What happened
On 28 March 2004, an Avid Speedwing (Modified), registration G-BUZM, was involved in a landing gear failure at Caernarfon, Wales. Following a routine flight from Llanbedr, the pilot performed a normal landing on Runway 26. During the landing roll, the pilot maintained the nose wheel off the ground until the aircraft slowed to approximately 30-36 mph. As the aircraft transitioned to the taxiway and was performing a left turn at a ground speed of roughly 4 mph, the nose landing gear suddenly collapsed.
There were no injuries to the pilot, though the aircraft sustained damage to the nose landing gear and the propeller.
The investigation
An engineering examination of the nose gear strut revealed a fracture at the site of a hole used to secure a stop bushing. Investigators found that the axis of this hole had been drilled in line with the longitudinal axis of the aircraft. Because this orientation placed the hole in the area of highest stress during fore and aft deflection—such as during touchdown—the holes had elongated over time. This led to the development of circumferential cracks originating from the bolt holes. While the crack surfaces near the holes showed signs of fatigue, the primary fracture was the result of an overload failure occurring at the moment of collapse.
Further investigation into the aircraft's history revealed that the failed nose gear was a second-hand component that had been installed approximately six months prior. The pilot had noted instances of nose wheel shimmy since the installation. The investigation also identified that the orientation of these holes was a known issue, with previous reports involving similar failures in other aircraft. While the original 1988 construction manual specified a perpendicular alignment, a 1993 update omitted this instruction, leading to incorrect drilling practices by some constructors.
Findings
- The nose gear strut failed due to a fracture at a bolt hole used to retain a stop bushing.
- The axis of the bolt hole was aligned with the longitudinal axis of the aircraft, placing it in the region of maximum stress during landing impacts.
- Fatigue cracking had developed around the holes due to the high-stress orientation.
- The final collapse was caused by an overload failure of the weakened strut.
- Inconsistencies in manufacturer manuals and a lack of widespread implementation of manufacturer recommendations contributed to the risk of incorrect installation.