What happened
On 16 April 2000, a Grumman American GA-7 Cougar, registration G-FLII, was operating as a 'Flying Eye' for a radio station at Elstree Aerodrome. After completing its flight duties, the aircraft landed on Runway 26 under calm conditions. Following a successful touchdown, the pilot taxied the aircraft toward the end of the runway to begin a backtrack.
As the aircraft initiated a right-hand turn to begin a left-hand turn around the end of the runway, the right main landing gear suddenly collapsed. The impact caused the right propeller tips to strike the runway surface and resulted in damage to the right wing tip, the right flap, and the cabin door entry step. The pilot and passenger, both wearing appropriate restraints, evacuated the aircraft without injury.
The investigation
Investigators examined the aircraft's landing gear system and the failed components. A metallurgical analysis of the right landing gear actuator rod end eye end revealed that the part had fractured due to overload. The examination showed significant plastic deformation and necking of the steel, though no pre-existing defects were found in the material itself.
The investigation also considered conflicting accounts of the cockpit environment. The pilot maintained that the landing gear lights had been verified as 'down-and-locked' prior to landing and that the gear selector remained in the 'DOWN' position. Conversely, the passenger reported seeing the pilot move the gear lever and hearing a warning horn and the sound of the undercarriage motor. However, the Flight Information Safety Officer (FISO) observed the collapse occurring during the turn at the end of the runway, rather than during the initial landing roll.
Findings
- The right main landing gear leg collapsed while the aircraft was performing a turn at the end of the runway.
- The failure was caused by a fracture of the landing gear actuator rod end eye end due to excessive tensile forces.
- Investigators considered whether a previous heavy landing incident on 9 February 2000 might have weakened the eye end through plastic deformation, leading to its eventual failure.
- An alternative theory suggested the eye end may have failed during the gear extension prior to this flight, allowing the gear to reach a downlocked position via the overcentre drag brace without the internal hydraulic lock, making it susceptible to collapse under sideloads during the turn.