FAA-H-8083-15B Instrument Flying Handbook

1-32 Alternate minimumsMINIMUMSPROFILESW-1, 16 DEC 2010 to 13 JAN 2011PLAN VIEWPILOT BRIEFING not authorizedAND Field elevationPROCEDURE NOTES Touchdown zone elevation PAPI Approach lights Figure 1-24. RNAV instrument approach charts. SE-4, 16 DEC 2010 to 13 JAN 2011SW-1, 16 DEC 2010 to 13 JAN 2011 MINI- PROFILE AIRPORT PLAN VIEW PILOT BRIEFING MUMS DIAGRAM AND PROCEDURE NOTES VASI AIRPORT SE-4, 16 DEC 2010 to 13 JAN 2011 DIAGRAM Runway lights pilot controlled

TheChapter2 Air Traffic Control System Introduction This chapter covers the communication equipment, communication procedures, and air traffic control (ATC) facilities and services available for a flight under instrument flight rules (IFR) in the National Airspace System (NAS). 2-1

Communication Equipment simplex operation). It is possible to communicate with some flight service stations (FSS) by transmitting on 122.1 MHz Navigation/Communication Equipment (selected on the communication radio) and receiving on a Civilian pilots communicate with ATC on frequencies in VHF omnidirectional range (VOR) frequency (selected on the very high frequency (VHF) range between 118.000 and the navigation radio). This is called duplex operation. 136.975 MHz. To derive full benefit from the ATC system, radios capable of 25 kHz spacing are required (e.g., 134.500, An audio panel allows a pilot to adjust the volume of the 134.575, 134.600). If ATC assigns a frequency that cannot selected receiver(s) and to select the desired transmitter. be selected, ask for an alternative frequency. [Figure 2-2] The audio panel has two positions for receiver selection, cabin speaker, and headphone (some units might Figure 2-1 illustrates a typical radio panel installation have a center “OFF” position). Use of a hand-held microphone consisting of a communications transceiver on the left and and the cabin speaker introduces the distraction of reaching a navigational receiver on the right. Many radios allow the for and hanging up the microphone. A headset with a boom pilot to have one or more frequencies stored in memory and microphone is recommended for clear communications. The one frequency active for transmitting and receiving (called microphone should be positioned close to the lips to reduce Figure 2-1. Typical navigation/communication installation. Figure 2-2. Audio panel. 2-2

the possibility of ambient flight deck noise interfering with transmissions to the controller. Headphones deliver the received signal directly to the ears; therefore, ambient noise does not interfere with the pilot’s ability to understand the transmission. [Figure 2-3] Headset Figure 2-4. Combination GPS-com unit. Boom microphone Radar and Transponders ATC radars have a limited ability to display primary returns, which is energy reflected from an aircraft’s metallic structure. Their ability to display secondary returns (transponder replies to ground interrogation signals) makes possible the many advantages of automation. Push-to-talk switch A transponder is a radar beacon transmitter/receiver installed in the instrument panel. ATC beacon transmitters send out interrogation signals continuously as the radar antenna rotates. When an interrogation is received by a transponder, a coded reply is sent to the ground station where it is displayed on the controller’s scope. A reply light on the transponder panel flickers every time it receives and replies to a radar interrogation. Transponder codes are assigned by ATC. Figure 2-3. Boom microphone, headset, and push-to-talk switch. When a controller asks a pilot to “ident” and the ident button is pushed, the return on the controller’s scope is intensified for Switching the transmitter selector between COM1 and precise identification of a flight. When requested, briefly push COM2 changes both transmitter and receiver frequencies. the ident button to activate this feature. It is good practice It is necessary only when a pilot wants to monitor one for pilots to verbally confirm that they have changed codes frequency while transmitting on another. One example is or pushed the ident button. listening to Automatic Terminal Information Service (ATIS) on one receiver while communicating with ATC on the Mode C (Altitude Reporting) other. Monitoring a navigation receiver to check for proper Primary radar returns indicate only range and bearing from identification is another reason to use the switch panel. the radar antenna to the target; secondary radar returns can display altitude, Mode C, on the control scope if the aircraft Most audio switch panels also include a marker beacon is equipped with an encoding altimeter or blind encoder. In receiver. All marker beacons transmit on 75 MHz, so there either case, when the transponder’s function switch is in the is no frequency selector. ALT position, the aircraft’s pressure altitude is sent to the controller. Adjusting the altimeter’s Kollsman window has Figure 2-4 illustrates an increasingly popular form of no effect on the altitude read by the controller. navigation/communication radio; it contains a global positioning system (GPS) receiver and a communications Transponders, when installed, must be ON at all times when transceiver. Using its navigational capability, this unit can operating in controlled airspace; altitude reporting is required determine when a flight crosses an airspace boundary or fix by regulation in Class B and Class C airspace and inside a and can automatically select the appropriate communications 30-mile circle surrounding the primary airport in Class B frequency for that location in the communications radio. airspace. Altitude reporting should also be ON at all times. 2-3

Communication Procedures AChaaracAterb Morse Code Telephony Phonic AAa (Pronunciation) Clarity in communication is essential for a safe instrument CBCBcb flight. This requires pilots and controllers to use terms that DDd are understood by both—the Pilot/Controller Glossary in the EEe Aeronautical Information Manual (AIM) is the best source of FFf terms and definitions. The AIM is revised twice a year and GGg new definitions are added, so the glossary should be reviewed hHh frequently. Because clearances and instructions are comprised IIi largely of letters and numbers, a phonetic pronunciation guide KJKJkj has been developed for both. [Figure 2-5] LLL MMm ATC must follow the guidance of the Air Traffic Control NNn Manual when communicating with pilots. The manual OPOPop presents the controller with different situations and prescribes QQq precise terminology that must be used. This is advantageous SRRSsr for pilots because once they have recognized a pattern or UTUTtu format, they can expect future controller transmissions VVv to follow that format. Controllers are faced with a wide WWw variety of communication styles based on pilot experience, XXx proficiency, and professionalism. YYy ZZz Pilots should study the examples in the AIM, listen to 111 other pilots communicate, and apply the lessons learned 222 to their own communications with ATC. Pilots should ask 333 for clarification of a clearance or instruction. If necessary, 444 use plain English to ensure understanding, and expect the 555 controller to reply in the same way. A safe instrument flight N6n is the result of cooperation between controller and pilot. OP78po Q9q Communication Facilities R0r The controller’s primary responsibility is separation of Figure 2-5. FPihgounreeti9c-5pr. oPnhuonnceiatitcioPnrognuuindcei.ation Guide. aircraft operating under IFR. This is accomplished with ATC facilities, to include the FSS, airport traffic control tower ground communication outlets (GCOs), and by using duplex (ATCT), terminal radar approach control (TRACON), and transmissions through navigational aids (NAVAIDs). The air route traffic control center (ARTCC). best source of information on frequency usage is the Airport/ Facility Directory (A/FD) and the legend panel on sectional Flight Service Stations (FSS) charts also contains contact information. A pilot’s first contact with ATC is usually through FSS, either by radio or telephone. FSSs provide pilot briefings, receive and process flight plans, relay ATC clearances, originate Notices to Airmen (NOTAMs), and broadcast aviation weather. Some facilities provide En Route Flight Advisory Service (EFAS), take weather observations, and advise United States Customs and Immigration of international flights. Telephone contact with Flight Service can be obtained by dialing 1-800-WX-BRIEF. This number can be used anywhere in the United States and connects to the nearest FSS based on the area code from which the call originates. There are a variety of methods of making radio contact: direct transmission, remote communication outlets (RCOs), 2-4

The briefer sends a flight plan to the host computer at the control); and transponder code. With the exception of the ARTCC (Center). After processing the flight plan, the transponder code, a pilot knows most of these items before computer sends flight strips to the tower, to the radar facility engine start. One technique for clearance copying is writing that handles the departure route, and to the Center controller C-R-A-F-T. whose sector the flight first enters. Figure 2-6 shows a typical strip. These strips are delivered approximately 30 minutes Assume an IFR flight plan has been filed from Seattle, prior to the proposed departure time. Strips are delivered to Washington to Sacramento, California via V-23 at 7,000 en route facilities 30 minutes before the flight is expected to feet. Traffic is taking off to the north from Seattle-Tacoma enter their airspace. If a flight plan is not opened, it will “time (Sea-Tac) airport and, by monitoring the clearance delivery out” 2 hours after the proposed departure time. frequency, a pilot can determine the departure procedure being assigned to southbound flights. The clearance limit When departing an airport in Class G airspace, a pilot receives is the destination airport, so write “SAC” after the letter C. an IFR clearance from the FSS by radio or telephone. It Write “SEATTLE TWO – V23” after R for Route because contains either a clearance void time, in which case an aircraft departure control issued this departure to other flights. Write must be airborne prior to that time, or a release time. Pilots “70” after the A, the departure control frequency printed on should not take off prior to the release time. Pilots can help the approach charts for Sea-Tac after F, and leave the space the controller by stating how soon they expect to be airborne. after the letter T blank—the transponder code is generated by If the void time is, for example, 10 minutes past the hour and computer and can seldom be determined in advance. Then, an aircraft is airborne at exactly 10 minutes past the hour, call clearance delivery and report “Ready to copy.” the clearance is void—a pilot must take off prior to the void time. A specific void time may be requested when filing a As the controller reads the clearance, check it against what flight plan. is already written down; if there is a change, draw a line through that item and write in the changed item. Chances ATC Towers are the changes are minimal, and most of the clearance is Several controllers in the tower cab are involved in handling copied before keying the microphone. Still, it is worthwhile an instrument flight. Where there is a dedicated clearance to develop clearance shorthand to decrease the verbiage that delivery position, that frequency is found in the A/FD and must be copied (see Appendix 1). on the instrument approach chart for the departure airport. Where there is no clearance delivery position, the ground Pilots are required to have either the text of a departure controller performs this function. At the busiest airports, pre- procedure (DP) or a graphic representation (if one is taxi clearance is required; the frequency for pre-taxi clearance available), and should review it before accepting a clearance. can be found in the A/FD. Taxi clearance should be requested This is another reason to find out ahead of time which DP is not more than 10 minutes before proposed taxi time. in use. If the DP includes an altitude or a departure control frequency, those items are not included in the clearance. It is recommended that pilots read their IFR clearance back to the clearance delivery controller. Instrument clearances can The last clearance received supersedes all previous clearances. be overwhelming when attempting to copy them verbatim, For example, if the DP says “Climb and maintain 2,000 feet, but they follow a format that allows a pilot to be prepared expect higher in 6 miles,” but upon contacting the departure when responding “Ready to copy.” The format is: clearance controller a new clearance is received: “Climb and maintain limit (usually the destination airport); route, including any 8,000 feet,” the 2,000 feet restriction has been canceled. This departure procedure; initial altitude; frequency (for departure rule applies in both terminal and Center airspace. Call sign—Northwest 196 Departure point—San Diego Altitude—37,000 feet Destination—Minneapolis Figure 9-6. Flight Strip. Figure 2-6. Flight strip. 2-5

When reporting “ready to copy” an IFR clearance before the strip has been received from the Center computer, pilots are advised “clearance on request.” The controller initiates contact when it has been received. This time can be used for taxi and pre-takeoff checks. The local controller is responsible for operations in the Class Figure 2-7.FCigoumrebi9n-e7d. rCaodmarbianned Rbaeadcaor nanadnBteenancao.n Antenna.348 D airspace and on the active runways. At some towers, 013 designated as IFR towers, the local controller has vectoring 057 authority. At visual flight rules (VFR) towers, the local 250 102 controller accepts inbound IFR flights from the terminal radar facility and cannot provide vectors. The local controller also 277 coordinates flights in the local area with radar controllers. 289 Although Class D airspace normally extends 2,500 feet above field elevation, towers frequently release the top 500 feet to 160 the radar controllers to facilitate overflights. Accordingly, when a flight is vectored over an airport at an altitude that appears to enter the tower controller’s airspace, there is no need to contact the tower controller—all coordination is handled by ATC. The departure radar controller may be in the same building as the control tower, but it is more likely that the departure radar position is remotely located. The tower controller will not issue a takeoff clearance until the departure controller issues a release. Terminal Radar Approach Control (TRACON) TRACONs are considered terminal facilities because they provide the link between the departure airport and the en route structure of the NAS. Terminal airspace normally extends 30 nautical miles (NM) from the facility with a vertical extent of 10,000 feet; however, dimensions vary widely. Class B and Class C airspace dimensions are provided on aeronautical charts. At terminal radar facilities, the airspace is divided into sectors, each with one or more controllers, and each sector is assigned a discrete radio frequency. All terminal facilities are approach controls and should be addressed as “Approach” except when directed to do otherwise (e.g., “Contact departure on 120.4.”). Terminal radar antennas are located on or adjacent to the Figure 2-8. Minimum vectoring altitude (MVA) chart. airport. Figure 2-7 shows a typical configuration. Terminal controllers can assign altitudes lower than published Figure 9-8. Minimum Vectoring Altitude Chart. procedural altitudes called minimum vectoring altitudes (MVAs). These altitudes are not published or accessible An aircraft is not cleared for takeoff until the departure to pilots, but are displayed at the controller’s position. controller can fit the flight into the departure flow. A pilot may [Figure 2-8] However, when pilots are assigned an altitude have to hold for release. When takeoff clearance is received, that seems to be too low, they should query the controller the departure controller is aware of the flight and is waiting before descending. for a call. All of the information the controller needs is on the departure strip or the computer screen; there is no need to When a pilot accepts a clearance and reports ready for takeoff, repeat any portion of the clearance to that controller. Simply a controller in the tower contacts the TRACON for a release. establish contact with the facility when instructed to do so by the tower controller. The terminal facility computer picks 2-6

