737 Flight Crew Operations Manual
Automatic Flight -
System Description
Boeing Proprietary. Copyright © Boeing. May be subject to export restrictions under EAR. See title page for details.
4.20.24 D6-27370-866-EGP
Takeoff or Go–Around
If windshear is encountered during F/D takeoff or go–around, the F/D pitch
command bar provides commands to maintain the target speed until vertical speed
decreases to approximately +600 fpm. At this point, the F/D pitch bar commands
a 15 degree nose–up pitch attitude. If vertical speed continues to decrease, the F/D
continues to command a 15 degree pitch attitude until a speed of approximately
stick shaker is reached. It then commands pitch attitudes which result in
intermittent activation of the stick shaker. As the airplane transits the windshear
condition, the F/D programming reverses. As climb rate increases above
approximately +600 fpm, the F/D commands pitch attitudes which result in
acceleration back to the target speed. The A/P and F/D both operate in a similar
manner during A/P or F/D go–around.
Approach and Landing
If windshear is encountered during an ILS approach, both the F/D and A/P attempt
to hold the airplane on altitude, or on glideslope after glideslope capture, without
regard to angle of attack or stick shaker limitations. Airspeed could decrease
below stick shaker and into a stall if the pilot does not intervene by pushing the
TO/GA switch or disconnecting the A/P and flying manually.
WARNING: Although the F/D, A/P and A/T may be performing as
previously described, severe windshear may exceed the
performance capability of the system and/or the airplane. In
this situation, the flight crew must, if necessary to avoid
ground contact, be prepared to disconnect the autothrottle,
advance thrust levers to the forward stop, disconnect the
autopilot and manually fly the airplane.
Command Speed Limiting and Reversion Modes
AFS command limiting and reversion operation is independent of the stall
warning and mach warning systems.
Command Speed Limiting
The AFS provides speed, pitch and thrust commands to avoid exceeding the
following limit speeds:
• Vmo/Mmo
• wing flap placards
• landing gear placard
•minimum speed.
The commanded speed can be equal to, but does not exceed a limit speed.
September 15, 2016
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