Hydraulic System

Introduction

The aircraft has three separate constant-pressure type hydraulic systems: utility, and two flight control systems. Each system is individually pressurized by a engine-driven hydraulic pump to 3,000 psi.

In the event of engine-driven pump failure, the secondary flight control system can be driven by a deployable Ram Air Turbine (RAT).

Utility System

This system has a 2.7-gallon reservoir pressurized by an engine pump. It supplies hydraulic power to the following:

• Rudder
• Landing gear and doors
• Wheel brakes
• Wing flaps
• Nose wheel steering
• Speed brake
• Automatic Flight Control System (AFCS)
• Gun and purge Door
• Ram Air Turbine Door

If system 1 pressure is too low to power the rudder, an automatic valve powers the rudder from the number 2 flight control system.

Emergency Flap Accumulator

If the utility hydraulic system or flap control fails, flaps can be lowered for landing using the emergency flap switch.

Emergency Nose Wheel Accumulator

If the utility hydraulic system fails, the emergency gear release can drop the main gear by gravity. On its own, the nose gear cannot be dropped by gravity, so an emergency accumulator is provided to drop the nose gear.

Flight Controls 1 & 2 Systems

Two independent and simultaneously operating hydraulic systems (1 and 2) actuate the primary flight control surfaces. Each systems is powered by its own engine pump, supplying half the power demand of control surfaces.

Failure of one systems doesn't affect the other. In the event of a frozen engine or engine pump failure, the number 2 hydraulic pressure can be maintained by a deploying the Ram Air Turbine.

In the event of utility system failure, the number 2 system also provides power to the rudder.

The following items are powered by these systems:

Item	Hydraulic System
Ailerons	1 & 2
Horizontal Stabilizer	1 & 2
Horizontal Stabilizer Trim	2
Rudder (in case of utility failure)	2

Ram Air Turbine (RAT)

This acts as an emergency hydraulic pump for the number 2 system. If engine RPM drops below 40%, the centrifugal switch triggers the RAT deployment automatically, unless there is weight on the nose gear's wheel. The RAT can also be deployed manually using the lever.

If the RAT door is open, an audible warning tone plays in the headset, and the landing gear handle knob light illuminates.

If the pump is no longer needed, it must be shut down manually using the lever in the cockpit.

Utility hydraulic pressure is required to open the RAT, but in the event of of utility hydraulic failure, stored energy in the Ram Air Turbine door emergency accumulator is used.

You can test deployment of the Ram Air Turbine in flight with the flight control hydraulic system test switch.

Emergency Wheel Brake Pump

In the event of utility hydraulic pressure loss, an electrically-driven pump pressurizes wheel brake accumulators if the pressure drops below 750 psi. When the aircraft is cold and dark, if you depress the wheel brake, the pump can be checked for correct function by listening for its sound.

Controls and Indicators

Hydraulic Pressure Indicator and Knob

This knob and gauge indicate the pressure of the selected system.

Ram Air Turbine Door Lever

Deploys the Ram Air Turbine manually, and automatically actuates if it deploys automatically.

Flight Control Hydraulic System Test Switch

Holding this switch at the SYS 2 OFF position closes the test valve ,removing hydraulic pressure for this system. Moving the switch to RAM TURB ON SYS 2 OFF removes hydraulic pressure from the number 2 system, and provide utility hydraulic power to the Ram Air Turbine, and opens the ram air turbine door lever.

After testing the lever, close the Ram Air Turbine Doors by moving the lever to the aft position.

Rudder Hydraulic Test Switch

This spring-loaded switch tests if the hydraulic summing valve is functioning correctly for the rudder actuator, ensuring that even in the event of insufficient utility pressure, the rudder functions using the number 2 system pressure.

Hold the switch in the ALTERNATE RUDDER position to shut off utility pressure, then the rudder can be moved. Confirm rudder pressure rises from nominal pressure up to 3,000 psi, matching the pressure of the number 2 hydraulic system.

Emergency Speed Brake Dump Lever

In the event of utility hydraulics failure with the speed brake in the open position, retract the speed brake. Without hydraulic pressure, this isn't possible. The dump lever releases any hydraulic pressure, allowing the speed brake to be retracted by airflow.

Emergency Gear Release

In the event of hydralic faailur, this lever deploys landing gear by gravity. Nose gear is deployed using hydraulic pressure stored in the emergency nose wheel accumulator.

Emergency Flap Switch

In the event of electrical flap control failure or utility hydraulic failure, this switch deploys wing flaps to the DOWN position.