Left Engine shutdown (PTU) 
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:
- The Left Engine fails (N3 < 45% rpm) or
- The Left Engine pump pressure is low (< 1275 psi)
When activated, the PTU supplements the Left hydraulic system electric motor-driven pump to operate the following:
- Nose Wheel Steering
- As installed - Hydraulic Driven Generator
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
- 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.
