Incident Overview
At approximately 1809 local time, during final approach to land at Carnarvon, the pilot observed that the landing gear had not extended correctly. The aircraft remained in the circuit area while the pilot attempted to lower the landing gear using manual and emergency methods. He also sought assistance from the company's duty pilot in Perth and engineers based in Carnarvon.
Pilot Actions and Decision Making
After exhausting all options to lower the gear, the pilot decided to land with the landing gear and flaps retracted. He rejected landing on sealed runways due to concerns about unnecessary damage and potential fire. He considered landing in a riverbed, alongside a sealed runway, or on dirt strips. The pilot declined an offer for a flare path on dirt runway 27, indicating he would use the available light. At 1856, he attempted a landing on runway 27.
Collision
On late final approach, the aircraft collided with a 1.5-meter-high levy bank located 270 meters short and 115 meters to the right of the runway threshold. The pilot was trapped in the wreckage for some time after the aircraft stopped. The passenger sustained slight injuries, while the pilot was seriously wounded.
Investigation Findings
Examination of the aircraft revealed that both hinges on the inboard landing gear door had fractured. The forward hinge failed due to fatigue, and the rear hinge failed due to overload. The fatigue crack initiated at a sharp forging flash on the inner radius and grew over approximately 4000 load cycles. Similar fatigue cracking had been identified on an earlier version of the hinge (part number 46653-00), but regular inspections were discontinued when hinges with part number 47529-32 (as fitted to VH-DEG) were introduced in 1980. A similar fatigue crack was found in the forward door hinge of another PA31 during the investigation.
The fractured hinges jammed the left main landing gear mechanism, preventing normal and emergency extension. The pilot's apprehension about wheels-up landings influenced his decision-making aimed at reducing fire risk and minimizing damage.
The investigation noted that the pilot was subjected to considerable radio traffic involving questions, directions, and suggestions, which distracted him from primary tasks. He indicated readiness to land on at least two occasions, but advice and questions from ground personnel overrode his intentions. By the time he made his final approach, it was dark and he could not see the ground.
The following factors were considered relevant: manufacturing defect (forging flash), inadequate inspection procedures, pilot apprehension, inordinate interference by ground advisors, cognitive task saturation, improper in-flight decisions, and the pilot's inability to see the levy bank.
Probable Cause
The landing gear malfunction occurred because the left main landing gear would not lower due to fractured hinges. The forward hinge failed from fatigue initiated at a forging flash; the rear hinge failed from overload. The jammed mechanism prevented gear extension by normal or emergency systems.