The stabilizer control has two paths. Each path has separate electrical control to one STCM. The logic function determines which of the paths operate and whether it is single or dual.
In single path operation, the PFCs command the ACEs to operate one STCM. The STCM then supplies hydraulic power to one motor and brake. The PFCs alternate which path operates.
In dual path operation, the PFCs command the ACEs to operate both STCMs. They supply hydraulic power to the two motors and two brakes.
The PFCs use the elevator actuation levels to determine single or dual path of stabilizer operation. An elevator command that is more than the lower level causes the PFCs to command the single path operation. When the elevator command is more than the upper level, the PFCs command the dual path operation.
Rate Control
The PFC uses air/ground and airspeed data to determine the stabilizer rate of speed. The rate control function controls the rate control solenoid on both STCMs. It energizes the solenoids to operate at low speed rate and de-energizes the solenoid to operate at high speed rate.
When the airplane is on the ground, the PFC commands the stabilizer at high speed.
In flight, during airplane acceleration, the stabilizer moves at high speed when the airspeed is less than 230 knots. More than 230 knots, the stabilizer moves at low speed.
In flight, during airplane deceleration, the stabilizer moves at low speed when the airspeed is more than 220 knots. Less than 220 knots, the stabilizer moves at high speed.
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Speed of Stabilizer Movement
The paths and the speed controls combine to result in four speeds of stabilizer movement.
When the PFCs command the dual path operation at high speed, the stabilizer moves at 0.5 degree per second. When the PFCs command the single path operation at high speed, the stabilizer moves at 0.25 degree per second.
When the PFCs command a dual path operation at low speed, the stabilizer moves at 0.2 degree per second. When the PFCs command a single path operation at low speed, the stabilizer moves at 0.1 degree per second.
Stabilizer Position Limits
The PFCs limit the movement of the stabilizer as a function of the flap position.
When the flaps are retracted, the PFCs stop the movement of the stabilizer at:
* +2.25 degrees of airplane nose down trim
* -10.25 degrees of airplane nose up trim.
When the flaps are extended, the PFCs stop the stabilizer movement at -10.25 degrees of airplane nose up trim. The PFCs do not limit the nose down trim. The SPM limit switches stop stabilizer movement at +3.75 degrees of nose down trim.
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Failure Monitor
The PFCs monitor the operation of the center and right STCMs individually for correct operation.
When it finds a system malfunction, the PFC failure monitor commands the ACE to energize and latch the auto shutdown relay. With the stabilizer cutout switch in the NORM position, the auto shutdown relay supplies power to close the motor operated shutoff valve of the defective STCM.
To command an auto shutdownshutdown, the failure monitor needs to detect one of three malfunctions:
*
Uncommanded stabilizer motion
*
No stabilizer motion
*
STCM defective response.
There is an unscheduled stabilizer motion when the stabilizer moves without a valid command. The PFC failure monitor shuts down the STCM that moved the stabilizer when this malfunction occurs.
When there is no stabilizer movement after a valid PFC command, the failure monitor shuts down the defective STCM. In single path operation, the failure monitor shuts down the defective STCM and transfers the operation to the other STCM. In dual path operation, the failure monitor shuts them both down.
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There is an STCM defective response when the PFCs find an incorrect command response. If the stabilizer moves at half speed in dual path operation, the PFCs shut down the defective STCM. If the failure monitor detects open or short circuits in the STCM solenoids, or a faulty ACE command to the rate solenoid, the monitor shuts down the defective STCM. 中国航空网 www.aero.cn 航空翻译 www.aviation.cn 本文链接地址：777 AMM 飞机维护手册 飞行操纵 Flight Controls 2(25)
