What happened
On 22 January 2003, an SC7 Skyvan 3A Variant 100, registration G-PIGY, was conducting a military parachute training programme at South Cerney Airfield in Gloucestershire. The aircraft had been moved from its base in Oxford to the airfield for the mission. Following two successful and uneventful lifts of paratroops, the aircraft attempted its third landing.
Upon touchdown, the left main landing gear collapsed. The aircraft veered to the left, traversing approximately 75 to 100 metres before coming to a halt. During the incident, the left wheel and a portion of the leg forging separated from the airframe. There were no fatalities and no injuries among the two crew members or the four passengers on board. The aircraft sustained damage to the left main landing gear.
The investigation
Investigators examined the failed landing gear lever, which is a trailing arm radius lever. A metallurgical analysis of the fracture surfaces revealed that the failure occurred in two distinct stages. The first stage involved an intergranular fracture characterized by corrosion products, suggesting that a crack had formed a significant period—possibly months—before the accident. The second stage was a clean, bright fracture indicative of a single ductile overload event.
Examination of the internal bore of the lever showed highly variable paint coverage, with areas where the coating was thin or contained pinholes. This lack of adequate protection allowed for corrosion to take hold. Additionally, investigators found a steel shim within the lever, indicating a previous undocumented repair that had restored the width of the component after material had been machined away. Because no component record cards existed for these specific landing gear levers, the exact history of this repair could not be verified.
Findings
- The primary cause of the failure was a stress corrosion crack that initiated in the internal bore of the landing gear lever.
- Inadequate cleaning and an incomplete paint finish provided insufficient protection against the environment, allowing corrosion to develop.
- The initial corrosion-induced crack created a stress concentration that eventually led to the final structural failure during the landing.
- While significant ruts were present on the airfield surface, there was no evidence that the landing was exceptionally heavy; however, such surface irregularities may have contributed to the overload.
- The lack of documented maintenance history for the specific landing gear components prevented a clear understanding of the repair's origin or the component's true usage cycles.