What happened
On October 28, 2000, a JJ Honda ultralight aircraft was engaged in a test flight near Bad Grönenbach, Germany. The pilot was flying to intercept his wife, who had departed from Dietmannsried approximately ten minutes earlier. While flying at an altitude of roughly 470 meters, the aircraft experienced a structural failure where the wing assembly collapsed.
Witnesses on the ground observed the wings of the aircraft folding upward. Shortly thereafter, an audible bang was heard, indicating the activation of the ballistic recovery system. Although the system was triggered, the parachute failed to deploy. The aircraft struck a farm track with high vertical velocity and minimal forward momentum, resulting in the fatal injury of the pilot and the destruction of the aircraft.
The investigation
The BFU examined the wreckage at a local airfield alongside experts from the German Ultralight Association (DULV). Investigators focused on the wing's crossbar tensioning device, finding that the shackle had been bent open, though the threads showed no signs of external force. It was noted that the pilot had performed maintenance on the wing a few days prior to the accident.
Regarding the ballistic recovery system (BRS 4 UL 2), the BFU found that the pack sleeve had partially pulled away from the parachute cap. Testing revealed that the force required to pull the sleeve away was only 15 N, significantly lower than the manufacturer's specifications. Additionally, the investigation looked into the sealing of the parachute container, noting that previous repackaging by a French firm (La Mouette) involved a silicone seal that could be difficult to remove, potentially interfering with deployment.
Findings
- The primary cause of the accident was that the shackle of the crossbar tensioning device was not secured by tightening the screw during the assembly of the wing.
- This oversight went undetected during the pre-flight inspection.
- The aerodynamic loads encountered during flight caused the unsecured shackle to bend open, leading to the structural failure of the wing.
- The ballistic parachute failed to deploy properly due to interference with aircraft components during the deployment sequence.