SET Out

The yellow electric pump is turned ON after the start of Engine 1 to prevent the PTU (Power Transfer Unit) from operating and to conserve PTU operating hours. Prior to starting Engine 2, the pump is turned OFF to facilitate the checking of the PTU’s correct operation by creating sufficient differential pressure between the Green (G) and Yellow (Y) hydraulic systems. In the event of a PTU failure, the ECAM system will display a fault indication.

SET In

The yellow electric pump is turned ON after Engine 2 is shut down because it may switch off due to an electrical transient when Engine 2 shuts down. In this scenario, the electric pump does not automatically restart once electrical power returns to normal. Therefore, the action of turning on the pump is performed after Engine 2 has been shut down.