(7)
Cruise airspeed tracking configuration is defined as not in approach or capture gain configuration.
(8)
Retard 1 is the landing maneuver retard. It occurs 0.8 seconds after Autopilot flare, or at 27 feet radio altitude if the Autothrottle is in speed mode and flaps are greater than 12.5 units.
(9)
If the selected N1 limit or target is invalid or exceeds the maximum N1 limit, the Autothrottle reverts to a throttle position limit. Reversion is further defined in Fig. 7.
B. PMC Status, Idle Logic, and Servo Inhibit (Fig. 8)
(1)
PMC Status
(a) The Performance Management Computer (PMC) is an engine mounted computer that controls fuel flow, so that N1 is directly related to the Power Lever Angle. It removes the variable effects of airspeed and air density. If the PMC is not ON, the forward limit of the servo drive is reduced to prevent engine overspeed.
(2)
Idle Logic
(a) If the engines are at low idle, acceleration gain is increased to improve the engine response time.
(3)
Thrust Reverser Not Stowed
(a) The Autothrottle servos are inhibited, if either thrust reverser is not stowed.
17. A/T Engage/Disengage (Fig. 9)____________________
A. Autothrottle System - Engage/Disengage
(1)
The Autothrottle is engaged by placing the solenoid held A/T switch to the ARM position. Interlock circuitry monitors the performance of the A/T computer and supplying sensors. If an abnormal condition is detected, the A/T automatically disengages.
(2)
The interlock circuitry consists of both hardware monitoring and software monitoring.
(3)
The interlock circuit automatically disengages the A/T upon termination of the flight or it is manually disengaged through the thrust lever mounted A/T disengage switches.
(4)
A disengage warning circuit provides flashing warning lights on the Flight Mode Annunciators (Autoflight Status Annunciators).
(5)
When the A/T switch is positioned to ARM, 28 volt dc is routed through the switch, through energized S3 and relaxed S4 and closes S5. The hardware A/T engage logic is routed through the A/T disengage switches to the A/T switch holding solenoid.
(6)
If either disengage switch is pressed, the holding solenoid relaxes and the A/T switch returns to OFF. Circuits monitor the update rate of the processor, and the relative position of the thrust levers. If the processor does not update, or if the thrust levers split by 10 degrees during a flare arm or flare engage annunciation, S3 relaxes, opening the engage interlock circuit.
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M528 ENGINE ACC UNIT (E3-2)
1 TO MASTER DIM AND TEST M917 AUTOTHROTTLE COMPUTER (E1-1)
PMC Status, Idle Logic, and Servo Inhibit
Figure 8
A 737-300/400/500MAINTENANCE MANUAL
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A
737-300/400/500MAINTENANCE MANUAL
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