Gulfstream G550 Operating Manual Download

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the cause of the hardover condition. If the cause of the condition is thought
to be momentary, and the use of the rudder is deemed necessary for
continued safe flight and landing, the hydraulic shut off valves may be reset
by cycling the RUDDER HYD S/O circuit breaker. If the cause has not been
rectified, the shut off valves will close and hydraulic boost for the rudder will
be unavailable. Loss of rudder hydraulic pressure will also prevent yaw
damper (and autopilot rudder) operation.

If only one hydraulic system is shut off to the rudder, the remaining system
will provide full boost to the rudder and yaw damper / autopilot rudder
operation. The amber caution CAS message of ”Rudder Hydraulics Off will
be accompanied by a blue advisory “Single Rudder” message.

To prevent the HOPS from shutting off hydraulic system pressure to the
rudder during normal flight maneuvers that may involve rapid changes in
rudder direction, HOPS activation is buffered by three elements:

•

The clearance between bracket plunger switches and the actuator
cam arm

•

Inertia in the build up of hydraulic pressures in the rudder actuator

•

The one half (½) second delay in electrically latching the shut off of
hydraulic pressure

E. Standby Rudder System:

In the event that both hydraulic systems fail during flight, the Auxiliary
(AUX) hydraulic pump can be used to pressurize the left hydraulic system
to actuate the rudder and yaw damper provided that fluid remains in the left
system reservoir and there is no leak in the left hydraulic system lines
connecting to the rudder actuator. The AUX hydraulic pump, located in the
right main landing gear wheel well, is powered by left essential DC bus and
can provide three thousand (3,000) psi at a flow rate of two (2) gallons per
minute. Normally the AUX is used to actuate the flaps, ground spoiler
servos, brakes and nose wheel steering in the event of a dual hydraulic
system failure. However a valve in the left hydraulic system plumbing,
controlled by the STBY RUD switch on the lower portion of the pilot
instrument panel, can be used to divert the total output of the AUX
hydraulic pump to the left hydraulic system piston of the rudder actuator.
Powering the rudder and yaw damper, especially at higher altitudes,
provides dutch roll compensation and avoids the airspeed restrictions
necessary without an operating yaw damper. As the aircraft descends to
lower altitudes and airspeeds during the approach phase, airloads on the
rudder are reduced and manual rudder control is adequate for steering
commands. The STBY RUD switch can then be selected off to enable the
AUX hydraulic pump to provide the pressure for flap extension, pressurize
ground spoiler servos, wheel brakes and nose wheel steering during
landing. If the STBY RUD switch is not selected off prior to landing, the
standby rudder valve will automatically close when the nose gear weight-
on-wheels (WOW) switch is compressed on landing, enabling AUX pump
power for stopping and steering the aircraft.