AIRPLANE
OPERATIONS
MANUAL
FLIGHT CONTROLS
REVISION 38
2-13-10
Page
9
Code
01
AOM-145/1114
Inadvertent Actuation Protection
A continuous command of any trim switch is limited to 3 seconds, even
if the trim switch is pressed longer than 3 seconds. As a result, when
manually actuating the trim, it is necessary to release the switch after
a 3-second actuation, then actuate it again to continue the trim
command. This feature intends to minimize the effects of an
inadvertent trim command of the main and backup trim switches or
Ground Spoiler/Speed Brake Unit. The autopilot command is not
limited in time and has another logic to preclude inadvertent actuation.
NOTE: For airplanes equipped with an HSCU -5009 MOD.2 or newer
and AWU -5 a TRIM voice message is provided to alert pilots
that the trim switch is being pressed for more than 3 seconds.
HSA Excessive Load Protection
The crew should keep the airplane trimmed to avoid excessive loads
on the Horizontal Stabilizer Actuator (HSA), especially after takeoff.
High loads on horizontal stabilizer may stall the HSA, inducing a
temporary loss of pitch trim command.
For airplanes equipped with an HSCU P/N 362100-1007 if the trim
switches are actuated for a period of time that totalizes 8 seconds
during the period when the horizontal stabilizer actuator is stalled, the
control unit will switch the associated system (main or backup) off and
the message PIT TRIM 1 (2) INOP will be permanently displayed on
the EICAS.
For airplanes equipped with an HSCU P/N 362100-1009, -5009 or
newer, if the pitch trim switches are actuated during the period when
the Horizontal Stabilizer Actuator is stalled, the message
PIT TRIM 1 (2) INOP will be displayed on the EICAS. The message
will disappear if the trim switch is released or any horizontal stabilizer
motion is detected. If the trim switches are actuated for a period of
time that totalizes 16 seconds during the period when the horizontal
stabilizer actuator is stalled, the control unit will switch the associated
system (main or backup) off and the message PIT TRIM 1 (2) INOP
will be permanently displayed on the EICAS.
NOTE: For airplanes equipped with EICAS version 18 and on, the
messages PIT TRIM 1 (2) INOP have been replaced with
PTRIM MAIN INOP or PTRIM BACKUP INOP.
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