphere is a compound curve. and a line perpendicular to the rotor shaft. The degree of the coning angle is determined by the relationship between the Compound gauge (air conditioning servicing equipment). centrifugal force acting on the blades and the aerodynamic A pressure gauge used to measure the pressure in the low lift produced by the blades. side of an air conditioning system. A compound gauge is calibrated from zero to 30 inches of mercury vacuum, and Constant (mathematical). A value used in a mathematical from zero to about 150-psi positive gauge pressure. computation that is the same every time it is used. For example, the relationship between the length of the circumference of Compressibility effect. The sudden increase in the total drag a circle and the length of its diameter is a constant, 3.1416. of an airfoil in transonic flight caused by formation of shock This constant is called by the Greek name of Pi (π). waves on the surface. Constant differential mode (cabin pressurization). Compression failure. A type of structural failure in wood The mode of pressurization in which the cabin pressure is caused by the application of too great a compressive load. A maintained a constant amount higher than the outside air compression failure shows up as a faint line running at right pressure. The maximum differential pressure is determined angles to the grain of the wood. by the structural strength of the aircraft cabin. G-9

Constant-displacement pump. A fluid pump that moves a Continuous-loop fire-detection system. A fire-detection specific volume of fluid each time it rotates; the faster the system that uses a continuous loop of two conductors pump turns, the more fluid it moves. Some form of pressure separated with a thermistor-type insulation. Under normal regulator or relief valve must be used with a constant- temperature conditions, the thermistor material is an displacement pump when it is driven by an aircraft engine. insulator; but if it is exposed to a fire, the thermistor changes into a conductor and completes the circuit between the two Constant-speed drive (CSD). A special drive system used to conductors, initiating a fire warning. connect an alternating current generator to an aircraft engine. The drive holds the generator speed (and thus its frequency) Control horn. The arm on a control surface to which the constant as the engine speed varies. control cable or push-pull rod attaches to move the surface. Constantan. A copper-nickel alloy used as the negative Control stick. The type of control device used in some lead of a thermocouple for measuring the cylinder head airplanes. A vertical stick in the flight deck controls the temperature of a reciprocating engine. ailerons by side-to-side movement and the elevators by fore- and-aft movement. Contactor (electrical component). A remotely actuated, heavy-duty electrical switch. Contactors are used in an aircraft Control yoke. The movable column on which an airplane electrical system to connect the battery to the main bus. control wheel is mounted. The yoke may be moved in or out to actuate the elevators, and the control wheel may be rotated Continuity tester. A troubleshooting tool that consists to actuate the ailerons. of a battery, a light bulb, and test leads. The test leads are connected to each end of the conductor under test, and if the Controllability. The characteristic of an aircraft that allows bulb lights up, there is continuity. If it does not light up, the it to change its flight attitude in response to the pilot’s conductor is open. movement of the flight deck controls. Continuous Airworthiness Inspection Program. An Conventional current. An imaginary flow of electricity that inspection program that is part of a continuous airworthiness is said to flow from the positive terminal of a power source, maintenance program approved for certain large airplanes through the external circuit to its negative terminal. The (to which 14 CFR Part 125 is not applicable), turbojet arrowheads in semiconductor symbols point in the direction multi-engine airplanes, turbopropeller-powered multi-engine of conventional current flow. airplanes, and turbine-powered rotorcraft. Converging duct. A duct, or passage, whose cross-sectional Continuous-duty solenoid. A solenoid-type switch designed area decreases in the direction of fluid flow. to be kept energized by current flowing through its coil for an indefinite period of time. The battery contactor in an aircraft Conversion coating. A chemical solution used to form an electrical system is a continuous-duty solenoid. Current flows airtight oxide or phosphate film on the surface of aluminum through its coil all the time the battery is connected to the or magnesium parts. The conversion coating prevents air from electrical system. reaching the metal and keeps it from corroding. Continuous-flow oxygen system. A type of oxygen system Convex surface. A surface that is curved outward. The outer that allows a metered amount of oxygen to continuously edges are lower than the center. flow into the mask. A rebreather-type mask is used with a continuous-flow system. The simplest form of continuous- Coriolis effect. The change in rotor blade velocity to flow oxygen system regulates the flow by a calibrated orifice compensate for a change in the distance between the center in the outlet to the mask, but most systems use either a manual of mass of the rotor blade and the axis rotation of the blade or automatic regulator to vary the pressure across the orifice as the blades flap in flight. proportional to the altitude being flown. Cornice brake. A large shop tool used to make straight bends across a sheet of metal. Cornice brakes are often called leaf brakes. G-10

