What happened
On 1 December 2007, a private flight involving a Wittman W10 Tailwind, registration G-BJWT, was conducting a straight-in approach to Runway 22 at Huckn．all Airfield. The pilot had been performing a local flight and was descending from 2,000 ft when the tower reported south-south-west winds of 20 knots, gusting to 30 knots.
During the landing phase, the aircraft experienced an initial touchdown followed by three subsequent bounces. The pilot later noted that a go-around should have been performed after the first bounce instead of attempting to cushion the landing. During this sequence, the right gear leg fractured and collapsed. This caused the aircraft to slide to a halt, resulting in no injuries to the two occupants, but causing significant damage to the propeller, engine mount, and undercarriage. The pilot successfully shut down the fuel and magnetos and requested assistance before exiting the aircraft with the passenger.
The investigation
The AAIB recovered the right and left main gear legs for metallurgical analysis. The investigation focused on the structural integrity of the undamped steel struts, which are made of 6150 heat-treatable alloy steel. The design specifications require the struts to be bent while red hot and then heat-treated and tempered to a specific Rockwell hardness (42-44).
Examination of the recovered components revealed that the material properties were inconsistent. While the surface of the metal was very hard (exceeding 600 HV), the core of the material was significantly softer, measuring approximately 200 HV. The investigation determined that the fracture was caused by a low-cycle, high-peak cyclic stress fatigue mechanism that originated at three distinct points within the leg.
Findings
- The failure of the right gear leg was directly attributed to incorrect heat treatment methods applied after the strut had been fabricated.
- The material exhibited non-uniform properties, with a soft center and a hard exterior.
- The fatigue failure could not be explained by standard service loading alone, as the material lacked uniform properties throughout its volume.
- The gear legs had been sent to a specialist organization for heat treatment, a process that was repeated several years prior when the wheel position was adjusted.