What happened
On 21 March 2001, a Lockheed L1-88C Electra, registration G-LOFD, was conducting night flying training exercises at Prestwick Airport, Scotland. The flight involved a training captain and a first officer undergoing conversion training. During the landing phase on Runway 13, the aircraft was configured with full flaps and landing gear extended.
As the aircraft approached the threshold, the commander took control to correct a drift toward the right of the centerline caused by a light crosswind. While the touchdown itself appeared normal, the aircraft immediately exhibited severe directional instability, veering sharply to the left. Despite the application of maximum reverse thrust and full right rudder, the pilot was unable to maintain the centerline. To prevent the aircraft from leaving the paved surface, the commander applied heavy braking at approximately 50 knots. The aircraft eventually came to rest approximately 1100 metres from the threshold, roughly 10 feet from the edge of the runway, at a heading 70 degrees left of the runway direction. There were no injuries to the two crew members.
The investigation
The investigation focused on the structural failure of the left main landing gear. Upon inspection, it was discovered that the lower piston oleo cylinder of the left gear leg had fractured just above the axle. This fracture caused the axle and the wheel/brake assemblies to separate from the leg. The departing components struck the runway, causing minor damage to the left flap and tailplane, and creating friction-induced flash fires from released hydraulic and oleo fluids. The impact of the fractured leg also destroyed a runway edge light.
Metallurgical analysis of the fractured piston cylinder at the AAIB facility revealed that the failure originated near the limit of normal piston travel. Scanning Electron Microscopy (SEM) identified brittle cleavage cracking in the chromium plating and intergranular cracking in the underlying steel. The investigation established that the chromium plating contained numerous cracks, likely caused by excessive grinding during manufacturing or refurbishment. These cracks allowed a corrosive environment to reach the high-strength steel substrate.
Findings
- The primary cause of the landing gear failure was stress corrosion cracking (SCC) within the steel substrate of the piston cylinder.
- The underlying steel was exposed to corrosive elements through cracks in the chromium plating.
- The cracks in the plating were attributed to excessive loads generated by grinding wheel operations during the component's manufacture or refurbishment.
- The failure was an overload fracture that occurred after the material had been weakened by the propagation of stress corrosion cracks.
- The component had completed 15,400 flight hours since its last overhaul, nearing its authorized 16,000-hour limit.