What happened
On 28 September 1999, a Piper PA-46 Malibu, registration N666LP, was performing a private flight when it experienced a loss of directional control during landing at Southampton Airport. After touching down on Runway 2/20, the aircraft initially followed a normal landing roll. However, the aircraft began to oscillate, veering left and right repeatedly.
During this period of instability, the aircraft departed the runway at approximately 30 to 35 knots. The excursion brought the aircraft to a halt roughly 50 metres from a stationary Jetstream aircraft, G-MAJA, which was waiting at holding point B1. There were no injuries to the two occupants of the Malibu, and no damage was sustained by either aircraft.
The investigation
Investigators examined the aircraft's nose landing gear assembly to determine why the steering had failed. The inspection identified a crack within the engine mounting frame at the specific point where the nose landing gear jack actuator is attached. This structural failure allowed the nose landing gear to shift slightly toward the retracted position, which caused the nosewheel steering mechanism to disengage and permitted the nosewheel to castor freely.
Metallurgical analysis performed in the United States revealed that the failure was caused by high stress/low cycle fatigue. The crack originated on the inside diameter of the tubing where two sections were welded together. While the tube material and welds were found to be satisfactory, the fatigue crack weakened the assembly until it reached a point of rapid failure due to overstressing.
Findings
- A fatigue crack in the engine mounting frame caused the nose landing gear to move toward the retracted position.
- This movement resulted in the disengagement of the nosewheel steering.
- The aircraft had previously experienced steering issues, though no specific fault had been identified at that time.
- The location of the crack was difficult to inspect visually due to its position within the assembly and the accumulation of dirt during service.
- The crack could potentially open and close during operation, making the defect difficult to detect during routine maintenance.