The #1 and #2 hydraulic pumps are driven by separate transmission accessory gearbox modules and supply 3000 PSI hydraulic pressure when the main rotor is turning. The backup hydraulic pump is powered by a 115 vac electric motor. If ac power is available, the backup pump is able to provide hydraulic pressure should one or both hydraulic pumps fail.

​

Each hydraulic pump is a constant pressure, variable volume pump. They maintain the required 3000 PSI over any rate of control movement for their own system. However, if the #1 and #2 hydraulic pumps are inoperative at the same time, there will be a slight restriction in the maximum rate of flight control movement. This is due to the backup pump's inability to provide the required volume because it exceeds the flow rate capability of the pumps.

Each pump has a pressure and return filter. The filters have indicator buttons that extend when the filter is clogged. Additionally, the return filter has a bypass capability, allowing hydraulic fluid to return from the system in the event of a filter clog. If a return filter were to become completely clogged and have no bypass capability, fluid would be blocked in the return lines causing a hydrostatic flight control lock up.

​

The #1 hydraulic pump supplies hydraulic pressure to the #1(first stage) fore, aft, and lateral primary servos and the #1 tail rotor servo.

The #2 hydraulic pump supplies hydraulic pressure to the #2(second stage) fore, aft, and lateral primary servos and the components of the pilot assist area; pitch, roll, and yaw SAS actuators, pitch boost servo, collective and yaw boost servos, and the pitch trim assembly. A pressure reducer in the pilot assist module reduces the 3000 PSI pump pressure to 1000 PSI for use by the pitch trim servo.

​

The backup hydraulic pump can supply hydraulic pressure to the #1 and/or #2 hydraulic systems independently or simultaneously. It is also the only pump that can supply hydraulic pressure to the 2nd stage tail rotor servo and the APU accumulator. The backup pump supplies hydraulic pressure to flight control components during ground checks (main rotors not turning). The backup pump will come on and provide pressure when any of the following conditions occur:

#1 Reservoir Low (caution light) #2 Hydraulic Pump (caution light)

#1 Hydraulic Pump (caution light) APU Accumulator Low (advisory light) #1 Tail Rotor Servo (caution light)

​

An automatic turn off feature is provided through a switch marked SERVO OFF, 1ST STG- NORM-2ND STG located on the MISC SWITCH panel on the lower console. In the NORM position both stages of the primary servos are on and operating. When the SERVO OFF switch is moved to the 1ST STG or 2ND STG position, the primary servos associated with that system are turned off. When the SERVO OFF switch is moved to 1ST STG, fluid to the #1 forward, aft, and lateral servos are turned off at the transfer module. A loss of pressure in the #2 primary servos will cause the first stage, turned off but has pressure, to automatically turn back on in case the backup system does not take over the function of the failed second stage. If the second stage is initially turned off, the sequence is reversed