Left Hydraulic System Right Hydraulic System
Up
Elevator
←
Down
Elevator
→
Up
Elevator
←
Down
Elevator
→
Hydraulic Actuator Shaft
Pressure
Switch
Pressure
Switch
Pressure
Switch
Pressure
Switch
In a similar manner, if a hydraulic malfunction causes the shaft of the
actuator to move in a direction opposite the commanded elevator direction,
the increased pressures in the wrong direction sides of the pistons would
close the monitoring switches, and movement of the actuator shaft would
cause the cam arm to contact the plunger switches on the external bracket,
and hydraulic pressure would be shut off to the elevator actuator after a
one tenth (1/10) of a second delay.
If a hydraulic malfunction in a single system (left or right) side of the
actuator moves the actuator shaft in a wrong direction, only the hydraulic
pressure of the malfunctioning system is shut off. For instance in a
stabilized condition, if the left hydraulic system piston attempts to move the
actuator shaft in the up direction, the increased pressure in the down
elevator side of the left piston will close the monitor switch and actuator
shaft displacement will close both the left and right hydraulic system up
elevator bracket plunger switches, completing the shut off circuit for the left
hydraulic system after a one tenth (1/10) second delay. (In this case
hydraulic pressure in the up elevator side of the right hydraulic system
piston will decrease due to the increase in area caused by actuator shaft
movement.) The elevator hydraulic actuator will continue to function using
the remaining hydraulic system.
The operation of the hydraulic shut off valves by the HOPS is signaled to
the MAUs (left elevator to MAU #1, right elevator to MAU #2) over ARINC-
429 connections. The shut off condition is monitored by the MWS, and a
CAS message corresponding to the condition is displayed on the CAS
window. If either or both hydraulic systems are shut off, an amber caution
message of “L (or) R Elevator Hydraulics Off” is displayed. If only a single
hydraulic system has been shut off, the remaining hydraulic system will
provide full elevator operation. If both hydraulic systems have been shut
off, manual elevator control may remain possible, depending upon the
cause of the hardover condition. If the cause of the condition is thought to
be momentary, and the use of the elevator is deemed necessary for
continued safe flight and landing, the hydraulic shut off valve(s) may be
reset by cycling the RIGHT ELEV HYD S/O and/or LEFT ELEV HYD S/O
circuit breaker. If the cause has not been rectified, the shut off valve(s) will
close and hydraulic boost for the elevator will be unavailable if both
hydraulic systems have been shut off. (HOPS is powered by the left
essential DC bus for the left elevator and the right essential DC bus for the
right elevator.)
To prevent the HOPS from shutting off hydraulic system pressure to the
elevator during normal flight maneuvers that may involve rapid changes in
elevator direction, HOPS activation is buffered by three elements:
• The clearance between bracket plunger switches and the actuator
OPERATING MANUAL
PRODUCTION AIRCRAFT SYSTEMS2A-27-00
Page 10
August 14/03
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