History of the Flight
The pilot had completed a 50-hour check and planned a short local flight. While taxiing to hold C of Runway 05 for engine checks, he turned left into the wind. He heard a loud thud, and the left wing dropped. He shut down the engine, turned off the master switch, and vacated the aircraft uninjured. External inspection revealed the left main landing gear had collapsed, but contrary to the pilot's expectation, the leg pointed aft rather than folding inward as during retraction.
Aircraft Examination
Main Landing Gear Assembly
The landing gear assembly attaches to the wing spar in the wheel well via forward and aft support fittings and gear support bearings. The retainer tube assembly connects the rear arm of the gear assembly to the aft support fitting. Examination of the left wheel well showed the landing gear mechanically disconnected from the wing. The forward support fitting was disrupted around the gear support bearing, with parts missing and fractured remains in the bracket. The centre of the forward fitting was bent away from the wing spar, and a hole was punched through the upper wing surface. Deep score marks were present around a circular cut-out in the spar web.
The aft support fitting was largely undamaged, with the aft gear support bearing intact and installed. The aft arm of the gear assembly was near the support fitting but not connected by the retainer tube assembly. When the access panel was opened, the retainer tube assembly was found loose in the access space. The barrel nut for the tube assembly bolt remained in place. The bolt and barrel nut threads were undamaged with some wear, and they could be screwed back together without play.
Maintenance History
The left main landing gear had been removed, serviced, and re-installed in 2019. Subsequent annual inspections were performed by three different maintenance organisations. The Piper Cherokee Maintenance Manual inspection instructions and the LAA generic maintenance schedule for the Permit to Fly specified inspections for the landing gear, but there was no specific check for the security of the retainer tube assembly bolt.
Analysis
The retainer tube assembly bolt had no thread damage and screwed back into the barrel nut without play. It is highly likely the bolt gradually unscrewed due to vibration since the 2019 re-installation. Annual inspections by three organisations did not include a specific check for bolt tightness, allowing it to unscrew over about five years. This released the aft arm of the landing gear from the bearing, leaving the gear held only by the forward arm. Forces during taxi tore the forward arm from its fitting and bearing, causing the gear collapse and the observed damage.
No similar PA-28R landing gear collapses involving the retainer tube assembly were found in UK or US accident data searches. Consultation with the manufacturer revealed that the PA-28R-201 maintenance manual specifies a torque of 40–50 in-lb for the retainer tube bolt. This specification will be incorporated into the PA-28R-180/200 maintenance manual at the next revision.
Conclusion
The landing gear collapse during taxi was likely caused by the left main landing gear retainer tube bolt releasing the aft landing gear arm, allowing the gear to collapse and cause significant damage to the wing. The manufacturer will update the maintenance manual to include a torque setting for the retainer tube bolt.