What happened
On June 15, 2002, a DHC-8-311, registration PH-SDU, was conducting a test flight at Maastricht Aachen Airport to prepare the aircraft for return to a leasing company. The flight crew, which included a captain, a co-pilot, and a company observer, was performing a series of checks, including an instrument approach. During the approach, the crew noticed that the right-hand main landing gear failed to provide a green light indication after extension. Although the gear could be retracted and extended, it failed to reach the required locked position. Despite attempting the alternate gear extension procedure, the issue persisted, leading the captain to proceed with the landing. During the landing rollout, the right-hand landing gear collapsed, resulting in considerable damage to the aircraft. There were no injuries among the three occupants.
The investigation
The investigation focused on the recent maintenance performed on the aircraft, as this was the first flight following a replacement of the right-hand landing gear. Investigators discovered that a hydraulic swivel assembly had been installed upside down. This error caused a swivel tube to become bent during the gear retraction process, which physically prevented the mechanism from reaching its mechanical lock position.
While the maintenance was performed by three experienced mechanics who had cross-checked each other's work, the technician responsible for the swivel tube was performing this specific gear change on this aircraft type for the first time. The inspection following the maintenance had focused on checking for oil leaks and ensuring proper lock wiring, but it did not catch the incorrect orientation of the tube. The investigation also noted that the alternate gear extension procedure used by the crew did not account for a scenario where the gear was permanently unlatched, and the crew had not received specific simulator training for such an event.
Findings
- The primary cause of the gear failure was the incorrect installation of a hydraulic swivel assembly, which was placed upside down.
- The improper installation led to a bent swivel tube, preventing the landing gear from locking into place.
- Post-maintenance inspections failed to identify the error because they were focused on leaks and wiring rather than the directional assembly of the tube.
- The existing alternate gear extension procedures and simulator training programs did not adequately prepare the crew for a landing with a gear that could not be mechanically locked.