Corrugated metal. Sheets of metal that have been made Cuno filter. The registered trade name for a particular style more rigid by forming a series of parallel ridges or waves of edge-type fluid filter. Cuno filters are made up of a stack in its surface. of thin metal disks that are separated by thin scraper blades. Contaminants collect on the edge of the disks, and they are Cotter pin. A split metal pin used to safety a castellated or periodically scraped out and allowed to collect in the bottom slotted nut on a bolt. The pin is passed through the hole in of the filter case for future removal. the shank of the bolt and the slots in the nut, and the ends of the pin are spread to prevent it backing out of the hole. Current. A general term used for electrical flow. See conventional current. Countersinking. Preparation of a rivet hole for a flush rivet by beveling the edges of the holes with a cutter of the Current limiter. An electrical component used to limit the correct angle. amount of current a generator can produce. Some current limiters are a type of slow-blow fuse in the generator output. Coverite surface thermometer. A small surface-type Other current limiters reduce the generator output voltage bimetallic thermometer that calibrates the temperature of an if the generator tries to put out more than its rated current. iron used to heat-shrink polyester fabrics. Cusp. A pointed end. Crabbing. Pointing the nose of an aircraft into the wind to compensate for wind drift. Cyclic pitch control. The helicopter control that allows the pilot to change the pitch of the rotor blades individually, at Crazing. A form of stress-caused damage that occurs in a a specific point in their rotation. The cyclic pitch control transparent thermoplastic material. Crazing appears as a series allows the pilot to tilt the plane of rotation of the rotor disk of tiny, hair-like cracks just below the surface of the plastic. to change the direction of lift produced by the rotor. Critical Mach number. The flight Mach number at which Dacron. The registered trade name for a cloth woven from there is the first indication of supersonic airflow over any polyester fibers. part of the aircraft structure. Damped oscillation. Oscillation whose amplitude decreases Cross coat. A double coat of aircraft finishing material in with time. which the second coat is sprayed at right angles to the first coat, before the solvents have evaporated from the first coat. Database. A body of information that is available on any particular subject. Cross-feed valve (fuel system component). A valve in a fuel system that allows any of the engines of a multi-engine Data bus. A wire or group of wires that are used to move aircraft to draw fuel from any fuel tank. Cross-feed systems data within a computer system. are used to allow a multi-engine aircraft to maintain a balanced fuel condition. Debooster valve. A valve in a power brake system between the power brake control valve and the wheel cylinder. This Cross-flow valve. An automatic flow-control valve installed valve lowers the pressure of the fluid going to the brake between the gear-up and gear-down lines of the landing gear and increases its volume. A debooster valve increases the of some large airplanes. When the landing gear is released smoothness of brake application and aids in rapid release from its uplocks, its weight causes it to fall faster than the of the brakes. hydraulic system can supply fluid to the gear-down side of the actuation cylinder. The cross-flow valve opens and Decay. The breakdown of the structure of wood fibers. Wood directs fluid from the gear-up side into the gear-down side. that shows any indication of decay must be rejected for use This allows the gear to move down with a smooth motion. in aircraft structure. CRT. Cathode-ray tube. Decomposition. The breakdown of the structure of wood fibers. Wood that shows any indication of decay must be Cryogenic liquid. A liquid which boils at temperatures of less rejected for use in aircraft structure. than about 110 °F (–163 °C) at normal atmospheric pressures. G-11

