What happened
On 5 February 2005, a Piper PA-23-250 Aztec, registration N54211, was conducting a post-maintenance engine test flight at Elstree Aerodrome. Following a successful takeoff and initial flight maneuvers, the pilot attempted to extend the landing gear for the approach. While the two main gear legs locked into position, the nose gear failed to lock down. A visual inspection via the engine nacelle mirror revealed the nose gear remained in a semi-retracted state.
In an attempt to rectify the issue, the pilot performed a go-around and subsequently tried several emergency procedures, including using the manual hand pump and the emergency gas blow-down bottle. Despite these efforts, the nose gear remained unsecured. The pilot eventually performed a flapless approach, shutting down both engines and feathering the propellers before touchdown. Upon landing, the nose gear collapsed, causing the aircraft's nose to scrape along the runway surface. There were no injuries to the pilot or the passenger.
The investigation
Investigators examined the aircraft's hydraulic system and maintenance history. The aircraft had recently undergone an annual inspection, and the flight in question was its first since that maintenance. During the investigation, congealed hydraulic fluid was discovered on the aircraft's belly and around the nose gear door. However, the specific source of the leak could not be identified because the aircraft's nose gear actuator and lines were inaccessible without jacking the aircraft, which was not possible at the time of the inspection.
Furthermore, the investigation looked into the secondary damage sustained during the recovery process. To attempt to lock the nose gear, a recovery team used a truck and ropes to lower the aircraft's tail. While the pilot was manually attempting to extend the nose gear, the main landing gear unexpectedly retracted, causing the aircraft to strike the ground and resulting in significant additional damage to the airframe and the tie-down ring.
Findings
- The nose landing gear failed to lock because of a loss of hydraulic fluid in the system, which deprived the actuator of the force required to overcome the slipstream.
- The primary cause of the nose gear failure was an unidentified hydraulic leak.
- The secondary collapse of the main gear during recovery occurred because the hydraulic system's design allows the movement of one actuator to displace fluid and move the others; manually extending the nose gear caused the main gear actuators to move toward the retract position, unlocking the main gear drag links.