(8)
A/T engagement on the ground is inhibited if the ADC, N1, or N1 target is invalid, or if FMC takeoff is not executed.
(9)
Disengagement through software is provided if the input sensor signals in use become invalid, or if the rate compensated throttle positions split by more than 10 degrees during flare arm or flare engage annunciation.
(10)
The latch is set when the A/T is engaged, arming gate 2. When A/T ENGAGED goes low, gate 2 enables the flasher and the A/T warning lights alternately flash red. The latch is reset through gate 1, cancelling the visual warning, by pressing a disengage switch, either warning light, or automatically after landing.
(11)
The Test switch on the Flight Mode Annunciator (Autoflight Status Annunciator) tests the A/T warning lights. In position one, amber is tested; in position two, red is tested.
B. Arm Mode Logic
(1)
During the arm mode, the A/T is engaged and ready to control the throttles; however, no active mode has been selected. The output to the servos is inhibited.
(2)
The A/T arm mode is enabled when the A/T is engaged and no A/T mode has been selected and throttle hold mode is not set.
18. A/T N1 Mode and Logic_____________________
A. N1 Commands (Fig. 10)
(1)
The N1 command function provides throttle rate commands to the servo drive to position the throttles such that the engines will operate at a predetermined N1 limit.
(2)
The rate commands are developed by comparing an N1 command to the engines N1 value, then limiting the N1 error as a function of the Autothrottle flight mode.
(3)
The N1 command is the selected FMC N1 rating or, for go-around, the internally computed reduced go-around N1, limited to the FMC go-around rating.
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A 737-300/400/500MAINTENANCE MANUAL
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BOEING PROPRIETARY - Copyright (C) - Unpublished Work - See title page for details.
A
737-300/400/500MAINTENANCE MANUAL
(4)
In the event the Autothrottle detects a FMC failure by loss of transmission from the FMC for a FMC N1 limit which is greater than the Autothrottle computer internally computed maximum N1 limit, the Autothrottle utilizes an internally computed reversion limit and the Autothrottle annunciates A/T limit. The Autothrottle takeoff mode is locked out if this condition exists.
(5)
The Autothrottle computer internally computed maximum N1 limit is calculated to be higher than the takeoff N1 limit with no airbleeds but lower than the engine red line RPM limit for all flight conditions. The limit is based on altitude and temperature, OAT during takeoff and TAT otherwise.
(6)
The Autothrottle computer internally computed N1 limit can be from 1% less to equal to the FMC climb N1 limits for normal engine bleed operation. The Autothrottle computed N1 limit is established as a function of altitude, MACH number, TAT, and engine rating.
(7)
The Autothrottle computed reduced go-around N1 is implemented to provide a more gentle transition from approach to go-around. Maximum go-around thrust at the FMC go-around rating is available if flight conditions require the higher thrust setting. The internally computed reduced go-around N1 is computed, based on altitude and weight, to provide a positive climb rate.
(8)
Normally the airplane weight is provided by the FMC; however, if the FMC is not valid, the Autothrottle provides an estimate of the weight.
(9)
The N1 error is limited to control the rate of throttle movement. When the Autothrottle mode is N1, but not takeoff or go-around, the throttle rate is limited to 3 degrees/second. If flight path angle rate from the Autopilot is enabled, the 3 degrees per second rate limit is modified. As flight path increases (climb or decreasing descent) towards 3 degrees/second, the limit decreases towards zero.
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