(a) Autotrim SAM Operation
 1)  The SAM contains ARM and CONTROL microprocessors to form a redundant system. Each processor receives inputs from its corresponding FCC and center FCC. The AUTOTRIM ARM input is an analog discrete signal from the FCC. Digital inputs from the FCC are the following: a) TRIM UP or TRIM DN ARM and CONTROL CMDS inputs b) Left or right SAM ENG inputs
 2)  If unscheduled stabilizer motion is detected by the corresponding SAM (stabilizer moves more than .3 degree in either direction without a valid FCC autotrim command), a ground is provided by the SAM to turn on the UNSCHED STAB TRIM light on panel P5. An UNSCHD STAB TRIM message is also displayed on EICAS display unit to alert the flight crews.
 3)  The FCC inputs are monitored to determine which FCCs are engaged. The input monitors also detect faults that set the FCC fault ball as follows: a) If four or more parity errors occur within eight
 successive samples, a fault is set for the
 corresponding FCC.
 b)  Autotrim command data which is identified as FAILED by the ARINC 429 status matrix is discarded and no trim data substituted. If four or more autotrim command inputs within eight successive samples are indicated as FAILED, a fault is set for the corresponding FCC (detected by the ARINC 429 sign status matrix).
 c)  If an autotrim command word is not received for 125 milliseconds for 2 consecutive frames, a fault is set for the corresponding FCC. Old data is used when new data is not received for one frame.
 4)  Input coincidence monitoring detects invalid autotrim commands. An invalid command is defined as non-coincidence of ARM and CONTROL autotrim digital discretes, coincidence of opposite direction ARM or CONTROL autotrim digital discretes, or an ARM or CONTROL autotrim command without ENGAGE digital discrete or analog ARM discretes. If an invalid command is received for two or more successive samples, a fault is set for the corresponding FCC.
 5)  An FCC fault is cleared in air if valid data is
 continuously received for two seconds from the
 corresponding FCC.

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 ALL  ú ú 08 Page 17 ú Jan 28/02
BOEING PROPRIETARY - Copyright (C) - Unpublished Work - See title page for details.
A
757
MAINTENANCE MANUAL

ARM MICROPROCESSOR (INPUTS SIMILAR TO CONTROL MICROPROCESSOR)ELEVATOR
STAB TRIM TRIM
FEEL POSITION DN INHIBIT DN

CMDNEUTRAL SHIFT + NOSE DN
-
COMPENSATION THRESHOLD
ARINC
CONTROL MICROPROCESSORFOR GND EFFECTS
429
ARINC
TRIM
RCVR
OWN NOSE UP XMTR
429
UP AUTOTRIM CMDS (OWN)
FCC
AUTOTRIM VALID
AUTOTRIM
A
CMDCONTROL (OWN)
INPUT AUTOTRIM VALID
THRESHOLD
VALID (OWN)
MONITOR ENGAGE AUTOTRIM
BENGAGE STAB TRIM
ARM (OWN) ENABLE
CUP INHIBIT ENGAGE
AUTOTRIM
REQUESTLEFT
ARM (OWN)
(OWN)
LEFT SAM SELECTED
DSAM
FCCF/BALL
RIGHT SAM SELECTED ENGAGE
SELECTION DRIVER HYD BRAKE PRESS
RIGHT FAULT
LOGIC MAN. ELEC SW MON FAULT
UNSCHEDULED
AUTOTRIM SAM FAULT
TRIMFAULT
STAB TRIM
ARM (CENTER)
ANNUNCIATION
VALID
E
TRIM AUTOTRIM
AUTOTRIMCMD
AUTOTRIM
VALID 1 ENGAGE
AUTOTRIM VALID
FCC
FENGAGE AUTOTRIM
VALID ENABLE
ARM (CENTER)
REQUEST DISENGAGE VALID 2
CENTER ENGAGE
DETECTED(CENTER)
(CENTER) LOGIC
FCC
AUTOTRIM VALID
STAB INPUT AUTOTRIM CMDS (CENTER)MONITOR
CONTROL (CENTER)
MOVEMENT DEAD
TRIM
AUTOTRIM ARM

ARINC
AUTOPILOT

429
PITCH

RCVR
ENGAGE ENERGIZED
SOLENOID

G LEFT SHELF MODULE IDENTIFIER
L FLIGHT CONTROL COMPUTER  LEFT STABILIZER TRIM/ELEVATOR ASYMMETRY LIMIT MODULE
INTERNALS SAME
AS LEFT FLIGHT
CONTROL COMPUTER

INTERNALS SAME AS
LEFT STABILIZER
TRIM/ELEVATOR
ASYMETRY LIMIT
MODULE EXCEPT
AS SHOWN
R FLIGHT CONTROL COMPUTER
INTERNALS SAME
AS LEFT FLIGHT
CONTROL COMPUTER

RIGHT SHELF MODULE IDENTIFIER
CTR FLIGHT CONTROL COMPUTER  RIGHT STABILIZER TRIM/ELEVATOR ASYMMETRY LIMIT MODULE
Automatic Stabilizer Trim SchematicFigure 7 (Sheet 1)
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