Hydraulic system event, Sydney Airport, New South Wales, on 4 October 2006, Bombardier de Havilland DHC-8-315, VH-TQY

On 4 October 2006, at approximately 1045 EST, while on a scheduled flight from Canberra, ACT to Sydney, NSW, a Bombardier de Havilland DHC-8-315 (Dash 8) aircraft, registered VH-TQY, experienced a hydraulic system failure while on approach to land at Sydney Airport.

The flight crew became aware of the system failure when they selected the landing gear to extend during the approach sequence. Shortly after, the low oil pressure caution light for the number 2 hydraulic engine pump illuminated. The crew established that the nose and right main landing gear doors had remained open, and the left gear door had closed after all the gears had been extended.

The flight crew issued a radio alert to air traffic services and the aircraft commenced a missed approach. The crew then carried out the relevant quick-reference handbook (QRH) checks and landed at Sydney Airport on runway 16L without further incident.

The investigation determined that a solenoid-sequence valve failed, which resulted in the loss of pressure and quantity of hydraulic fluid from the aircraft's number 2 hydraulic system. Failure of the solenoid-sequence valve was due to the fracture of three of the four bolts that had clamped the two halves of the component together. Each of the fractured bolts had failed due to metal fatigue from exposure to in-service cyclic stresses that had developed during the operation of the aircraft's hydraulic system.