F. Analog Inputs
(1)
Analog inputs are provided by ADC-1, both N1 tachometers, the angle of airflow vane, the flap position transmitter, the low range radio altimeter, both rate generators in the servo actuator assemblies, and both Power Lever Angle Synchros.
(2)
Discrete logic is also provided as follows: thrust reverser not stowed and idle logic from the engine accessory unit, ground/air logic from the landing gear accessory unit, flare logic from both Flight Control Computers, power management control on/off logic from airplane wiring, the TO/GA switch discrete, landing gear lever position logic from the landing gear lever switch, discrete logic from the throttle servo assembly mounted torque switches, and discrete program pin connections identifying the fast/slow pointer bias required (airplanes without EFIS) and the type of engines installed on the airplane.
(3)
The various analog and discrete inputs are converted through A/D converters, for use by the A/T computers digital processor; and in some cases, are used directly by hardware circuitry in the computer.
G. Engage/Disengage
(1)
The engage/disengage function is provided by the A/T ARM switch, A/T disengage switches, and internal circuitry and logic of the A/T computer.
(2)
The A/T engage interlock monitors computer operation, validity of the input sensor signals in use, relative throttle lever positions, and the A/T disengage switches. Additionally, to engage the Autothrottle on the ground, the FMC must have takeoff executed, or A/T BITE in progress.
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737-300/400/500MAINTENANCE MANUAL
(3)
The A/T disengages if the computer fails, an input signal in use becomes invalid, or if the thrust levers split by more than 10 degrees and there is a DFCS Flare Arm or Flare Engage annunciation. The A/T automatically disengages after touchdown, or is manually disengaged through either disengage switch.
(4)
The A/T warning light on each Flight Mode Annunciator (Autoflight Status Annunciator) provides a flashing warning if the disengagement is due to an invalid condition. The warning light is reset by pressing either warning light or either disengage switch.
Mode Control
(1)
When engaged, the A/T mode is either automatically selected by the Autopilot, or manually selected through switches on the MCP. During takeoff and go-around, and during certain abnormal conditions, the A/T mode is controlled by mode logic within the A/T computer.
(2)
Autopilot or manual requests for a specific A/T mode is transmitted through the MCP by discrete word bits on the ARINC 429 digital data bus.
(3)
The engaged A/T mode is displayed on both the captain's and the first officer's Flight Mode Annunciator (Electronic Attitude Director Indicator).
Clutch Control
(1)
Electromagnetic clutches in the servo assemblies are energized when the A/T is engaged, except during throttle hold, and when the throttles are restrained, either manually or when driven to the aft stop. Restraint is detected by the torque switches.
Signal Processing
(1)
Airspeed and N1 command errors are computed by their respective command functions. The appropriate command is selected by the servo drive, and used to modify the throttle position commands. If a throttle position error exists, the servo drive repositions the throttles. Throttle rate feedback is provided by generators in the servo assemblies. Throttle position feedback is provided by Power Lever Angle Synchros, mounted on the engines.
(2)
N1 command error is used to control the throttle position, during takeoff, during N1 climbs when the Autopilot/Flight director is providing airspeed control, when N1 mode is manually selected through the MCP, and during both reduced and maximum go-around.
(3)
Speed command error is used when the N1 command error is not
selected.ARINC 429 Output
(1)
The A/T provides data to the Flight Control computers, the Flight Management Computer, and the Electronic Flight Instrument System symbol generators (airplanes with EFIS), through an ARINC 429 digital data bus.
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