27 Stabilizer

B737NG/27/305 Stabilizer

Boeing B737-600/700/800/900

Stabilizer Training manual For training purposes only LEVEL 3

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This publication was created by Sabena technics training department, Brussels-Belgium, following ATA 104 specifications. The information in this publication is furnished for informational and training use only, and is subject to change without notice. Sabena technics training assumes no responsibility for any errors or inaccuracies that may appear in this publication. No part of this publication may be reproduced, stored in a retrieval system, or transmitted, in any form or by any means, electronic, mechanical, photocopying, recording, or otherwise, without the prior written permission of Sabena technics training.

Contact address for course registrations course schedule information Sabena technics training [email protected]

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List of Effective Pages. 1.......................... 15 - 04 - 2009 2.......................... 15 - 04 - 2009 3.......................... 15 - 04 - 2009 4.......................... 15 - 04 - 2009 5.......................... 15 - 04 - 2009 6.......................... 15 - 04 - 2009 7.......................... 15 - 04 - 2009 8.......................... 15 - 04 - 2009 9.......................... 15 - 04 - 2009 10........................ 15 - 04 - 2009 11......................... 15 - 04 - 2009 12........................ 15 - 04 - 2009 13........................ 15 - 04 - 2009 14........................ 15 - 04 - 2009 15........................ 15 - 04 - 2009 16........................ 15 - 04 - 2009 17........................ 15 - 04 - 2009 18........................ 15 - 04 - 2009 19........................ 15 - 04 - 2009 20........................ 15 - 04 - 2009 21........................ 15 - 04 - 2009 22........................ 15 - 04 - 2009 23........................ 15 - 04 - 2009 24........................ 15 - 04 - 2009 25........................ 15 - 04 - 2009 26........................ 15 - 04 - 2009 27........................ 15 - 04 - 2009 28........................ 15 - 04 - 2009 29........................ 15 - 04 - 2009 30........................ 15 - 04 - 2009 31........................ 15 - 04 - 2009 32........................ 15 - 04 - 2009 EFFECTIVITY ALL

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Table of Contents. 1. GENERAL..................................................................................................6 2. SYSTEM DESCRIPTION............................................................................8 3. COMPONENTS.......................................................................................14 3.1. Forward Control Mechanism.................................................................14 3.2. Cutout Switches and Colum Switching Modules...................................16 3.3. AFT Components..................................................................................18 3.4. Brake Mechanism.................................................................................20 3.5. Stabilizer...............................................................................................22 3.6. Stabilizer Trim Limit Switches................................................................24 4. ELECTRIC TRIM SYSTEM........................................................................26 4.1. Main Electric Trim.................................................................................26 4.2. A/P Stabilizer Trim Function...................................................................30

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List of Illustrations. AFT COMPONENTS................................................................................................................. 19 CUTOUT SWITCHES................................................................................................................ 17 ELECTRIC TRIM....................................................................................................................... 27 FORWARD CONTROL MECHANISM........................................................................................ 15 HORIZONTAL STABILIZER - GENERAL......................................................................................... 7 HORIZONTAL STABILIZER TRIM CONTROL SYSTEM - GENERAL DESCRIPTION............................. 9 STABILIZER.............................................................................................................................. 23 STABILIZER AUTO TRIM COMMANDS...................................................................................... 31 STABILIZER BRAKES................................................................................................................. 21 STABILIZER CONTROL CABLE AND CHAIN ADJUSTMENT......................................................... 24 STABILIZER SYSTEM - SHEET 1................................................................................................. 11 STABILIZER SYSTEM - SHEET 2................................................................................................. 13 STABILIZER TRIM LIMIT SWITCHES........................................................................................... 25 THS - TRIM CONTROL SCHEMATIC......................................................................................... 28

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Abbreviations and Acronyms A/P A/S C/W DC DFCS FCC FCCS G/A GRD LE MLG NLG PCU S/B SOV TE cntl sec stab vlv xfer

