Auto Piolet

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IntroductionThis chapter introduces automated flight control in theadvanced avionics cockpit. You will learn to use an autopilotsystem that can signi cantly reduce workload during criticalphases of ight. The two-axis autopilot system installed inmost general aviation aircraft controls the pitch and roll of theaircraft. The autopilot can operate independently, controlling

heading and altitude, or it can be coupled to a navigationsystem and y a programmed course or an approach withglideslope. In addition to learning how to use the autopilot,you must also learn when to use it and when not to use it.

Automated Flight ControlChapter 4


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You will learn how the autopilot and the ight managementsystem (FMS)/area navigation (RNAV) unit combine tocreate a fairly automated form of ight that places you ina managerial role. While the autopilot relieves you frommanually manipulating the ight controls, you must maintainvigilance over the system to ensure that it performs theintended functions and the aircraft remains within acceptableparameters of altitudes, airspeeds, and airspace limits.

Autopilot ConceptsAn autopilot can be capable of many very time intensivetasks, helping the pilot focus on the overall status of theaircraft and ight. Good use of an autopilot helps automatethe process of guiding and controlling the aircraft. Autopilotscan automate tasks, such as maintaining an altitude,climbing or descending to an assigned altitude, turning toand maintaining an assigned heading, intercepting a course,guiding the aircraft between waypoints that make up aroute programmed into an FMS, and ying a precision ornonprecision approach. You must accurately determine theinstalled options, type of installation, and basic and optionalfunctions available in your speci c aircraft.

Many advanced avionics installations really include twodifferent, but integrated, systems. One is the autopilotsystem, which is the set of servo actuators that actually dothe control movement and the control circuits to make theservo actuators move the correct amount for the selectedtask. The second is the ight director (FD) component. TheFD is the brain of the autopilot system. Most autopilots can

y straight and level. When there are additional tasks of

nding a selected course (intercepting), changing altitudes,and tracking navigation sources with cross winds, higherlevel calculations are required.

The FD is designed with the computational power toaccomplish these tasks and usually displays the indications tothe pilot for guidance as well. Most ight directors accept datainput from the air data computer (ADC), Attitude HeadingReference System (AHRS), navigation sources, the pilotscontrol panel, and the autopilot servo feedback, to namesome examples. The downside is that you must program theFD to display what you are to do. If you do not preprogram

the FD in time, or correctly, FD guidance may be inaccurate.

The programming of the FD increases the workload for thepilot. If that increased workload is offset by allowing theautopilot to control the aircraft, then the overall workloadis decreased. However, if you elect to use the FD display,but manually y the aircraft, then your workload is greatlyincreased.

In every instance, you must be absolutely sure what modes theFD/autopilot is in and include that indicator or annunciatorin the crosscheck. You must know what that particularmode in that speci c FD/autopilot system is programmed toaccomplish, and what actions will cancel those modes. Due tonumerous available options, two otherwise identical aircraftcan have very different avionics and autopilot functionalcapabilities.

How To Use an Autopilot FunctionThe following steps are required to use an autopilot function:

1. Specify desired track as de ned by heading, course,series of waypoints, altitude, airspeed, and/or verticalspeed.

2. Engage the desired autopilot function(s) and verifythat, in fact, the selected modes are engaged bymonitoring the annunciator panel.

3. Verify that desired track is being followed by theaircraft.

4. Verify that the correct navigation source is selectedto guide the autopilots track.

5. Be ready to y the aircraft manually to ensure propercourse/clearance tracking in case of autopilot failureor misprogramming.

6. Allow the FD/autopilot to accomplish the modesselected and programmed without interference, ordisengage the unit. Do not attempt to help theautopilot perform a task. In some instances this hascaused the autopilot to falsely sense adverse conditionsand trim to the limit to accomplish its tasking. In morethan a few events, this has resulted in a total loss ofcontrol and a crash.

Speci cation of Track and AltitudeA track is a speci c goal, such as a heading or course. Agoal can also be a level altitude, a selected airspeed, or aselected vertical speed to be achieved with the power atsome setting. Every autopilot uses knobs, buttons, dials,or other controls that allow the pilot to specify goals.Figure 4-1 shows an autopilot combined with conventionalnavigation instruments. Most autopilots have indicators for

the amount of servo travel or trim being used. These can beearly indicators of adverse conditions, such as icing or powerloss. Rarely will a trim indicator ever indicate full travel innormal operation. Consistently full or nearly full travel ofthe trim servos may be a sign of a trim servo failure, a shiftin weight resulting in a balance problem, or airfoil problemssuch as icing or inadvertent control activation.


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Knobs on the autopilot control panel can be usedto enter assigned altitudes and vertical speeds.

ARORM

The OBS knob on theCDI is used to specify target courses.

YD

ThC ta

A heading knob on thedirection indicator is usedto specify target headings.

Figure 4-1. A simple autopilot.

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Vertical speedselection

Altimeter setting

ertical s eed

Altitudeu e

Heading

Vertical speedindicator

This primary flight display offers separate windows used to input course, heading, altitude, and vertical speed targets.

