Autoflight

Autopilot and flight director, autothrottle, yaw damper and the FMS/AFCS.

Notes

Free

Main ideas

The AUTOPILOT (AP) flies the aircraft by driving servo actuators on the flight controls to hold or capture a target — attitude, heading, altitude, vertical speed or a navigation path — selected on the mode control panel; modes include HDG, ALT, V/S, NAV, LOC and G/S (approach).
The FLIGHT DIRECTOR (FD) computes the same guidance but only DISPLAYS command cues (command bars) on the attitude display for the pilot to fly by hand — it does not move the controls.
AUTOTHROTTLE/AUTOTHRUST manages engine thrust automatically to hold a target speed or thrust setting, coordinating with the autopilot's pitch mode.
A YAW DAMPER senses yaw rate and moves the rudder to damp the Dutch-roll oscillation and coordinate turns; it is largely independent of the main autopilot.
The FLIGHT MANAGEMENT SYSTEM (FMS) holds the route and performance data, computes the lateral/vertical profile and commands the AP and autothrottle through the AFCS — the whole is the automatic flight control system.
⚠ Exam trap: the flight DIRECTOR only shows guidance cues for the pilot to follow, whereas the AUTOPILOT actually moves the controls via servos; the yaw damper's job is to damp Dutch roll.

Solved examples

During an approach the flight director command bars are displayed but the autopilot is disengaged. Who is flying the aircraft?
The pilot is flying it by hand. The flight director is computing the guidance to the localiser and glideslope and showing it as command bars, but with the autopilot off nothing is driving the servos — the pilot manually flies the aircraft to keep the command bars centred. Engaging the autopilot would let it fly those same commands automatically.

Mind map

Free

Quiz

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