Introduction
On 22 June 2024, a Piper PA-28-161, registration G-SACS, experienced a landing gear failure during takeoff at Sherburn-in-Elmet Airfield, Yorkshire. The aircraft was conducting a training flight with one instructor and one student pilot. The right main landing gear oleo and wheel assembly separated from the landing gear cylinder but remained connected via the brake hose. The damage to the aircraft included significant damage to the wing, fuselage, and landing gear. Neither occupant was injured.
History of the Flight
The flight was a practice forced landing lesson that also included two touch-and-go landings. After the second touch-and-go, ground crew in a rescue vehicle radioed the aircraft to report that the right main wheel had become detached and was hanging by a hose. The instructor took control and flew along the runway while ground crew and another pilot visually confirmed the issue. The instructor then flew several circuits to burn fuel and allow emergency services to prepare. The aircraft landed on grass Runway 28; upon touchdown it veered approximately 90 degrees to the right and stopped with the right wheel detached from the hose. Both instructor and student exited the aircraft safely.
Aircraft Examination
The Piper PA-28-161 (serial number 2841047, manufactured 1988) had accumulated 18,607 flying hours and was owned and operated by a flight training school since 1989. Examination revealed that the torque link attachment lugs on the main landing gear cylinder had fractured. This allowed the oleo and wheel assembly to fall free from the cylinder while remaining attached by the brake hose. The landing gear is a fixed tricycle type.
Previous Occurrences and Safety Documentation
Failure of the torque link attachment lugs due to fatigue is a known issue with cast main landing gear cylinders fitted to PA-28 and PA-32 aircraft manufactured between 1961 and 1977, and later on PA-28-161 variants up to 1994. Forged cylinders are not as susceptible to such cracking. Piper Service Bulletin SB1131A specifies inspection of the cast cylinder lugs at 100-hour intervals using visual inspection followed by dye penetrant if cracks are not found under 10x magnification. This bulletin is not mandated in the UK. The aircraft had the SB applied at its last annual inspection at 18,268 hours, with subsequent visual-only inspections at 100-hour intervals. The failure occurred 339 hours after the last dye penetrant inspection.
Two previous occurrences of similar failures were investigated by the AAIB. Safety Recommendation 2024-001 was made to the UK CAA, but the CAA determined the failure rate did not meet the threshold for an Airworthiness Directive. Instead, the CAA issued Safety Notice SN-2024/002 on 3 June 2024 to raise awareness and request reporting of cracking occurrences. After this accident, the operator applied SB1131A with dye penetrant to its six-aircraft fleet and found two additional aircraft with cracked torque link lugs.
The applicable Piper parts catalogue (761-538 for PA-28-151/161) states: “Forged assemblies recommended for aircraft used in training operations per Piper Service Bulletin 1131 – Latest Revision.” SB1131A does not include this recommendation nor account for number of landings.
Safety Action
Piper plans to revise all applicable parts catalogues and maintenance manuals at the next revision to include the statement: “Used if [cast] MLG Cylinder has not been replaced per Piper Service Bulletin 1131. For Service only. Forged assemblies recommended for aircraft used in training operations per Piper Service Bulletin 1131 - Latest Revision.”
Conclusion
The right main landing gear torque link attachment lugs failed due to fatigue cracking, causing the wheel assembly and oleo to fall free from the landing gear cylinder during flight. The cracks were not identified by visual inspection. The CAA continues to monitor occurrences of lug cracking on the PA-28 and PA-32 fleets.