up the transponder and initiates tracking as soon as it detects Air Route Traffic Control Center (ARTCC) the assigned code. For this reason, the transponder should ARTCC facilities are responsible for maintaining separation remain on standby until takeoff clearance has been received. between IFR flights in the en route structure. Center radars (Air Route Surveillance Radar (ARSR)) acquire and track The aircraft appears on the controller’s radar display as a transponder returns using the same basic technology as target with an associated data block that moves as the aircraft terminal radars. [Figure 2-11] moves through the airspace. The data block includes aircraft identification, aircraft type, altitude, and airspeed. Earlier Center radars display weather as an area of slashes (light precipitation) and Hs (moderate rainfall), as illustrated A TRACON controller uses Airport Surveillance Radar in Figure 2-12. Because the controller cannot detect higher (ASR) to detect primary targets and Automated Radar levels of precipitation, pilots should be wary of areas Terminal Systems (ARTS) to receive transponder signals; showing moderate rainfall. Newer radar displays show the two are combined on the controller’s scope. [Figure 2-9] weather as three levels of blue. Controllers can select the level of weather to be displayed. Weather displays of higher At facilities with ASR-3 equipment, radar returns from levels of intensity can make it difficult for controllers to precipitation are not displayed as varying levels of intensity, see aircraft data blocks, so pilots should not expect ATC and controllers must rely on pilot reports and experience to keep weather displayed continuously. to provide weather avoidance information. With ASR-9 equipment, the controller can select up to six levels of Center airspace is divided into sectors in the same manner intensity. Light precipitation does not require avoidance as terminal airspace; additionally, most Center airspace is tactics but precipitation levels of moderate, heavy, or divided by altitudes into high and low sectors. Each sector extreme should cause pilots to plan accordingly. Along has a dedicated team of controllers and a selection of radio with precipitation, the pilot must additionally consider the frequencies because each Center has a network of remote temperature, which if between –20° and +5 °C causes icing transmitter/receiver sites. All Center frequencies can be found even during light precipitation. The returns from higher levels in the back of the A/FD in the format shown in Figure 2-13; of intensity may obscure aircraft data blocks, and controllers they are also found on en route charts. may select the higher levels only on pilot request. When uncertainty exists about the weather ahead, ask the controller Each ARTCC’s area of responsibility covers several states; if the facility can display intensity levels—pilots of small when flying from the vicinity of one remote communication aircraft should avoid intensity levels 3 or higher. site toward another, expect to hear the same controller on different frequencies. Tower En Route Control (TEC) At many locations, instrument flights can be conducted Center Approach/Departure Control entirely in terminal airspace. These tower en route control The majority of airports with instrument approaches do not (TEC) routes are generally for aircraft operating below lie within terminal radar airspace and, when operating to or 10,000 feet, and they can be found in the A/FD. Pilots desiring from these airports, pilots communicate directly with the to use TEC should include that designation in the remarks Center controller. Departing from a tower-controlled airport, section of the flight plan. the tower controller provides instructions for contacting the appropriate Center controller. When departing an airport Pilots are not limited to the major airports at the city pairs without an operating control tower, the clearance includes listed in the A/FD. For example, a tower en route flight from instructions such as “Upon entering controlled airspace, an airport in New York (NYC) airspace could terminate contact Houston Center on 126.5.” Pilots are responsible at any airport within approximately 30 miles of Bradley for terrain clearance until reaching the controller’s MVA. International (BDL) airspace, such as Hartford (HFD). Simply hearing “Radar contact” does not relieve a pilot of [Figure 2-10] this responsibility. A valuable service provided by the automated radar If obstacles in the departure path require a steeper- equipment at terminal radar facilities is the Minimum Safe than-standard climb gradient (200 feet per nautical mile Altitude Warnings (MSAW). This equipment predicts an (FPNM)), then the controller advises the pilot. However, aircraft’s position in 2 minutes based on present path of it is the pilot’s responsibility to check the departure airport flight—the controller issues a safety alert if the projected listing in the A/FD to determine if there are trees or wires path encounters terrain or an obstruction. An unusually in the departure path. When in doubt, ask the controller for rapid descent rate on a nonprecision approach can trigger the required climb gradient. such an alert. 2-7

Academy Planned View Display System data area 0013 31 29 89 A Untracked target Nonselect code with mode C ILS 28R OP Trackball position symbol LVL LO 03 04 (inhibited when not in use) Arrival/departure tabular list 12 49 ° Tracked target center EM Controlled partial data block 085 Partial data as seen by S C B AAL629 1104 A ° N AAL728 Targets in suspend status if worked by N 040 D DAL629 1102 M 030 20 Tracked primary target N C N41463 1124 B N F N44125 R1°1°D0R3 °° 7N A UAL246 C N44125 5N RDR 15 S 4N 055 2AAL12 CD 7AAL13 SD050 N 3DAL191 CN 5NWA194 SD Untracked target select UAL132 4N1212T SN Coast/suspend tabular list code with mode C 040 22 ILLEGAL ENTRY MHD Readout area Preview area ARTS III. Indicates downwind alignment Runway 16 guide for 100L and 28R Runway’s 100R Airport center Radar Delta 4210 Runway’s 100L Scale: one line = 1 mile VOR location Outer marker Aircraft number: N1388V Obstacles Type aircraft: Cessna 421 Alt: 4,000’ Descending, 180 knots Indicates downwind alignment guide for 100R and 28L Various controls for the tower operator to select Figure 2-9. The top image is a display as seen by controlleBrRsITEinScaonpeasicrreternaffic facility. It is an ARTS III (Automated Radar Terminal System). The display shown provides an explanation of the symbols in the graphic. The lower figure is an example of the Digital Bright Radar Indicator Tower Equipment (DBRITE) screen as seen by tower personnel. It provides tower controllers with a visual display of the airport surveillance radar, beacon signals, and data received from ARTS III. The display shown provides an explanation of the symbols in the graphic. 2-8

Figure 2-10. A portion of the New YoFrkigaurreea9to-1w0e.rAenporortuiotenloisftth(feroNmewthYeoArk/FarDe)a.Tower En Route List. 2-9

Figure 2-11. Center radar displays. Figure 2-12. A center controller’s scope. Figure 2-13. A/FD center frequencies listing. A common clearance in these situations is “When able, Another common Center clearance is “Leaving (altitude) proceed direct to the Astoria VOR…” The words “when able” fly (heading) or proceed direct when able.” This keeps the mean to proceed to the waypoint, intersection, or NAVAID terrain/obstruction clearance responsibility in the flight deck when the pilot is able to navigate directly to that point using until above the minimum IFR altitude. A controller cannot onboard available systems providing proper guidance, usable issue an IFR clearance until an aircraft is above the minimum signal, etc. If provided such guidance while flying VFR, the IFR altitude unless it is able to climb in VFR conditions. pilot remains responsible for terrain and obstacle clearance. Using the standard climb gradient, an aircraft is 2 miles On a Center controller’s scope, 1 NM is about ⁄1 28 of an inch. from the departure end of the runway before it is safe to When a Center controller is providing Approach/Departure turn (400 feet above ground level (AGL)). When a Center control services at an airport many miles from the radar controller issues a heading, a direct route, or says “direct antenna, estimating headings and distances is very difficult. when able,” the controller becomes responsible for terrain Controllers providing vectors to final must set the range on and obstruction clearance. their scopes to not more than 125 NM to provide the greatest possible accuracy for intercept headings. Accordingly, at locations more distant from a Center radar antenna, pilots should expect a minimum of vectoring. 2-10

ATC Inflight Weather Avoidance ATC radar systems cannot detect turbulence. Generally, Assistance turbulence can be expected to occur as the rate of rainfall or intensity of precipitation increases. Turbulence associated ATC Radar Weather Displays with greater rates of rainfall/precipitation is normally more ATC radar systems are able to display areas of precipitation severe than any associated with lesser rates of rainfall/ by sending out a beam of radio energy that is reflected back to precipitation. Turbulence should be expected to occur near the radar antenna when it strikes an object or moisture, which convective activity, even in clear air. Thunderstorms are a may be in the form of rain drops, hail, or snow. The larger form of convective activity that implies severe or greater the object, or the denser its reflective surface, the stronger turbulence. Operation within 20 miles of thunderstorms the return. Radar weather processors indicate the intensity should be approached with great caution, as the severity of of reflective returns in terms of decibels with respect to the turbulence can be markedly greater than the precipitation radar reflectively factor (dBZ). intensity might indicate. ATC systems cannot detect the presence or absence of Weather Avoidance Assistance clouds. ATC radar systems can often determine the intensity ATC’s first duty priority is to separate aircraft and issue of a precipitation area, but the specific character of that area safety alerts. ATC provides additional services to the extent (snow, rain, hail, VIRGA, etc.) cannot be determined. For possible, contingent upon higher priority duties and other this reason, ATC refers to all weather areas displayed on factors including limitations of radar, volume of traffic, ATC radar scopes as “precipitation.” frequency congestion, and workload. Subject to the above factors/limitations, controllers issue pertinent information All ATC facilities using radar weather processors with the on weather or chaff areas; and if requested, assist pilots, to ability to determine precipitation intensity describes the the extent possible, in avoiding areas of precipitation. Pilots intensity to pilots as: should respond to a weather advisory by acknowledging the advisory and, if desired, requesting an alternate course of 1. “LIGHT” (< 30 dBZ) action, such as: 2. “MODERATE” (30 to 40 dBZ) 1. Request to deviate off course by stating the direction and number of degrees or miles needed to deviate from 3. “HEAVY” (>40 to 50 dBZ) the original course; 4. “EXTREME” (>50 dBZ) 2. Request a change of altitude; or ARTCC controllers do not use the term “LIGHT” because 3. Request routing assistance to avoid the affected their systems do not display “LIGHT” precipitation area. Because ATC radar systems cannot detect the intensities. ATC facilities that, due to equipment limitations, presence or absence of clouds and turbulence, such cannot display the intensity levels of precipitation, describe assistance conveys no guarantee that the pilot will not the location of the precipitation area by geographic position or encounter hazards associated with convective activity. position relative to the aircraft. Since the intensity level is not Pilots wishing to circumnavigate precipitation areas available, the controller states, “INTENSITY UNKNOWN.” by a specific distance should make their desires clearly known to ATC at the time of the request for ARTCC facilities normally use a Weather and Radar services. Pilots must advise ATC when they can Processor (WARP) to display a mosaic of data obtained from resume normal navigation. multiple NEXRAD sites. The WARP processor is only used in ARTCC facilities. IFR pilots shall not deviate from their assigned course or altitude without an ATC clearance. Plan ahead for possible There is a time delay between actual conditions and those course deviations because hazardous convective conditions displayed to the controller. For example, the precipitation can develop quite rapidly. This is important to consider data on the ARTCC controller’s display could be up to 6 because the precipitation data displayed on ARTCC radar minutes old. When the WARP is not available, a secondary scopes can be up to 6 minutes old, and thunderstorms can system, the narrowband ARSR is utilized. The ARSR system develop at rates exceeding 6,000 feet per minute (fpm). When can display two distinct levels of precipitation intensity that encountering weather conditions that threaten the safety of is described to pilots as “MODERATE” (30 to 40 dBZ) and the aircraft, the pilot may exercise emergency authority as “HEAVY to EXTREME” (>40 dBZ). 2-11

stated in 14 CFR part 91, section 91.3 should an immediate 3. Cloud tops and bases; and deviation from the assigned clearance be necessary and time does not permit approval by ATC. 4. The presence of hazards such as ice, hail, and lightning. Generally, when weather disrupts the flow of air traffic, Approach Control Facility greater workload demands are placed on the controller. Requests for deviations from course and other services An approach control facility is a terminal ATC facility should be made as far in advance as possible to better that provides approach control service in the terminal area. assure the controller’s ability to approve these requests Services are provided for arriving and departing VFR and promptly. When requesting approval to detour around IFR aircraft and, on occasion, en route aircraft. In addition, weather activity, include the following information to for airports with parallel runways with ILS or LDA facilitate the request: approaches, the approach control facility provides monitoring of the approaches. 1. The proposed point where detour commences; Approach Control Advances 2. The proposed route and extent of detour (direction and distance); Precision Runway Monitor (PRM) Over the past few years, a new technology has been installed 3. The point where original route will be resumed; at airports that permits a decreased separation distance between parallel runways. The system is called a Precision 4. Flight conditions (instrument meteorological Runway Monitor (PRM) and is comprised of high-update conditions (IMC) or visual meteorological conditions radar, high-resolution ATC displays, and PRM-certified (VMC); controllers. [Figure 2-14] 5. Whether the aircraft is equipped with functioning airborne radar; and 6. Any further deviation that may become necessary. To a large degree, the assistance that might be rendered by ATC depends upon the weather information available to controllers. Due to the extremely transitory nature of hazardous weather, the controller’s displayed precipitation information may be of limited value. Obtaining IFR clearance or approval to circumnavigate Figure 2-14. High-resolution ATC displays used in PRM. hazardous weather can often be accommodated more readily in the en route areas away from terminals because there PRM Radar is usually less congestion and, therefore, greater freedom The PRM uses a Monopulse Secondary Surveillance Radar of action. In terminal areas, the problem is more acute (MSSR) that employs electronically-scanned antennas. because of traffic density, ATC coordination requirements, Because the PRM has no scan rate restrictions, it is capable complex departure and arrival routes, and adjacent airports. of providing a faster update rate (up to 1.0 second) over As a consequence, controllers are less likely to be able to conventional systems, thereby providing better target accommodate all requests for weather detours in a terminal presentation in terms of accuracy, resolution, and track area. Nevertheless, pilots should not hesitate to advise prediction. The system is designed to search, track, process, controllers of any observed hazardous weather and should and display SSR-equipped aircraft within airspace of over specifically advise controllers if they desire circumnavigation 30 miles in range and over 15,000 feet in elevation. Visual of observed weather. and audible alerts are generated to warn controllers to take corrective actions. Pilot reports (PIREPs) of flight conditions help define the nature and extent of weather conditions in a particular area. These reports are disseminated by radio and electronic means to other pilots. Provide PIREP information to ATC regarding pertinent flight conditions, such as: 1. Turbulence; 2. Visibility; 2-12

PRM Benefits and services available along the planned route of flight. [Figure 2-16] Always know where the nearest VFR Typically, PRM is used with dual approaches with conditions can be found, and be prepared to head in that centerlines separated less than 4,300 feet but not less direction if the situation deteriorates. than 3,000 feet (under most conditions). [Figure 2-15] Separating the two final approach courses is a No A typical IFR flight, with departure and arrival at airports with Transgression Zone (NTZ) with surveillance of that zone control towers, would use the ATC facilities and services in provided by two controllers, one for each active approach. the following sequence: The system tracking software provides PRM monitor controllers with aircraft identification, position, speed, 1. FSS: Obtain a weather briefing for a departure, projected position, as well as visual and aural alerts. destination and alternate airports, and en route conditions, and then file a flight plan by calling Control Sequence 1-800-WX-BRIEF. The IFR system is flexible and accommodating if pilots 2. ATIS: Preflight complete, listen for present conditions do their homework, have as many frequencies as possible and the approach in use. written down before they are needed, and have an alternate in mind if the flight cannot be completed as planned. 3. Clearance Delivery: Prior to taxiing, obtain a Pilots should familiarize themselves with all the facilities departure clearance. Intersection Alpha Intersection Beta NO TNROANTSRGARNESSGSRIEOSNSZIOONNEZO(NNTEZ()NTZ) 26L 26R 8L 8R Figure 2-15. Aircraft management using PRM. (Note the no transgression zone (NTZ) and how the aircraft are separated.) Figure 9-XX. ATC displays used in PRM. 2-13

