What happened
During a non-scheduled air transport flight from Forrestania to Perth, the crew of VH-WAJ, a Metro aircraft, encountered a total loss of hydraulic system pressure. This failure rendered the landing gear, nose wheel steering, and flaps inoperable, though a reserve pressure accumulator provided limited braking capability.
Following a flapless landing, the captain decided to taxi the aircraft toward the operator's hangar. The crew incorrectly believed that hydraulic pressure had been restored and that the brakes remained functional. While taxiing on a slight slope near the hangar, the crew applied the brakes, but they proved ineffective. The aircraft subsequently struck the hangar, resulting in damage to the right propeller and the right wingtip.
The investigation
Investigators determined that the hydraulic pressure loss was caused by a fluid leak originating from a cracked hydraulic pipe union flare located in the left main landing gear wheel well.
Post-flight analysis revealed that the captain's workload had increased significantly due to managing the in-flight emergency, which included handling radio communications, performing checklists, and guiding the first officer through the manual extension of the landing gear. The captain also transitioned from the monitoring role to the pilot flying role during the approach and landing.
Several factors contributed to the erroneous decision to continue taxiing. The crew observed a positive pressure indication on the main hydraulic gauge, which was actually a result of the manual gear extension process, and they noted no visible fluid on the runway. Furthermore, the captain did not verify the status of the brake accumulator gauge after the landing.
Findings
- The captain's decision to continue taxiing was influenced by a disruption in task prioritization following the emergency.
- The first officer's limited experience and lack of familiarity with non-normal procedures outside of a simulator environment reduced their ability to assist with workload distribution and crew resource management.
- A lack of communication with a tow vehicle and the presence of other taxiway traffic likely created self-imposed pressure on the captain to move the aircraft toward the hangar.
- The depletion of the reserve accumulator pressure was not immediately apparent to the crew during initial brake testing after stopping.