Figure 4-2. Entering goals on a primary flight display.

Primary fight displays (PFDs) often integrate all controlsthat allow modes to be entered for the autopilot. The PFDshown in Figure 4-2 offers knobs that allow you to entermodes without turning attention away from the primary ightinstruments. Modes entered using the controls on a PFD aretransferred to the autopilot.

Engagement of Autopilot FunctionEvery autopilot offers a collection of buttons that allow youto choose and engage autopilot modes and functions. Buttonsused to engage autopilot modes appear along the bottomof the autopilot shown in Figure 4-1. The system shownin Figure 4-3 does not use a separate device for autopilotcontrols; it integrates the autopilot function buttons intoanother cockpit display.

Veri cation of Autopilot Function EngagementIt is very important to verify that an autopilot mode hasengaged, and the aircraft is tracking the intended ight


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AP YD

FD HDG

NAV APR

ALT MENU

VS NOSEUP

FLC NOSEDOWN

NAV

NAV

Figure 4-3. An integrated avionics system with an autopilot.

WPT KGNB DIS 53.5 NM DTK 274 TRK 360

GPS AP YD ALT

.

Y

A

Figure 4-4. Engaged autopilot modes shown at the top of a PFD.

pro le. Every autopilot displays which autopilot modes are

currently engaged, and most indicate an armed mode thatactivates when certain parameters are met, such as localizerinterception. The autopilot shown in Figure 4-1 displays theactive modes on the front of the unit, just above the controls.The integrated autopilot shown in Figure 4-4 displays thecurrently engaged autopilot mode along the top of the PFD.

How Autopilot Functions Work Once an autopilot mode has been engaged, the autopilot:

1. Determines which control movements are required tofollow the ight pro le entered by the pilot, and

2. Moves the controls to affect tracking of the ightpro le.

Determination of Control Movements Required To Achieve GoalsSuppose you wish to use the autopilot/FD to turn to anassigned heading of 270. The heading knob is used toselect the new heading. Before any control movements aremade, the autopilot/FD must rst determine which controlmovements are necessary (e.g., left or right turn). To do so,the FD/autopilot must rst determine the aircrafts currentheading and bank angle, determine amount and directionof the turn, and then choose an appropriate bank angle,usually up to 30 or less. To make these determinations, theFD gathers and processes information from the aircraftsADC (airspeed and altitude), magnetic heading referenceinstrument, and navigation systems.

Carrying Out Control MovementsOnce the FD/autopilot has determined which controlmovements are necessary to achieve the flight change,the autopilot has the task of carrying out those controlmovements. Every autopilot system features a collection ofelectromechanical devices, called servos, that actuate theaircraft control surfaces. These servos translate electricalcommands into motion, the muscle that actually movesthe control surfaces.

Flight DirectorFlight Director FunctionsAn FD is an extremely useful aid that displays cues to guidepilot or autopilot control inputs along a selected and computed

ightpath. [Figure 4-5] The ight director usually receivesinput from an ADC and a ight data computer. The ADCsupplies altitude, airspeed and temperature data, headingdata from magnetic sources such as ux valves, headingselected on the HSI (or PFD/multi-function display (MFD)/ electronic horizontal situation indicator (EHSI)), navigation

data from FMS, very high frequency omnidirectional range(VOR)/distance measuring equipment (DME), and RNAVsources. The ight data computer integrates all of the datasuch as speed, position, closure, drift, track, desired course,and altitude into a command signal.

The command signal is displayed on the attitude indicatorin the form of command bars, which show the pitch and roll


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880 B

050 060 070 080 090 100 110 120 00

Heading

Degrees of attitude

Horizon

Figure 4-5. A flight director.

inputs necessary to achieve the selected targets. To use theight director command bars, which are usually shaped as

inverted chevrons, or V-shaped symbols, the pilot simply iesto the bars. Some older models use crossed bars, leading thepilot to the selected point. In both types, you simply keepthe aircraft symbol on the attitude indicator aligned with thecommand bars, or allow the autopilot to make the actualcontrol movements to y the selected track and altitude.

Using the Flight Director (FD) Flight Director Without AutopilotThe FD and autopilot systems are designed to work together,but it is possible to use the ight director without engagingthe autopilot, or the autopilot without the FD, dependingon the installation. Without autopilot engagement, the FDpresents all processed information to the pilot in the form ofcommand bar cues, but you must manually y the airplaneto follow these cues to y the selected ightpath. In effect,you tell the FD what needs to happen and the FD commandbars tell you what to do. This adds to your workload, sinceyou must program the FD for each procedure or maneuver tobe accomplished, while actually ying the aircraft. In manycases, you will have a decreased workload if you simplydisable the FD and y using only the ight instruments.

Flight Director With AutopilotWhen the aircraft includes both a ight director and anautopilot, you may elect to use ight director cues withoutengaging the autopilot. It may or may not be possible to usethe autopilot without also engaging the ight director. Youneed to be familiar with the system installed. When youengage the autopilot, it simply follows the cues generated bythe ight director to control the airplane along the selectedlateral and vertical paths.

