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MAINTENANCE MANUAL
8) STCM fault is set if a hydraulic brake is released without a valid SRM output trim command, or a hydraulic brake is not released when a valid SRM trim command is present and the stabilizer is within its trim limits.
9) The Mach/speed trim system initializes on a Mach number/computed airspeed value and then moves the stabilizer according to the compensation schedule shown in Fig. 3. As Mach number/computed airspeed increases, the stabilizer moves the airplane nose-up to increase the force on the column, increasing airplane stability , and vice versa for decreasing Mach number/computed airspeed.
10) The SRM contains the stabilizer software trim limits. If the Mach/speed trim commands encounter these limits, the commands are stopped (to avoid loop error), and no reinitialization occurs. At these limits, the Mach/speed trim can only command the stabilizer in the opposite direction away from the electrical trim limit.
11) Any interrupt of the Mach/speed trim mode will result in reinitialization to the airspeed existing at the time when the mode re-engages. The Mach/speed trim mode can be interrupted by the following: a) Manual electric trim b) Alternate electric trim c) Engaging/disengaging autopilot mode d) Engaging/disengaging aisle stand stabilizer trim cutout
switches e) Engaging/disengaging control column stabilizer trim cutout switches
12) Any one of the following faults will cause the SRM to disengage the Mach/speed trim function and the other SRM to engage the function: a) Primary DADC source invalid b) Mach/speed loop error c) Stab trim fault in the active SRM d) Invalid stabilizer position from the FCU e) Improper brake release within the associated STCM f) A nonrecoverable SRM module fault g) A second failure of the air/ground inputs. h) Loss of 28v Stab Trim source.
13) If any of the following conditions is detected, the Mach/speed trim function is latched off: a) No valid air/ground discrete selection (2nd fault)
detected by both SRMs.
b) DADC comparison fault
c) Both DADC faulty
d) Both stabilizer secondary brake discrete faulty
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e) Both stabilizer position signals faulty
f) A nonrecoverable SRM module fault of both SRMs
g) A stab trim fault in both SRMs.
h) Loss of both 28v Stab Trim sources.
14) Loss of Mach/speed trim function is annunciated to flight crew with the STAB SPEED TRIM status level message displayed on the EICAS display.
(c) Monitors in SRM
1) Each SRM has its own input monitors and interface monitors that detect faults and abnormal operation of the components. The result of a component failure on a detected fault is transmitted as an LRU fault to the CMC. The fault messages will appear on the EICAS display.
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MACH/SPEED TRIM SYSTEM - ADJUSTMENT/TEST
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TASK 22-24-00-705-001
1. Mach/Speed Trim System Test___________________________
A. General
(1) The Mach/Speed Trim System is part of the Stabilizer Trim/Rudder Ratio Module (SRM). For the test of the Mach/Speed Trim System, refer to AMM 22-22-00/501.
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