What happened
On 2 May 2013, a Jabiru UL aircraft, registration G-BZEN, was completing a training flight at Wicken to conclude its mission. Upon touching down, the pilot experienced a loud impact and felt the left wing drop. Initially believing a tyre had burst, the pilot applied right stick input to alleviate pressure from the left mainwheel. However, as the aircraft slowed, the wing dropped again. To protect the engine and propeller from potential shock-loading, the pilot shut down the engine. The aircraft was unable to maintain its heading and veered off the runway onto the grass, coming to a stop with the nose and right wheel on the ground. There were no injuries to the pilot or the passenger.
The investigation
The investigation focused on the structural failure of the left landing gear. Examination of the wreckage revealed that the left cantilever spring leg had partially detached from the fuselage, twisting forward and underneath the aircraft. The investigation established that the three mounting bolts securing the leg had failed. Specifically, the inner bolt had bent, while the outer bolts had both fractured and bent. The remains of all three bolts showed signs of significant wear and distress. It was determined that the failure likely began with one outboard bolt, which then overloaded the remaining two.
Findings
- The left landing gear leg collapsed due to the failure of three mounting bolts.
- The aircraft was using the original 5/16 inch diameter mounting bolts instead of the larger 3/8 inch diameter bolts recommended by Jabiru Service Bulletin 008-1.
- The investigation found that the aircraft had not been updated with the recommended larger bolts or the 500-hour life limit for the bolts specified in Service Bulletin 052-2.
- The mounting bolts were found to be in a worn and distressed condition prior to the failure.