Figure 2-16. ATC facilities, services, and radio call signs. 2-14

4. Ground Control: Noting that the flight is IFR, receive 3. ARTCC: After takeoff, establish contact with Center. taxi instructions. During the flight, pilots may be in contact with multiple ARTCC facilities; ATC coordinates the hand-offs. 5. Tower: Pre-takeoff checks complete, receive clearance to takeoff. 4. EFAS/HIWAS: Coordinate with ATC before leaving their frequency to obtain inflight weather information. 6. Departure Control: Once the transponder “tags up” with the ARTS, the tower controller instructs the pilot 5. Approach Control: Center hands off to approach to contact Departure to establish radar contact. control where pilots receive additional information and clearances. If a landing under VMC is possible, 7. ARTCC: After departing the departure controller’s pilots may cancel their IFR clearance before landing. airspace, aircraft is handed off to Center, who coordinates the flight while en route. Pilots may Letters of Agreement (LOA) be in contact with multiple ARTCC facilities; they The ATC system is indeed a system and very little happens by coordinate the hand-offs. chance. As a flight progresses, controllers in adjoining sectors or adjoining Centers coordinate its handling by telephone 8. EFAS/ Hazardous Inflight Weather Advisory Service or by computer. Where there is a boundary between the (HIWAS): Coordinate with ATC before leaving their airspace controlled by different facilities, the location and frequency to obtain inflight weather information. altitude for hand-off is determined by Letters of Agreement (LOA) negotiated between the two facility managers. This 9. ATIS: Coordinate with ATC before leaving their information is not available to pilots in any Federal Aviation frequency to obtain ATIS information. Administration (FAA) publication. For this reason, it is good practice to note on the en route chart the points at which 10. Approach Control: Center hands off to approach hand-offs occur. Each time a flight is handed off to a different control where pilots receive additional information facility, the controller knows the altitude and location—this and clearances. was part of the hand-off procedure. 11. Tower: Once cleared for the approach, pilots are instructed to contact tower control; the flight plan is canceled by the tower controller upon landing. A typical IFR flight, with departure and arrival at airports without operating control towers, would use the ATC facilities and services in the following sequence: 1. FSS: Obtain a weather briefing for departure, destination, and alternate airports, and en route conditions, and then file a flight plan by calling 1-800-WX-BRIEF. Provide the latitude/longitude description for small airports to ensure that Center is able to locate departure and arrival locations. 2. FSS or UNICOM: ATC clearances can be filed and received on the UNICOM frequency if the licensee has made arrangements with the controlling ARTCC; otherwise, file with FSS via telephone. Be sure all preflight preparations are complete before filing. The clearance includes a clearance void time. Pilots must be airborne prior to the void time. 2-15

2-16

HumanChapter 3 Factors Introduction Human factors is a broad field that examines the interaction between people, machines, and the environment for the purpose of improving performance and reducing errors. As aircraft became more reliable and less prone to mechanical failure, the percentage of accidents related to human factors increased. Some aspect of human factors now accounts for over 80 percent of all accidents. Pilots, who have a good understanding of human factors, are better equipped to plan and execute a safe and uneventful flight. Flying in instrument meteorological conditions (IMC) can result in sensations that are misleading to the body’s sensory system. A safe pilot needs to understand these sensations and effectively counteract them. Instrument flying requires a pilot to make decisions using all available resources. The elements of human factors covered in this chapter include sensory systems used for orientation and illusions in flight. For more information about physiological and psychological factors, medical factors, aeronautical decision-making (ADM), and crew resource management (CRM), refer to the Pilot’s Handbook of Aeronautical Knowledge. 3-1

Sensory Systems for Orientation altitude does not restore a pilot’s vision in the same transitory period used at the climb altitude. Orientation is the awareness of the position of the aircraft and of oneself in relation to a specific reference point. The eye also has two blind spots. The day blind spot is the Disorientation is the lack of orientation, and spatial location on the light sensitive retina where the optic nerve disorientation specifically refers to the lack of orientation fiber bundle (which carries messages from the eye to the with regard to position in space and to other objects. brain) passes through. This location has no light receptors, and a message cannot be created there to be sent to the brain. Orientation is maintained through the body’s sensory organs The night blind spot is due to a concentration of cones in an in three areas: visual, vestibular, and postural. The eyes area surrounding the fovea on the retina. Because there are maintain visual orientation. The motion sensing system in no rods in this area, direct vision on an object at night will the inner ear maintains vestibular orientation. The nerves in disappear. As a result, off-center viewing and scanning at the skin, joints, and muscles of the body maintain postural night is best for both obstacle avoidance and to maximize orientation. When healthy human beings are in their natural situational awareness (SA). (See the Pilot’s Handbook of environment, these three systems work well. When the Aeronautical Knowledge and the Aeronautical Information human body is subjected to the forces of flight, these senses Manual (AIM) for detailed reading.) can provide misleading information. It is this misleading information that causes pilots to become disoriented. The brain also processes visual information based upon color, relationship of colors, and vision from objects around us. Eyes Figure 3-1 demonstrates the visual processing of information. Of all the senses, vision is most important in providing The brain assigns color based on many items, to include an information to maintain safe flight. Even though the human object’s surroundings. In the figure below, the orange square eye is optimized for day vision, it is also capable of vision on the shaded side of the cube is actually the same color in very low light environments. During the day, the eye uses as the brown square in the center of the cube’s top face. receptors called cones, while at night, vision is facilitated by the use of rods. Both of these provide a level of vision optimized for the lighting conditions that they were intended. That is, cones are ineffective at night and rods are ineffective during the day. Rods, which contain rhodopsin (called visual purple), are especially sensitive to light and increased light washes out the rhodopsin compromising the night vision. Hence, when strong light is momentarily introduced at night, vision may be totally ineffective as the rods take time to become effective again in darkness. Smoking, alcohol, oxygen deprivation, and age affect vision, especially at night. It should be noted that at night, oxygen deprivation, such as one caused from a climb to a high altitude, causes a significant reduction in vision. A return back to the lower Figure 3-1. Rubik’s cube graphic depicting the visual processing of information. 3-2

Isolating the orange square from surrounding influences necessary. White flight deck lighting (dim lighting) should will reveal that it is actually brown. The application to a real be available when needed for map and instrument reading, environment is evident when processing visual information especially under IMC conditions. that is influenced by surroundings. The ability to pick out an airport in varied terrain or another aircraft in a light haze are Since any degree of dark adaptation is lost within a few examples of problems with interpretation that make vigilance seconds of viewing a bright light, pilots should close one eye all the more necessary. when using a light to preserve some degree of night vision. During night flights in the vicinity of lightning, flight deck Figure 3-2 illustrates problems with perception. Both tables lights should be turned up to help prevent loss of night vision are the same lengths. Objects are easily misinterpreted in due to the bright flashes. Dark adaptation is also impaired by size to include both length and width. Being accustomed to exposure to cabin pressure altitudes above 5,000 feet, carbon a 75-foot-wide runway on flat terrain is most likely going to monoxide inhaled through smoking, deficiency of Vitamin influence a pilot’s perception of a wider runway on uneven A in the diet, and prolonged exposure to bright sunlight. terrain simply because of the inherent processing experience. During flight in visual meteorological conditions (VMC), Vision Under Dim and Bright Illumination the eyes are the major orientation source and usually Under conditions of dim illumination, aeronautical charts and provide accurate and reliable information. Visual cues aircraft instruments can become unreadable unless adequate usually prevail over false sensations from other sensory flight deck lighting is available. In darkness, vision becomes systems. When these visual cues are taken away, as they more sensitive to light. This process is called dark adaptation. are in IMC, false sensations can cause the pilot to quickly Although exposure to total darkness for at least 30 minutes is become disoriented. required for complete dark adaptation, a pilot can achieve a moderate degree of dark adaptation within 20 minutes under An effective way to counter these false sensations is to dim red flight deck lighting. recognize the problem, disregard the false sensations, rely on the flight instruments, and use the eyes to determine the Red light distorts colors (filters the red spectrum), especially aircraft attitude. The pilot must have an understanding of on aeronautical charts, and makes it very difficult for the the problem and the skill to control the aircraft using only eyes to focus on objects inside the aircraft. Pilots should instrument indications. use it only where optimum outside night vision capability is Figure 3-2. Shepard’s tables illustrating problems with perception as both tables are the same length. 3-3

Ears To illustrate what happens during a turn, visualize the The inner ear has two major parts concerned with orientation: aircraft in straight-and-level flight. With no acceleration of the semicircular canals and the otolith organs. [Figure 3-3] The the aircraft, the hair cells are upright, and the body senses semicircular canals detect angular acceleration of the body, that no turn has occurred. Therefore, the position of the hair while the otolith organs detect linear acceleration and gravity. cells and the actual sensation correspond. The semicircular canals consist of three tubes at approximate right angles to each other, each located on one of three axes: Placing the aircraft into a turn puts the semicircular canal and pitch, roll, or yaw as illustrated in Figure 3-4. Each canal is its fluid into motion, with the fluid within the semicircular filled with a fluid called endolymph fluid. In the center of canal lagging behind the accelerated canal walls. [Figure 3-5] the canal is the cupola, a gelatinous structure that rests upon This lag creates a relative movement of the fluid within the sensory hairs located at the end of the vestibular nerves. It canal. The canal wall and the cupula move in the opposite is the movement of these hairs within the fluid that causes direction from the motion of the fluid. sensations of motion. The brain interprets the movement of the hairs to be a turn in Because of the friction between the fluid and the canal, it the same direction as the canal wall. The body correctly senses may take about 15–20 seconds for the fluid in the ear canal that a turn is being made. If the turn continues at a constant to reach the same speed as the canal’s motion. rate for several seconds or longer, the motion of the fluid in Semicircular canals Tcuobnutalainrindgucetnsdolymph Utricle The motion sensing system is Saccule located in each inner ear in the approximate position shown. Cochlea Ampullae Semicircular canals Cupola Endolymph fluid Ampulla of a Otolith organ Figure 3-3. Inner ear orientation. semicircular Cupola canal Sensory hairs Filaments of hair cells Vestibular nerve Hair cells Vestibular nerve PITCH YAW The semicircular tubes are ROLL YAW arranged at approximately right angles to each other, in the roll, pitch, and yaw axes. ROLL PITCH Bone Ear canal Eardrum Eustachian tube Figure 3-4. Angular acceleration and the semicircular tubes. 3-4

Endolymph Cupola Tube No turning Start of turn Constant rate turn Turn stopped No sensation. Sensation of turning as moving fluid deflects No sensation after fluid Sensation of turning in hairs. accelerates to same opposite direction as moving speed as tube wall. fluid deflects hairs in opposite direction. Figure 3-5. Angular acceleration. Normal the canals catches up with the canal walls. The hairs are no Head tilted back longer bent, and the brain receives the false impression that turning has stopped. Thus, the position of the hair cells and Accelerating the resulting sensation during a prolonged, constant turn in Figure 3-6. Linear acceleration. either direction results in the false sensation of no turn. Illusions Leading to Spatial When the aircraft returns to straight-and-level flight, the fluid Disorientation in the canal moves briefly in the opposite direction. This sends a signal to the brain that is falsely interpreted as movement The sensory system responsible for most of the illusions in the opposite direction. In an attempt to correct the falsely leading to spatial disorientation is the vestibular system. perceived turn, the pilot may reenter the turn placing the Visual illusions can also cause spatial disorientation. aircraft in an out-of-control situation. Vestibular Illusions The Leans The otolith organs detect linear acceleration and gravity in a A condition called “the leans” can result when a banked similar way. Instead of being filled with a fluid, a gelatinous attitude, to the left for example, may be entered too slowly membrane containing chalk-like crystals covers the sensory to set in motion the fluid in the “roll” semicircular tubes. hairs. When the pilot tilts his or her head, the weight of these [Figure 3-5] An abrupt correction of this attitude sets the crystals causes this membrane to shift due to gravity, and fluid in motion, creating the illusion of a banked attitude to the sensory hairs detect this shift. The brain orients this new the right. The disoriented pilot may make the error of rolling position to what it perceives as vertical. Acceleration and the aircraft into the original left banked attitude, or if level deceleration also cause the membrane to shift in a similar flight is maintained, feel compelled to lean in the perceived manner. Forward acceleration gives the illusion of the head vertical plane until this illusion subsides. tilting backward. [Figure 3-6] As a result, during takeoff and while accelerating, the pilot may sense a steeper than normal climb resulting in a tendency to nose-down. Nerves Nerves in the body’s skin, muscles, and joints constantly send signals to the brain, which signals the body’s relation to gravity. These signals tell the pilot his or her current position. Acceleration is felt as the pilot is pushed back into the seat. Forces, created in turns, can lead to false sensations of the true direction of gravity and may give the pilot a false sense of which way is up. Uncoordinated turns, especially climbing turns, can cause misleading signals to be sent to the brain. Skids and slips give the sensation of banking or tilting. Turbulence can create motions that confuse the brain as well. Pilots need to be aware that fatigue or illness can exacerbate these sensations and ultimately lead to subtle incapacitation. 3-5

