What happened
On 5 August 2018, a Piper PA-28R-180, registration G-FBWH, landed at Sligo Airport following a cross-country flight from Weston Airport. During the landing rollout on Runway 29, approximately 150 metres after touchdown, the pilot felt a significant impact, and the right wing dipped. While the aircraft initially appeared to handle normally, a subsequent inspection revealed that the right-hand main undercarriage had partially collapsed, causing the upper part of the shock strut to puncture the aircraft's wing skin.
Prior to the landing at Sligo, the pilot had encountered a landing gear indication issue after departing Weston Airport. Although the pilot performed a touch-and-go maneuver to troubleshoot the gear-in-transit light and subsequently believed the gear was properly retracted, the structural failure occurred during the final landing phase.
The investigation
The AAIU examined the aircraft's undercarriage assembly and found that the aft support fitting's retainer tube and attachment bolt had detached and were found loose within the wing area. The investigation focused on the condition of the hardware, noting that the attachment bolt had been fitted with an unauthorized washer, which reduced the effective grip length of the bolt.
Investigators also analyzed the condition of the retainer tube, which showed significant wear and gouging. The examination of the bolt and tube suggested that the components had been improperly seated during a previous installation, likely to overcome resistance or a tight fit. Furthermore, there was no evidence that a slippage mark had been applied to the bolt head as required by the manufacturer's service manual.
Findings
- The primary cause of the partial collapse was the migration and separation of the aft retainer tube and attachment bolt.
- The installation of the right-hand undercarriage was incorrect, as the retainer tube was not properly seated.
- The use of an unapproved washer between the bolt and the retainer tube reduced the bolt's grip length, compromising the security of the assembly.
- The retainer tube itself was in poor condition and showed evidence of previous improper installation.
- A visual inspection through the under-wing access panel may not be sufficient to confirm if the bolt is correctly secured.