Fairchild SA227-AC, VH-IAW

The crew of the Fairchild Metroliner was conducting endorsement training in the Cowra area when they advised air traffic services (ATS) that their aircraft had a hydraulic failure and they were returning to Bankstown. An uncertainty phase was declared by ATS and the aircraft returned to Bankstown where a flapless landing was carried out.

The subsequent maintenance inspection found a cracked hydraulic pipe in the left landing gear wheel-well that had allowed the loss of the hydraulic oil contents from the power pack. The crack was in the bend radius of the pipe and was not visible to the naked eye. The crack only became apparent with the application of more than 800 psi of hydraulic pressure to the system during the maintenance inspection. The pipe was changed and the aircraft returned to service.

The pilot in command reported that he had experienced two similar hydraulic pipe failures in this aircraft type and the company fleet had five or six similar failures in the preceding twelve months. He also reported that he had a concern that the escaping oil in this situation could have started a wheel-well fire.

The design of the hydraulic system is such that, when a failure occurs in one of these hydraulic pipes, there is no redundancy. As a result, the leak drains the contents from the hydraulic reservoir, which is the common source of hydraulic fluid for both the left and right engine-driven hydraulic pumps. Without hydraulic services, nosewheel steering, anti-skid braking, flap operation and normal landing gear retraction and extension would not be available to the pilot.