737 MAX Flight Crew Operations Manual
Automatic Flight -
System Description
4.20.10
MN-FLT-OH-201
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.
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.
March 1, 2021