Autopilot Airspeed Control wheel Direct Current Digital Flight Control System Flight Control Computer Flight Control Computer System Go-around Ground Leading Edge Main Landing Gear Nose Landing Gear Power Control Unit Speedbrake Shutoff valve trailing edge control section stabilizer valve transfer

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1. GENERAL. The horizontal stabilizer controls the pitch trim of the airplane about the lateral axis. The horizontal stabilizer is on the aft section of the fuselage. The pilots manually control the position of the horizontal stabilizer with the stabilizer trim switches. Also, the pilots can use the stabilizer trim wheels on each side of the control stand. When the autopilot engages, it controls the position of the horizontal stabilizer. During autopilot or main electric operation, the actuator backdrives the stabilizer trim wheels.

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2. SYSTEM DESCRIPTION. The pilots control the horizontal stabilizer manually by the stabilizer trim wheels or electrically by the stabilizer trim switches. The autopilot controls the stabilizer automatically through the digital flight control system (DFCS). Manual Operation - Stabilizer Trim Wheels. The pilots use the stabilizer trim wheels on the control stand to manually move the forward and aft cable drums. The aft cable drum moves the gearbox and jackscrew. When the jackscrew moves, the horizontal stabilizer also gives a mechanical input to the elevator, through the neutral shift rods. Movement of the manual trim wheels also moves the stabilizer indicator pointer. Electric Operation - Stabilizer Trim Switches. The pilots operate two stabilizer trim switches for main electric pitch trim control. The switches are on the outboard side of each control wheel. The switches control electric input to the stabilizer trim and send signals to the flight data acquisition unit (FDAU). When the trim actuator operates, it moves the stabilizer gearbox. When the stabilizer gearbox moves, it moves the stabilizer jackscrew which moves the horizontal stabilizer. The gearbox also back drives the stabilizer aft and forward cable drums. Movement of the forward cable drum moves the manual trim wheels and stabilizer indicator pointer. Limit switches control the main electric and autopilot movement of the stabilizer. Autopilot Operation. The DFCS gives electric input to the stabilizer trim actuator. During autopilot operation, the stabilizer trim actuator operates at different speeds than during manual electric operation. Stabilizer position sensors A and B Send signals to the flight control computers (FCCs) in the DFCS. Stabilizer position sensor A sends stabilizer position to FCC a and the FDAU. Stabilizer position sensor B sends stabilizer position to FCC B (see ATA26).

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Stabilizer. The stabilizer consists of a left, right, and center section. It pivots at a hinge point located at the aft end of the center section. A ball nut is attached to the front spar fitting that connects to the jackscrew. The stabilizer moves to a maximum of 4,2° leading edge up and 12,9° leading edge down. Stabilizer Trim Limit Switches (5). Cam operated trim limit switches control the stabilizer trim range. When the stabilizer moves, a cam operates five limit switches. Stabilizer Trim Cutout Switches. Pilots use the main electric or autopilot stabilizer trim cutout switches to stop the stabilizer trim actuator if there is an uncommanded motion or runaway of the trim actuator. Stabilizer Column Cutout Switches. During electric trim operation, if the pilot gives an opposite direction to elevator control input, the column switching modules make the stabilizer electric trim stop. If either of the column cutout switches fail, the stabilizer trim override switch allows operation of the stabilizer trim control switches. Stabilizer Trim Override Switch. The pilots use the stabilizer trim override switch on the aisle stand to bypass the column cutout switches if one or both fail. Flaps Up Switch. The flaps up switch controls the main electric operation speed of the stabilizer trim actuator. The autopilot electric control of the stabilizer trim actuator does not go through the flaps up switch.

