Fairchild Industries Inc 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.