Common Error: Blindly Following Flight DirectorCuesThe convenience of ight director cues can invite xation oroverreliance on the part of the pilot. As with all automatedsystems, you must remain aware of the overall situation.Never assume that ight director cues are following a routeor course that is free from error. Rather, be sure to includenavigation instruments and sources in your scan. Remember,the equipment will usually perform exactly as programmed.Always compare the displays to ensure that all indicationsagree. If in doubt, y the aircraft to remain on cleared trackand altitude, and reduce automation to as minimal as possibleduring the problem processing period. The rst priority fora pilot always is to y the aircraft.

Common Error: Confusion About Autopilot EngagementPilots sometimes become confused about whether or not

ight director cues are being automatically carried out by

the autopilot, or left to be followed manually by the pilot.Veri cation of the autopilot mode and engagement statusof the autopilot is a necessary technique for maintainingawareness of who is ying the aircraft.

Follow RouteThe FD/autopilots navigation function can be used to guidethe aircraft along the course selected on the navigationindicator. Since the navigation display in most advancedavionics cockpits can present indications from a variety ofnavigation systems, you can use the autopilots navigationfunction to follow a route programmed into the FMS using

VOR, global positioning system (GPS), inertial navigationsystem (INS), or other navigation data sources.

Following a Route Programmed in the FMSFigure 4-6 demonstrates how to use the navigation function tofollow a route programmed into the FMS. With the navigationfunction engaged, the FD/auto-pilot steers the aircraft alongthe desired course to the active waypoint. Deviations fromthe desired course to the new active waypoint are displayedon the navigation indicator. When the aircraft reaches theactive waypoint, the FMS computer automatically sequencesto the next waypoint in the route, unless waypoint sequencingis suspended.

It is important to note that the normal navigation functionprovides only lateral guidance. It does not attempt to controlthe vertical path of the aircraft at any time. You must alwaysensure the correct altitude or vertical speed is maintained.


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The CDI is coupled to the area navigation computer, so the autopilot streets the aircraftalong the desired track to the active waypoint showing on the navigation computer.

VOL/IDPUSH

11GPS

VS

The autopilot NAV function steers the aircraft to keep the CDI needle centered.

Figure 4-6. Using the navigation function to follow the programmed flight route.

When combined, use of the FMS and the FD/autopilotsnavigation function result in an automated form of ight thatwas formerly limited to very complex and expensive aircraft.This same level of avionics can now be found in single-enginetraining airplanes. While it is easy to be complacent and letdown your guard, you must continuously monitor and stayaware of automated systems status and function and thetrack of the aircraft in relation to the ight plan and air traf ccontrol (ATC) clearance.

GPS Steering (GPSS) FunctionMany autopilots offer a global positioning system steering(GPSS) function. GPSS does all of the same actions asthe navigation function, but achieves a higher degree ofprecision by accepting inputs directly from the GPS receiver.Consequently, the GPSS function follows the desired track tothe active waypoint more aggressively, permitting only smallexcursions from the desired course. On some installations,pressing the autopilot NAV button twice engages the GPSSfunction.

Following a VOR RadialThe FD/autopilots navigation function can also be used todirectly track VOR radials. The navigation display must becon gured to show indications from one of the aircrafts VORreceivers. Once you have tuned and identi ed a VOR stationand selected the desired radial, you can select the navigationmode to track the selected radial. Figure 4-7 demonstrateshow to use the navigation mode to follow a VOR radial.

When the navigation mode is used to follow a route de nedby VOR radials, you must still tune and identify each newVOR facility manually and select the appropriate radialsalong the way. The autopilots navigation function cannotautomatically manipulate the VOR receiver. However, somehighly automated FMS units tune and identify VORs along ade ned route, such as Victor or Jet routes. You should checkthe FMS documentation and installed options.


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The CDI is coupled to the VOR receiver, so the NAV functionsteers the aircraft along the desired track to the selected radial.

Figure 4-7. Using the navigation mode to follow a VOR radial.

Depending on the FMS, the highly automated ight thatresults when the navigation mode is used to follow apublished route from the database uses a different skill setfrom using the navigation mode to track discreetly tuned VORradials. Learning how to select preprogrammed routes fromthe database of airways can be challenging. Programmingor tuning discreet VORs en route in turbulent conditionspresents different challenges. Either skill set can result in agreater sharing of duties between pilot and technology andan increase in safety.

Fly HeadingThe heading mode is used to steer the aircraft automaticallyalong a pilot selected heading. Using the FD/autopilot to ya heading is a simple matter of selecting the assigned headingand then engaging the heading function or, more commonly,accomplished by rst engaging the heading mode and gentlyturning the heading selection knob to the new heading. Gentlyturning the knob with the mode already engaged allows youto make a smooth change from level to turning ight. Many

autopilots make an abrupt bank if engaged when there is a bigchange to be made in heading or track. The heading functionis illustrated in Figure 4-8.

