What happened
On 16 July 2016, a DA 40 Diamond Star, registration G-CBFA, was taxiing at Old Warden Aerodrome in Bedfordshire following a private flight. The aircraft, which was carrying the pilot and two passengers, had recently landed on a dry grass runway. During the taxi towards the parking area, the pilot noted the aircraft felt unusually sluggish, as if moving through soft ground. As the pilot applied engine power to continue, the nose landing gear wheel detached, causing the aircraft to tip forward. The propeller struck the ground, causing the engine to stop. There were no injuries to the occupants, and all three individuals were able to exit the aircraft without assistance.
The investigation
The investigation focused on the structural integrity of the nose landing gear leg. Technical examination by a metallurgical consultant determined that the component had suffered a fatigue fracture. This crack had progressed halfway across the part before the remaining material failed under overload, leading to the separation of the nosewheel assembly.
Investigators reviewed the maintenance history, noting that the nose gear leg was a part number subject to an Airworthiness Directive (AD) requiring regular inspections. The most recent inspection, conducted via dye penetrant, had taken place 3 and a half hours of flight time prior to the accident, with no defects identified. The investigation also considered the aircraft's recent usage, noting it had been used for basic flight training involving 85 takeoffs and landings, primarily on grass surfaces, in the 33 flight hours since the last inspection.
Findings
- The failure of the nose gear leg was caused by a fatigue fracture.
- The aircraft had been operating primarily from grass runways for flight training purposes.
- The nose gear leg was subject to mandatory inspections due to a history of similar failures.
- While the recent inspection was performed correctly, the intense loading associated with frequent takeoffs and landings on grass surfaces may have contributed to the crack propagation.
- The pilot had noted unusual taxiing characteristics at a previous airfield, which may have been the initial signs of the component's degradation.