What happened
On 3 May 2023, a Piper PA-28-181, registration G-CCAV, was taxiing at London Biggin Hill Airport following a routine landing. During the taxi phase, the nose landing gear wheel fork fractured, causing the nosewheel to detach from the aircraft. This failure caused the propeller to strike the runway surface, which subsequently stopped the engine. There were no fatalities and no injuries to the pilot or the passenger on board.
The investigation
The AAIB examined the nose landing gear assembly, which consists of a wheel, fork, and strut. Investigators found that the aluminium fork had fractured through all four bolt holes used to attach it to the attachment block. Microscopic analysis of the fracture faces revealed fatigue striations, indicating that fatigue crack growth had occurred.
Evidence of corrosion was found within the bolt holes. Specifically, a steel bush located in one of the aft bolt holes showed signs of exfoliation corrosion, likely caused by galvanic action between the steel bush and the aluminium fork. The investigation also noted that while a maintenance inspection in March 2022 had addressed corrosion on the nosewheel hub and fork surface, the assembly had not been disassembled to inspect the internal interface between the fork and the attachment block. Furthermore, wear and paint loss were observed where the fork met the attachment block, suggesting the possibility that the attachment bolts were under-torqued.
Findings
- The primary cause of the failure was fatigue cracks propagating from the four attachment bolt holes in the aluminium fork.
- These fatigue cracks originated from pre-existing corrosion damage within the bolt holes.
- Galvanic corrosion likely contributed to the degradation of the aluminium fork due to the presence of an unprotected steel bush.
- The use of aerodynamic wheel spats may have trapped moisture, particularly when the aircraft was parked on grass, accelerating the corrosion process.
- There were no specific manufacturer-mandated corrosion inspections for this landing gear assembly unless the aircraft was operating in high-humidity or salty environments.
Safety action
Following the investigation, the CAA has taken action to issue a Safety Notice. This notice will advise UK operators and maintenance organisations to include inspections of the fork and attachment block interface within their routine maintenance programmes to identify any signs of corrosion or cracking.