What happened
On 17 January 2024, an Extra EA 300/L, registration G-OLAD, was conducting a private familiarisation flight at Northrepps Aerodrome in Norfolk. The flight, which involved three circuits and landings on a grass runway, concluded with a landing approximately halfway along the displaced threshold. Immediately following touchdown, the main landing gear collapsed. The impact caused the propeller and engine to strike the ground, and the aircraft came to a halt on the left side of the runway. There were no fatalities and no injuries to the pilot or the passenger.
The investigation
The AAIB examined the wreckage and found that both mainwheel assemblies had detached from their axles. The investigation established that the fasteners connecting the axles to the landing gear legs had failed because the nuts were pulled from the attachment bolts. Specifically, the four axle attachment bolts on each wheel were found to be bent with stripped threads, and none of the eight nuts were recovered from the site.
Evidence from the runway surface suggested the right tyre was not rotating upon touchdown and that the right mainwheel assembly detached prior to the left. The investigation also noted that the aircraft had undergone a main landing gear leg assembly replacement 111 hours earlier. During that maintenance task, the existing axle attachment bolts were reused with new nuts.
Findings
- The failure of the axle fasteners was caused by the nuts being pulled from the bolt threads under load.
- The damage to the bolts is consistent with side forces being applied to the tyres during landing.
- It is possible that the bolt threads had been damaged during the previous removal and refitting of the axles.
- While the pilot noted that firm landings and heavy braking are common at this airfield, the occupants did not perceive this specific landing as being harder than usual.
- The soft surface of the grass runway may have increased landing gear flex and the tendency for the aircraft to dig in, introducing higher loads into the assembly.
- The maintenance manual used for the previous gear replacement did not contain the prominent instruction to use new bolts found in manuals for other Extra models.
Safety action
The aircraft manufacturer is implementing safety actions to update all applicable maintenance manuals. This will include adding a prominent instruction to ensure new bolts are used whenever axles are refitted.