Part 4
Page 5
AP101B-7200-15
Emergencies
HYDRAULIC SYSTEM MALFUNCTIONS
13. The hydraulic system uses OX19 fluid which is pressurised to
between 220PSI and 850PSI (nominally 450PSI) by Engine Driven
Pumps (EDPs) on Numbers 2 and 3 engines. The system provides
hydraulic pressure for operation of the bomb doors, wing trailing edge
flaps and the main undercarriage landing gear. Hydraulic system
pressure is indicated on the pressure gauge fitted to the accumulator
adjacent to the hydraulic reservoir aft of the main spar. This gauge
should be checked regularly in flight and during ground servicing to
detect the onset of a malfunction.
Engine Driven Pump Failure
14. In the event of failure of both EDPs the manual hand pump, fitted
adjacent to the hydraulic reservoir, can be used to operate the hydraulic
system services. Note that the hand pump may not be sufficiently
effective to operate the large capacity jacks of the undercarriage
system.
Automatic Cut Out Valve Malfunction
15. The Automatic Cut Out Valve (ACOV) regulates the hydraulic
supply pressure to all hydraulic services. Upon service selection the
system pressure gauge will register a decrease in pressure. When
the pressure reaches 220PSI the ACOV cuts in until service travel is
complete when the ACOV cuts out at approximately 850PSI.
16. The failure of any service may be associated with an ACOV
malfunction. Cross reference to the system pressure gauge is
fundamental in order to carry out fault diagnosis.
17. If the ACOV fails to operate the service selector, undercarriage, flap
or bomb doors, should be returned to its previous setting. If there are
no secondary indications of service malfunction, a further selection may
be considered in an effort to stimulate ACOV operation and subsequent
service travel. Experience suggests that bomb door selection can ‘free’
a malfunctioning ACOV. If all else fails the ACOV, accessible below the
hydraulic reservoir, may be encouraged to operate by hand pressure.
UNCONTROLLED DOCUMENT - NOT FOR USE IN FLIGHT OR TO BE PRINTED
UNCONTROLLED DOCUMENT - NOT FOR USE IN FLIGHT OR TO BE PRINTED