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compares the difference between these two signals and
calculates the mach trim commands.
FCC Controlled Neutral Shift Enable Commands
The FCNSE command to the mach trim actuator does not
change until one of these conditions occur:
* Manual electric trim occurs
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EFFECTIVITY
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* Autopilot electric trim occurs
* Flap position change occurs
* FCC enters FCNSE region because either engine N1 is more
than 18 percent
* FCC exits FCNSE region because both engine N1s are less
than 18 percent.
After the change occurs, the FCC calculates the new FCNSE
command.
Mach Trim Select Signal
The FCC uses this data to find out which FCC should supply the
mach trim signals:
* Airplane is on the ground
* Is the other, foreign, FCC good
* Which FCC is FCC A.
Mach Trim Warning Signal
If the FCC finds that the mach trim function is not good, it stores
the failures in its BITE memory. It also supplies a mach trim
warning signal.
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General
Both FCCs calculate the mach trim signals to control the mach
trim actuator. However, only one FCC operates the actuator.
The FCC also sends a mach trim warning signal to the flight
control panel when the mach trim function fails in the FCC.
FCC Selection For Mach Trim Function
Both FCCs determine which FCC should supply the mach trim
command signals, however, only FCC B sends the mach trim
select signal to the IFSAU. In the IFSAU, K4 and K5 control
which FCC supplies the mach trim signals to the actuator.
If the mach trim select signal is a high, the relays are not
energized and FCC A supplies the signals. If the mach trim
select signal is a low, the relays are energized and FCC B
supplies the signals.
When you turn on power to the airplane, FCC A controls the
mach trim actuator. If power is not turned off, each time the
airplane lands, the FCCs change which FCC controls the mach
trim actuator. If the mach trim function in one FCC fails, the
other FCC always controls the mach trim actuator.
Mach Trim Signals
The mach trim excitation signals supplies 26v ac excitation
power to the mach trim position sensor in the actuator. The
sensor position signals goes directly to both FCCs.
The brake in the actuator holds the output shaft so it does not
move. When the actuator receives the 28v dc brake release
power, it releases the brake.
The 115v ac motor excitation power supplies the excitation
signal to the actuator motor. The motor command signals can
now turn the motor to drive the output arm in or out. This causes
the elevator feel and centering unit and the neutral shift sensor
to turn.
The mach trim select status signal in the FCC is a ground if that
FCC was selected. If it is an open, the other FCC was selected.
Mach Trim Fail Warning Light
If the mach trim function in the FCC is good, it grounds its mach
trim warning signal. These signals energize relays K1 and K2 in
the flight control panel. The mach trim fail light does not come
on. If both mach trim functions fail, both relays deenergize and
the light comes on.
If only one function fails, the light does not come on. However, if
you push either master caution recall switch when there is one
failure, the mach trim fail light comes on. If you then push the
master caution reset switch, the light goes off.
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EFFECTIVITY
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DFCS - FUNCTIONAL DESCRIPTION - MACH TRIM COMMANDS
DFCS - FUNCTIONAL DESCRIPTION - MACH TRIM COMMANDS
EFFECTIVITY
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