Automatic Flight -System Description

737 Operations Manual
Two independent radio altimeters provide radio altitude to the related FCC. The Captain’s radio altimeter provides radio altitude to the A/T. With a radio altimeter inoperative the autopilot will disconnect two seconds after LOC and GS capture, and the A/T will not retard at flare.
Flight Director Display
Turning a F/D switch ON displays command bars on the respective pilot’s ADI 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 pilot’s F/D modes are controlled by the master FCC, and both FMA displays show the same mode status.
The master FCC is indicated by illumination of the related 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 ADIs. 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.
June 4, 2004   4.20.3
Automatic Flight -System Description 737 Operations Manual

AFDS Status Annunciation
The following AFDS status annunciations are displayed in the A/P status display located on the EADI:
.  
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).

AFDS Flight Mode Annunciations
The flight mode annunciations are displayed on the EADI. The modes are in these categories:
.  
autothrottle

.
pitch

.  
roll

Engaged or captured modes are shown at the top of the flight mode annunciation boxes in large green letters. Armed modes are shown in smaller white letters at the bottom of the flight mode annunciation boxes.
Autothrottle Modes
.  
N1 – The autothrottle maintains thrust at the selected N1 limit displayed
on the thrust mode display or thrust mode annunciator

.  
GA – The autothrottle maintains thrust at reduced go–around setting or
full go–around N1 limit

.  
RETARD – Displayed while autothrottle moves thrust levers to the aft
stop; RETARD mode is followed by ARM mode

.  
FMC SPD – The autothrottle maintains speed commanded by the FMC;
the autothrottle is limited to the N1 value shown on the thrust mode
display or thrust mode annunciator

.  
MCP SPD – The autothrottle maintains speed set in the MCP IAS/MACH
display; the autothrottle is limited to the N1 value shown on the thrust
mode display or thrust mode annunciator

.  
THR HLD – The thrust lever autothrottle servos are inhibited. The pilot
can set the thrust levers manually

.  
ARM – No autothrottle mode engaged. The thrust lever autothrottle
　
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