You should note that, when using the heading mode, the FD/ autopilot ignores the pilot-programmed route in the FMS orany VOR radials you set. When in heading mode, the FD/ autopilot will y the selected heading until fuel starvation.

Maintain Altitude

The autopilots altitude mode maintains an assignedbarometric altitude. When the altitude mode is engaged, theautopilot seeks to maintain the same barometric pressure(altitude) that the aircraft was ying at the time that thealtitude mode was engaged. Figure 4-9 shows how to engagethe altitude mode for one manufacturers autopilot.

In addition to determining and carrying out the pitchcommands necessary to maintain the flights assignedaltitude, most autopilots are also able to trim the aircraft.


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ft0055

YD BAROARM


A L T S E L

DN

UP

FT

Press the altitude button whenaircraft reaches the desired altitude.

YD BAROARM

The autopilot maintains the altitude until fuel starvation.

ALT

Figure 4-9. Maintaining an altitude using the altitude hold mode.

060 Heading

YD BAROARM


A L T S E L

DN

UP

FT

Press to engage the heading function.

The autopilot maintains the heading until fuel starvation.

HDG

SET

YD ARM

Set the heading bug to the desired heading.

Figure 4-8. Flying an assigned heading using the heading mode.

An autotrim system is capable of automatically making anyneeded adjustments to the pitch trim to maintain the aircraftat the desired altitude and in a properly trimmed condition.Pitch control pressure applied with the altitude hold modeengaged will cause the autopilot to trim against you.

Climbs and DescentsVertical SpeedThe autopilots vertical speed mode allows you to performconstant-rate climbs and descents. Figure 4-10 illustratesthe use of the vertical speed mode for one autopilot that isintegrated with a PFD.

When you engage the vertical speed mode, the FD/autopilotwill attempt to maintain the speci ed vertical speed until youchoose a different setting in autopilot, the aircraft reaches anassigned altitude set into the assigned altitude selector/alerter,

or the autopilot is disconnected. If an altitude selector is notinstalled or functioning, the pilot has the task of leveling offat the assigned altitude, which requires monitoring progressand manually engaging the autopilots altitude hold functiononce the aircraft reaches the desired altitude. You must bevery careful to specify an appropriate vertical speed, as theaircraft will y itself into a stall if you command the autopilotto climb at a rate greater than the aircrafts powerplant(s) is/

are capable of supporting. You also need to monitor descentairspeeds diligently to ensure compliance with V NE /V MO andVA or turbulence penetration speeds if there is doubt aboutsmooth air conditions. As discussed in the previous chapter,you should be cognizant of the powerplant temperaturesreciprocating powered aircraft and bleed air requirementsfor turbine-powered aircraft.

Vertical Speed With Altitude CaptureSome FD/autopilots have an altitude select/capture feature.The altitude select/capture feature is illustrated in Figure 4-11.The altitude select/capture feature combines use of theactivated vertical speed mode and an armed altitude holdmode. To use this feature, the vertical speed function isinitially engaged. The altitude hold mode usually armsautomatically when a different altitude is selected for captureand vertical speed is activated. With an altitude select/captureoption or feature, the altitude hold mode disengages thevertical speed mode upon capture of the selected altitude oncethe vertical speed function completes the necessary climb ordescent. Once the aircraft reaches the assigned altitude, thevertical speed function automatically disengages, and thealtitude mode changes from armed to engaged. The changefrom vertical speed mode to altitude hold mode is the capturemode, or transition mode. Any changes made by the pilotduring this short phase usually result in a cancellation of thecapture action, allowing the aircraft to continue the climb ordescent past the selected altitude. Again, be familiar with theaircrafts equipment. Let the system complete programmedtasks, and understand what it will do if interrupted.

Many FD/autopilot altitude selectors include an altitude alertfeature, an auditory alert that sounds or chimes as the aircraftapproaches or departs the selected altitude.

Catching Errors: Armed Modes Help Prevent Forgotten Mode ChangesYou have already seen how remembering to make a neededmode change in the future can be an error-prone process. Notcanceling the armed function allows the altitude select modeto relieve the pilot from needing to remember to engage thefunction manually once the aircraft has reached the selectedaltitude. Do not interrupt the altitude armed or capture mode,unless prepared to manually control the process.


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1 Enter the desired vertical speed.

2 Press the vertical speed button

3 The autopilot attempts to maintain the dialed vertical speed.

VS

Figure 4-10. Performing a constant-rate climb or descent using the vertical speed function.

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2 Simultaneously press to engage the vertical speedfunction and to arm the altitude function.

1 Enter the target altitude and desired vertical speed.

3 The autopilot attempts to maintain the target verticalspeed until reaching and capturing the target altitude.

VS

ALT

Figure 4-11. Climbs and descents to capture using the altitude select/capture feature.


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WPT KGNB DIS 53.5 NM DTK 274 TRK 274

GPS AP YD VS ALT800 FPM

Armed functions are shown in white.

Engaged functions are shown in green.

AP = autopilot engagedYD = yaw dampenerVS = vertical speed engaged

Figure 4-12. A mode annunciator showing armed and engagedautopilot modes.

