Autoflight and autothrottle

Two flight directors, a two-axis autopilot and a yaw damper make up the AFCS, run by two identical flight guidance computers. The autothrottle moves the thrust levers. The flight mode annunciator on each PFD shows what each of them is doing.

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What it does

Flight guidance, autopilot and autothrottle

Flight mode annunciator strip with TO active and HOLD armed on the left and a green AT under an arrow in the centre. Below, three tables: armed modes in white (TO, SPD, RETARD, HOLD, THRUST), active modes in green (TO, HOLD, SPD, RETARD, THRUST, GA) and in amber (LIM, OSPD), and the AT status: green engaged, white TO armed, amber disengaged or engagement inhibited. — The autothrottle side of the flight mode annunciator: modes on the left, AT status in the centre. Tap to enlarge

Three ways to fly: by hand on raw data with the flight directors off, by hand following the command bars, or with the autopilot coupled to the flight director.
One flight director guides both pilots' displays. In precision approach and go-around each one guides its own side.
The autopilot moves the ailerons and elevators through servos. When the pitch axis is out of trim, the flight guidance computer has the horizontal stabilizer moved to retrim.
The yaw damper coordinates turns and damps the yaw oscillations that lead to Dutch roll. It moves the rudder up to ±5° and does not move the pedals.
The autothrottle drives both thrust levers between IDLE and the TO detent. It works in all phases of flight, with or without the autopilot and flight director.
The active vertical flight director mode decides the autothrottle mode.

Flight mode annunciator
Four sections, left to right	Autothrottle modes, lateral modes, AP, YD and AT status, vertical modes
Top line, green	Active modes
Bottom line, white	Armed modes
AT status green	Engaged
AT status white	TO armed
AT status amber	Not engaged
Arrow by the AP and AT status	Points to the coupled flight director side

Engage and disengage

Flight guidance panel and controls

Thrust lever quadrant with the autothrottle installed: detents APR, TO, CLB, IDLE, REV and MAX REV, the GUST LOCK lever, an AT DISENGAGE button across the front of each lever and a TOGA switch on each side. A detail of one lever knob shows the TO/GA switch on top, the AT DISENGAGE button on the forward face and the AT ENGAGE switch on the aft face. — Thrust levers with the autothrottle: TO/GA switch, AT DISENGAGE button and AT ENGAGE switch on each lever. Tap to enlarge

The flight guidance panel (FGP) is on the glare shield, in reach of both pilots. It holds the flight director, autopilot and yaw damper controls.
The autopilot does not engage without the yaw damper, and disengaging the yaw damper also disengages the autopilot. The yaw damper can be engaged on its own.
Engaging the autopilot also needs both FGCs serviceable, the primary stab trim channel engaged with no trim fault, and no significant instability.
The autopilot comes off with either MSW, the stab trim switches, the AP button, AP/YD DISC, either TO/GA switch or the YD button. It disengages by itself at stall warning or on a system fault.
The thrust levers move with the autothrottle. You can override it by moving them, which takes more force than normal.

Controls
FD	Selects the onside flight director, with the basic pitch and roll modes
AP	Press to engage, press again to disengage. Green AP on the PFD.
YD	Engages the yaw damper
AP/YD DISC	Bar down: autopilot and yaw damper off together. The yaw damper cannot engage while the bar is down.
XFR	Selects the left or right flight director to command the autopilot
MSW, control wheel	Disengages the autopilot. While held, the stabilizer, configuration, Mach, aileron and rudder trims and the stall pusher are inoperative. Also cancels the red flashing AP after a fault disconnect.
AP/FD SYNC, control wheel	Synchronizes the flight director. With the autopilot engaged the servos let go while it is held, so you fly by hand without disconnecting.
AT ENGAGE, aft face of each thrust lever	Engages the autothrottle
AT DISENGAGE, forward face	Disengages the autothrottle. After an automatic disengage it also stops the flashing AT and the aural.
TO/GA, on each thrust lever	Before the takeoff roll: takeoff modes. In the air: go-around modes, and the autopilot disengages.

Lateral and vertical

Flight director and autopilot modes

Flight guidance panel. At each end an FD button above a CRS knob marked PUSH DIRECT. From the left: NAV, HDG with a PUSH SYNC knob, APPR, 1/2 BANK and B/C; FLC above the SPEED knob marked PUSH IAS/MACH; VS and VNAV beside the DOWN/UP wheel; ALT above the ALT knob marked PUSH CANCEL; then AP, YD, XFR and the AP/YD DISC bar. — The flight guidance panel: lateral modes on the left, vertical modes in the middle, autopilot controls on the right. Tap to enlarge

Lateral modes: ROLL, TO, HDG, NAV, GA, APPR, BC and 1/2 BANK. ROLL is the default. It holds the heading, or the bank angle when that is over 5°.
NAV arms when you select it, with the source (FMS1, VOR1, LOC1 and so on) in white. It captures only with valid navigation data.
APPR is used for every approach. It arms the localizer and the glideslope. The glideslope is selected by itself, inbound, with a valid localizer.
Vertical modes include PTCH, ALTS and ALT, TO, VNAV, VGP, FLC, VS, GS and GA. PTCH holds the pitch attitude, FLC an IAS or Mach, VS the vertical speed.
Set an altitude with the ALT knob and the flight director climbs or descends to it, then levels off. The ALT button holds the altitude you are at.
In the air, TO/GA puts both flight directors in GA and they work independently. The autopilot disengages, the yaw damper stays on. A captured LNV is kept.