Deciduous. A type of tree that sheds its foliage at the end of Detent. A spring-loaded pin or tab that enters a hole or groove the growing season. Hardwoods come from deciduous trees. when the device to which it is attached is in a certain position. Detents are used on a fuel valve to provide a positive means Dedicated computer. A small digital computer, often built of identifying the fully on and fully off position of the valve. into an instrument or control device that contains a built-in program that causes it to perform a specific function. Detonation. An explosion, or uncontrolled burning of the fuel-air mixture inside the cylinder of a reciprocating engine. Deep-vacuum pump. A vacuum pump capable of removing Detonation occurs when the pressure and the temperature almost all of the air from a refrigeration system. A deep- inside the cylinder become higher than the critical pressure vacuum pump can reduce the pressure inside the system to and temperature of the fuel. Detonation is often confused a few microns of pressure. with preignition. Deflator cap. A cap for a tire, strut, or accumulator air valve Deviation error. An error in a magnetic compass caused that, when screwed onto the valve, depresses the valve stem by localized magnetic fields in the aircraft. Deviation error, and allows the air to escape safely through a hole in the side which is different on each heading, is compensated by the of the cap. technician “swinging” the compass. A compass must be compensated so the deviation error on any heading is no Deicer system. A system that removes ice after it has formed greater than 10 degrees. on an aircraft. Dewar bottle. A vessel designed to hold liquefied gases. It Delamination. The separation of the layers of a laminated has double walls with the space between being evacuated to material. prevent the transfer of heat. The surfaces in the vacuum area are made heat-reflective. Delivery air duct check valve. An isolation valve at the discharge side of the air turbine that prevents the loss of Differential aileron travel. Aileron movement in which the pressurization through a disengaged cabin air compressor. upward-moving aileron deflects a greater distance than the one moving downward. The up aileron produces parasite drag Delta airplane. An airplane with a triangular-shaped wing. to counteract the induced drag caused by the down aileron. This wing has an extreme amount of sweepback on its leading Differential aileron travel is used to counteract adverse yaw. edge, and a trailing edge that is almost perpendicular to the longitudinal axis of the airplane. Differential pressure. The difference between two pressures. An airspeed indicator is a differential-pressure gauge. It Delta connection (electrical connection). A method of measures the difference between static air pressure and pitot connecting three electrical coils into a ring or, as they are air pressure. drawn on a schematic diagram as a triangle, a delta (D). Differential-voltage reverse-current cutout. A type of Denier. A measure of the fineness of the yarns in a fabric. reverse-current cutout switch used with heavy-duty electrical systems. This switch connects the generator to the electrical Density altitude. The altitude in standard air at which the bus when the generator voltage is a specific amount higher density is the same as that of the existing air. than the battery voltage. Density ratio (σ). The ratio of the density of the air at a Digital multimeter. An electrical test instrument that can be given altitude to the density of the air at sea level under used to measure voltage, current, and resistance. The indication standard conditions. is in the form of a liquid crystal display in discrete numbers. Derated (electrical specification). Reduction in the rated Dihedral. The positive angle formed between the lateral axis voltage or current of an electrical component. Derating is of an airplane and a line that passes through the center of the done to extend the life or reliability of the device. wing or horizontal stabilizer. Dihedral increases the lateral stability of an airplane. Desiccant (air conditioning component). A drying agent used in an air conditioning system to remove water from the refrigerant. A desiccant is made of silica-gel or some similar material. G-12

Diluter-demand oxygen system. A popular type of oxygen Downwash. Air forced down by aerodynamic action below system in which the oxygen is metered to the mask, where and behind the wing of an airplane or the rotor of a helicopter. it is diluted with cabin air by an airflow-metering aneroid Aerodynamic lift is produced when the air is deflected assembly which regulates the amount of air allowed to downward. The upward force on the aircraft is the same as dilute the oxygen on the basis of cabin altitude. The mixture the downward force on the air. of oxygen and air flows only when the wearer of the mask inhales. The percentage of oxygen in the air delivered to the Drag (helicopter rotor blade movement). Fore-and-aft mask is regulated, on the basis of altitude, by the regulator. movement of the tip of a helicopter rotor blade in its plane A diluter-demand regulator has an emergency position which of rotation. allows 100 percent oxygen to flow to the mask, by-passing the regulating mechanism. Dragging brakes. Brakes that do not fully release when the brake pedal is released. The brakes are partially applied all Dipole antenna. A half wavelength, center-fed radio antenna. the time, which causes excessive lining wear and heat. The length of each of the two arms is approximately one fourth of the wavelength of the center frequency for which Drag wire. A structural wire inside a Pratt truss airplane the antenna is designed. wing between the spars. Drag wires run from the front spar inboard, to the rear spar at the next bay outboard. Drag wires Dirigible. A large, cigar-shaped, rigid, lighter-than-air flying oppose the forces