The indications on the autopilot in Figure 4-11 do notdistinguish between functions that are armed or engaged.

The more sophisticated annunciator shown in Figure 4-12 usescolor coding to distinguish between armed and engagedautopilot functions.

Common Error: Failure To Arm the Altitude ModeThe most common error made by pilots during climbs anddescents is failure to arm the altitude mode to capture theassigned altitude. In many instances, this happens when thecrew does not correctly adjust the altitude selector or alerter.Sometimes, this malfunction occurs when the altitude isadjusted at the same time the system is attempting to gointo the capture mode. This situation typically results in theaircraft climbing or descending beyond the assigned altitude,which may result in an altitude deviation. Altitude deviationsare among the most common mishaps reported by pilots toNASAs Aviation Safety and Reporting System (ASRS). Inany event, always monitor the actions of the FD/autopilotsystem and be prepared to y the aircraft manually.

Awareness: Altitude Alerting SystemsAltitude alerting systems were mandated for commercial

jet transports in the early 1970s in response to a growingnumber of altitude deviations in airline operations. Althoughthey helped reduce the total number of altitude deviations,altitude alerting systems also made possible a new kind oferror. Altitude deviation reports submitted to the AviationSafety and Reporting System (ASRS) indicate that pilotssometimes rely too much on the altitude alerting system,using it as a substitute for maintaining altitude awareness.Instead of monitoring altitude, pilots sometimes simply listenfor the alert. This phenomenon is one instance of what humanfactors experts call primary-secondary task inversionwhenan alert or alarm designed as a secondary backup becomesthe primary source of information. In the case of the altitude

alerting system, when the alerting system is missed, or youare distracted, nothing is left to prevent an altitude deviation.You must remember that the altitude alerting system isdesigned as a backup, and be careful not to let the alertingsystem become the primary means of monitoring altitude.Most airline operators have a standard operating procedurethat requires pilots to call out approaching target altitudesbefore the altitude alerting system gives the alert. Common

errors occur when setting 10,000 feet versus 11,000 feet.Too many ones and zeros can confuse a fatigued, busy pilot,resulting in setting an incorrect altitude.

Awareness: Automatic Mode ChangesDistinguishing between armed and engaged addscomplexity to the process of maintaining mode awareness.In addition to autopilot functions that are engaged by thepilot, some autopilot functions engage and disengageautomatically. Automatic mode changes add to the challengeof keeping track of which autopilot functions are currentlyengaged and which functions are set to become engaged.You can minimize confusion by always verifying the statusannunciations on the FMs, PFD/MFD, and the autopilotmode annunciator after any change of heading, altitude,or vertical speed. The veri cation process forces you tocarefully consider the con guration of the FMS and FD/ autopilot. Determine if engaging the autopilot cancels certainFD modes. Some units interact, and when the autopilot isengaged, some FD modes are automatically canceled, notablyaltitude hold or selection.

Learning: The Importance of Understanding

One way to learn the steps required to use an autopilot issimply to memorize them. This approach focuses solely onthe button and control manipulations required to perform eachprocedure. Although this approach to learning may appearto be the quickest, studies have shown that pilots who takethe time to develop a deeper understanding of how a systemworks give themselves three important advantages. Thesepilots are better able to:

1. Work through situations that differ from the ones theylearned and practiced during training,

2. Transition from one manufacturers system to another,and

3. Recall procedures after not having practiced them forsome time.

Investing time to understand FD/autopilot functions pays off.For example, in many systems, once the aircraft reaches theselected altitude and levels off as indicated by the altitudemode annunciator, the pilot can select the next altitude inthe window. Then, upon receiving the clearance to climb


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or descend, the pilot must select only the vertical mode. Inmany systems, the vertical speed mode is indicated and thealtitude mode is indicated as armed and ready to capturethe selected altitude. Only the power requires pilot manualcontrol.

Power ManagementUnless the aircraft has an autothrottle system, you must adjust

the power to an appropriate setting when performing anyclimb, descent, or level-off. You cannot allow the aircraftto exceed any applicable speed limitations during a descent.During a climb at a vertical speed that the aircraft cannotsustain, the FD/autopilot may command a pitch that resultsin a stall.

Essential Skills

1. Use the FD/autopilot to climb or descend to andautomatically capture an assigned altitude.

2. Determine the indications of the armed or capture

mode, and what pilot actions will cancel those modes.3. Determine if the system allows resetting of the armed

or capture mode, or if manual control is the only optionafter cancellation of these modes.

4. Determine the available methods of activating thealtitude armed or capture mode.

5. Determine the average power necessary for normalclimbs and descents. Practice changing the power tothese settings in coordination with making the FD/ autopilot mode changes.

6. Determine and record maximum climb vertical speedsand power settings for temperatures and altitudes.Ensure the values are in agreement with values inAFM/POH for conditions. Make note of highestpractical pitch attitude values, conditions, and loading.Remember powerplant factors (e.g., minimumpowerplant temperature, bleed air requirements) andairframe limitations (e.g., VA in setting power).

