BMS F-16C/D 4.34, Flight Manual

Page: 135 / 234

T.O. BMS1F-16CM-1 BMS 4.34 Change 2.00
BMS 4.34 Dash 1
© Red Dog 2012-2019
Page: 135
1.10 HYDRAULIC SYSTEM
Hydraulic pressure is supplied by two independent, concurrently running engine driven pumps A & B.
Should one of the systems fail the remaining system provides sufficient hydraulic pressure. This hardly
ever happens currently in BMS. It is indeed much more common to see both systems A & B fail at the
same time in BMS. In that case a third hydraulic pump driven by the EPU provides emergency
hydraulic pressure for a limited time to system A.
HYD PRESS indicators
There are two hydraulic pressure indicators located on the right aux console, one each for systems A
and B. They are powered by the emergency bus. In flight the normal position of the needles should be
pointing
at 12 o’clock (approximately 3100 psi).
HYD/OIL PRESS warning light
Located on the right glareshield the HYD/OIL PRESS light comes on whenever system A or B
pressure drops below 1000 psi or when the engine OIL pressure drops below 10 psi. The light is
powered by the battery bus.
1.11 EMERGENCY POWER UNIT (EPU)
The EPU is a self-contained system whose purpose is to provide emergency electrical power and
hydraulic pressure. The EPU automatically activates (if the EPU switch is in NORM) whenever both
MAIN & STBY GEN drop offline and/or when both hydraulic systems pressure drop below 1000 psi.
A safety pin prevents the EPU from switching on automatically during the engine start sequence. Once
the engine is running and prior to testing EPU operation, the EPU pin should be removed. This is done
through the ATC menu (Ground page). Failure to remove the pin would prevent proper EPU testing
and proper EPU operation if need in an inflight emergency.
The EPU can also be operated manually by placing the EPU switch to ON.
When the EPU is operating power is supplied to the emergency bus (the non-essential and essential
buses are unpowered). Hydraulic system A is also supplemented by EPU hydraulic pressure.
The EPU uses engine bleed-air to operate if engine RPM is sufficient. When bleed-air becomes
insufficient EPU uses hydrazine to operate. Hydrazine is a highly toxic gas and is contained in a
specific tank allowing around 10 minutes of EPU operation.
EPU lights
EPU RUN light located on the EPU panel: comes on whenever the EPU is running.
HYDRAZN light: comes on whenever the EPU is consuming hydrazine.
AIR light: comes on whenever the EPU is using engine bleed-air. This light remains on when the EPU
is using hydrazine to augment engine bleed-air.
EPU indicators
The EPU FUEL % REMAIN indicator located on the right aux console is graduated from 0 to 100%
and indicates the amount of hydrazine remaining in the tank. When this hydrazine is depleted and
engine bleed-air is not sufficient to maintain EPU operation the aircraft receives no power or hydraulic
pressure and the only option is ejection.
When the EPU is activated plan to land as soon as practicable, especially if engine bleed-air is not
going to be sufficient to run the EPU. Remember, once you start using hydrazine you have about ten
minutes of power and hydraulic pressure left.
Unfortunately when the EPU is fired up in BMS it is usually because the engine is no longer operating,
so the EPU is not able to run for very long on engine bleed-air alone before you slow down too much.