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y'a 02 pour a/p stab trim actuator

à l'interieur un convertisseur 115 AC au 28 VDC

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Manual Operation - Stabilizer Trim Switches The pilots operate the stabilizer trim control switches for main electric pitch trim control. The switches are on the outboard side of each control wheel. This gives electric input to the stabilizer trim actuator. The motor operates and drives the gearbox and stabilizer jackscrew. The stabilizer pivots at each rear spar. A ball nut attached to the front spar moves the stabilizer to a maximum of 4.2 degrees leading edge up and 12.9 degrees leading edge down. During electric trim operation, if the pilot gives an opposite direction elevator control input, the column switching modules make the stabilizer electric trim stop. Manual Operation - Stabilizer Trim Wheels The pilots use the stabilizer trim wheels for manual pitch trim control. The wheels are on each side of the control stand. Operation of the stabilizer trim wheels moves a chain that drives the forward cable drum. The forward cable drum moves the cables connected to the aft cable drum. When the aft cable drum moves, it drives the gearbox, jackscrew, and stabilizer.

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Elevator Neutral Shift Input. The elevator neutral shift rods are pogo type control rods with a spring inside. When the stabilizer moves, it moves the two elevator neutral shift rods. The neutral shift rods move a torque tube and crank assembly which moves the mach trim actuator. When the mach trim actuator moves because of the neutral shift rod input, it acts as a link and turns the elevator feel and centering unit housing. This creates a new neutral position for the elevators. Each rod also provides protection, in both directions (push or pull) if there is jam between the stabilizer and the elevator feel and centering unit. The pilot must supply approximately 180 pounds of additional force to extend or compress the springs inside the rods. The breakout force of each rod is 90 pounds. See the elevator and tab control system section for more information on the elevator operation.

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3. COMPONENTS. 3.1. Forward Control Mechanism. The pilot uses the stabilizer forward control mechanism for manual input. Location. The forward control mechanism is in the flight deck and the forward equipment compartment. The trim wheels and the sprocket are splined to a control wheel shaft. Operation. Manual control is accomplished by rotating either trim wheel on the control stand operation of the forward control mechanism drives the jackscrew and gearbox assembly via the cables to position the stabilizer. During electrical operation of the stabilizer the jackscrew and gearbox assembly drives the forward control mechanism, through the cables, to provide stabilizer position indication and rotate the trim wheels. A stabilizer position indicator provides continuous indication of stabilizer trim. Operation of the forward control mechanism drives a jackshaft through a flexible cable and transmits motion to a linkage that positions the indicator. A scale on the control stand is calibrated in units of trim and has an area outlined to indicate the proper takeoff stabilizer range, referred to as the GREEN RANGE. Maintenance Practices. The forward cable drum assembly is mounted in a housing which is attached to structure by one horizontal and two vertical suspension points. Turnbuckles at these suspension points can be adjusted to align the forward mechanism and obtain proper chain and cable tension.

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3.2. Cutout Switches and Colum Switching Modules. The stabilizer trim cutout and column cutout switches disable stabilizer electric trim. The stabilizer trim override switch lets you bypass the column cutout switches. Column Cutout Switches. The column cutout switches contain a set of cam-operated switches. The cutout switches also contain two relays. When the control column moves in the opposite direction from the stabilizer trim direction, electric trim stops.

A/P Stab Trim Cutout Switch. When the A/P stab trim cutout switches are in the cutout position, the FCC cannot control the stabilizer trim electric actuator. The switches open and do not let the trim commands and clutch signal go to the actuator. Stabilizer Trim Override Switch. The stabilizer trim override switch bypasses the column cutout switches. The pilot uses this switch to operate the electric trim if both column cutout switches fail.

A shear out lever on the input shaft of the assembly prevents a jammed switch assembly from jamming the control columns. When the main electric trim is in operation, switches in the column switching module open. This does not let the FCC clutch signal go to the trim actuator. The FCC and the main electric trim cannot control the trim actuator at the same time. If the pilot commands the control column forward or aft, signals go to the two FCCs. These signals do not allow the FCC to supply trim commands that do not agree with the pilot. Stabilizer Trim Cutout Switches. The pilot uses the stabilizer trim cutout switches to stop a runaway electric trim condition.

