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.
4.20.8 D6-27370-866-EGP
YK981 - YQ456
If pitch is manually overridden while in ALT HOLD at the selected altitude, ALT
HOLD changes to CWS P. If control force is released within 250 feet of the
selected altitude, CWS P changes to ALT ACQ, the airplane returns to the selected
altitude, and ALT HOLD engages. If the elevator force is held until more than 250
feet from the selected altitude, pitch remains in CWS P.
Roll CWS with a CMD Engage Switch Selected
The roll axis engages in CWS while the pitch axis is in CMD when:
• a command roll mode has not been selected or was deselected
YK981 - YQ456
• A/P roll has been manually overridden with control wheel force. The
force required for override is greater than the normal CWS control
wheel force.
• flying beyond FMS end of route or into a route discontinuity.
CWS R is annunciated on the FMAs while this mode is engaged.
CWS R with a CMD engage switch illuminated can be used to capture a selected
radio course while the VOR/LOC or APP mode is armed. Upon intercepting the
radial or localizer, the F/D and A/P annunciations change from CWS R to
VOR/LOC engaged, and the A/P tracks the selected course.
Autothrottle System
The A/T system provides automatic thrust control from the start of takeoff through
climb, cruise, descent, approach and go–around or landing. In normal operation,
the FMC provides the A/T system with N1 limit values.
The A/T moves the thrust levers with a separate servo motor on each thrust lever.
Following manual positioning, the A/T may reposition the thrust levers to comply
with computed thrust requirements except while in the THR HLD and ARM
modes.
The A/T system operates properly with the EECs ON or in ALTN. In either case,
the A/T uses the FMC N1 limits. During A/T operation, it is recommended that
both EECs be ON or both be in ALTN, as this produces minimum thrust lever
separation.
Autothrottle Engagement
Moving the A/T Arm switch to ARM, arms the A/T for engagement in the N1,
MCP SPD or FMC SPD mode. The A/T Arm switch is magnetically held at ARM
and releases to OFF when the A/T becomes disengaged.
September 15, 2016
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