Circumstances
On 21 January 2004 at 1533 UTC, a Piper PA-34-200 Seneca (registration G-TEST) was completing an instrument training detail at Stapleford Aerodrome, Essex. The aircraft made a visual landing on the asphalt runway 22 with full flap. After a normal touchdown, the commander applied slight to moderate braking after rolling approximately 70% of the runway distance. Without warning, the right main landing gear collapsed, causing the aircraft to veer 90° to the right before coming to rest near the runway edge. No occupants were injured. The crew consisted of three persons; no passengers were on board.
Examination of the Right Main Landing Gear Oleo Strut
The right main landing gear oleo strut, a cylindrical tube, had fractured near its lower end within the half-fork assembly that mounts the wheel axle. The wheel and half-fork assembly broke away, and the remaining oleo tube contacted the runway. The tube was an interference fit inside the wheel fork forging, secured by a fore-aft bolt across the diameter. The fracture plane passed through the forward bolt hole and just above the aft hole. The upper fracture surface was heavily abraded by the runway, but the separated lower portion, protected by the half-fork, was examined metallurgically. The failure originated from a fatigue mechanism at the forward bolt hole, propagating about 25% of the circumference before a rearward bending overload caused separation. Fatigue cracking initiated in the bore from multiple sites with slow progression, possibly starting shortly after the component entered service. The bore surface finish was very poor due to abusive machining during drilling (blunt drill, lack of lubricant, or excessive feed speed), significantly reducing fatigue resistance. The aft bolt hole had similarly poor surface finish but no fatigue cracks.
Aircraft History
The aircraft was built in 1974 but entered the UK register in July 1989. In August 1991, an incident occurred where the right landing gear collapsed due to a trunnion housing failure; the lower landing gear section (including the oleo tube and wheel fork) was not replaced, so these may be original items. No repair was evident on the oleo tube; as the tube, half-fork, and wheel axle are delivered as a complete assembly, the machining abuse likely occurred at manufacture.
Conclusion
The landing gear failure resulted from a fatigue crack in the right main landing gear oleo strut, initiated from machining abuse at the forward bolt hole, and propagated by normal service loads until overload separation.