Coriolis Illusion attempt to climb or stop the descent. This action tightens the The coriolis illusion occurs when a pilot has been in a turn spiral and increases the loss of altitude; hence, this illusion is long enough for the fluid in the ear canal to move at the same referred to as a graveyard spiral. [Figure 3-7] At some point, speed as the canal. A movement of the head in a different this could lead to a loss of control by the pilot. plane, such as looking at something in a different part of the flight deck, may set the fluid moving and create the illusion Somatogravic Illusion of turning or accelerating on an entirely different axis. A rapid acceleration, such as experienced during takeoff, This action causes the pilot to think the aircraft is doing a stimulates the otolith organs in the same way as tilting the maneuver that it is not. The disoriented pilot may maneuver head backwards. This action creates the somatogravic illusion the aircraft into a dangerous attitude in an attempt to correct of being in a nose-up attitude, especially in situations without the aircraft’s perceived attitude. good visual references. The disoriented pilot may push the aircraft into a nose-low or dive attitude. A rapid deceleration For this reason, it is important that pilots develop an by quick reduction of the throttle(s) can have the opposite instrument cross-check or scan that involves minimal effect with the disoriented pilot pulling the aircraft into a head movement. Take care when retrieving charts and nose-up or stall attitude. other objects in the flight deck—if something is dropped, retrieve it with minimal head movement and be alert for Inversion Illusion the coriolis illusion. An abrupt change from climb to straight-and-level flight can stimulate the otolith organs enough to create the illusion of Graveyard Spiral tumbling backwards or inversion illusion. The disoriented As in other illusions, a pilot in a prolonged coordinated, pilot may push the aircraft abruptly into a nose-low attitude, constant-rate turn, will have the illusion of not turning. During possibly intensifying this illusion. the recovery to level flight, the pilot experiences the sensation of turning in the opposite direction. The disoriented pilot may Elevator Illusion return the aircraft to its original turn. Because an aircraft tends An abrupt upward vertical acceleration, as can occur in to lose altitude in turns unless the pilot compensates for the an updraft, can stimulate the otolith organs to create the loss in lift, the pilot may notice a loss of altitude. The absence illusion of being in a climb. This is called elevator illusion. of any sensation of turning creates the illusion of being in a The disoriented pilot may push the aircraft into a nose-low level descent. The pilot may pull back on the controls in an Correct path Graveyard spin Graveyard spiral Figure 3-7. Graveyard spiral. 3-6

attitude. An abrupt downward vertical acceleration, usually the brain on a constant basis. “Seat of the pants” flying is in a downdraft, has the opposite effect with the disoriented largely dependent upon these signals. Used in conjunction pilot pulling the aircraft into a nose-up attitude. with visual and vestibular clues, these sensations can be fairly reliable. However, because of the forces acting upon Visual Illusions the body in certain flight situations, many false sensations Visual illusions are especially hazardous because pilots rely can occur due to acceleration forces overpowering gravity. on their eyes for correct information. Two illusions that lead [Figure 3-8] These situations include uncoordinated turns, to spatial disorientation, false horizon and autokinesis, are climbing turns, and turbulence. concerned with only the visual system. Demonstration of Spatial Disorientation False Horizon A sloping cloud formation, an obscured horizon, an aurora There are a number of controlled aircraft maneuvers a pilot borealis, a dark scene spread with ground lights and stars, can perform to experiment with spatial disorientation. While and certain geometric patterns of ground lights can provide each maneuver normally creates a specific illusion, any false inaccurate visual information, or false horizon, for aligning sensation is an effective demonstration of disorientation. Thus, the aircraft correctly with the actual horizon. The disoriented even if there is no sensation during any of these maneuvers, pilot may place the aircraft in a dangerous attitude. the absence of sensation is still an effective demonstration in that it shows the inability to detect bank or roll. There are Autokinesis several objectives in demonstrating these various maneuvers. In the dark, a stationary light will appear to move about when stared at for many seconds. The disoriented pilot could lose 1. They teach pilots to understand the susceptibility of control of the aircraft in attempting to align it with the false the human system to spatial disorientation. movements of this light called autokinesis. 2. They demonstrate that judgments of aircraft attitude Postural Considerations based on bodily sensations are frequently false. The postural system sends signals from the skin, joints, and 3. They help lessen the occurrence and degree of muscles to the brain that are interpreted in relation to the disorientation through a better understanding of the Earth’s gravitational pull. These signals determine posture. relationship between aircraft motion, head movements, Inputs from each movement update the body’s position to and resulting disorientation. 4. They help instill a greater confidence in relying on flight instruments for assessing true aircraft attitude. Level Coordinated turn Pull out Level skid Forward slip Uncoordinated turn Skid, slip, and uncoordinated turns feel alike. Pilots feel they are being forced sideways in their seat. Figure 3-8. Sensations from centrifugal force. 3-7

A pilot should not attempt any of these maneuvers at immediately returns his or her head to an upright position. low altitudes or in the absence of an instructor pilot or an The instructor pilot should time the maneuver so the roll is appropriate safety pilot. stopped as the pilot returns his or her head upright. An intense disorientation is usually produced by this maneuver, and the Climbing While Accelerating pilot experiences the sensation of falling downward into the With the pilot’s eyes closed, the instructor pilot maintains direction of the roll. approach airspeed in a straight-and-level attitude for several seconds, and then accelerates while maintaining straight- In the descriptions of these maneuvers, the instructor pilot is and-level attitude. The usual illusion during this maneuver, doing the flying, but having the pilot do the flying can also without visual references, is that the aircraft is climbing. be a very effective demonstration. The pilot should close his or her eyes and tilt their head to one side. The instructor pilot Climbing While Turning tells the pilot what control inputs to perform. The pilot then With the pilot’s eyes still closed and the aircraft in a straight- attempts to establish the correct attitude or control input with and-level attitude, the instructor pilot now executes, with a eyes closed and head tilted. While it is clear the pilot has no relatively slow entry, a well-coordinated turn of about 1.5 idea of the actual attitude, he or she will react to what the positive G (approximately 50° bank) for 90°. While in the senses are saying. After a short time, the pilot will become turn, without outside visual references and under the effect of disoriented, and the instructor pilot then tells the pilot to the slight positive G, the usual illusion produced is that of a look up and recover. The benefit of this exercise is the pilot climb. Upon sensing the climb, the pilot should immediately experiences the disorientation while flying the aircraft. open the eyes and see that a slowly established, coordinated turn produces the same feeling as a climb. Coping with Spatial Disorientation Diving While Turning To prevent illusions and their potentially disastrous Repeating the previous procedure, with the exception that consequences, pilots can: the pilot’s eyes should be kept closed until recovery from the turn is approximately one-half completed can create this 1. Understand the causes of these illusions and remain sensation. With the eyes closed, the usual illusion is that the constantly alert for them. Take the opportunity to aircraft is diving. understand and then experience spatial disorientation illusions in a device, such as a Barany chair, a Tilting to Right or Left Vertigon, or a Virtual Reality Spatial Disorientation While in a straight-and-level attitude, with the pilot’s eyes Demonstrator. closed, the instructor pilot executes a moderate or slight skid to the left with wings level. This creates the illusion of 2. Always obtain and understand preflight weather the body being tilted to the right. The same illusion can be briefings. sensed with a skid to the right with wings level, except the body feels it is being tilted to the left. 3. Before flying in marginal visibility (less than 3 miles) or where a visible horizon is not evident such as flight Reversal of Motion over open water during the night, obtain training and This illusion can be demonstrated in any of the three planes of maintain proficiency in airplane control by reference motion. While straight and level, with the pilot’s eyes closed, to instruments. the instructor pilot smoothly and positively rolls the aircraft to approximately a 45° bank attitude. This creates the illusion 4. Do not continue flight into adverse weather conditions of a strong sense of rotation in the opposite direction. After or into dusk or darkness unless proficient in the use of this illusion is noted, the pilot should open his or her eyes flight instruments. If intending to fly at night, maintain and observe that the aircraft is in a banked attitude. night-flight currency and proficiency. Include cross- country and local operations at various airfields. Diving or Rolling Beyond the Vertical Plane This maneuver may produce extreme disorientation. While 5. Ensure that when outside visual references are used, in straight-and-level flight, the pilot should sit normally, they are reliable, fixed points on the Earth’s surface. either with eyes closed or gaze lowered to the floor. The instructor pilot starts a positive, coordinated roll toward a 6. Avoid sudden head movement, particularly during 30° or 40° angle of bank. As this is in progress, the pilot takeoffs, turns, and approaches to landing. tilts his or her head forward, looks to the right or left, then 7. Be physically tuned for flight into reduced visibility. Ensure proper rest, adequate diet, and, if flying at night, allow for night adaptation. Remember that illness, medication, alcohol, fatigue, sleep loss, and 3-8

mild hypoxia are likely to increase susceptibility to Water Refraction spatial disorientation. Rain on the windscreen can create an illusion of being at a higher altitude due to the horizon appearing lower than it is. 8. Most importantly, become proficient in the use of This can result in the pilot flying a lower approach. flight instruments and rely upon them. Trust the instruments and disregard your sensory perceptions. Haze Atmospheric haze can create an illusion of being at a greater The sensations that lead to illusions during instrument distance and height from the runway. As a result, the pilot flight conditions are normal perceptions experienced by has a tendency to be low on the approach. Conversely, pilots. These undesirable sensations cannot be completely extremely clear air (clear bright conditions of a high attitude prevented, but through training and awareness, pilots can airport) can give the pilot the illusion of being closer than ignore or suppress them by developing absolute reliance he or she actually is, resulting in a high approach that may on the flight instruments. As pilots gain proficiency in cause an overshoot or go around. The diffusion of light due instrument flying, they become less susceptible to these to water particles on the windshield can adversely affect illusions and their effects. depth perception. The lights and terrain features normally used to gauge height during landing become less effective Optical Illusions for the pilot. Of the senses, vision is the most important for safe Fog flight. However, various terrain features and atmospheric Flying into fog can create an illusion of pitching up. Pilots conditions can create optical illusions. These illusions who do not recognize this illusion often steepen the approach are primarily associated with landing. Since pilots quite abruptly. must transition from reliance on instruments to visual cues outside the flight deck for landing at the end of an Ground Lighting Illusions instrument approach, it is imperative they be aware of the Lights along a straight path, such as a road or lights on potential problems associated with these illusions and take moving trains, can be mistaken for runway and approach appropriate corrective action. The major illusions leading lights. Bright runway and approach lighting systems, to landing errors are described below. especially where few lights illuminate the surrounding terrain, may create the illusion of less distance to the Runway Width Illusion runway. The pilot who does not recognize this illusion will A narrower-than-usual runway can create an illusion the often fly a higher approach. aircraft is at a higher altitude than it actually is, especially when runway length-to-width relationships are comparable. How To Prevent Landing Errors Due to [Figure 3-9A] The pilot who does not recognize this illusion Optical Illusions will fly a lower approach with the risk of striking objects along the approach path or landing short. A wider-than-usual To prevent these illusions and their potentially hazardous runway can have the opposite effect with the risk of leveling consequences, pilots can: out high and landing hard or overshooting the runway. 1. Anticipate the possibility of visual illusions during Runway and Terrain Slopes Illusion approaches to unfamiliar airports, particularly at night An upsloping runway, upsloping terrain, or both can create or in adverse weather conditions. Consult airport an illusion the aircraft is at a higher altitude than it actually diagrams and the Airport/Facility Directory (A/FD) is. [Figure 3-9B] The pilot who does not recognize this for information on runway slope, terrain, and lighting. illusion will fly a lower approach. Downsloping runways and downsloping approach terrain can have the opposite effect. 2. Make frequent reference to the altimeter, especially during all approaches, day and night. Featureless Terrain Illusion An absence of surrounding ground features, as in an 3. If possible, conduct aerial visual inspection of overwater approach, over darkened areas, or terrain made unfamiliar airports before landing. featureless by snow, can create an illusion the aircraft is at a higher altitude than it actually is. This illusion, sometimes 4. Use Visual Approach Slope Indicator (VASI) or referred to as the “black hole approach,” causes pilots to fly Precision Approach Path Indicator (PAPI) systems a lower approach than is desired. for a visual reference or an electronic glideslope, whenever they are available. 3-9

Narrower runway Wider runway Figure 3-9A Runway width illusion Normal Approach Normal Approach • A narrower-than-usual runway can 25 created an illusion that the aircraft 25 is higher than it actually is, leading to a lower approach. 25 25 • A wider-than-usual runway can create an illusion that the aircraft is lower than it actually is, leading to a higher approach. Narrower runway Wider runway 25 25 Downsloping runway Upsloping runway Figure 3-9B Runway slope illusion Normal Approach Normal Approach • A downsloping runway can create the illusion that the aircraft is lower than it actually is, leading to a higher approach. • An upsloping runway can create the illusion that the aircraft is higher than it actually is, leading to a lower approach. Downsloping runway Upsloping runway Normal approach Approach due to illusion Figure 3-9. Runway width and slope illusions. 5. Utilize the visual descent point (VDP) found on many nonprecision instrument approach procedure charts. 6. Recognize that the chances of being involved in an approach accident increase when some emergency or other activity distracts from usual procedures. 7. Maintain optimum proficiency in landing procedures. 3-10

CAhaepterr4odynamic Factors Introduction Several factors affect aircraft performance including the atmosphere, aerodynamics, and aircraft icing. Pilots need an understanding of these factors for a sound basis for prediction of aircraft response to control inputs, especially with regard to instrument approaches, while holding, and when operating at reduced airspeed in instrument meteorological conditions (IMC). Although these factors are important to the pilot flying visual flight rules (VFR), they must be even more thoroughly understood by the pilot operating under instrument flight rules (IFR). Instrument pilots rely strictly on instrument indications to precisely control the aircraft; therefore, they must have a solid understanding of basic aerodynamic principles in order to make accurate judgments regarding aircraft control inputs. 4-1

The Wing LR To understand aerodynamic forces, a pilot needs to understand basic terminology associated with airfoils. Chord line MC/4 D Figure 4-1 illustrates a typical airfoil. C/4 The chord line is the straight line intersecting the leading and trailing edges of the airfoil, and the term chord refers to the chord line longitudinal length (length as viewed from the side). The mean camber is a line located halfway between the C upper and lower surfaces. Viewing the wing edgewise, the mean camber connects with the chord line at each end. The V Relative wind mean camber is important because it assists in determining Figure 4-2. Angle of attack and relative wind. aerodynamic qualities of an airfoil. The measurement of the maximum camber; inclusive of both the displacement Flightpath is the course or track along which the aircraft is of the mean camber line and its linear measurement from flying or is intended to be flown. the end of the chord line, provide properties useful in evaluating airfoils. Review of Basic Aerodynamics The Four Forces The four basic forces [Figure 4-3] acting upon an aircraft in The instrument pilot must understand the relationship flight are lift, weight, thrust, and drag. and differences between several factors that affect the performance of an aircraft in flight. Also, it is crucial to Lift understand how the aircraft reacts to various control and Lift is a component of the total aerodynamic force on an power changes, because the environment in which instrument airfoil and acts perpendicular to the relative wind. Relative pilots fly has inherent hazards not found in visual flying. The wind is the direction of the airflow with respect to an airfoil. basis for this understanding is found in the four forces acting This force acts straight up from the average (called mean) on an aircraft and Newton’s Three Laws of Motion. center of pressure (CP), which is called the center of lift. It should be noted that it is a point along the chord line of an Relative Wind is the direction of the airflow with respect to airfoil through which all aerodynamic forces are considered an airfoil. to act. The magnitude of lift varies proportionately with speed, air density, shape and size of the airfoil, and AOA. Angle of Attack (AOA) is the acute angle measured between During straight-and-level flight, lift and weight are equal. the relative wind, or flightpath and the chord of the airfoil. [Figure 4-2] Mean camber line Upper camber Leading edge Mean chord line Lower camber Trailing edge Figure 4-1. The airfoil. 4-2