Course InterceptsFlying an Assigned Heading To Intercept aCourse or VOR Radial

You can use the navigation mode in combination with theheading function to y an assigned heading to intercepta course. The procedure illustrated in Figure 4-13 takesadvantage of the ability to arm the navigation mode whilethe heading mode is engaged.

Figure 4-13 illustrates selecting the assigned heading, settingup your FD/FMS autopilot for the assigned course, engagingthe heading mode, and arming the navigation function. Oncethe aircraft reaches the course, the autopilot automaticallydisengages the heading function and engages the navigationmode.

On most FD/autopilots, courses can be intercepted by rst

using the heading bug to select an intercept course and thenengaging the heading function. Alternatively, engaging thenavigation function in some units causes the FD/autopilotto select an intercept heading, engage the heading function,and arm the navigation function. This can be a cause forcon ict if ATC assigns an intercept heading, but the FD isprogrammed to use one angle. In those instances, you needto set the heading into the FD/autopilot, y, and controlthe intercept until the aircraft is close enough to completethe intercept and capture without deviating from the ATCinstructions. At that point you can select and arm thenavigation mode, which completes the intercept and beginstracking the selected course.

Essential Skills

1. Use the FD/autopilot to y an assigned heading tocapture and track a VOR and/or RNAV course.

2. Determine if the FD/autopilot uses preprogrammedintercepts or set headings for navigation courseinterceptions.

3. Determine the indications of navigation mode armedconditions.

4. Determine parameters of preprogrammed interceptmodes, if applicable.

5. Determine minimum and maximum intercept anglelimitations, if any.


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RangeView

AuxOFF

BearingOFF

NavGPS1

Baro Set29.92"

VSI Bug0 FPM

Alt Bug5000 FT

Hdg Bug270

Hdg SyncRange View

SACDTK 24019.1 NM00:07:22

-20

270

D E C R I N C R


VS

AP

VS x 100

HDG NAV

D E C R I N C R


VS

AP

VS x 100

NAV

1 Enter the desired heading and engage the heading function.

3 As the autopilot captures the course, the heading function automaticallydisengages, and the navigation function switches from armed to engaged.

2 Arm the navigation function.

Figure 4-13. Flying an assigned heading to intercept a course.

Coupled ApproachesThe approach function is similar to the navigation mode, but

ies the selected course with the higher degree of precisionnecessary for instrument approaches and allows glideslopetracking in the vertical dimension. Most autopilots featurea separate button that allows you to engage the approachfunction, as shown in Figure 4-14. (NOTE: Usually, thismode is not used with most GPS receivers. The GPS approachRNP (required navigation performance) of 0.3 induces thenecessary ight tracking precision. This mode is used only

if speci cally stated as a command in the avionics handbookfor that equipment in that aircraft).

Like the navigation function, the approach mode can be usedto execute precision and nonprecision approaches that relyon types of ground-based navigation facilities (e.g., VOR,VOR/DME, and localizer approaches).

ILS ApproachesCoupled ILS approaches make use of the autopilotsglideslope function. Figure 4-15 shows the procedure forone type of autopilot.

Note that you cannot directly arm or engage the glideslopefunction. The autopilot must usually be engaged rst inthe approach and altitude modes. When the FD/autopilotbegins to sense the glideslope, the glideslope function willautomatically arm. When the aircraft intercepts the glideslope,the glideslope function engages automatically, and uses theaircrafts pitch control to remain on the glideslope. It isimportant to note that, generally, the glideslope functioncan capture the glideslope only from below or on glideslope.

RNAV Approaches With Vertical GuidanceCoupled RNAV approaches with vertical guidance work inthe same way as coupled ILS approaches. Lateral and verticalguidance commands are generated by the FMS/NAV andsent to the FD/autopilot. The same approach and glideslope


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YD BAROARM


A L T S E L

DN

UP

Press to engage the approach function.APR

The autopilot should maintain a greateraccuracy of track in the approach mode.

NAV

APR

Figure 4-14. Flying a coupled nonprecision approach.

D E C R I N C R


VS

AP

VS x 100

NAV APR ALT

D E C R I N C R


VS

AP

VS x 100

NAV APR ALT GS

D E C R I N C R


VS

AP

VS x 100

NAV APR GSNAV APR GS

When the glideslope has been captured, the autopilotautomatically disengages the altitude function and

engages the glideslope function. The pilot mustadjust power and drag (flaps and landing gear) tocontrol airspeed.

NAV APR ALT GS

When the aircraft comes within reception range of theglideslope, the autopilot automatically arms theglideslope function.

NAV APR ALT

Use the approach and altitude functions to establishthe aircraft on the localizer.

X

X

X

Figure 4-15. Flying a coupled precision approach.

functions of the autopilot are used in the same way to carryout the lateral and vertical guidance and control of the aircraft.This process is transparent to the pilot. Most VNAVfunctions do not qualify as approach vertical functions andmany FMS/GPS units inhibit that function during approaches.