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TRIM/DIRECTION -CLONNE WHEEL AU SENS OPPOSE

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3.3. AFT Components. The horizontal stabilizer trim control system components in the aft section of the airplane move the leading edge of the stabilizer. The horizontal stabilizer components are in section 48, aft of the rear pressure bulkhead. The gearbox connects to the bulkhead in the fuselage by the lower gimbal. The upper gimbal connects the ball nut to the stabilizer front spar fitting.

Brakes. The gearbox has two internal brakes and a mechanical clutch. Both of the brakes are ratchet type brakes. The clutch lets the stabilizer manual trim wheel input override the stabilizer trim actuator input. Stab Position Sensor. Stabilizer position sensor B is on the right side of the elevator feel and centering unit. It shows on the graphic. Stabilizer position sensor A is on the left side of the elevator feel and centering unit and is not shown.

The stabilizer trim actuator is a multi-speed DC motor. It receives commands from the stab trim control switch or the autopilot. Controls. The pilot or autopilot controls the stabilizer trim actuator. The pilot also controls the aft cable drum position with the stabilizer trim wheels. This is the priority for control of the stabilizer : - Manual, - Electric, - Autopilot. The jackscrew gearbox receives inputs from the stabilizer manual trim wheel cables and the stabilizer trim actuator. The stabilizer manual trim wheel cables turn the aft cable drum. The aft cable drum or the stabilizer trim actuator turns gears in the gearbox to turn the jackscrew. When the jackscrew turns, the leading edge of the stabilizer moves. The gimbals permit fore and aft motion of the jackscrew as the stabilizer moves.

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3.4. Brake Mechanism. Stabilizer Brakes. A primary brake system and an auxiliary brake assembly work together to prevent aerodynamic loads on the stabilizer from rotating the jackscrew when the control system is not being operated. When the jackscrew shaft is driven by the jackscrew gearbox, the primary brake is unlocked by the increased airload and the auxiliary brake is unlocked by a brake unlock gear. The auxiliary brake system is provided in case of primary brake system failure. When the jackscrew is turned by the jackscrew gearbox, the auxiliary brake system is released through a gear driven by the gearbox. If the primary brake system fails, the jackscrew shaft rotation applies the auxiliary brake to prevent any additional shaft rotation. Manual input from the trim wheels causes the lower clutch member to cam down against the spring and disconnects the shaft from the clutch drive gear. This effectively disconnects both electric actuators. The primary brake system in the stabilizer trim gearbox prevents any aerodynamic loads on the stabilizer from rotating the jackscrew when the control system is not being operated. When the jackscrew shaft is driven by the jackscrew gearbox in a direction which increases the airloads on the stabilizer, a brake plate rotates through a ratchet producing a clicking sound in the assembly.

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TRIM

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3.5. Stabilizer. Purpose. The horizontal stabilizer supplies long-term pitch control of the airplane. Location. The horizontal stabilizer is at the aft section of the fuselage. Physical Description. The horizontal stabilizer assembly consists of a left and right section attached to a center section. Functional Description. The horizontal stabilizer moves a total of 17.1° in these directions : - 4.2° stabilizer leading edge up (airplane nose down trim), - 12.9° stabilizer leading edge down (airplane nose up trim). NOTE : The maximum leading edge up and leading edge down positions are measured from the stabilizer neutral position (0.0° or 4 units of trim). Markers on the fuselage show the maximum leading edge up, leading edge down, and the neutral positions

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3.6. Stabilizer Trim Limit Switches. The stabilizer trim limit switches limit the range of horizontal stabilizer motion. There are different limits for : Manual, Autopilot, And for flaps up, And flaps down. The takeoff warning switches tell the pilot of incorrect stabilizer position at takeoff. The stabilizer trim limit switches are on the left side of the horizontal stabilizer jackscrew attach fitting. The five switches mount on vertical brackets attached to structure. They are cam operated microswitches. The cam mounts to a support tube which connects to the stabilizer center section jackscrew attach fitting. Functional Description. The cam moves with the horizontal stabilizer and operates the five switches. The switches have these functions : - (S145) Nose down autopilot and flaps not up electric limit switch, operates at 0.05 units. - (S546) Nose down takeoff warning switch, operates at 1.50 units. - (S844) Nose down flaps up electric limit switch, operates at 3.95 units. - (S132) Nose up takeoff warning switch, operates at 8.75 units. - (S144) Nose up autopilot limit switch, operates at 14.50 units. NOTE : The stabilizer trim limit switches are adjustable.

