Left Engine shutdown (PTU) Show Schematic only

Left engine shutdown

Leak from Left System Leak from Center System Leak from Right System Normal system operation Shutdown Right Engine Reserve brakes Ram Air Turbine (automatically operates when both engines have failed) Ram Air Turbine Manual Deployment Switch Alternate Brakes Left Thrust Reverser Rudder Ratio Landing Gear - Normal System Operation Spoilers Yaw Dampers Ailerons ETOPS equiped aircraft only Flaps and Slats - Normal System Operation Nosewheel Steering Elevators Spoilers Rudder Elevator Feel Stabilizer Ailerons Normal Brakes Right Thrust Reverser Power Transfer Unit Spoilers

Note: The C2 electric motor-driven pump is inhibited (load-shed) if both are switched ON but only one bus is powered.

Power Transfer Unit (PTU)

The Left Hydraulic system reservoir has a stand pipe to maintain reserve hydraulic fluid for use by the Power Transfer Unit in the event of a left system hydraulic Leak.

The Power Transfer Unit (PTU) is a hydraulic motor pump which transfers hydraulic power from the right system to the Left system.

The PTU is automatically activated if:

When activated, the PTU supplements the Left hydraulic system electric motor-driven pump to operate the following:


PTU operation is inhibited if the right engine is not operating (N3 < 45% rpm).

When the engine-driven and electric motor-driven pumps are inoperative, the EICAS status page displays the PTU output pressure.

PTU Manual Switch

The PTU can be operated by moving the PTU Manual Control Switch on the right side panel to the ON position. This provides power to the PTU control valve by-passing the left and right engine-run/out logic and the left EDP pressure switch. The valve then opens to operate the PTU the same as automatic operation.

PTU Faults

AMM The PTU indication circuit will cause a POWER XFER UNIT EICAS Status message to be displayed if:
  • the PTU is not producing pressure when demanded or
  • the PTU is producing pressure when not demanded or
  • the PTU is producing pressure when the right engine is not running.

Ram Air Turbine