Power ManagementSince most autopilots are not capable of manipulating powersettings, you must manage the throttle to control airspeed

throughout all phases of the approach. The power changesneeded during altitude changes must supply the necessarythrust to overcome the drag. The pilot must coordinate thepowerplant settings with the commands given to the FD/ autopilot. Remember, the FD/autopilot can control theaircrafts pitch attitude only for altitude or airspeed, but notboth. The FD/autopilot attempts to perform as programmedby you, the pilot. If the climbing vertical speed selectionis too great, the aircraft increases the pitch attitude until itachieves that vertical speed, or the wing stalls. Selection ofan airspeed or descent rate that is too great for the powerselected can result in speeds beyond the airframe limitations.

Leveling off from a descent, without restoring a cruise powersetting results in a stall as the FD/autopilot attempts to holdthe altitude selected.

Essential Skills

1. Use the FD/autopilot to couple to a precision approach.

2. Use the FD/autopilot to couple to a nonprecisionapproach.

3. Use the FD/autopilot to couple to an RNAV approach.

4. Determine the power setting required to fly theapproaches.

5. Determine the power settings necessary for leveloffduring nonprecision approaches and go-aroundpower settings for both precision and nonprecisionapproaches.


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6. Determine the speeds available for the minimumrecommended powerplant settings. It is useful todetermine if an ATC clearance can be accepted forclimbs, altitudes, and descents.

Deciding When To Use the FD/AutopilotIn addition to learning how to use the FD/autopilot, you mustalso learn when to use it. Since there are no de nitive rulesabout when an FD/autopilot should or should not be used,you must learn to consider the bene ts and disadvantages ofusing the FD/autopilot in any given situation.

One of the most valuable bene ts of using the FD/autopilotis delegating the constant task of manipulating the aircraftscontrols to the equipment, which do nothing other thancomply with the pilots programming. This allows youmore time to manage and observe the entire ight situation.Managing the ight versus actually moving the controlsallows more time for:

1. Programming. Especially when ying under IFR,changes to a route are inevitable. Even when thepilot is pro cient in using FMS/RNAV, this taskrequires focusing some attention on the programmingtask. The FD/autopilot keeps the aircraft on theprogrammed heading or course and altitude while thepilot makes the necessary changes to the ight plan.If programmed correctly, the aircraft maintains thecorrect track and altitude.

2. Distracting tasks/workload. Similarly, the FD/ autopilot is used to control basic aircraft movementwhile the pilot focuses attention on tasks such asreviewing charts, brie ng and con guring for aninstrument approach, updating weather information,etc. The FD/autopilot can also be a great help inother high workload situations, such as ying in abusy terminal area or executing a missed approach inadverse weather conditions.

3. Maintaining autopilot skills. The FD/autopilots abilityto help manage pilot workload depends heavily on thepilots pro ciency in using it. Regular practice with thevarious autopilot functions (especially the approachfunctions) is essential to develop and maintain the

knowledge and skills necessary to maximize itsutilization.

4. Emergencies. The FD/autopilot can be extremelyuseful during an emergency. It can reduce pilotworkload and facilitate efforts to troubleshoot theemergency.

Disadvantages of using the FD/autopilot include thefollowing:

1. Forgetting to maintain manual flying skills. It isimportant to practice ying without the FD/autopilotoften enough to maintain pro ciency in basic yingskills and the instrument cross-check and scan. Onecommon pitfall of advanced avionics is the pilotstendency to forget to maintain hard-earned skills forinstrument ight. All equipment will fail at some time.The competent pilot is ready and prepared to make atransition to aircraft piloting at any time.

2. Turbulence. The pilots operating handbook (POH)and FD/autopilot ight manual supplements for manyaircraft discourage or prohibit use of the autopilotsaltitude hold function during moderate or severeturbulence. Some FD/autopilot systems may defaultor disengage if certain trim or control limits areencountered during turbulent conditions. You shouldconsult the ight manual to ensure the aircraft is

not operated outside speci ed limits. The aircraftsightpath and mode indications should always be

monitored to ensure what modes are active.

3. Minimum altitude. Autopilots are certi ed for useabove a speci ed minimum altitude above groundlevel (AGL). Some higher performance and higherservice ceiling aircraft require autopilot control abovecertain airspeeds and altitudes. The ight manualand operations manual (if any) should be consultedto ensure that the pilot does not operate the aircraftoutside speci ed limits. For higher safety standards,commercial operators must observe restrictions inTitle 14 of the Code of Federal Regulations (14 CFR)sections 121.579, 125.328, and 135.93, according totheir regulatory classi cation. Adoption of these limitsby private operators would add a safety margin to

ights conducted under 14 CFR part 91 regulationsin many cases.

4. Possible malfunction. If at any time the pilot observesunexpected or uncommanded behavior from theautopilot, he or she should disengage the autopilotuntil determination of the cause and its resolution.Most autopilot systems have multiple methods of

disengagement; you should be immediately aware ofall of them. Also be aware of the methods to cancelthe FD display to avoid confusing information.


