What happened
On 28 January 2008, a Robin HR200/120, registration G-GBXF, was conducting a refresher training flight at Alderney, Channel Islands. During the landing phase on Runway 26, the instructor noted that the aircraft experienced a touchdown that was heavier than usual. Following this impact, the aircraft began to veer toward the right, and the instructor observed the right wing dropping. Despite the application of full opposite aileron, the aircraft could not be corrected, though the instructor successfully steered the plane onto the grass adjacent to the runway. The crew, consisting of two people, exited the aircraft without injury.
Post-flight inspections revealed that the lower section of the right main landing gear's wheel and axle unit had detached from the aircraft. The impact also caused minor damage to the flap trailing edge and some paint scoring on the underside of the wing.
The investigation
Investigators examined the wreckage and performed a metallurgical analysis of the fractured oleo piston tube. The examination revealed that the tube had failed due to fatigue cracking at the lower of two grooves where a seal and circlip are positioned. The investigation also determined that the failure of the torque-link bolt and the brake hose occurred as a consequence of the piston tube separating from the outer cylinder, rather than being the primary cause of the incident.
While the service history of the specific landing gear unit could not be verified, the investigation noted that the gear is maintained on an 'on-condition' basis. There were no recorded instances of pressure loss or fluid leaks from this component prior to the accident. Evidence from debris found within the unit suggested that the piston tube may have been partially separated from the outer cylinder for some time, potentially exiting and re-entering the cylinder during previous flights.
Findings
- The primary cause of the landing gear detachment was a fatigue crack in the oleo piston tube.
- The heavier-than-normal touchdown loads during the flight likely caused the weakened tube to deflect rearwards and separate from the leg.
- The failure of the torque-link bolt and the brake hose was a secondary effect of the piston tube's separation.
- There were no injuries to the two crew members on board.