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BOEING PROPRIETARY - Copyright (C) - Unpublished Work - See title page for details.
(b)
(c)
(d)
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757 MAINTENANCE MANUAL
6) HYD PRESS SW a) The HYD PRESS SW faultball is set when the hydraulic low discrete and the hydraulic high discrete from the electric hydraulic pump pressure switch are in the same state (both high or low). This faultball can be cleared by pressing the RESET switch.
7) STCM a) STCM faultball is set when the STCM secondary brake released (brake pressure switch S1 closed) for two seconds without a valid trim command or when the secondary brake is not released (brake pressure switch S1 opened) within two seconds of a valid trim command. STCM monitor is disabled during standby manual trim or column manual trim commands.
8) SPM a) SPM faultball is set if the stabilizer position signal input exceeds the nose up stabilizer travel limit or an open circuit occurs for longer than 1.5 seconds. b) Faultball can be reset by pushing the RESET switch. On ground, SPM faultball will clear immediately if valid data is received.
9) AIR/GND a) AIR/GND faultball is set by a comparison disagreement of the three air/ground inputs to the SAM. Faultball will autoreset with a GND/AIR or AIR/GND transition.
10) FSEU a) FSEU faultball is set when a disagreement exists between the three flaps position inputs from the flap slat electronic units (FSEU).
b) FSEU faultball may be cleared by cycling the flaps (extend-retract-extend or retract-extend-retract). 11) ELEV ASY L ACT
a) ELEV ASY L ACT faultball is set by an elevator asymmetry limiter fault. The faultball is set if a disagreement between commanded and actual position exists for 9 seconds or if the actuator feedback signal shows both extended and retracted conditions at the same time.
When any SAM's faultball is set, a white STAB TRIM message is
also displayed on EICAS.
1) Pressing the RESET switch on the front panel of the SAM
clears all faultballs unless fault is still present.
The amber STAB TRIM message and light indicator are set when
the SAM detects a half rate trim during electric trim mode or
only one of the STCM secondary brakes is released after
received manual electric trim command.
The UNSCD STAB TRIM message on EICAS and light indicator are
illuminated when the SAM unscheduled trim monitor detects that
the stabilizer moves more than 0.3 degrees in either direction
without a valid SAM trim command in the appropriate direction.
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757
MAINTENANCE MANUAL
(11)
Fault Indications on the Spoiler Control Module (SCM)
(a)
Fault Isolation in the SCM
1) The redundancy management function of the SCM checks the circuitry and input signals for possible fault conditions. It issues "switch" or "switch inhibit" actions as required to maintain system operation and to determine first or second fault status. This circuitry also generates applicable panel light and/or EICAS indications and sends fault data to the maintenance monitor.
2) AIRPLANES WITH -100 SERIES SCMs; The maintenance monitor determines which units are at fault (RVDT, LVDT, PCA, or SCM), and sets the appropriate faultballs on the SCM front panel.
3) AIRPLANES WITH -200 SERIES SCMs; The maintenance monitor detects faults and records the applicable fault message into memory. To identify the defective airplane components, you must operate the BITE display on the SCM front panel to show the fault messages and fault details (Figs. 12, 13). See the SCM front panel for the other items available with the BITE display.
4) Figure 8 is a block diagram of the SCM showing inputs from the control wheel RVDTs and the speed brake LVDTs to each of the three subchannels: active (A), standby (B), and model (C). Subchannel A normally drives the spoiler PCAs. Feedback from the PCA is used for nulling the command signal and is also fed to the threshold monitors in the B and C subchannels for comparison with the command signals. The servo amplifiers in subchannel B are also monitored.
5) Redundancy management first checks the servo amplifiers in subchannel B (SAL and SAR). A bad amplifier results in a "switch inhibit" decision since the standby subchannel is inoperative. If the servos check good, the command signals in subchannels B and C are compared with the PCA feedback signals in the threshold monitors (BR, BL, CR, and CL).
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