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A 737-300/400/500MAINTENANCE MANUAL

S145 STAB L.E.M255 STABILIZER TRIM SERVO (STA 1088)LIMIT SW UP
Stabilizer Trim Interface SchematicFigure 11
EFFECTIVITYùùùùùùùùùùùùùùùùùùùùùùùùùùùùùù. AIRPLANES WITH EFIS ú

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737-300/400/500MAINTENANCE MANUAL
 (3)  
Stabilizer trim command is provided by either speed trim or A/P.

 (4)  
The trim up/down commands also pass through the column switching module and A/P trim cutout switches. Prior to going to the trim servo, the signals pass through nose up or nose down limit switches which limit the amount of stabilizer travel which can be commanded by the FCC.

 (5)  
The power required by the trim servo motor is three phase. Switching of the power input provides the control for proper directional rotation. A trim down command energizes the power relay which applies power through relaxed contacts of trim up and high speed relays. When the trim up command is received, both the power and motor direction relays are energized. The motor direction relay changes the power input to the motor to cause opposite rotation. The high speed motor is energized when the flaps are down to increase trim response.

 (6)  
The trim valid logic monitor is used in the engage interlock circuit. If a trim up and trim down exist at the same time, the A/P is disengaged. This logic is effective at all times; however, the main use is during dual channel operation. During dual channel operation stabilizer trim commands are paralleled. Therefore, if one unit commands trim up and the other trim down the A/P is disengaged.

 C. Stabilizer Trim Warning Lights (Fig. 12)
 (1)  
The FCC's provide an output to warning light circuits based on operational status of stabilizer trim systems.

 (2)  
The speed trim warning annunciator only illuminates when both FCC's provide logic to speed trim light circuits. Warning light logic is based on input sensors being valid. This includes N1 inputs, stabilizer position, computed airspeed and inertial vertical speed. There must not be a simultaneous trim up and tirm down command. Stab trim clutch wrap around must be present. Also, detector 2 detects movement of the stabilizer after a stab trim command signal has been initiated.

 NOTE: The inertial vertical speed is invalid until the IRS is
____ aligned which cause the illumination of the speed trim warning annunciator.
 EFFECTIVITYùùùùùùùùùùùùùùùùùùùùùùùùùùùùùù. AIRPLANES WITH EFIS ú

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A 737-300/400/500MAINTENANCE MANUAL

 E01732
 EFFECTIVITYùùùùùùùùùùùùùùùùùùùùùùùùùùùùùù. AIRPLANES WITH EFIS ú

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737-300/400/500MAINTENANCE MANUAL
 (3)  The stabilizer Out of Trim Warning light is illuminated by three differenct detectors. A delay of 10 seconds prevents nuisance warnings. The Stab Out of Trim light is inhibited when GS is engaged and flare is active. However, this inhibit logic does not extinguish the light if illuminated prior to passing through the 100 feet altitude. The stabilizer warning detector areas follows:
 (a)  
Detector 1. This unit detects a difference of 3° between the elevator position and elevator A/P actuator. This detector also activates a holding circuit which requires that the elevator A/P actuator commands be reduced to within 0.5° of the neutral shift position.
　
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