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PTU and open a valve in the pressure control
module. This allows utility hydraulic system pressure to
operate the hydraulic motor pump on that PTU, pressurizing
the flight control hydraulic system. Consequently,
the flight controls can be operated on the ground for
maintenance and checks without the rotors turning.
When both switches ar ON, No. 1 and No. 2 flight control
hydraulic systems will be pressurized. Both hydraulic
motor pumps of the PTU’s supply pressure for flight control
operation, When the switches are OFF, the solenoid
valves are closed and the flight controls cannot be operated
unless the rotors are turning. Power for these
switches is supplied by the No. 2 DC bus through the
HYDRAULICS PWR XFER circuit breaker on the No. 2
PDP.
2-6-6. RAMP PWR Switch.
WARNING
When the RAMP PWR switch is at OFF, be
sure the RAMP CONTROL valve is not
moved from STOP. Operating the valve
from STOP to UP or DN may cause the
ramp to free fall.
The RAMP PWR switch is on the lower right side of the
UTIL hydraulic portion of the HYD control panel (fig.
2-6-1). The switch has three positions labeled ON, OFF,
and EMERG. At ON, the ramp isolation valve in the utility
system pressure control module is open, allowing system
pressure for normal ramp operation. At OFF, the
ramp isolation valve is closed, isolating the ramp system
from the remaining utility systems. This prevents loss of
utility system fluid if the ramp system fails. At EMERG,
electrical power is supplied to the RAMP EMER switch,
allowing the ramp and cargo door to be opened and
closed from the cockpit. Power to operate the RAMP
EMER switch and ramp isolation valve is supplied by the
No. 1 DC bus through the HYDRAULICS UTIL SYS
CONT circuit breaker on the No. 1 PDP.
2-6-7. BRK STEER Isolation Switch.
The BRK STEER isolation switch is on the HYD control
panel (fig. 2-6-1). It is a guarded two-position switch labeled
ON and OFF. At ON, the brake and steering isolation
valve in the utility system pressure control module is
open, allowing system pressure for normal brake and
steering operation. At OFF, the brake and steering isolation
valve is closed, isolating the brake and steering subsystems
from the remaining utility systems. ON is the
normal flight position. OFF is used when there has been
a hydraulic failure in the brake or steering system. Setting
the switch to OFF in this case prevents loss of system
fluid. This allows the remaining utility subsystems to continue
to function normally. The brake system contains an
accumulator which allows limited system operation in a
hydraulic failure. The swivel lock system also has a small
accumulator which keeps the swivel locks locked with the
system isolated. Power to operate the BRK STEER
switch and valve is supplied through the HYDRAULICS
BRK STEER circuit breaker on the No. 1 PDP.
2-6-8. RAMP EMER Control Switch.
WARNING
The RAMP EMER control switch is intended
for emergency use only during
smoke and fume elimination procedures.
Inadvertent operation of the cargo ramp
and cargo door from the cockpit may result
in injury to personnel or damage to
equipment.
The momentary, guarded, three-position RAMP EMERG
(ramp emergency) control switch is located on the UTIL
hydraulic portion of the HYD control panel (fig. 2-6-1).
This switch allows the pilot, in an emergency condition,
to raise or lower the ramp to a partially open, fully open,
or fully closed position. The switch is labeled UP, HOLD,
and DN (down), and is spring loaded to the center
(HOLD) position. the switch is active only when the
RAMP PWR switch is set to EMERG. For up operation,
the ramp will move only while the momentary switch is
held in the UP position, and will stop as soon as the
switch is released. For down operation, the switch has a
minimum 5 second function which allows the pilot to lower
the ramp for 5 seconds by momentarily moving the
switch to DN and immediately releasing it. The downward
ramp movement will stop 5 seconds after the switch
is selected to the DN position (5 second timer circuit). If
the ramp and cargo door (ramp tongue) are in the fully
retracted into the ramp. The ramp can be further lowered
in 5 second intervals, by momentarily reselecting the DN
position when the ramp stops. The downward motion of
the ramp may be stopped at any time by momentarily
setting the RAMP EMERG switch to the UP position. The
ramp can also be lowered continuously (for more than 5
seconds) by holding the switch in the DN position until the
　
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