that try to drag the wing backward. machine. Dirigibles are made of a rigid truss structure covered with fabric. Gas bags inside the structure contain the lifting Drill motor. An electric or pneumatic motor that drives a gas, which is either helium or hydrogen. chuck that holds a twist drill. The best drill motors produce high torque, and their speed can be controlled. Disc area (helicopter specification). The total area swept by the blades of a helicopter main rotor. Drip stick. A fuel quantity indicator used to measure the fuel level in the tank when the aircraft is on the ground. The Divergent oscillation. Oscillation whose amplitude increases drip stick is pulled down from the bottom of the tank until with time. fuel drips from its opened end. This indicates that the top of the gauge inside the tank is at the level of the fuel. Note the Diverging duct. A duct, or passage, whose cross-sectional number of inches read on the outside of the gauge at the point area increases in the direction of fluid flow. it contacts the bottom of the tank, and use a drip stick table to convert this measurement into gallons of fuel in the tank. DME. Distance measuring equipment. Dry air pump. An engine-driven air pump which used carbon Dope proofing. The treatment of a structure to be covered vanes. Dry pumps do not use any lubrication, and the vanes with fabric to keep the solvents in the dope from softening are extremely susceptible to damage from the solid airborne the protective coating on the structure. particles. These pumps must be operated with filters in their inlet so they will take in only filtered air. Dope roping. A condition of aircraft dope brushed onto a surface in such a way that it forms a stringy, uneven surface Dry ice. Solidified carbon dioxide. Dry ice sublimates, or rather than flowing out smoothly. changes from a solid directly into a gas, at a temperature of –110 °F (–78.5 °C). Double-acting actuator (hydraulic system component). A linear actuator moved in both directions by fluid power. Dry rot. Decomposition of wood fibers caused by fungi. Dry rot destroys all strength in the wood. Double-acting hand pump (hydraulic system component). A hand-operated fluid pump that moves fluid during both Ductility. The property of a material that allows it to be strokes of the pump handle. drawn into a thin section without breaking. Doubler. A piece of sheet metal used to strengthen and stiffen Dummy load (electrical load). A noninductive, high-power, a repair in a sheet metal structure. 50-ohm resistor that can be connected to a transmission line in place of the antenna. The transmitter can be operated into Downtime. Any time during which an aircraft is out of the dummy load without transmitting any signal. commission and unable to be operated. G-13

Duralumin. The name for the original alloy of aluminum, EICAS. Engine Indicating and Crew Alerting System. magnesium, manganese, and copper. Duralumin is the same as the modern 2017 aluminum alloy. Ejector. A form of jet pump used to pick up a liquid and move it to another location. Ejectors are used to ensure that Dutch roll. An undesirable, low-amplitude coupled the compartment in which the boost pumps are mounted is oscillation about both the yaw and roll axes that affects many kept full of fuel. Part of the fuel from the boost pump flowing swept wing airplanes. Dutch roll is minimized by the use of through the ejector produces a low pressure that pulls fuel from a yaw damper. the main tank and forces it into the boostpump sump area. Dutchman shears. A common name for compound-action Elastic limit. The maximum amount of tensile load, in sheet metal shears. pounds per square inch, a material is able to withstand without being permanently deformed. Dynamic pressure (q). The pressure a moving fluid would have if it were stopped. Dynamic pressure is measured in Electromotive force (EMF). The force that causes electrons pounds per square foot. to move from one atom to another within an electrical circuit. Electromotive force is an electrical pressure, and it Dynamic stability. The stability that causes an aircraft to is measured in volts. return to a condition of straight and level flight after it has been disturbed from this condition. When an aircraft is disturbed Electron current. The actual flow of electrons in a circuit. from the straight and level flight, its static stability starts it back Electrons flow from the negative terminal of a power source in the correct direction; but it overshoots, and the corrective through the external circuit to its positive terminal. The forces are applied in the opposite direction. The aircraft arrowheads in semiconductor symbols point in the direction oscillates back and forth on both sides of the correct condition, opposite to the flow of electron current. with each oscillation smaller than the one before it. Dynamic stability is the decreasing of these restorative oscillations. ELT (emergency locator transmitter). A self-contained radio transmitter that automatically begins transmitting on EADI. Electronic Attitude Director Indicator. the emergency frequencies any time it is triggered by a severe impact parallel to the longitudinal axis of the aircraft. ECAM. Electronic Centralized Aircraft