5) Spoiler PCA feedback RVDT faults require an additional step for detection (Fig. 11). The threshold monitor detects a difference between the command and feedback signals and causes a "switch" decision. This is because both B and C subchannels detect errors.
6) After the subchannels have been switched, the PCA will receive a signal from a different RVDT. If either the control wheel transducer or the speedbrake lever transducer were at fault, the threshold error would go away after the changeover, and the applicable XDCR faultball would be set.
7) If the fault does not go away within 1.4 seconds of the changeover, the PCA is at fault. The PCA faultball will be set on the SCM which made the "switch" decision. There is no way to tell if the faultball is set from a defective PCA on the right or the left wing.
8) The module faultball indicates a problem with the SCM itself and can be set in one of three ways: a) When there is a fault detected in either subchannel B
or subchannel C, but not both (a "switch inhibit"
decision), no other faults have been detected, and time
T1 (0.4 sec) has elapsed,
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SPEED BRAKE LVDTS
SPOILER PCA RVDTS
* = BAD RVDT
A = ACTIVE SUB-CHANNEL B = STANDBY SUB-CHANNEL C = MODEL SUB-CHANNEL
= SUB-CHANNEL DETECTING ERROR
PCA RVDT Failure Detection
Figure 11
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b) When there is a fault detected in B and C subchannels (i.e., a "switch" decision), no other faults have been detected, and time T2 (1.4 sec) has elapsed; and
c) When an RVDT or LVDT fault is indicated by the comparator circuit and a "switch inhibit" decision has been made (fault in B or C but not both).
9) Pushing the RESET button on the SCM front panel clears any faultballs which are set. If fault still exists, faultballs will set again when the RESET button is released.
(d) AIRPLANES WITH -200 SERIES SCMs; Maintenance Monitor 1) The maintenance monitor reads and compares the three input
signals from the captain's control wheel transducers. If one input signal does not agree with the other two signals, the maintenance monitor moves the control away from the defective transducer (Fig. 10A). A CW RVDT FAULT message and fault details are stored in the existing fault memory to identify the defective control wheel RVDT unit (Fig. 13).
(12)
AIRPLANES WITH -100 SERIES SCMs;
Fault Logic Anomalies
(a)
The faultball logic is designed to indicate failures of the units they address. Other failures, however, can cause faultballs to set. Module faultballs can be set by a fault in the Air/Ground system itself or in any of the individual relays that provide air/ground discretes to the SCM. Truck tilt switch failures can also set SCM module faultballs. Breaks in the wiring between any of the transducers (LVDTs and RVDTs) and the SCM can cause module faultballs to set. These problems are addressed in the Control System Electronics Unit Fault Isolation, 27-09-00-1.
C.
Control
(1)
The CSEU module operates automatically whenever it is powered; it has no operating controls or adjustments.
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