Right aileron Pitch Lift Yaw Weight Horizontal Vertical stabilizer stabilizer Rudder x Drag Thrust Roll Left Elevator aileron Wing zy Figure 4-3. The four forces and three axes of rotation. • Skin Friction Drag Weight Covering the entire “wetted” surface of the aircraft is a thin Weight is the force exerted by an aircraft from the pull of layer of air called a boundary layer. The air molecules on the gravity. It acts on an aircraft through its center of gravity (CG) surface have zero velocity in relation to the surface; however, and is straight down. This should not be confused with the the layer just above moves over the stagnant molecules center of lift, which can be significantly different from the below because it is pulled along by a third layer close to CG. As an aircraft is descending, weight is greater than lift. the free stream of air. The velocities of the layers increase as the distance from the surface increases until free stream Thrust velocity is reached, but all are affected by the free stream. Thrust is the forward force produced by the powerplant/ The distance (total) between the skin surface and where free propeller or rotor. It opposes or overcomes the force of drag. stream velocity is reached is called the boundary layer. At As a general rule, it acts parallel to the longitudinal axis. subsonic levels the cumulative layers are about the thickness of a playing card, yet their motion sliding over one another Drag creates a drag force. This force retards motion due to the Drag is the net aerodynamic force parallel to the relative viscosity of the air and is called skin friction drag. Because wind and is generally a sum of two components: induced skin friction drag is related to a large surface area its affect drag and parasite drag. on smaller aircraft is small versus large transport aircraft where skin friction drag may be considerable. Induced Drag Induced drag is caused from the creation of lift and increases • Interference Drag with AOA. Therefore, if the wing is not producing lift, induced drag is zero. Conversely, induced drag decreases with airspeed. Interference drag is generated by the collision of airstreams creating eddy currents, turbulence, or restrictions to smooth Parasite Drag flow. For instance, the airflow around a fuselage and around Parasite drag is all drag not caused from the production of the wing meet at some point, usually near the wing’s root. lift. Parasite drag is created by displacement of air by the These airflows interfere with each other causing a greater drag aircraft, turbulence generated by the airfoil, and the hindrance than the individual values. This is often the case when external of airflow as it passes over the surface of the aircraft or items are placed on an aircraft. That is, the drag of each item components. All of these forces create drag not from the individually, added to that of the aircraft, are less than that production of lift but the movement of an object through an of the two items when allowed to interfere with one another. air mass. Parasite drag increases with speed and includes skin friction drag, interference drag, and form drag. 4-3

• Form Drag deceleration is commonly used to indicate a decrease. This law governs the aircraft’s ability to change flightpath and Form drag is the drag created because of the shape of a speed, which are controlled by attitude (both pitch and bank) component or the aircraft. If one were to place a circular and thrust inputs. Speeding up, slowing down, entering disk in an air stream, the pressure on both the top and bottom climbs or descents, and turning are examples of accelerations would be equal. However, the airflow starts to break down that the pilot controls in everyday flight. [Figure 4-5] as the air flows around the back of the disk. This creates turbulence and hence a lower pressure results. Because the Time total pressure is affected by this reduced pressure, it creates a drag. Newer aircraft are generally made with consideration to this by fairing parts along the fuselage (teardrop) so that turbulence and form drag is reduced. Total lift must overcome the total weight of the aircraft, which 150 hp 2,000 lb is comprised of the actual weight and the tail-down force used to control the aircraft’s pitch attitude. Thrust must overcome 300 hp 2,000 lb Force = Acceleration total drag in order to provide forward speed with which to Mass produce lift. Understanding how the aircraft’s relationship between these elements and the environment provide proper interpretation of the aircraft’s instruments. Newton’s First Law, the Law of Inertia Figure 4-5. Newton’s Second Law of Motion: the Law of Momentum. Newton’s First Law of Motion is the Law of Inertia. It states that a body at rest will remain at rest, and a body in motion Newton’s Third Law, the Law of Reaction will remain in motion, at the same speed and in the same Newton’s Third Law of Motion is the Law of Reaction, direction until affected by an outside force. The force with which states that for every action there is an equal and which a body offers resistance to change is called the force of opposite reaction. As shown in Figure 4-6, the action of inertia. Two outside forces are always present on an aircraft the jet engine’s thrust or the pull of the propeller lead to the in flight: gravity and drag. The pilot uses pitch and thrust reaction of the aircraft’s forward motion. This law is also controls to counter or change these forces to maintain the responsible for a portion of the lift that is produced by a wing, desired flightpath. If a pilot reduces power while in straight- from the downward deflection of the airflow around it. This and-level flight, the aircraft will slow due to drag. However, downward force of the relative wind results in an equal but as the aircraft slows there is a reduction of lift, which causes opposite (upward) lifting force created by the airflow over the aircraft to begin a descent due to gravity. [Figure 4-4] the wing. [Figure 4-6] Newton’s Second Law, the Law of Momentum Atmosphere Newton’s Second Law of Motion is the Law of Momentum, which states that a body will accelerate in the same direction The atmosphere is the envelope of air which surrounds the as the force acting upon that body, and the acceleration Earth. A given volume of dry air contains about 78 percent will be directly proportional to the net force and inversely nitrogen, 21 percent oxygen, and about 1 percent other gases proportional to the mass of the body. Acceleration refers such as argon, carbon dioxide, and others to a lesser degree. either to an increase or decrease in velocity, although Outside Net force forces Net forces Path Path Apply down elevator Figure 4-4. Newton’s First Law of Motion: the Law of Inertia. 4-4

Reaction Action In the standard atmosphere, sea level pressure is 29.92 inches Reaction of mercury (\"Hg) and the temperature is 15 °C (59 °F). The Action standard lapse rate for pressure is approximately a 1  \"Hg decrease per 1,000 feet increase in altitude. The standard Figure 4-6. Newton’s Third Law of Motion: the Law of Reaction. lapse rate for temperature is a 2  °C (3.6  °F) decrease per 1,000 feet increase, up to the top of the stratosphere. Since Although seemingly light, air does have weight and a one all aircraft performance is compared and evaluated in square inch column of the atmosphere at sea level weighs the environment of the standard atmosphere, all aircraft approximately 14.7 pounds. About one-half of the air by performance instrumentation is calibrated for the standard weight is within the first 18,000 feet. The remainder of the atmosphere. Because the actual operating conditions rarely, air is spread over a vertical distance in excess of 1,000 miles. if ever, fit the standard atmosphere, certain corrections must apply to the instrumentation and aircraft performance. For Air density is a result of the relationship between temperature instance, at 10,000 ISA predicts that the air pressure should be and pressure. Air density is inversely related to temperature 19.92 \"Hg (29.92 \"Hg – 10 \"Hg = 19.92 \"Hg) and the outside and directly related to pressure. For a constant pressure to be temperature at –5  °C (15  °C – 20  °C). If the temperature maintained as temperature increases, density must decrease, or the pressure is different than the International Standard and vice versa. For a constant temperature to be maintained Atmosphere (ISA) prediction an adjustment must be made to as pressure increases, density must increase, and vice versa. performance predictions and various instrument indications. These relationships provide a basis for understanding instrument indications and aircraft performance. Pressure Altitude Layers of the Atmosphere Pressure altitude is the height above the standard datum There are several layers to the atmosphere with the plane (SDP). The aircraft altimeter is essentially a sensitive troposphere being closest to the Earth’s surface extending to barometer calibrated to indicate altitude in the standard about 60,000 feet at the equator. Following is the stratosphere, atmosphere. If the altimeter is set for 29.92 \"Hg SDP, the mesosphere, ionosphere, thermosphere, and finally the altitude indicated is the pressure altitude-the altitude in the exosphere. The tropopause is the thin layer between the standard atmosphere corresponding to the sensed pressure. troposphere and the stratosphere. It varies in both thickness and altitude but is generally defined where the standard The SDP is a theoretical level where the pressure of the lapse (generally accepted at 2 °C per 1,000 feet) decreases atmosphere is 29.92 \"Hg and the weight of air is 14.7 psi. significantly (usually down to 1 °C or less). As atmospheric pressure changes, the SDP may be below, at, or above sea level. Pressure altitude is important as a International Standard Atmosphere (ISA) basis for determining aircraft performance, as well as for The International Civil Aviation Organization (ICAO) assigning flight levels to aircraft operating at or above 18,000 established the ICAO Standard Atmosphere as a way feet. The pressure altitude can be determined by either of of creating an international standard for reference and two methods: (1) by setting the barometric scale of the performance computations. Instrument indications and altimeter to 29.92 \"Hg and reading the indicated altitude, or aircraft performance specifications are derived using this (2) by applying a correction factor to the indicated altitude standard as a reference. Because the standard atmosphere is according to the reported altimeter setting. a derived set of conditions that rarely exist in reality, pilots need to understand how deviations from the standard affect Density Altitude both instrument indications and aircraft performance. Density altitude is pressure altitude corrected for nonstandard temperature. As the density of the air increases (lower density altitude), aircraft performance increases. Conversely, as air density decreases (higher density altitude), aircraft performance decreases. A decrease in air density means a high density altitude; an increase in air density means a lower density altitude. Density altitude is used in calculating aircraft performance. Under standard atmospheric conditions, air at each level in the atmosphere has a specific density; under standard conditions, pressure altitude and density altitude identify the same level. Density altitude, then, is the vertical distance above sea level in the standard atmosphere at which a given density is to be found. It can be computed using 4-5

a Koch Chart or a flight computer with a density altitude 1.8 function. [Figure 4-7] 1.6 1.5 CL-MAX Stall Altitude and Temperature Effects Airport pressure altitude—Thousand of feet1.4 (read your altmeter set to 29.92 \"Hg) TO FIND the effect of altitude temperature 1.2 CONNECT the temperature and airport altitude by straight line Lift Coefficient - CL READ the increase in take-off distance and the decrease in rate of 1.0 climb from standard sea level values here 0.8 120 110 0.6 100 0.4 90 Percent decrease 18 0.2 80 in rate of climb 70 14 0 60 0 2 4 6 8 10 12 14 16 18 20 22 24 50 90 12 40 220800 80 10 2 11 20 30 140 70 8 20 100 6 Angle of Attack (degrees) 10 60 60 4 40 0 20 40 Figure 4-8. Relationship of lift to AOA. 20 −10 Add this percent to your 0 0 2 reduced, pitch must be increased. The pilot controls pitch −20 normal take off distance 0 through the elevators, which control the AOA. When back −30 pressure is applied on the elevator control, the tail lowers and the nose rises, thus increasing the wing’s AOA and lift. −40 −2 Under most conditions the elevator is placing downward pressure on the tail. This pressure requires energy that is Figure 4-7. Koch chart sample. taken from aircraft performance (speed). Therefore, when the CG is closer to the aft portion of the aircraft the elevator If a chart is not available, the density altitude can be estimated downward forces are less. This results in less energy used for by adding 120 feet for every degree Celsius above the ISA. For downward forces, in turn resulting in more energy applied example, at 3,000 feet PA, the ISA prediction is 9 °C (15 °C – to aircraft performance. [lapse rate of 2 °C per 1,000 feet x 3 = 6 °C]). However, if the actual temperature is 20  °C (11  °C more than that predicted Thrust is controlled by using the throttle to establish or by ISA) then the difference of 11 °C is multiplied by 120 feet maintain desired airspeeds. The most precise method equaling 1,320. Adding this figure to the original 3,000 feet of controlling flightpath is to use pitch control while provides a density altitude of 4,320 feet (3,000 feet + 1,320 feet). simultaneously using power (thrust) to control airspeed. In order to maintain a constant lift, a change in pitch requires a Lift change in power, and vice versa. Lift always acts in a direction perpendicular to the relative If the pilot wants the aircraft to accelerate while maintaining wind and to the lateral axis of the aircraft. The fact that lift is altitude, thrust must be increased to overcome drag. As referenced to the wing, not to the Earth’s surface, is the source the aircraft speeds up, lift is increased. To prevent gaining of many errors in learning flight control. Lift is not always altitude, the pitch angle must be lowered to reduce the AOA “up.” Its direction relative to the Earth’s surface changes as and maintain altitude. To decelerate while maintaining the pilot maneuvers the aircraft. altitude, thrust must be decreased to less than the value of drag. As the aircraft slows down, lift is reduced. To prevent The magnitude of the force of lift is directly proportional to losing altitude, the pitch angle must be increased in order to the density of the air, the area of the wings, and the airspeed. increase the AOA and maintain altitude. It also depends upon the type of wing and the AOA. Lift increases with an increase in AOA up to the stalling angle, Drag Curves at which point it decreases with any further increase in AOA. In conventional aircraft, lift is therefore controlled by varying When induced drag and parasite drag are plotted on a graph, the AOA and speed. the total drag on the aircraft appears in the form of a “drag curve.” Graph A of Figure 4-9 shows a curve based on thrust Pitch/Power Relationship versus drag, which is primarily used for jet aircraft. Graph B An examination of Figure 4-8 illustrates the relationship between pitch and power while controlling flightpath and airspeed. In order to maintain a constant lift, as airspeed is 4-6

