Mach Trim - BOMBARDIER LEARJET 40 Pilot's Manual

MACH TRIM

Mach trim is a fully automatic system installed to increase longitudinal
stability and counteract nose-down tendency at high Mach numbers. A
circuit card in the #1 IC performs all the computational aspects for
Mach trim and signals the primary trim actuator to apply trim as nec-
essary. Airspeed information provided by the ADCs is used by the IC
in computing the trim requirement.
The pitch trim selector (Figure 5-4), located on the center pedestal, must
be in the PRI position for Mach trim to be functional and the autopilot
must be disengaged for the Mach trim to become active. If the autopilot
is engaged, it performs the pitch trim function using the secondary trim
actuator and the Mach trim is in a passive mode. Mach trim automati-
cally becomes active at 0.725 M
increases and nose down as Mach decreases. When the horizontal sta-
bilizer position changes, two Mach trim position sensors apply feed-
back signals to the IC. Mach trim is interrupted whenever the manual
trim is activated. The system resynchronizes to function about the new
horizontal stabilizer position when manual trim is released. If the IC
detects a fault within the Mach trim system function, a fail is posted on
the CAS and the overspeed cue on the airspeed indicator will also ad-
just to indicate a Mach limit of 0.76 to 0.78 M
The following CAS illuminations are specific to the Mach trim:
CAS
MACH TRIM FAIL
MACH TRIM FAIL
PM-132A
. Nose up trim will be applied as Mach
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Color
Amber Mach trim function has failed and aircraft
speed is greater than 0.76 to 0.78M
White Mach trim function has failed and aircraft
speed is equal to or less than 0.76 to 0.78M
Pilot's Manual
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