(1)  
Inertial reference units (IRU) No. 1 and 2 provide pitch and roll attitude, normal, longitudinal and flight path vertical acceleration plus IRU valid logic via an ARINC 429 digital data bus.

 (2)  
Digital Air Data computers No. 1 and 2 provide ARINC 429 digital data consisting of altitude, MACH, total air temperature (TAT) and airspeed. Digital Air Data computer No. 1 provides DADC valid logic and three-wire computed airspeed data.

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A
737-300/400/500MAINTENANCE MANUAL
 (3)  
Radio Altimeter No. 1 provides radio altitude and radio altitude valid logic.

 (4)  
Left ALPHA vane provides angle of attack.

 (5)  
Logic in the landing gear accessory box provides an in-air/on-ground discrete.

 (6)  
Left flap position transmitter provides flap position information.

 (7)  
Flight Management Computer provides ARINC 429 data consisting of flight mode select and system discretes, target N1, continuous N1 limit, climb N1 limit, cruise N1 limit, go-around N1 limit, FMC minimum speed, SAT, and gross weight signals.

 (8)  
N1 transmitters provide N1 signals.

 (9)  
Power Lever Angle (PLA) synchros provide engine power lever position feedback.

 (10)
 Autothrottle servomechanisms provide rate feedback.

 (11)
 DFCS control panel provides Autothrottle engage logic and ARINC 429 digital data. This data, which is generated in the DFCS computer, consists of N1 select, SPEED select, target airspeed, target mach, and selected DFCS modes.

 (12)
 Landing gear up/down logic is provided by a landing gear position switch.

 (13)
 Torque switch mechanisms provide torque switch logic.

 K.  Electrical power for the Autothrottle system is provided by No. 1 electronic power bus via 115 volt ac circuit breaker, A/T SYST AC, and 28 volt dc circuit breaker, A/T SYST DC, located on load control center P18.
 2.  Autothrottle Computer_____________________
 A.  The Autothrottle computer performs the necessary computations for automatic control of engine thrust, and provides throttle positioning commands to the servomechanisms.
 B.  The A/T computer is mounted on the E1-1 shelf, in the electronics equipment area. The computer is housed in a 1/2 ATR, rack-mounted, enclosure, weighing approximately 21 pounds. Rear mounted electrical connectors provide the interface with the airplane wiring. Two rack-mounted swivel bolts lock the computer in the rack.
 C.  The A/T computer contains a built-in test program, accessed through the Flight Management System-control display unit. The built-in test is capable of performing a quick A/T verification, for use during turnaround; or an extensive diagnostic routine, for use during overnight maintenance. The alpha-numeric test readout on the front of the computer is intended for use during bench testing of the computer.
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A 737-300/400/500MAINTENANCE MANUAL
 3.  Autothrottle Servomechanisms
____________________________
 A.  The A/T servomechanisms provide the electromechanical interface between the autothrottle computer and the throttle cables.
 B.  Separate servomechanisms are provided for throttle control of each engine. They are located between the floor beams, in the aft area of the electronic equipment area. The servomechanism for engine-1 is located on the left.
 C.  Each servomechanism is comprised of an actuator assembly, a torque switch mechanism, a torque switch assembly, and an optional throttle position potentiometer. All except the torque switch mechanism are line replaceable.
 D.  The torque switch mechanism is installed in-line with the throttle cables. Replacement requires rigging of the throttles. This mechanism consists of input and output quadrants, a torque sensing mechanism, a friction brake to prevent throttle creep, and an override detent mechanism. The torque sensing mechanism activates the torque switch, when override force exceeds 2 pounds nominal on the thrust lever. The override detent mechanism allows the pilot to override the servo, in event of a clutch control failure. Override requires 18 pounds nominal force, at the throttle levers.
　
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