A Jet Aircraft B Propeller-Driven Aircraft 4,000 27 Power Required Inches Hg Thrust Required 3,000 Total drag Parasite Total power Parasite 2,000 drag 25 required power 1,000 Minimum required drag or 23 L/DMAX L/DMAX Minimum power required 18 Induced drag Power Required Induced drag 0 0 0 100 200 300 400 500 0 100 200 300 400 500 Airspeed Airspeed Figure 4-9. Thrust and power required curves. additional power is needed to maintain a slower airspeed. This region exists at speeds slower than the minimum drag point of Figure 4-9 is based on power versus drag, and it is used (L/DMAX on the thrust required curve, Figure 4-9) and is for propeller-driven aircraft. This chapter focuses on power primarily due to induced drag. Figure 4-10 shows how one versus drag charts for propeller-driven aircraft. power setting can yield two speeds, points 1 and 2. This is because at point 1 there is high induced drag and low parasite Understanding the drag curve can provide valuable insight drag, while at point 2 there is high parasite drag and low into the various performance parameters and limitations of induced drag. the aircraft. Because power must equal drag to maintain a steady airspeed, the curve can be either a drag curve or a Region of power required curve. The power required curve represents reversed Region of the amount of power needed to overcome drag in order to command normal maintain a steady speed in level flight. command The propellers used on most reciprocating engines achieve peak propeller efficiencies in the range of 80 to 88 percent. 12 As airspeed increases, the propeller efficiency increases until it reaches its maximum. Any airspeed above this maximum Airspeed point causes a reduction in propeller efficiency. An engine that produces 160 horsepower will have only about 80 percent of that power converted into available horsepower, approximately 128 horsepower. The remainder is lost energy. This is the reason the thrust and power available curves change with speed. Regions of Command Figure 4-10. Regions of command. The drag curve also illustrates the two regions of command: the region of normal command, and the region of reversed Control Characteristics command. The term “region of command” refers to the Most flying is conducted in the region of normal command: relationship between speed and the power required to for example, cruise, climb, and maneuvers. The region of maintain or change that speed. “Command” refers to the input reversed command may be encountered in the slow-speed the pilot must give in terms of power or thrust to maintain a phases of flight during takeoff and landing; however, for new speed once reached. most general aviation aircraft, this region is very small and is below normal approach speeds. The “region of normal command” occurs where power must be added to increase speed. This region exists at speeds higher Flight in the region of normal command is characterized than the minimum drag point primarily as a result of parasite by a relatively strong tendency of the aircraft to maintain drag. The “region of reversed command” occurs where the trim speed. Flight in the region of reversed command is 4-7

characterized by a relatively weak tendency of the aircraft to Reversed Command maintain the trim speed. In fact, it is likely the aircraft exhibits The characteristics of flight in the region of reversed command no inherent tendency to maintain the trim speed in this area. are illustrated at point B on the curve in Figure 4-10. If the For this reason, the pilot must give particular attention to aircraft is established in steady, level flight at point B, lift is precise control of airspeed when operating in the slow-speed equal to weight, and the power available is set equal to the phases of the region of reversed command. power required. When the airspeed is increased greater than point B, an excess of power exists. This causes the aircraft Operation in the region of reversed command does not imply to accelerate to an even higher speed. When the aircraft is that great control difficulty and dangerous conditions exist. slowed to some airspeed lower than point B, a deficiency However, it does amplify errors of basic flying technique— of power exists. The natural tendency of the aircraft is to making proper flying technique and precise control of the continue to slow to an even lower airspeed. aircraft very important. This tendency toward instability happens because the Speed Stability variation of excess power to either side of point B magnifies Normal Command the original change in speed. Although the static longitudinal stability of the aircraft tries to maintain the original trimmed The characteristics of flight in the region of normal command condition, this instability is more of an influence because of are illustrated at point A on the curve in Figure 4-11. If the increased induced drag due to the higher AOA in slow- the aircraft is established in steady, level flight at point A, speed flight. lift is equal to weight, and the power available is set equal to the power required. If the airspeed is increased with no Trim changes to the power setting, a power deficiency exists. The aircraft has a natural tendency to return to the initial The term trim refers to employing adjustable aerodynamic speed to balance power and drag. If the airspeed is reduced devices on the aircraft to adjust forces so the pilot does not with no changes to the power setting, an excess of power have to manually hold pressure on the controls. One means is exists. The aircraft has a natural tendency to speed up to to employ trim tabs. A trim tab is a small, adjustable hinged regain the balance between power and drag. Keeping the surface, located on the trailing edge of the elevator, aileron, aircraft in proper trim enhances this natural tendency. The or rudder control surfaces. (Some aircraft use adjustable static longitudinal stability of the aircraft tends to return the stabilizers instead of trim tabs for pitch trim.) Trimming is aircraft to the original trimmed condition. accomplished by deflecting the tab in the direction opposite to that in which the primary control surface must be held. Power Required Region of Power The force of the airflow striking the tab causes the main reversed A deficit control surface to be deflected to a position that corrects the command Region of unbalanced condition of the aircraft. normal Because the trim tabs use airflow to function, trim is a function command of speed. Any change in speed results in the need to re-trim the aircraft. An aircraft properly trimmed in pitch seeks to return Power Excess to the original speed before the change. It is very important deficit power for instrument pilots to keep the aircraft in constant trim. This reduces the pilot’s workload significantly, allowing attention Excess Little or no excess to other duties without compromising aircraft control. B power C power or power deficit Slow-Speed Flight Airspeed Figure 4-11. Region of speed stability. Anytime an aircraft is flying near the stalling speed or the region of reversed command, such as in final approach for a An aircraft flying in steady, level flight at point C is in normal landing, the initial part of a go around, or maneuvering equilibrium. [Figure 4-11] If the speed were increased in slow flight, it is operating in what is called slow-speed flight. or decreased slightly, the aircraft would tend to remain at If the aircraft weighs 4,000 pounds, the lift produced by the that speed. This is because the curve is relatively flat and aircraft must be 4,000 pounds. When lift is less than 4,000 a slight change in speed does not produce any significant pounds, the aircraft is no longer able to sustain level flight, and excess or deficiency in power. It has the characteristic of consequently descends. During intentional descents, this is an neutral stability (i.e., the aircraft’s tendency is to remain at important factor and is used in the total control of the aircraft. the new speed). 4-8

However, because lift is required during low speed flight Uncontrolled Turbulence and is characterized by high AOA, flaps or other high lift devices are needed to either change the camber of the airfoil, or delay the boundary level separation. Plain and split flaps [Figure 4-12] are most commonly used to change the camber of an airfoil. It should be noted that with the application of flaps, the aircraft will stall at a lower AOA. For example, if the basic wing stalls at 18° without flaps, then with the addition of flaps to the CL-MAX position, the new AOA that the wing will stall is 15°. However, the value of lift (flaps extended to the CL-MAX position) produces more lift than lift at 18° on the basic wing. Plain Split Figure 4-12. Plain and split flaps. Delaying the boundary layer separation is another way to Controlled Vortices increase CL-Max. Several methods are employed (such as suction and use of a blowing boundary layer control), but the Figure 4-13. Vortex generators. most common device used oFnowgelenerral aviation light aircraft is the vortex generator. Small strips of metal placed along accept minor speed changes knowing that when the pitch is the wing (usually in front of the control surfaces) create returned to the initial setting, the speed returns to the original turbulence. The turbulence in turn mixes high energy air from setting. This reduces the pilot’s workload. outside the boundary layer with boundary layer air. The effect is similar to other boundary layer devices. [Figure 4-13] Aircraft are usually slowed to a normal landing speed when on the final approach just prior to landing. When slowed to Small Airplanes 65 knots, (1.3 VSO), the airplane will be close to point C. Most small airplanes maintain a speed well in excess of 1.3 [Figure 4-14] At this point, precise control of the pitch and times VSO on an instrumenStloapttperdoach. An airplane with a power becomes more crucial for maintaining the correct speed. stall speed of 50 knots (VSO) has a normal approach speed Pitch and power coordination is necessary because the speed of 65 knots. However, this same airplane may maintain 90 stability is relatively neutral since the speed tends to remain knots (1.8 VSO) while on the final segment of an instrument at the new value and not return to the original setting. In approach. The landing gear will most likely be extended at addition to the need for more precise airspeed control, the pilot the beginning of the descent to the minimum descent altitude, normally changes the aircraft’s configuration by extending or upon intercepting the glideslope of the instrument landing landing flaps. This configuration change means the pilot must system. The pilot may also select an intermediate flap setting be alert to unwanted pitch changes at a low altitude. for this phase of the approach. The airplane at this speed has good positive speed stability, as represented by point A on Figure 4-11. Flying in this regime permits the pilot to make slight pitch changes without changing power settings, and 4-9

L Vertical Excess power is the available power over and above that component of lift required to maintain horizontal flight at a given speed. Although the terms power and thrust are sometimes Resultant lift used interchangeably (erroneously implying they are synonymous), distinguishing between the two is important L when considering climb performance. Work is the product of a force moving through a distance and is usually independent Horizontal of time. Power implies work rate or units of work per unit component of lift of time, and as such is a function of the speed at which the force is developed. Thrust, also a function of work, means L the force which imparts a change in the velocity of a mass. Weight During takeoff, the aircraft does not stall even though it may be in a climb near the stall speed. The reason is that W excess power (used to produce thrust) is used during this flight regime. Therefore, it is important if an engine fails Figure 4-14. Forces in a turn. after takeoff, to compensate the loss of thrust with pitch and airspeed. If allowed to slow several knots, the airplane could enter the region of reversed command. At this point, the airplane For a given weight of the aircraft, the angle of climb depends could develop an unsafe sink rate and continue to lose speed on the difference between thrust and drag, or the excess unless the pilot takes a prompt corrective action. Proper pitch thrust. When the excess thrust is zero, the inclination of the and power coordination is critical in this region due to speed flightpath is zero, and the aircraft is in steady, level flight. instability and the tendency of increased divergence from When thrust is greater than drag, the excess thrust allows a the desired speed. climb angle depending on the amount of excess thrust. When thrust is less than drag, the deficiency of thrust induces an Large Airplanes angle of descent. Pilots of larger airplanes with higher stall speeds may find the speed they maintain on the instrument approach is near 1.3 Acceleration in Cruise Flight VSO, putting them near point C [Figure 4-11] the entire time Aircraft accelerate in level flight because of an excess of the airplane is on the final approach segment. In this case, power over what is required to maintain a steady speed. This precise speed control is necessary throughout the approach. It is the same excess power used to climb. Upon reaching the may be necessary to temporarily select excessive, or deficient desired altitude with pitch being lowered to maintain that thrust in relation to the target thrust setting in order to quickly altitude, the excess power now accelerates the aircraft to its correct for airspeed deviations. cruise speed. However, reducing power too soon after level off results in a longer period of time to accelerate. For example, a pilot is on an instrument approach at 1.3 VSO, a speed near L/DMAX, and knows that a certain power Turns setting maintains that speed. The airplane slows several knots below the desired speed because of a slight reduction in the Like any moving object, an aircraft requires a sideward force power setting. The pilot increases the power slightly, and the to make it turn. In a normal turn, this force is supplied by airplane begins to accelerate, but at a slow rate. Because the banking the aircraft in order to exert lift inward, as well as airplane is still in the “flat part” of the drag curve, this slight upward. The force of lift is separated into two components increase in power will not cause a rapid return to the desired at right angles to each other. [Figure 4-14] The upward speed. The pilot may need to increase the power higher acting lift together with the opposing weight becomes the than normally needed to maintain the new speed, allow the vertical lift component. The horizontally acting lift and its airplane to accelerate, then reduce the power to the setting opposing centrifugal force are the horizontal lift component, that maintains the desired speed. or centripetal force. This horizontal lift component is the sideward force that causes an aircraft to turn. The equal and Climbs opposite reaction to this sideward force is centrifugal force, which is merely an apparent force as a result of inertia. The ability for an aircraft to climb depends upon an excess power or thrust over what it takes to maintain equilibrium. 4-10

The relationship between the aircraft’s speed and bank angle turn, while decreasing the bank angle increases the radius of to the rate and radius of turns is important for instrument turn. This means that intercepting a course at a higher speed pilots to understand. The pilot can use this knowledge to requires more distance, and therefore, requires a longer lead. properly estimate bank angles needed for certain rates of turn, If the speed is slowed considerably in preparation for holding or to determine how much to lead when intercepting a course. or an approach, a shorter lead is needed than that required for cruise flight. Rate of Turn The rate of turn, normally measured in degrees per second, Coordination of Rudder and Aileron Controls is based upon a set bank angle at a set speed. If either one Any time ailerons are used, adverse yaw is produced. Adverse of these elements changes, the rate of turn changes. If the yaw is caused when the ailerons are deflected as a roll motion aircraft increases its speed without changing the bank angle, (as in turn) is initiated. In a right turn, the right aileron is the rate of turn decreases. Likewise, if the speed decreases deflected upward while the left is deflected downward. Lift is without changing the bank angle, the rate of turn increases. increased on the left side and reduced on the right, resulting in a bank to the right. However, as a result of producing lift Changing the bank angle without changing speed also causes on the left, induced drag is also increased on the left side. the rate of turn to change. Increasing the bank angle without The drag causes the left wing to slow down, in turn causing changing speed increases the rate of turn, while decreasing the nose of the aircraft to initially move (left) in the direction the bank angle reduces the rate of turn. opposite of the turn. Correcting for this yaw with rudder, when entering and exiting turns, is necessary for precise control of The standard rate of turn, 3° per second, is used as the main the airplane when flying on instruments. The pilot can tell if reference for bank angle. Therefore, the pilot must understand the turn is coordinated by checking the ball in the turn-and- how the angle of bank varies with speed changes, such slip indicator or the turn coordinator. [Figure 4-16] as slowing down for holding or an instrument approach. Figure 4-15 shows the turn relationship with reference to a As the aircraft banks to enter a turn, a portion of the wing’s constant bank angle or a constant airspeed, and the effects on vertical lift becomes the horizontal component; therefore, rate of turn and radius of turn. A rule of thumb for determining without an increase in back pressure, the aircraft loses altitude the standard rate turn is to divide the airspeed by ten and during the turn. The loss of vertical lift can be offset by add 7. An aircraft with an airspeed of 90 knots takes a bank increasing the pitch in one-half bar width increments. Trim angle of 16° to maintain a standard rate turn (90 divided by may be used to relieve the control pressures; however, if used, 10 plus 7 equals 16°). it has to be removed once the turn is complete. Radius of Turn In a slipping turn, the aircraft is not turning at the rate The radius of turn varies with changes in either speed or appropriate to the bank being used, and the aircraft falls to bank. If the speed is increased without changing the bank the inside of the turn. The aircraft is banked too much for the angle, the radius of turn increases, and vice versa. If the speed rate of turn, so the horizontal lift component is greater than is constant, increasing the bank angle reduces the radius of the centrifugal force. A skidding turn results from excess of Radius≈1,500 Radius≈3,500 Radius≈6,500 Radius≈8,000 Radius≈3,500 Radius≈2,000 Figure 4-15. Turns. 4-11

