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 5.  Column Actuated Cutout Switch
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 A.  A column actuated cutout switch assembly stops powered stabilizer trim when either control column is moved in the direction opposing the stabilizer trim, the assembly located below the cockpit floor contains a set of cam operated switches which de-energize the PSTA clutches and the main control relay which interrupts motor power. The switches are wired so that when column motion input is the same as the trim direction, either main electric or autopilot trim will continue.
 B.  A shear out lever on the input shaft of the assembly prevents a jammed switch assembly from jamming the control columns.
 C.  A column actuated stab trim switch override located on the aisle stand will bypass the column actuated switch assembly. When this switch is placed in this override position, the main electric trim will operate when commanded regardless of control column position. This switch is guarded to ensure normal operation of the column actuated cutout switch.
 6.  Stabilizer Jackscrew and Gearbox Assembly (Fig. 1 and 4)
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 A.  The stabilizer jackscrew and gearbox assembly positions the stabilizer by converting PSTA or cable drum rotary motion to linear motion. The stabilizer jackscrew and gearbox assembly consists of a ball nut and jackscrew, a gimbal assembly, a cable drum, and the gearbox consisting of gearing and brakes. The gearbox is connected to a bulkhead in the fuselage by a lower gimbal which allows fore and aft angular motion as the stabilizer is positioned. An upper gimbal connects the ball nut to the stabilizer front spar fitting. This gimbal prevents any binding of the screw while the ball nut positions the stabilizer. A safety rod is installed in the jackscrew shaft to support the stabilizer in the event of jackscrew failure.
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BOEING PROPRIETARY - Copyright (C) - Unpublished Work - See title page for details.
A

737-300/400/500
MAINTENANCE MANUAL

ELECTRO 
MAGNETIC 
CLUTCH  JACKSCREW 
MOTOR  SAFETY  AUXILIARY 
ROD  BRAKE 
ASSEMBLY 
SEE  A 
BRAKE 
UNLOCK 
GEAR 
DRIVE  RATCHET 
GEAR  PAWL 
CLUTCH 
REDUCTION  DRIVE 
GEAR  GEAR 
TORQUE LIMITER  PRIMARY BRAKES 
CLUTCH 
AUTOPILOT 
TRIM SERVO 
TRIM SERVO  UPPER CLUTCH  INPUT GEAR 
INPUT GEAR  MEMBER 
LOWER CLUTCH 
MEMBER 
RELEASE CAM AND 
ROLLER ASSEMBLY 
(4 LOCATIONS) 
CLUTCH SPRING 
CABLE DRUM 
UNLOCK RING 
RATCHET RING 
UNLOCK ROLLER 
(4 LOCATIONS) 
PAWL 
(4 LOCATIONS) 
JACKSCREW 
AUXILIARY BRAKE 
(TOP VIEW) 
A 

Stabilizer Jackscrew and Gearbox Assembly
Figure 4

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 ALL  ú ú 01 Page 8 ú Nov 15/97
BOEING PROPRIETARY - Copyright (C) - Unpublished Work - See title page for details.
A
737-300/400/500MAINTENANCE MANUAL
 B.  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.
 C.  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.
 7.  Primary Stabilizer Trim Actuator (Fig. 1)________________________________
 A.  The primary stabilizer trim actuator provides power to actuate the stabilizer during normal operation. The actuator consists of a two speed,three phase induction motor, two electromagnetic clutches, a speed change relay and a torque limiting clutch. The trim motor is powered by 115 volt, three phase, 400 cycle power and is capable of emergency operation on two phase power supply. Electromagnetic clutches control the direction of rotation of the output shaft and are powered by 28 volts dc. The speed change relay, is also powered by 28 volts dc, determines output shaft speed as a function of flap position. High speed (with flaps extended beyond zero degrees) is three times faster than low speed (for flaps retracted). A mechanical clutch on the output shaft limits the maximum output torque to protect components in jackscrew gearbox.
　
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