The RVDT of the left SPM sends a stabilizer position feedback signal to the L1 ACE, the RVDT of the center SPM to the C ACE, and the RVDT of the right SPM to the R ACE.
The limit switches in the center SPM control the signal from the C ACE to the center STCM. The limit switches in the right SPM control the signal from the R ACE to the right STCM. The limit switches of the left SPM are not used.
Alternate Pitch Trim Switches
The alternate pitch trim levers move alternate pitch trim switches which send signals to the AIMS cabinets.
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General
The stabilizer cutout switches and auto shutdown relays supply power to the shutoff valves in the STCMs. These valves control hydraulic power to the stabilizer motor and brake.
Cutout Switches
With the cutout switch in the CUTOUT position, 28v dc power goes directly to the close side of the shutoff valve motor. As the valve completes its travel to the closed position, limit switches in the motor assembly move to the ready-to-open position.
With the cutout switch back to the NORM position, power goes through the de-energized shutdown relay to drive the valve back to the open position. The motor limit switches then return to the ready-to-close position.
Auto Shutdown Relays
The PFCs command the ACEs to energize the auto shutdown relays for:
*
An uncommanded stabilizer movement
*
A no stabilizer motion fault
*
An STCM defective response.
The PFCs monitor the left and right STCMs individually for stabilizer operation. If a PFC finds a system malfunction, it commands the ACE to energize the left or right stabilizer auto shutdown relay in relation to the STCM that has a defect. The ACE then latches the auto shutdown relay. The energized auto shutdown relay supplies power to close its shutoff valve.
Indications
Unscheduled stabilizer motion when there is an auto shutdown failure causes a STABILIZER warning message to show.
A FLIGHT CONTROLS caution message shows if both stabilizer channels are defective.
A STABILIZER C or a STABILIZER R advisory message shows if the center or right channel shuts down or if one of the cutout switches is in the CUTOUT position.
The advisory message STABILIZER CUTOUT shows when both cutout switches are in the CUTOUT position.
Training Information Point
Maintenance personnel can use the stabilizer cutout switches to do fault isolation of stabilizer system malfunctions.
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A maintenance action is necessary to unlatch the auto shutdown relays. After correction of the fault, the stabilizer system ground test unlatches the PFC auto shutdown commands to the ACEs when the system passes the test.
You can also use the PFC disconnect switch on the P5 panel with the C and R cutout switches to unlatch the auto shutdown relays. Because the ACE latch can be manually reset only in direct mode, the PFC disconnect switch first must be in the DISC position. With the cutout switch of the shutdown STCM in the CUTOUT position, the auto shutdown relay de-energizes. The ACE monitors the power removal from the auto shutdown relay and resets its auto shutdown latch.
When the cutout switch moves back to the NORM position, the auto shutdown relay stays de-energized and permits the STCM shutoff valve to open. This permits the pilot to control the stabilizer in direct mode.
If the stabilizer motion fault continues when the PFC disconnect switch moves back to the NORM position, the PFCs immediately command the ACEs to energize and latch the auto shutdown relays.
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HORIZONTAL STABILIZER CONTROL -FUNCTIONAL DESCRIPTION -NORMAL MODE 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(23)