Coordinated Turn Slipping Turn Skidding Turn D.C. D.C. D.C. ELEC. ELEC. ELEC. LR LR LR TURN COORDINATOR 2 MIN TURN TURN COORDINATOR TURN COORDINATOR DC ELEC L 2 MIN. R L 2 MIN. R 2 MIN TURN L 2 MIN. R 2 MIN TURN DC ELEC DC ELEC NO PITCH NO PITCH NO PITCH INFORMATION INFORMATION INFORMATION Coordinated Turn Slipping Turn Skidding Turn rudder into turn Note the slight differences in rudder placement. Figure 4-16. Adverse yaw. Load Factor centrifugal force over the horizontal lift component, pulling Any force applied to an aircraft to deflect its flight from a the aircraft toward the outside of the turn. The rate of turn straight line produces a stress on its structure; the amount of is too great for the angle of bank, so the horizontal lift this force is termed load factor. A load factor is the ratio of component is less than the centrifugal force. the aerodynamic force on the aircraft to the gross weight of the aircraft (e.g., lift/weight). For example, a load factor of 3 An inclinometer, located in the turn coordinator, or turn and means the total load on an aircraft’s structure is three times bank indicator indicates the quality of the turn, and should its gross weight. When designing an aircraft, it is necessary be centered when the wings are banked. If the ball is off of to determine the highest load factors that can be expected in center on the side toward the turn, the aircraft is slipping and normal operation under various operational situations. These rudder pressure should be added on that side to increase the “highest” load factors are called “limit load factors.” rate of turn or the bank angle should be reduced. If the ball is off of center on the side away from the turn, the aircraft Aircraft are placed in various categories (i.e., normal, utility, is skidding and rudder pressure toward the turn should be and acrobatic) depending upon the load factors they are relaxed or the bank angle should be increased. If the aircraft designed to take. For reasons of safety, the aircraft must be is properly rigged, the ball should be in the center when the designed to withstand certain maximum load factors without wings are level; use rudder and/or aileron trim if available. any structural damage. The increase in induced drag (caused by the increase in AOA necessary to maintain altitude) results in a minor loss of airspeed if the power setting is not changed. 4-12

The specified load may be expected in terms of aerodynamic ice or prevent its formation. On the other hand, fuel-injected forces, as in turns. In level flight in undisturbed air, the aircraft engines usually are less vulnerable to icing but still wings are supporting not only the weight of the aircraft, but can be affected if the engine’s air source becomes blocked centrifugal force as well. As the bank steepens, the horizontal with ice. Manufacturers provide an alternate air source that lift component increases, centrifugal force increases, and the may be selected in case the normal system malfunctions. load factor increases. If the load factor becomes so great that an increase in AOA cannot provide enough lift to support In turbojet aircraft, air that is drawn into the engines creates the load, the wing stalls. Since the stalling speed increases an area of reduced pressure at the inlet, which lowers the directly with the square root of the load factor, the pilot temperature below that of the surrounding air. In marginal should be aware of the flight conditions during which the icing conditions (i.e., conditions where icing is possible), load factor can become critical. Steep turns at slow airspeed, this reduction in temperature may be sufficient to cause ice structural ice accumulation, and vertical gusts in turbulent to form on the engine inlet, disrupting the airflow into the air can increase the load factor to a critical level. engine. Another hazard occurs when ice breaks off and is ingested into a running engine, which can cause damage to Icing fan blades, engine compressor stall, or combustor flameout. When anti-icing systems are used, runback water also can One of the greatest hazards to flight is aircraft icing. The refreeze on unprotected surfaces of the inlet and, if excessive, instrument pilot must be aware of the conditions conducive to reduce airflow into the engine or distort the airflow pattern in aircraft icing. These conditions include the types of icing, the such a manner as to cause compressor or fan blades to vibrate, effects of icing on aircraft control and performance, effects possibly damaging the engine. Another problem in turbine of icing on aircraft systems, and the use and limitations of engines is the icing of engine probes used to set power levels aircraft deice and anti-ice equipment. Coping with the hazards (for example, engine inlet temperature or engine pressure ratio of icing begins with preflight planning to determine where (EPR) probes), which can lead to erroneous readings of engine icing may occur during a flight and ensuring the aircraft is instrumentation operational difficulties or total power loss. free of ice and frost prior to takeoff. This attention to detail extends to managing deice and anti-ice systems properly The type of ice that forms can be classified as clear, rime, or during the flight, because weather conditions may change mixed, based on the structure and appearance of the ice. The rapidly, and the pilot must be able to recognize when a change type of ice that forms varies depending on the atmospheric of flight plan is required. and flight conditions in which it forms. Significant structural icing on an aircraft can cause serious aircraft control and Types of Icing performance problems. Structural Icing Clear Ice Structural icing refers to the accumulation of ice on the A glossy, transparent ice formed by the relatively slow exterior of the aircraft. Ice forms on aircraft structures and freezing of super cooled water is referred to as clear ice. surfaces when super-cooled droplets impinge on them and [Figure 4-17] The terms “clear” and “glaze” have been used freeze. Small and/or narrow objects are the best collectors of droplets and ice up most rapidly. This is why a small protuberance within sight of the pilot can be used as an “ice evidence probe.” It is generally one of the first parts of the airplane on which an appreciable amount of ice forms. An aircraft’s tailplane is a better collector than its wings, because the tailplane presents a thinner surface to the airstream. Induction Icing Figure 4-17. Clear ice. Clear Ice Ice in the induction system can reduce the amount of air available for combustion. The most common example of reciprocating engine induction icing is carburetor ice. Most pilots are familiar with this phenomenon, which occurs when moist air passes through a carburetor venturi and is cooled. As a result of this process, ice may form on the venturi walls and throttle plate, restricting airflow to the engine. This may occur at temperatures between 20 °F (–7 °C) and 70 °F (21 °C). The problem is remedied by applying carburetor heat, which uses the engine’s own exhaust as a heat source to melt the 4-13

for essentially the same type of ice accretion. This type of ice is denser, harder, and sometimes more transparent than rime ice. With larger accretions, clear ice may form “horns.” [Figure 4-18] Temperatures close to the freezing point, large amounts of liquid water, high aircraft velocities, and large droplets are conducive to the formation of clear ice. Figure 4-19. Rime ice. Rime Ice Mixed Ice Mixed ice is a combination of clear and rime ice formed on the same surface. It is the shape and roughness of the ice that is most important from an aerodynamic point of view. Figure 4-18. ClCealerairceIcbeuiBlduupildwuitph whoirthnsH. orns General Effects of Icing on Airfoils The most hazardous aspect of structural icing is its aerodynamic Rime Ice effects. [Figure 4-20] Ice alters the shape of an airfoil, reducing A rough, milky, opaque ice formed by the instantaneous or the maximum coefficient of lift and AOA at which the aircraft very rapid freezing of super cooled droplets as they strike stalls. Note that at very low AOAs, there may be little or no the aircraft is known as rime ice. [Figure 4-19] The rapid effect of the ice on the coefficient of lift. Therefore, when freezing results in the formation of air pockets in the ice, cruising at a low AOA, ice on the wing may have little effect giving it an opaque appearance and making it porous and on the lift. However, note that the ice significantly reduces brittle. For larger accretions, rime ice may form a streamlined the CL-max, and the AOA at which it occurs (the stall angle) extension of the wing. Low temperatures, lesser amounts of is much lower. Thus, when slowing down and increasing the liquid water, low velocities, and small droplets are conducive AOA for approach, the pilot may find that ice on the wing, to the formation of rime ice. which had little effect on lift in cruise now, causes stall to Airfoil with ice CL (coefficient of lift) CD (coefficient of drag) Clean Clean airfoil airfoil Airfoil Angle of Attack with ice Angle of Attack Figure 4-20. Aerodynamic effects of icing. 4-14

occur at a lower AOA and higher speed. Even a thin layer of ice at the leading edge of a wing, especially if it is rough, can have a significant effect in increasing stall speed. For large ice shapes, especially those with horns, the lift may also be reduced at a lower AOA. The accumulation of ice affects the coefficient of drag of the airfoil. [Figure 4-20] Note that the effect is significant even at very small AOAs. A significant reduction in CL-max and a reduction in the Upper Surface Frost Leading Edge Ice Formations AOA where stall occurs can result from a relatively small CL-MAX ice accretion. A reduction of CL-max by 30 percent is not w unusual, and a large horn ice accretion can result in reductions f of 40 percent to 50 percent. Drag tends to increase steadily as ice accretes. An airfoil drag increase of 100 percent is not unusual, and for large horn ice accretions, the increase can be 200 percent or even higher. Ice on an airfoil can have other effects not depicted in these i curves. Even before airfoil stall, there can be changes in the pressure over the airfoil that may affect a control surface at Angle of Attack the trailing edge. Furthermore, on takeoff, approach, and landing, the wings of many aircraft are multi-element airfoils Figure 4-21. Effect of ice and frost on lift. with three or more elements. Ice may affect the different elements in different ways. Ice may also affect the way in which the air streams interact over the elements. Ice can partially block or limit control surfaces, which C of L limits or makes control movements ineffective. Also, if the extra weight caused by ice accumulation is too great, the aircraft may not be able to become airborne and, if in flight, the aircraft may not be able to maintain altitude. Therefore any accumulation of ice or frost should be removed before attempting flight. Another hazard of structural icing is the possible uncommanded CG Tail download and uncontrolled roll phenomenon, referred to as roll upset, Weight associated with severe inflight icing. Pilots flying aircraft certificated for flight in known icing conditions should be Figure 4-22. Downward force on the tailplane. aware that severe icing is a condition outside of the aircraft’s certification icing envelope. Roll upset may be caused by deployment of flaps or increasing speed, may increase the airflow separation (aerodynamic stall), which induces self- negative AOA of the tail. With ice on the tailplane, it may deflection of the ailerons and loss of or degraded roll handling stall after full or partial deployment of flaps. [Figure 4-23] characteristics [Figure 4-21]. These phenomena can result from severe icing conditions without the usual symptoms of Since the tailplane is ordinarily thinner than the wing, it is a ice accumulation or a perceived aerodynamic stall. more efficient collector of ice. On most aircraft the tailplane is not visible to the pilot, who therefore cannot observe how Most aircraft have a nose-down pitching moment from the well it has been cleared of ice by any deicing system. Thus, it wings because the CG is ahead of the CP. It is the role of the is important that the pilot be alert to the possibility of tailplane tailplane to counteract this moment by providing a downward stall, particularly on approach and landing. force. [Figure 4-22] The result of this configuration is that actions which move the wing away from stall, such as 4-15

CG If any of the above symptoms occur, the pilot should: Icing • Immediately retract the flaps to the previous setting and apply appropriate nose-up elevator pressure; Aircraft nose Weight pitches down • Increase airspeed appropriately for the reduced flap extension setting; Figure 4-23. Ice on the tailplane. • Apply sufficient power for aircraft configuration Piper PA-34-200T (Des Moines, Iowa) and conditions. (High engine power settings may The pilot of this flight, which took place on January 9, adversely impact response to tailplane stall conditions 1996, said that upon crossing the runway threshold and at high airspeed in some aircraft designs. Observe the lowering the flaps 25°, “the airplane pitched down.” The manufacturer’s recommendations regarding power pilot “immediately released the flaps and added power, but settings.); the airplane was basically uncontrollable at this point.” The pilot reduced power and lowered the flaps before striking • Make nose-down pitch changes slowly, even in the runway on its centerline and sliding 1,000 feet before gusting conditions, if circumstances allow; and coming to a stop. The accident resulted in serious injury to the pilot, the sole occupant. • If a pneumatic deicing system is used, operate the system several times in an attempt to clear the tailplane Examination of the wreckage revealed heavy impact of ice. damage to the airplane’s forward fuselage, engines, and wings. Approximately one-half inch of rime ice was Once a tailplane stall is encountered, the stall condition observed adhering to the leading edges of the left and right tends to worsen with increased airspeed and possibly may horizontal stabilizers and along the leading edge of the worsen with increased power settings at the same flap vertical stabilizer. setting. Airspeed, at any flap setting, in excess of the airplane manufacturer’s recommendations, accompanied by uncleared The National Transportation Safety Board (NTSB) ice contaminating the tailplane, may result in a tailplane stall determined the probable cause of the accident was the pilot’s and uncommanded pitch down from which recovery may not failure to use the airplane’s deicing system, which resulted be possible. A tailplane stall may occur at speeds less than in an accumulation of empennage ice and a tailplane stall. the maximum flap extended speed (VFE). Factors relating to this accident were the icing conditions and the pilot’s intentional flight into those known conditions. Propeller Icing Ice buildup on propeller blades reduces thrust for the same aerodynamic reasons that wings tend to lose lift and increase drag when ice accumulates on them. The greatest quantity of ice normally collects on the spinner and inner radius of the propeller. Propeller areas on which ice may accumulate and be ingested into the engine normally are anti-iced rather than deiced to reduce the probability of ice being shed into the engine. Tailplane Stall Symptoms Effects of Icing on Critical Aircraft Systems Any of the following symptoms, occurring singly or in In addition to the hazards of structural and induction icing, combination, may be a warning of tailplane icing: the pilot must be aware of other aircraft systems susceptible to icing. The effects of icing do not produce the performance • Elevator control pulsing, oscillations, or vibrations; loss of structural icing or the power loss of induction icing but can present serious problems to the instrument pilot. • Abnormal nose-down trim change; Examples of such systems are flight instruments, stall warning systems, and windshields. • Any other unusual or abnormal pitch anomalies (possibly resulting in pilot induced oscillations); Flight Instruments Various aircraft instruments including the airspeed indicator, • Reduction or loss of elevator effectiveness; altimeter, and rate-of-climb indicator utilize pressures sensed by pitot tubes and static ports for normal operation. • Sudden change in elevator force (control would move nose-down if unrestrained); and • Sudden uncommanded nose-down pitch. 4-16

