TM 1-1520-238-10
Change 9
9-17
9.12 HYDRAULIC SYSTEM FAILURES.
9.12.1 PRI HYD PSI and UTIL HYD PSI Light On.
WARNING
Failure of both primary and secondary
drives to the accessory gearbox would
result in the complete loss of all AC pow-
er, PAS air and the failure of both the Pri-
mary Hydraulic System and the Utility
Hydraulic System. All electrical system,
sights, communications and lighting
equipment not powered by the emergen-
cy bus would be lost. The crew must acti-
vate the Emergency Hydraulics and Land
Without Delay. The Emergency Hydrau-
lics uses the same accumulator pressure
needed to start the APU. Perform a dual
engine shutdown immediately after land-
ing.
1. EMER HYD switch – On.
2. LAND WITHOUT DELAY.
3. EMER ENGINES SHUT DOWN – Perform
WARNING
Immediate emergency action must fol-
low failure of both hydraulic systems.
It is impossible to control the flight
path of the aircraft without hydraulics.
The crew must activate the Emergen-
cy Hydraulics and Land Without Delay.
Any hesitation could result in loss of
helicopter control. Failure of the pri-
mary hydraulic system will also result
in loss of the Stability Augmentation
System. With emergency hydraulic
power in use, hydraulic power avail-
ability is a function of the frequency
and magnitude of the control inputs
and G loading placed on the aircraft.
Flight control inputs must be kept to a
minimum, as hydraulic pressure may
only be available for 30 to 41 seconds.
The Emergency Hydraulics uses the
same accumulator pressure needed to
start the APU. Perform an emergency
dual engine shutdown immediately af-
ter landing.
The amount of control movement may
be reduced to zero depending on the
severity and location of hydraulic fluid
loss within the utility hydraulic sys-
tem. Once the EMERG HYD switch is
turned ON, it must remain ON.
Hydraulic power available is limited to
a maximum of one 180 turn and four
full collective applications (a full col-
lective application is defined as one
movement from full down to full up or
from full up to full down).
Failure of both primary and secondary
drives to the accessory gearbox
would result in the complete loss of all
AC power, PAS air and the failure of
both the Primary Hydraulic System
and the Utility Hydraulic System. All
electrical system, sights, communica-
tions and lighting equipment not pow-
ered by the emergency bus would be
lost.
9.12.2 PRI HYD PSI and OIL LOW UTIL HYD Light
On.
In the event of a PRI HYD PSI failure and OIL LOW
UTIL HYD condition, hydraulic power to the tail rotor servo
may be lost. This may require a landing in accordance
with TAIL ROTOR FIXED PITCH MALFUNCTION para-
graph 9.9.5.
1. LAND AS SOON AS POSSIBLE.
