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757
MAINTENANCE MANUAL
SCM 1L (TYPICAL)
Redundancy Management Schematic Figure 8
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757 MAINTENANCE MANUAL
AIRPLANES WITH -100 SERIES SCMs; If the detected fault is caused by a bad transducer (input or feedback), the maintenance monitor will determine which transducer is bad. If no fault is detected in the transducers, the fault is in the module itself. Timing for the fault logic is given below:
T0 = 0.0 sec: Starts at the leading edge of the failure logic (SAL+SAR+BL+CL+CR) of the B or C subchannel.
T1 = 0.4 sec: A "switch" or "switch inhibit" decision is
made. If "switch inhibit", the maintenance monitor checks for SB or CW transducer
failures.
T2 = 1.4 sec: Gives the spoiler panel time to move to the commanded position after a channel switch. If the fault does not clear, a PCA fault-ball is set. If it does clear, a different applicable faultball will be set (SB or CW XDCR or MODULE FAULT).
AIRPLANES WITH -200 SERIES SCMs; If the detected fault is caused by one of the inputs to the SCM, a fault message for the input will be stored in the SCM memory. If no input fault is detected, then either the PCA or the SCM module is defective. Timing for the fault logic is given below:
T0 = 0.0 sec: Starts at the leading edge of the failure logic (SAL+SAR+BL+CL+CR) of the B or C subchannel.
T1 = 0.4 sec: A "switch" or "switch inhibit" decision is made.
T2 = 1.4 sec: If a "switch inhibit" decision was made at time T1, a module fault is set. If a "switch" decision was made at time T1 and the spoiler panel does not move to the commanded position, a PCA fault is set.
An explanation of how the redundancy management and the maintenance monitor work will be discussed below using the captain's inputs and a failure of control wheel RVDT #2.
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MAINTENANCE MANUAL
(b) Redundancy Management 1) The captain's control wheel RVDTs 1, 2, and 3 are connected to the active (A), standby (B), and model (C) subchannels in each of the SCMs in the left CSEU as shown in Fig. 9. The captain's speed brake lever LVDTs 1A, 2A, and 3A are connected in a similar arrangement. The first officer's inputs are connected to the SCMs in the right CSEU using the same pattern. In this example, all subchannel B servo amplifiers are assumed to check good. Captain's control wheel RVDT #2 is bad. 2) In SCM 1L, the threshold monitor of subchannel B detects a difference in the command from RVDT #2 and the feedback from the spoiler PCA which has been driven to the correct position by subchannel A (i.e., RVDT #1). Thus a "switch inhibit" decision is made by redundancy management. Spoiler control remains with subchannel A. 3) In SCM 2L, the model subchannel, C, receives the bad signal from RVDT #2 and so an error is detected between it and the PCA feedback. A "switch inhibit" decision is made here, also. 4) Module 3L has the bad RVDT #2 signal applied to the active subchannel, A, which drives the spoiler panels to the wrong position. The threshold monitors in both subchannels B and C detect errors between their (good) commands and the (bad) feedback signal. These dual errors result in a "switch" decision by redundancy management. Control of the spoiler panels is switched to subchannel B. 中国航空网 www.aero.cn 航空翻译 www.aviation.cn 本文链接地址：757 AMM 飞机维护手册 飞行操纵 FLIGHT CONTROLS 1(45)