Monitor. Elevator downspring. A spring in the elevator control Eccentric brushing. A special bushing used between the system that produces a mechanical force that tries to lower the rear spar of certain cantilever airplane wings and the wing elevator. In normal flight, this spring force is overcome by the attachment fitting on the fuselage. The portion of the bushing aerodynamic force from the elevator trim tab. But in slow flight that fits through the hole in the spar is slightly offset from that with an aft CG position, the trim tab loses its effectiveness and which passes through the holes in the fitting. By rotating the the downspring lowers the nose to prevent a stall. bushing, the rear spar may be moved up or down to adjust the root incidence of the wing. Elevons. Movable control surfaces on the trailing edge of a delta wing or a flying wing airplane. These surfaces operate together Eddy current damping (electrical instrument damping). to serve as elevators, and differentially to act as ailerons. Decreasing the amplitude of oscillations by the interaction of magnetic fields. In the case of a vertical-card magnetic EMI. Electromagnetic interference. compass, flux from the oscillating permanent magnet produces eddy currents in a damping disk or cup. The Empennage. The tail section of an airplane. magnetic flux produced by the eddy currents opposes the flux from the permanent magnet and decreases the oscillations. Enamel. A type of finishing material that flows out to form a smooth surface. Enamel is usually made of a pigment Edge distance. The distance between the center of a rivet suspended in some form of resin. When the resin cures, it hole and the edge of the sheet of metal. leaves a smooth, glossy protective surface. EFIS. Electronic Flight Instrument System. EHSI. Electronic Horizontal Situation Indicator. G-14

Energizing brake. A brake that uses the momentum of the Expansion wave. The change in pressure and velocity of a aircraft to increase its effectiveness by wedging the shoe supersonic flow of air as it passes over a surface which drops against the brake drum. Energizing brakes are also called servo away from the flow. As the surface drops away, the air tries brakes. A single-servo brake is energizing only when moving to follow it. In changing its direction, the air speeds up to a in the forward direction, and a duo-servo brake is energizing higher supersonic velocity and its static pressure decreases. when the aircraft is moving either forward or backward. There is no change in the total energy as the air passes through an expansion wave, and so there is no sound as there is when Epoxy. A flexible, thermosetting resin that is made by air passes through a shock wave. polymerization of an epoxide. Epoxy has wide application as a matrix for composite materials and as an adhesive that Extruded angle. A structural angle formed by passing metal bonds many different types of materials. It is noted for its heated to its plastic state through specially shaped dies. durability and its chemical resistance. FAA Form 337. The FAA form that must be filled in and Equalizing resistor. A large resistor in the ground circuit submitted to the FAA when a major repair or major alteration of a heavy-duty aircraft generator through which all of the has been completed. generator output current flows. The voltage drop across this resistor is used to produce the current in the paralleling circuit Federal Aviation Administration Flight Standards that forces the generators to share the electrical load equally. District Office (FAA FSDO). An FAA field office serving an assigned geographical area staffed with Flight Standards Ethylene dibromide. A chemical compound added to personnel who serve the aviation industry and the general aviation gasoline to convert some of the deposits left by public on matters relating to certification and operation of the tetraethyl lead into lead bromides. These bromides are air carrier and general aviation aircraft. volatile and will pass out of the engine with the exhaust gases. Fading of brakes. The decrease in the amount of braking Ethylene glycol. A form of alcohol used as a coolant for action that occurs with some types of brakes that are applied liquid-cooled engines and as an anti-icing agent. for a long period of time. True fading occurs with overheated drum-type brakes. As the drum is heated, it expands in a Eutectic material. An alloy or solution that has the lowest bell-mouthed fashion. This decreases the amount of drum possible melting point. in contact with the brake shoes and decreases the braking action. A condition similar to brake fading occurs when there Evacuation (air conditioning servicing procedure). is an internal leak in the brake master cylinder. The brakes A procedure in servicing vapor-cycle cooling systems. are applied, but as the pedal is held down, fluid leaks past A vacuum pump removes all the air from the system. the piston, and the brakes slowly release. Evacuation removes all traces of water vapor that could condense out, freeze, and block the system. Fairing. A part of a structure whose primary purpose is to produce a smooth surface or a smooth junction where two Evaporator (air conditioning component). The component surfaces join. in