22-CONTENTS
BEJ Page 12 Nov 15/98
BOEING PROPRIETARY - Copyright (C) - Unpublished Work - See title page for details.
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737-300/400/500MAINTENANCE MANUAL
CHAPTER 22 - AUTOFLIGHT
TABLE OF CONTENTS
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Chapter Section Subject_______ Subject ____ Effectivity
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Adjustment/Test 501 ALL SERVOMECHANISM COMPONENTS -22-31-91 AUTOTHROTTLE Removal/Installation 401 ALL SYNCHRO - AUTOTHROTTLE POWER 22-31-11
LEVER ANGLE Removal/Installation 401 ALL Adjustment/Test 501 ALL
22-CONTENTS
BEJ Page 13 Nov 15/98
BOEING PROPRIETARY - Copyright (C) - Unpublished Work - See title page for details.
A
737-300/400/500MAINTENANCE MANUAL
AUTO FLIGHT - DESCRIPTION AND OPERATION
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1. General_______
A. The automatic flight control systems (AFCS) consist of three independent systems: digital flight control system (DFCS), yaw damper system, and autothrottle system. These systems provide automatic airplane stabilization about the pitch, roll, and yaw axes and control the airplane with selective guidance from radio, heading, flight management computer, and air data computer inputs.
B. The DFCS system is a two-axis (pitch and roll) system which operates the elevators and ailerons to automatically maintain altitude, airspeed and/or guide the airplane to designated locations and make automatic landings. Control functions are also translated into flight director commands for display on the pilots' attitude director indicators (ADI's) [electronic attitude director indicators (EADI's)]. thereby providing the pilots' flight attitude commands during manual operation or allowing the pilots to monitor autopilot operation. Automatic stabilizer trimming relieves sustained elevator loads which might be incurred due to fuel burnoff.
C. The yaw damper systems operate the rudders to correct any periodic yaw oscillations (dutch roll).
D. An autothrottle system automatically maintains selected airspeeds or Mach during cruise conditions and maintains selected engine thrust settings when making flight director controlled take-offs or autopilot/flight director controlled landing approaches by adjusting engine thrust levers.
2. Digital Flight Control System_____________________________
A. The DFCS incorporates two separate channels (A, B). Each channel controls the pitch and roll axes and provides mach trim and speed trim control. Flight director commands and flag logic are connected to the captain's ADI [EADI] (system A) and the first officer's ADI [EADI] (system B). DFCS control of the airplane is enabled by engaging channel A or B switch on DFCS mode select panel. When dual channel option is provided, channels A and B can be engaged simultaneously when making fail-passive automatic landings.
B. The Mach Trim System provides automatic respositioning of the elevators as a function of Mach number. As the airplane enters the Mach tuck region, the elevator is repositioned to provide a new neutral in an upward direction which is proportional to the increase in Mach. The Mach Trim System operates with or without the autopilot system engaged. The Mach Trim System operates in conjunction with the elevator hydraulic power control units and stabilizer/elevator neutral shift mechanism. Each flight control computer (FCC) includes a Mach trim computer with automatic switching to other system if failure occurs. Refer to Chapter 27, Elevator and Tab Control System.
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BOEING PROPRIETARY - Copyright (C) - Unpublished Work - See title page for details.
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737-300/400/500MAINTENANCE MANUAL
C. The speed trim system actuates the stabilizer trim to maintain positive speed control. The system may be required during takeoff or go-around with low gross weight, aft CG and high thrust. The system is operational when autopilot is not engaged, stabilizer is not trimming, and control column displacement switches are not actuated. Each FCC contains speed trim computer with automatic monitoring and automatic switching between systems (when no faults). The monitoring automatically selects the operational channel when a single channel failure occurs.
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