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Miscellaneous Autopilot TopicsAutopilot Mode AwarenessIn addition to performing the basic aircraft control andnavigation function described previously, some autopilotsare capable of automatically switching from one functionto another. These automatic mode changes can complicatethe task of maintaining mode awareness, but every autopilothas some form of ight mode annunciator that shows whichautopilot functions are currently engaged. The autopilotshown in Figure 4-4 displays the name of any autopilotmode that is currently engaged just above the button used toengage the function. It is important to develop two habits:

1. Checking the ight mode annunciator after entering acommand to ensure that the selected function is indeedarmed or engaged, as appropriate.

2. Including the ight mode annunciator in the scan tomaintain continuous awareness of what mode is activeand what is armed to activate next.

Positive Exchange of ControlsWhen control of the aircraft is transferred between two pilots,it is important to acknowledge this exchange verbally. Thepilot relinquishing control of the aircraft should state, Youhave the ight controls. The pilot assuming control of theaircraft should state, I have the ight controls, and thenthe pilot relinquishing control should restate, You havethe ight controls. Following these procedures reduces thepossibility of confusion about who is ying the aircraft atany given time.

Using an FD/autopilot system can present an opportunity forconfusion. When engaging the autopilot, it is a good idea toannounce that the autopilot is being engaged, what autopilotmode is being used, and then to con rm the settings usingthe ight mode annunciator. It has been general practicefor many years in many aircraft to rst engage the FD todetermine what instructions it was going to transmit to theautopilot. This is determined by reading the FDs commandbars. If the commands shown agree with your perception ofthe control motions to be made, then engage the autopilotto y the entered course and vertical mode. A caution atthis point: some FDs cancel the altitude hold mode when

the autopilot is engaged. Always ensure that, after autopilotengagement, the desired modes are still active.

Prefighting the AutopilotThe POH or aircraft flight manual (AFM) supplementfor each FD/autopilot system contains a pre ight checkprocedure that must be performed before departure. Aswith other pre ight inspection items, this check allows youto ensure that the autopilot is operating correctly, beforedepending on it in the air.

Autopilot and Electric Trim System FailuresIt is vital that you become immediately familiar with theprocedures required to disconnect or disable the electric trimand autopilot systems. Electric trim and autopilot failures canoccur in the form of failure indications; unusual, unexpected,or missing actions; or, in the extreme case, a runaway servoactuator in the autopilot or trim system.

The rst and closest method of disconnecting a malfunctioningautopilot is the autopilot disconnect switch, typically mountedon the control yoke. This switch is usually a red button, oftenmistaken by new pilots for the radio transmit button. Youneed to know which buttons activate which functions.

Most systems may be disconnected by the mode buttons onthe autopilot control panel. However, there are some failures(shorted relays, wires, etc.) that remove control of the servoactuator from the control unit itself. In those rare instances,the pilot must nd and pull the circuit breakers that interruptpower to both the trim and autopilot systems. Some trimsystems have separate circuit breakers for trim motors thatoperate different control surfaces (roll, pitch, yaw). Manypilots have installed small plastic collars on the autopilotto facilitate nding and pulling the correct autopilot circuitbreaker to kill the power to that circuit. Ensure that youunderstand all functions and equipment are lost if those (andin fact, any circuit breaker) are disabled. In too many cases, acircuit breaker installed in an aircraft supplies power to morefunctions than the label implies. To be absolutely sure, checkthe wiring diagrams, and do not pull circuit breakers unlessthe POH/AFM directs that speci c action.

Another method of maintaining ight control when facedwith a failed trim or autopilot system is the control yoke. Mostautopilot and trim systems use a simple clutch mechanismthat allows you to overpower the system by forcing thecontrol yoke in the desired direction. This is usually checkedduring the afterstart/pretakeoff/ runup check.

Essential Skills

1. Demonstrate the proper pre ight and ground check ofthe FD/autopilot system.

2. Demonstrate all methods used to disengage anddisconnect an autopilot.

3. Demonstrate how to select the different modes andexplain what each mode is designed to do and whenit will become active.

4. Explain the flight director (FD) indications andautopilot annunciators, and how the dimming functionis controlled.


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Chapter SummaryAutomated ight control can make a long ight easy foryou by relieving you of the tedious second-by-secondmanipulation and control of the aircraft. Overdependenceon automated flight controls can cost you hard-earnedaircraft handling skills, and allow you to lose the situationalawareness important to safe ight. You must practice yourskills and cross-check.

Automated ight controls require you to study and learn thesystems programming and mode selection actions. You mustalso learn what actions disconnect the autopilot, whethercommanded or not. In pre ight planning you must determinethe limitations on the autopilot and what the installation inthat aircraft permits.

It is important for you to be aware of what functions areautomated and what activates those functions, and theactions or conditions that cancel or inhibit those functions.

Remember that, in most aircraft, you must set the powerand manage the powerplant(s). Even in very expensiveaircraft equipped with autothrottle, you must monitor thepowerplant(s) and be ready to intervene to ensure operationwithin safe parameters.

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