a vapor-cycle cooling system in which heat from the aircraft cabin is absorbed into the refrigerant. As the heat is Fairlead. A plastic or wooden guide used to prevent a steel absorbed, the refrigerant evaporates, or changes from a liquid control cable rubbing against an aircraft structure. into a vapor. The function of the evaporator is to lower the cabin air temperature. FCC. Federal Communications Commission. Expander-tube brake. A brake that uses hydraulic fluid FCC. Flight Control Computer. inside a synthetic rubber tube around the brake hub to force rectangular blocks of brake-lining material against the Feather (helicopter rotor blade movement). Rotation of a rotating brake drum. Friction between the brake drum and helicopter rotor blade about its pitch-change axis. the lining material slows the aircraft. Ferrous metal. Any metal that contains iron and has magnetic characteristics. G-15

Fiber stop nut. A form of a self-locking nut that has a fiber Flap (helicopter rotor blade movement). Up-and-down insert crimped into a recess above the threads. The hole in movement of the tip of a helicopter rotor blade. the insert is slightly smaller than the minor diameter of the threads. When the nut is screwed down over the bolt threads, Flap overload valve. A valve in the flap system of an airplane the opposition caused by the fiber insert produces a force that that prevents the flaps being lowered at an airspeed which prevents vibration loosening the nut. could cause structural damage. If the pilot tries to extend the flaps when the airspeed is too high, the opposition caused File. A hand-held cutting tool used to remove a small amount by the air flow will open the overload valve and return the of metal with each stroke. fluid to the reservoir. Fill threads. Threads in a piece of fabric that run across the Flash point. The temperature to which a material must be width of the fabric, interweaving with the warp threads. Fill raised for it to ignite, but not continue to burn, when a flame threads are often called woof, or weft, threads. is passed above it. Fillet. A fairing used to give shape but not strength to Flat pattern layout. The pattern for a sheet metal part that an object. A fillet produces a smooth junction where two has the material used for each flat surface, and for all of the surfaces meet. bends, marked out with bend-tangent lines drawn between the flats and bend allowances. Finishing tape. Another name for surface tape. See surface tape. Flight controller. The component in an autopilot system that allows the pilot to maneuver the aircraft manually when the Fishmouth splice. A type of splice used in a welded tubular autopilot is engaged. structure in which the end of the tube whose inside diameter is the same as the outside diameter of the tube being spliced Fluid. A form of material whose molecules are able to flow is cut in the shape of a V, or a fishmouth, and is slipped over past one another without destroying the material. Gases and the smaller tube welded. A fishmouth splice has more weld liquids are both fluids. area than a butt splice and allows the stresses from one tube to transfer into the other tube gradually. Fluid power. The transmission of force by the movement of a fluid. The most familiar examples of fluid power systems Fire pull handle. The handle in an aircraft flight deck that is are hydraulic and pneumatic systems. pulled at the first indication of an engine fire. Pulling this handle removes the generator from the electrical system, shuts off the Flutter. Rapid and uncontrolled oscillation of a flight fuel and hydraulic fluid to the engine, and closes the compressor control surface on an aircraft that is caused by a dynamically bleed air valve. The fire extinguisher agent discharge switch unbalanced condition. is uncovered, but it is not automatically closed. Fly-by-wire. A method of control used by some modern Fire zone. A portion of an aircraft designated by the aircraft in which control movement or pressures exerted by manufacturer to require fire-detection and/or fire-extinguishing the pilot are directed into a digital computer where they are equipment and a high degree of inherent fire resistance. input into a program tailored to the flight characteristics of the aircraft. The computer output signal is sent to actuators Fitting. An attachment device that is used to connect at the control surfaces to move them the optimum amount components to an aircraft structure. for the desired maneuver. Fixed fire-extinguishing system. A fire-extinguishing Flying boat. An airplane whose fuselage is built in the form system installed in an aircraft. of a boat hull to allow it to land and takeoff from water. In the past, flying boats were a popular form of large airplane. Flameout. A condition in the operation of a gas turbine engine in which the fire in the engine unintentionally goes out. Flying wing. A type of heavier-than-air aircraft that has no fuselage or separate tail surfaces. The engines and useful load Flap (aircraft control). A secondary control on an airplane are carried inside the wing, and movable control surfaces on wing that changes its camber to increase both its lift and its drag. the trailing edge provide both pitch and roll control. G-16