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STABILIZER TRIM LIMIT SWITCHES

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4. ELECTRIC TRIM SYSTEM. 4.1. Main Electric Trim. General. The stabilizer trim actuator gets 115 volt, three-phase, 400 Hz AC power. Power comes from transfer bus 2. The stabilizer trim actuator has an internal AC to DC converter that powers a brushless DC motor. Control power is 28v dc from bus 2. Normal Sequence. The pilots operate the switches on either control wheel. This sends control power to energize the stab trim control relay R64. Three-phase AC power goes to the motor. The range of stabilizer trim is limited in both directions by the stabilizer trim limit switches.

During autopilot operation, the stabilizer trim speed changes. When the flaps are up, the low speed trim is 0.09 units per second. When the flaps are not up, the high speed trim is 0.27 units per second. Stabilizer Trim Cut Out Switch. If there is a stabilizer runaway condition, the pilots can use the stabilizer trim cut out switch (S272) to interrupt power to the electric motor. Cut Out - Elevator Column Input. When the pilot moves the elevator column out of the neutral range, switches inside the column cutout switches open in a direction opposite to column movement. Relays and another set of switches allow the actuator to operate the stabilizer in the same direction as the column movement. The pilot uses the stab trim override switch to bypass the column cutout switches, if both fail internally.

Trim Speed Change. The flaps up switch (S245) controls the speed of trim. When the flaps are up, the switch is open and low speed trim is engaged. Low speed trim moves the stabilizer at 0.2 units per second. When the flaps are not up, the switch closes and sends a signal to the stabilizer trim actuator to engage high speed trim. High speed trim moves the stabilizer at 0.4 units per second. A/P Controls. The trim actuator gets the trim commands from the FCC and moves the stabilizer. It sends a signal to the FCCs to tell them what speed the actuator is in. If the flaps are down, the actuator operates three times as fast as when the flaps are up.

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4.2. A/P Stabilizer Trim Function. General. The FCC supplies trim signals to the stabilizer when the autopilot is engaged. The stabilizer trim function calculates these signals : - A/P stab trim nose up, - A/P stab trim nose down. The autopilot calculates how far it can move the elevator (elevator authority) and how far it commands the elevator to move (elevator command). If the ratio of the command to the authority is too large, the autopilot will trim the stabilizer to lower this ratio. If it did not do this, the elevator movement may reach its limit and the autopilot could no longer move the elevator in one direction. If the autopilot is in the pitch go-around (G/A) mode, the authority is 9°. The autopilot uses these signals to calculate the elevator authority : - Total air pressure, - Static air pressure, - Stabilizer position. If the flaps are up, the autopilot uses the A/P elevator command. If the flaps are down, the autopilot uses these signals to calculate the elevator command :

Stabilizer Trim Detector The trim detector looks at the ratio of the elevator command to the elevator authority. If the elevator command is more than 15% of the elevator authority for a limited time, it will supply a trim nose up or trim nose down signal. It will stop the signal when the elevator command is less than 4% of the elevator authority. Column Switching Module. When the main electric trim is in operation, switches in the column switching module open. This does not let the FCC clutch signal go to the trim actuator. The FCC and the main electric trim cannot control the trim actuator at the same time. If the Pilot commands the control column forward or aft, signals go to the two FCCs. These signals do not allow the FCC to supply trim commands that do not agree with the pilot. Stabilizer Trim Electric Actuator. The trim actuator gets the trim commands from the FCC and moves the stabilizer. It sends a signal to the FCCS to tell them what speed the actuator is in. If the flaps are down, the actuator operates three times as fast as when the flaps are up.

- Elevator position, - Neutral shift sensor position, - Flare spring bias.

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27 Stabilizer

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