Approaching Missed Approach altitude –
.
Pitch mode
engages in
ALT ACQ
.
A/T engages
in MCP SPD
Flap retract altitude
. Retract flaps on schedule
Above 400 feet RA
. Select roll
mode
Push TO/GA switches
. A/T engages in G/A
Automatic Flight -System Description 737 Operations Manual
AFS Operation in Windshear General
The autopilot and flight director provide positive corrective action to counteract most windshears. The autothrottle system also aids in windshear recovery by providing quick response to any increase or decrease in speed. The commanded levels of power may be beyond what the average pilot might consider necessary but, in fact, are required by the situation.
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 V2 + 20 kts 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 V2 + 20 kts. 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 pressing 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/airspeed warning systems.
Copyright . The Boeing Company. See title page for details.
4.20.24 December 1, 2000
Automatic Flight -System Description 737 Operations Manual
FLASHING
FLASHING
IAS/MACH
UNDERSPEED LIMITING OVERSPEED LIMITING
-
V/S mode performance - V or M limit
MO MO reversion - Landing gear limit
-
Minimum speed - Flap limit
MCP SPEED CONDITION SYMBOLS
As installed
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 will not exceed a limit speed.
Speeds greater than Vmo/Mmo cannot be selected from the MCP. Speeds can be
selected which exceed flap and gear placards or are less than minimum speed. Minimum speed is based on angle of attack and is approximately 1.3 Vs for the current flap configuration. It is sensed by the angle of attack vanes, one on either side of the forward fuselage.
If a speed greater than a placard speed, or less than minimum speed is selected, the AFS allows acceleration or deceleration to slightly short of the limit, then commands the limit speed. The overspeed or underspeed limiting symbol appears in the MCP IAS/Mach display when the commanded speed cannot be reached.
Either pitch or thrust, whichever is engaged in a speed mode, attempts to hold the limit speed. The commanded limit speed and MCP speed condition symbol, remain until another speed is selected which does not exceed the limit. A speed 15 kts greater than the minimum speed must be selected to remove the underspeed limiting symbol.
Automatic Flight -System Description 737 Operations Manual
Reversion Modes
During some flight situations, speed control by the AFDS or A/T alone could be insufficient to prevent exceeding a limit speed. If this occurs, AFDS or A/T modes automatically revert to a more effective combination. The reversion modes are:
.
Placard limit reversion
.
Minimum airspeed reversion
.
Performance limit reversion (airplanes without –4 FCC).
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