.  
pushing either TO/GA switch after touchdown with both A/Ps engaged in
CMD

.  
pushing an illuminated A/P ENGAGE switch

.  
pushing the A/P DISENGAGE bar down

.  
activating either pilot’s control wheel trim switch

.  
moving the STAB TRIM AUTOPILOT cutout switch to CUTOUT

.  
either left or right IRS system failure or FAULT light illuminated

.  
loss of electrical power or a sensor input which prevents proper operation
of the engaged A/P and mode

.  
loss of respective hydraulic system pressure.

Note: Loss of the system A engine-driven hydraulic pump, and a heavy demand on system A, may cause A/P A to disengage.
AFS Failures
Power interruption or loss may cause disengagement of the AFDS and/or A/T. Re–engagement is possible after power is restored.
Copyright . The Boeing Company. See title page for details.
4.20.2   June 1, 2005

Automatic Flight -System Description

737 Flight Crew Operations Manual
Dual channel A/P operation is possible only when two generators are powering the busses.
Two independent radio altimeters provide radio altitude to the respective FCCs. With a radio altimeter inoperative, the autopilot will disconnect two seconds after LOC and GS capture.
Flight Director Display
Turning a F/D switch ON displays command bars on the respective pilot’s attitude indicator if command pitch and roll modes are engaged. If command pitch and roll modes are not engaged, the F/D command bars do not appear. The F/Ds can be operated with or without the A/P and A/T. F/D command modes can be used with an A/P engaged in CWS.
F/D commands operate in the same command modes as the A/P except:
.  
the takeoff mode is a F/D only mode

.  
dual F/D guidance is available for single engine operation

.  
the F/D has no landing flare capability. F/D command bars retract from

view at approximately 50 feet RA on an ILS approach. Normally, FCC A drives the captain’s command bars and FCC B drives the first officer’s command bars. With both F/D switches ON, the logic for both pilots’ F/D modes is controlled by the master FCC, and both FMA displays show the same mode status.
The master FCC is indicated by illumination of the respective master (MA) F/D indicator light. The master FCC is determined as follows:
.  
with neither A/P engaged in CMD, the FCC for the first F/D turned on is
the master

.  
with one or both A/Ps engaged in CMD, the FCC for the first A/P in CMD
is the master FCC, regardless of which F/D is turned on first.

F/D modes are controlled directly from the respective FCC under certain conditions. This independent F/D operation occurs when neither A/P is engaged in CMD, both F/D switches are ON and one of the following mode conditions exists:
.  
APP mode engaged with LOC and G/S captured

.  
GA mode engaged and below 400 feet RA

.  
TO mode engaged and below 400 feet RA.

Independent F/D operation is indicated by illumination of both MA lights. When independent operation terminates, the MA light extinguishes on the slaved side.
If a generator is lost during a F/D TO or GA, or while in dual F/D APP mode below 800 feet, the FCC on the unaffected side positions the F/D command bars on both attitude indicators. If the F/D MA light on the affected side had been illuminated, it extinguishes upon electrical bus transfer.
Copyright . The Boeing Company. See title page for details.
September 27, 2004   4.20.3
Automatic Flight -System Description 737 Flight Crew Operations Manual

AFDS Status Annunciation
The following AFDS status annunciations are displayed in the A/P status display located above the attitude indicator on the outboard display unit:
.  
CMD (one or both autopilots are engaged)

.  
FD (the flight director is ON and the autopilot is either OFF or engaged in
CWS)

.  
CWS P (pitch mode engaged in CWS)

.  
CWS R (roll mode engaged in CWS)
YA613 - YA809, YC411 - YK104

.  
SINGLE CH (for single A/P ILS approach, annunciates after localizer
capture and remains on for entire approach. For dual A/P ILS approach,
annunciates after localizer capture and extinguishes after pitch monitor
confidence test is successfully completed).

AFDS Flight Mode Annunciations
The flight mode annunciations are displayed just above the attitude indicator on the outboard display unit. The mode annunciations, from left to right, are:
　
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