History of the Flight
On 3 May 2023, at approximately 1120 UTC, a Piper PA-28-181, registration G-CCAV, was taxiing after a normal landing at London Biggin Hill Airport. During taxi, part of the nose landing gear failed, causing the nosewheel to detach and the propeller to strike the runway surface, stopping the engine. The pilot and the sole passenger were not injured.
Aircraft Information
G-CCAV was manufactured in 1980 and operated as a training aircraft until 2003, when it suffered a landing accident that caused significant damage, particularly to the nose landing gear and associated structure. The aircraft was rebuilt, but no records of the work were kept. The aircraft had always been fitted with aerodynamic wheel spats and was predominantly parked on a hard standing, though there was evidence of parking on grass.
In March 2022, the aircraft underwent an annual inspection. The work sheet noted that the nosewheel was removed due to heavy corrosion, which was cleaned and the fork re-protected, and nosewheel hub corrosion was rectified and repainted. However, the fork assembly was not removed from the strut assembly during these tasks.
Investigation
Examination of the fork and strut assembly revealed that the fork had fractured through all four of the attachment block bolt holes. Two pieces of the fork and all bolts remained attached to the strut assembly, showing heavy abrasion from the runway. Wear and paint loss were present on the upper surface of the fork where it contacted the attachment block.
Scanning Electron Microscope analysis of the four fork pieces showed fatigue striations characteristic of fatigue crack growth, though most surface detail was damaged by corrosion. Corrosion pits and additional cracks were observed in all bolt holes. In the aft right hole, a steel bush had corroded and lacked visible protective coating. The upper part of this hole exhibited exfoliation corrosion, possibly due to galvanic corrosion between the aluminium fork and steel bush. No documentation regarding the bush's installation was found.
The attachment block hole for the strut assembly showed extensive corrosion pitting, cracking around the lower edge, and areas of intergranular corrosive attack.
Findings
The failure of the nose landing gear was caused by fatigue cracks propagating simultaneously from the four attachment bolt holes. While initiation points could not be identified due to corrosion, evidence suggested they originated from corrosion damage. The steel bush likely contributed to galvanic and exfoliation corrosion in its hole, though it was deemed unlikely to have initiated cracks in the other holes.
During maintenance in March 2022, the interface between the fork and attachment block was not inspected or disassembled. Wear and lack of paint between the fork and block indicated possible under-torqued bolts, which could have allowed relative movement and further preload reduction, potentially contributing to fatigue initiation.
The presence of aerodynamic wheel spats may have trapped moisture, especially when parked on grass, increasing corrosion risk.
Safety Action
The Australian Civil Aviation Safety Authority had issued Airworthiness Bulletin 32-019 in April 2009 after a series of nose landing gear failures, recommending periodic inspection of the fork-to-block interface. However, no similar instructions were issued by the FAA, CAA, or EASA. The manufacturer's maintenance manuals only specified a 200-hour corrosion inspection for landing gear in salty or high-humidity environments.
In response, the UK CAA announced plans to issue a Safety Notice advising operators and maintenance organisations to inspect the fork assembly at the interface between the fork and attachment block as part of routine maintenance, looking for corrosion or cracking.
Conclusion
The nose landing gear fork of G-CCAV failed due to fatigue cracks from the four attachment bolt holes, which initiated from corrosion damage. No mandated corrosion inspections exist for landing gear except in salty or high-humidity environments.