Key numbers
1/2 BANK, maximum commanded bank	15°
1/2 BANK selected automatically, climbing through	31,600 ft
GA pitch command	8° nose up
Lateral TO and GA, bank authority	5°
VS wheel, each click	100 ft/min
VS range	±8,000 fpm
Pitch wheel, each click	0.5°
Level-off alert, before the selected altitude	About 1,000 ft
Altitude deviation alert	More than 200 ft

Takeoff to touchdown

Autothrottle modes

Autothrottle modes through a typical flight, with the flight director vertical modes that go with them. Tap to enlarge

TO arms with either AT ENGAGE switch on the ground: both engines running, takeoff flaps set, V-speeds posted, levers below 23° (mid-travel), below 60 kt and flight director vertical mode TO. TO and AT show white.
TO goes active when the levers pass midway, and the servo carries them on to the TO detent. TO and AT turn green, HOLD arms.
HOLD: above 60 kt with the levers in TO, the autothrottle stops moving them. HOLD stays until 400 ft above airport elevation, then the armed mode takes over.
THRUST holds a fixed setting: the CLB detent to climb, IDLE to descend. It is active when FLC is the vertical mode.
SPD moves the levers between IDLE and just below CLB to hold the SPEED bug. It is active with any vertical mode other than TO, GA and FLC, and when the flight director is off.
RETARD arms below 200 ft AGL in SPD, gear down and flaps 30, not in a steep approach, with the radio altimeter working. Below 50 ft AGL it brings the levers to IDLE. After touchdown the autothrottle disengages with no alert.
GA: TO/GA drives the levers to the TO detent.

Alerts and disengagement
LIM, flashing amber	Thrust cannot hold the selected speed
OSPD, flashing amber	More than 3 kt or 0.01 Mach over VFE, VMO or MMO: the levers go toward IDLE
Overspeed too fast for the autothrottle	FLC OSPD, and the autothrottle disengages
AT DISENGAGE pressed	Amber AT flashes briefly and one "AUTOTHROTTLE" sounds
Automatic disengage	Amber AT flashes and "AUTOTHROTTLE, AUTOTHROTTLE" sounds until an AT DISENGAGE button is pressed
Automatic disengage, causes	Lever override, engine failure, stick shaker, a system fault, or an engine mismatch over 35% N1 or 15% N2
Engine failure	The autothrottle disengages. Within the limits below it can be engaged again, and then moves only the operating engine's lever.
TO/GA on one engine	The autothrottle disengages. Push the operating lever to TO by hand.

What not to exceed

Limits and abnormals

Typical autothrottle modes: HOLD up to 400 ft above the airport, RETARD armed at 200 ft and active at 50 ft radio altitude. Tap to enlarge

Key numbers
Autopilot minimum engage height (climb, en route, descent)	700 ft AGL
Autopilot minimum use, precision approach, glidepath 3.5° or less	80 ft AGL
Autopilot minimum use, precision approach, glidepath between 3.5° and 4.5°	160 ft AGL
Autopilot minimum use, visual and non-precision approach	200 ft AGL
Maximum altitude, yaw damper off	31,000 ft
Autothrottle takeoff, before 80 KIAS	AT engaged, levers in the TO detent, takeoff N1 checked, HOLD active
Radio altitude unavailable or invalid	Autothrottle off before 200 ft AGL
Abnormal procedure landing, flaps less than 30°	Autothrottle off before 200 ft AGL
Engine failure on takeoff	No autothrottle until the flaps are up and the aircraft is at en route climb speed
Single engine go-around	No autothrottle until the flaps are up and the aircraft is at en route climb speed
Touch and go landings	No autothrottle

Do not overpower the autopilot on purpose. Do not press XFR while making inputs on an FMS CDU.
If an engine fails in a climb in or just below altitude capture, the flight director or autopilot may not hold the selected speed, and the autothrottle may already be reducing thrust. The crew may have to step in.
AP STAB TRIM FAIL is an amber caution: the autopilot cannot trim the horizontal stabilizer. Its procedure starts with one Immediate Action Item.
With SEC STAB TRIM ON or STAB TRIM OFF, the autopilot is inoperative.

The full module

The slides take you through the controls, the flight director and autothrottle modes from takeoff to landing, and the abnormals, then a 10-question test.

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