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closes, isolating the BFCM return from the combined
system return. When the combined pressure exceeds
500 psi, the priority valve opens allowing the backup
system return to flow into the combined system return.
A check valve isolatesb ackup systemp ressurefr om the
combined system when the BFCM is energized.
2.16.4.1 Backup Flight Control Operation. The
BFCM may be operated in two modes: emergency and
ground test. In the emergency mode, the BFCM is controlled
by the EMERG FLT HYD switch, on the MASTER
TEST panel. The switch has three positions:
(AUTO) LOW, LOW, and HIGH mode. Electric power
to the motor is supplied by the right main ac electrical
bus through the FLT HYD BACKUP PH A (2Al), PH
B (2Cl). and PH C (2El) circuit breakers located on
right main ac circuit breaker panel (No. 2) in the rear
cockpit. Loss ofboth engine-driven electrical generators
eliminates in-flight use of the BFCM.
Never use the three-phase circuit breakers
(PH A, PH B, and PH C) to start or shut off
the BFCM as damage to the motor may result.
These circuits must be engaged prior to
any system test.
ORIGINAL 2-72

NAVAIR 01.Fl4AAD-1
Automatic control of the BFCM is provided by the
closing of both flight and combined hydraulic system
pressure switches. Since the switches are set at 2,100
psi, both flight and combined hydraulic system pressures
must drop below 2,100 psi before the BFCM is
turned on in the automatic low mode. Once in this automatic
mode of operation, the BFCM cannot be turned
offunless eitherorboth flight and combined systems are
pressurized above 2,400 psi. The EMERG FLT HYD
switch is used to select the low or high mode. Either of
these positions overrides the circuitry of the automatic
low mode and the BFCM will remain on even if either
or both system pressures become pressurized above
2,400 psi. When the BFCM pump reaches 500 psi, the
ON flag appears in the selected window at the bottom
of the hydraulic pressure indicator.
When operatedin conjunctionw ith zeroc ombineds
ystemp ressures, omeB FCM hydraulic
fluid will be forced out by thermal expansion.
The BFCM will remain fully serviced and will
operaten ormally as long as the elevatedt emperaturesa
re maintained.O nceo perating,t he
BFCM should not be turned off in flight without
combineds ystemp ressurea vailablet o reservice
it. Doing so would result in fluid
contraction and an underserviced condition
thatc ouldp revents ubsequenptu mp operation.
If either the flight or the combined hydraulic
systemp ressured ropsb elow 2,100 psi without
illuminating the HYD PRESS caution
light, the automatic low mode of the backup
flight control system may be inoperative.
2.16.4.2 Ground Operations. Ground checks of
the BFCM are performed by the pilot using the EMER
FLT BYD switch. Before performing ground checks,
the combined and brake system accumulators must be
chargedT. he BFCM hasa small volume capacity, 1,000
cc (61 cubic inches) when full, but will decrease in
volume to 500 cc (30.5 cubic inches) when the aircratt
is not in use. Below 500 cc (30.5 cubic inches), cavitation
of the pump and overheating of the motor may
occur. If the accumulators are not charged prior to starting
the BFCM, depletion ofthe reservoir hydraulic fluid
will occur. If this occurs too frequently, system damage
and failure may result. Both hydraulic system pressures
should indicate zero in order to fully test independent
operation of the BFCM.
A 180 “F thermal cutoff switch is bypassed
when the BFCM is selected on
with the EMERG FLT BYD switch. Prolonged
ground operation in the emergency
mode will result in BFCM burnout.
Since flight control demands can exceed
BFCM capability, all surface demands
must be performed slowly and cautiously
in order not to exceed the output rate of the
system. Excessive system demands will
causet hep ump to cavitatea ndt he motor to
overheat. Checks should be made slowly
enought o ensurec ontinuouso n indication
in the hydraulic pressure indicator.
2.16.4.2.1 Ground Test Mode. The ground test
mode of operation is controlled by the AUX BYD
CONT switch on the ground test panel in the rearcockpit.
In this mode, the BFCM operates in the high mode
only. Ground test from the rear cockpit is electrically
inhibited when the aircraft is on internal electrical
power. For ground inspection purposes, protrusion of a
red-tipped button on either the inlet or outlet filter cases
is a positive indication of a dirty filter. Both such indications
　
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