What happened
On April 8, 2017, a two-seat D4BK Fascination ultralight aircraft departed from Dingolfing for a flight to Kempten. The aircraft was carrying a pilot and one passenger. During the cruise phase, while flying at speeds between 20 and 22 km/s (200-220 km/h), the pilot heard a dull thud. Following this sound, the aircraft became difficult to control, and the flight controls felt "soft."
In response to the loss of control, the pilot attempted to deploy the aircraft's emergency parachute system. Although the deployment handle could be pulled approximately 10 cm, the system failed to activate. The pilot subsequently performed an emergency landing on the grass runway at Vilsbiburg airfield. The aircraft experienced several hard impacts upon landing, resulting in heavy damage to the airframe, including a visible crack in the fuselage tube. There were no injuries to the occupants.
The investigation
The BFU examined the aircraft's fuselage and the emergency recovery system. Investigators discovered a circumferential crack in the fuselage tube, located approximately 1,650 mm forward of the horizontal stabilizer attachment point. The crack extended through the composite structure, and white stress fractures were visible in a symmetrical pattern on both the upper and lower sections of the fracture plane. An inspection of the fiberglass layup confirmed that the construction met the original design specifications.
Additionally, the investigation of the parachute system revealed that the deployment mechanism had been pinched, which prevented the successful activation of the recovery system.
Findings
- A structural failure occurred in the fuselage tube, characterized by a circumferential crack and internal white stress fractures.
- The aircraft's flight controls became ineffective following the structural failure.
- The emergency parachute system failed to deploy due to a pinched release mechanism.