When covered by ice these instruments display incorrect The pilot of an aircraft, which is not certificated or equipped information thereby presenting serious hazard to instrument for flight in icing conditions, should avoid all icing conditions. flight. Detailed information on the operation of these The aforementioned guides provide direction on how to do instruments and the specific effects of icing is presented in this, and on how to exit icing conditions promptly and safely Chapter 5, Flight Instruments. should they be inadvertently encountered. Stall Warning Systems The pilot of an aircraft, which is certificated for flight in icing conditions can safely operate in the conditions for Stall warning systems provide essential information to pilots. which the aircraft was evaluated during the certification These systems range from a sophisticated stall warning vane process but should never become complacent about icing. to a simple stall warning switch. Icing affects these systems Even short encounters with small amounts of rough icing in several ways resulting in possible loss of stall warning to can be very hazardous. The pilot should be familiar with all the pilot. The loss of these systems can exacerbate an already information in the Aircraft Flight Manual (AFM) or Pilot’s hazardous situation. Even when an aircraft’s stall warning Operating Handbook (POH) concerning flight in icing system remains operational during icing conditions, it may conditions and follow it carefully. Of particular importance be ineffective because the wing stalls at a lower AOA due are proper operation of ice protection systems and any to ice on the airfoil. airspeed minimums to be observed during or after flight in icing conditions. There are some icing conditions for Windshields which no aircraft is evaluated in the certification process, such as super-cooled large drops (SLD). These subfreezing Accumulation of ice on flight deck windows can severely water droplets, with diameters greater than 50 microns, restrict the pilot’s visibility outside of the aircraft. Aircraft occur within or below clouds and sustained flight in these equipped for flight into known icing conditions typically have conditions can be very hazardous. The pilot should be familiar some form of windshield anti-icing to enable the pilot to see with any information in the AFM or POH relating to these outside the aircraft in case icing is encountered in flight. One conditions, including aircraft-specific cues for recognizing system consists of an electrically heated plate installed onto these hazardous conditions within clouds. the airplane’s windshield to give the pilot a narrow band of clear visibility. Another system uses a bar at the lower end The information in this chapter is an overview of the hazards of the windshield to spray deicing fluid onto it and prevent of aircraft icing. For more detailed information refer to ice from forming. On high performance aircraft that require AC 91-74, Pilot Guide: Flight in Icing Conditions, AC 91- complex windshields to protect against bird strikes and 51, Effect of Icing on Aircraft Control and Airplane Deice withstand pressurization loads, the heating element often is and Anti-Ice Systems, AC 20-73, Aircraft Ice Protection a layer of conductive film or thin wire strands through which and AC 23.143-1, Ice Contaminated Tailplane Stall (ICTS). electric current is run to heat the windshield and prevent ice from forming. Antenna Icing Because of their small size and shape, antennas that do not lay flush with the aircraft’s skin tend to accumulate ice rapidly. Furthermore, they often are devoid of internal anti-icing or deicing capability for protection. During flight in icing conditions, ice accumulations on an antenna may cause it to begin to vibrate or cause radio signals to become distorted and it may cause damage to the antenna. If a frozen antenna breaks off, it can damage other areas of the aircraft in addition to causing a communication or navigation system failure. Summary Ice-contaminated aircraft have been involved in many accidents. Takeoff accidents have usually been due to failure to deice or anti-ice critical surfaces properly on the ground. Proper deicing and anti-icing procedures are addressed in two other pilot guides, Advisory Circular (AC) 120-58, Pilot Guide: Large Aircraft Ground Deicing and AC 135-17, Pilot Guide: Small Aircraft Ground Deicing. 4-17

4-18

FlightChapter5 Instruments Introduction Aircraft became a practical means of transportation when accurate flight instruments freed the pilot from the necessity of maintaining visual contact with the ground. Flight instruments are crucial to conducting safe flight operations and it is important that the pilot have a basic understanding of their operation. The basic flight instruments required for operation under visual flight rules (VFR) are airspeed indicator (ASI), altimeter, and magnetic direction indicator. In addition to these, operation under instrument flight rules (IFR) requires a gyroscopic rate-of-turn indicator, slip-skid indicator, sensitive altimeter adjustable for barometric pressure, clock displaying hours, minutes, and seconds with a sweep-second pointer or digital presentation, gyroscopic pitch-and-bank indicator (artificial horizon), and gyroscopic direction indicator (directional gyro or equivalent). 5-1

Aircraft that are flown in instrument meteorological integrated into the electrically heated pitot tube. [Figure 5-1] conditions (IMC) are equipped with instruments that provide These ports are in locations proven by flight tests to be in attitude and direction reference, as well as navigation undisturbed air, and they may be paired, one on either side of instruments that allow precision flight from takeoff to landing the aircraft. This dual location prevents lateral movement of with limited or no outside visual reference. the aircraft from giving erroneous static pressure indications. The areas around the static ports may be heated with electric The instruments discussed in this chapter are those required heater elements to prevent ice forming over the port and by Title 14 of the Code of Federal Regulations (14 CFR) blocking the entry of the static air. part 91, and are organized into three groups: pitot-static instruments, compass systems, and gyroscopic instruments. Three basic pressure-operated instruments are found in The chapter concludes with a discussion of how to preflight aircraft instrument panels flown under IFR. These are the these systems for IFR flight. This chapter addresses additional ASI, sensitive altimeter, and vertical speed indicator (VSI). avionics systems such as Electronic Flight Information All three instruments receive static air pressure for operation Systems (EFIS), Ground Proximity Warning System with only the ASI receiving both pitot and static pressure. (GPWS), Terrain Awareness and Warning System (TAWS), [Figure 5-2] Traffic Alert and Collision Avoidance System (TCAS), Head Up Display (HUD), etc., that are increasingly being Blockage of the Pitot-Static System incorporated into general aviation aircraft. Errors in the ASI and VSI almost always indicate a blockage of the pitot tube, the static port(s), or both. Moisture Pitot/Static Systems (including ice), dirt, or even insects can cause a blockage in both systems. During preflight, it is very important to make Pitot pressure, or impact air pressure, is sensed through an sure the pitot tube cover is removed and that static port open-end tube pointed directly into the relative wind flowing openings are checked for blockage and damage. around the aircraft. The pitot tube connects to the ASI or an air data computer depending on your aircraft's configuration. Blocked Pitot System If the pitot tube drain hole becomes obstructed, the pitot Static Pressure system can become partially or completely blocked. When Static pressure is also used by the ASI as well as the other dynamic pressure cannot enter the pitot tube opening, the ASI pitot static instruments for determining altitude and vertical no longer operates. If the drain hole is open, static pressure speed. Static pressure may be sensed at one or more locations equalizes on both sides of the diaphram in the ASI and the on an aircraft. Some may be flush mounted on the fuselage or 322099...098 Drain hole Baffle plate Pitot pressure chamber Ram air Static hole Pitot tube Drain hole Static hole Static port Heater (100 watts) Heater (35 watts) Static chamber Pitot heater switch Alternate static source Figure 5-1. A typical electrically heated pitot-static head. Figure 3-1. A typical electrically heated poitot-static head. 5-2

When the alternate static source pressure is used, the following instrument indications are observed: 1. The altimeter indicates a slightly higher altitude than actual.322099...089 2. The ASI indicates an airspeed greater than the actual airspeed. 3. The VSI shows a momentary climb and then stabilizes if the altitude is held constant. For more information on static system blockages and how to best react to such situations, refer to the Pilot’s Handbook of Aeronautical Knowledge (FAA-H-8083-25A). Figure 5-2. AFitgyupricea3l -p2it.oAt-stytaptiiccaslypsitteomt-.static system. Effects of Flight Conditions The static ports are located in a position where the air at indicated airspeed slowly drops to zero. If the pitot tube ram their surface is as undisturbed as possible. But under some pressure hole and drain hole become obstructed, the ASI flight conditions, particularly at a high angle of attack with operates like an altimeter as the aircraft climbs and descends. the landing gear and flaps down, the air around the static Refer to the Pilot’s Handbook of Aeronautical Knowledge port may be disturbed to the extent that it can cause an error (FAA-H-8083-25A) for more in depth information on in the indication of the altimeter and ASI. Because of the blocked pitot systems along with different scenarios and importance of accuracy in these instruments, part of the how they effect the ASI. certification tests for an aircraft is a check of position error in the static system. The Pilot’s Operating Handbook (POH)/Aircraft Flight Manual (AFM) contains any corrections that must be applied to the airspeed for the various configurations of flaps and landing gear. Blocked Static System Pitot/Static Instruments When a static system becomes blocked but the pitot tube remains clear the ASI continues to operate but is inaccurate. Sensitive Altimeter When the aircraft is operated above the altitude where the A sensitive altimeter is an aneroid barometer that measures static ports became blocked the airspeed indicates lower the absolute pressure of the ambient air and displays it in than the actual airspeed because the trapped static pressure terms of feet or meters above a selected pressure level. is higher than normal for that altitude. The opposite holds true for operations at lower altitudes; a faster than actual Principle of Operation airspeed is displayed due to the relatively low static pressure The sensitive element in a sensitive altimeter is a stack of trapped in the system. evacuated, corrugated bronze aneroid capsules. [Figure 5-3] The air pressure acting on these aneroids tries to compress A blockage of the static system can also affect the altimeter them against their natural springiness, which tries to expand and VSI. Trapped static pressure causes the altimeter to them. The result is that their thickness changes as the air freeze at the altitude where the blockage occurred. In the case pressure changes. Stacking several aneroids increases the of the VSI, a blocked static system produces a continuous dimension change as the pressure varies over the usable zero indication. range of the instrument. An alternate static source is provided in some aircraft to Below 10,000 feet, a striped segment is visible. Above this provide static pressure should the primary static source altitude, a mask begins to cover it, and above 15,000 feet, become blocked. The alternate static source is normally found all of the stripes are covered. [Figure 5-4] inside of the flight deck. Due to the venturi effect of the air flowing around the fuselage, the air pressure inside the flight Another configuration of the altimeter is the drum-type. deck is lower than the exterior pressure. [Figure 5-5] These instruments have only one pointer that 5-3

Aneroid 1,000 ft. pointer 100 ft. pointer 10,000 ft. pointer Altimeter setting window Static port Altitude indication scale Barometric scale adjustment knob Crosshatch flag A crosshatched area appears on some altimeters when displaying an altitude below 10,000 feet MSL. Figure 5-3. Sensitive altimeter components. Figure 3-3. Sensitive amltiamrkeetedr icnomthpoounseamndesntosf. feet, is geared to the mechanism that drives the pointer. To read this type of altimeter, first look at 8 9 0 II00 FEET 23232909...809 the drum to get the thousands of feet, and then at the pointer 7 to get the feet and hundreds of feet. CALIBRATED ALT TO A sensitive altimeter is one with an adjustable barometric scale allowing the pilot to set the reference pressure from which the 20,000 FEET altitude is measured. This scale is visible in a small window called the Kollsman window. A knob on the instrument adjusts 654 the scale. The range of the scale is from 28.00 to 31.00 inches of mercury (\"Hg), or 948 to 1,050 millibars. Figure 5-4. ThrFeeig-puorien3te-r4a. lTtihmreeete-pr.ointer altimeter. Rotating the knob changes both the barometric scale and the altimeter pointers in such a way that a change in the barometric 90 I scale of 1 \"Hg changes the pointer indication by 1,000 feet. This is the standard pressure lapse rate below 5,000 feet. 8 0 6, 5 0 0 2 When the barometric scale is adjusted to 29.92 \"Hg or 1,013.2 millibars, the pointers indicate the pressure altitude. The pilot 7 MB ALT displays indicate altitude by adjusting the barometric scale to the local altimeter setting. The altimeter then indicates the 3I N H G height above the existing sea level pressure. 2992 Altimeter Errors A sensitive altimeter is designed to indicate standard changes 654 from standard conditions, but most flying involves errors caused by nonstandard conditions and the pilot must be able to modify the indications to correct for these errors. There are two types of errors: mechanical and inherent. Figure 5-5. DrumF-itgyuperea3lt-i5m.eDterru.m-type altimeter. Mechanical Altimeter Errors makes one revolution for every 1,000 feet. Each number represents 100 feet and each mark represents 20 feet. A drum, A preflight check to determine the condition of an altimeter consists of setting the barometric scale to the local altimeter 5-4

setting. The altimeter should indicate the surveyed elevation Under extremely cold conditions, pilots may need to add an of the airport. If the indication is off by more than 75 feet from appropriate temperature correction determined from the chart the surveyed elevation, the instrument should be referred in Figure 5-7 to charted IFR altitudes to ensure terrain and to a certificated instrument repair station for recalibration. obstacle clearance with the following restrictions: Differences between ambient temperature and/or pressure causes an erroneous indication on the altimeter. • Altitudes specifically assigned by Air Traffic Control (ATC), such as “maintain 5,000 feet” shall not be Inherent Altimeter Error corrected. Assigned altitudes may be rejected if the pilot decides that low temperatures pose a risk of When the aircraft is flying in air that is warmer than standard, inadequate terrain or obstacle clearance. the air is less dense and the pressure levels are farther apart. When the aircraft is flying at an indicated altitude of 5,000 • If temperature corrections are applied to charted feet, the pressure level for that altitude is higher than it would IFR altitudes (such as procedure turn altitudes, final be in air at standard temperature, and the aircraft is higher approach fix crossing altitudes, etc.), the pilot must than it would be if the air were cooler. If the air is colder advise ATC of the applied correction. than standard, it is denser and the pressure levels are closer together. When the aircraft is flying at an indicated altitude ICAO Cold Temperature Error Table of 5,000 feet, its true altitude is lower than it would be if the The cold temperature induced altimeter error may be air were warmer. [Figure 5-6] significant when considering obstacle clearances when temperatures are well below standard. Pilots may wish to Cold Weather Altimeter Errors increase their minimum terrain clearance altitudes with a A correctly calibrated pressure altimeter indicates true corresponding increase in ceiling from the normal minimum altitude above mean sea level (MSL) when operating within when flying in extreme cold temperature conditions. Higher the International Standard Atmosphere (ISA) parameters of altitudes may need to be selected when flying at low terrain pressure and temperature. Nonstandard pressure conditions are clearances. Most flight management systems (FMS) with corrected by applying the correct local area altimeter setting. air data computers implement a capability to compensate for cold temperature errors. Pilots flying with these systems Temperature errors from ISA result in true altitude being should ensure they are aware of the conditions under which higher than indicated altitude whenever the temperature is the system automatically compensates. If compensation is warmer than ISA and true altitude being lower than indicated applied by the FMS or manually, ATC must be informed altitude whenever the temperature is colder than ISA. that the aircraft is not flying the assigned altitude. Otherwise, True altitude variance under conditions of colder than ISA vertical separation from other aircraft may be reduced creating temperatures poses the risk of inadequate obstacle clearance. a potentially hazardous situation. The table in Figure 5-7, derived from International Civil Aviation Organization 5,000 foot pressure level 4,000 foot pressure level 3,000 foot pressure level 2,000 foot pressure level 1,000 foot pressure level Sea level 30°C 15°C 0°C Figure 5-6. The loss of altitude experieFnigceudrew3h-e6n. fElyfifnecgtsinotfonaonnastraenadwahrderteemthpeearairtuisrecoolndaern(amltoimreedteern. se) than standard. 5-5