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.
D6-27370-866-EGP 4.20.9
A general summary of A/T mode engagement is as follows:
• A/T SPD or N1 modes automatically engage when AFDS command
pitch modes become engaged
• engaging LVL CHG or VNAV climb modes automatically engages the
A/T N1 mode
• engaging LVL CHG or VNAV descent modes automatically engages the
A/T in RETARD and then ARM when thrust is at idle
• if not in a VNAV mode, engagement of ALT ACQ or ALT HOLD
automatically engages the A/T in the MCP SPD mode; otherwise the
A/T remains in FMC SPD
• engagement of G/S capture automatically engages the A/T in the MCP
SPD mode
• alpha floor automatically engages the A/T when armed.
Autothrottle Disengagement
Any of the following conditions or actions disengages the A/T:
• moving the A/T Arm switch to OFF
• pushing either A/T Disengage switch
• an A/T system fault is detected
• two seconds have elapsed since landing touchdown
The thrust levers should normally be aligned to no more than one full knob width
difference during all ranges of normal operation with symmetrical thrust.
The autothrottle also disengages if it is engaged in a Speed mode, Retard for
descent mode, or an N1 mode other than A/T GA mode AND;
• thrust levers become separated more than 10 degrees
• significant thrust difference along with control wheel roll input of 10
degrees or more at any point throughout the entire flight envelope
A/T disengagement is followed by A/T Arm switch releasing to OFF and flashing
red A/T Disengage lights. The A/T Disengage lights do not illuminate when the
A/T automatically disengages after landing touchdown.
Automatic Flight Operations
The phases of flight for automatic flight operations are:
Automatic Flight Takeoff and Climb
Takeoff is a flight director only function of the TO/GA mode. Flight director pitch
and roll commands are displayed and the autothrottle maintains takeoff N1 thrust
limit as selected from the FMC. The autopilot may be engaged after takeoff.
• Takeoff and climb
•Enroute
• Approach and landing
• Go–around
September 15, 2016
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