What happened
On August 27, 2005, a Schempp-Hirth Nimbus 3T motor glider was participating in a glider tow flight departing from the Fürth-Seckendorf airfield. The flight was being conducted under favorable weather conditions with nearly calm winds. This was the pilot's first flight in this specific aircraft type following its recent acquisition.
Shortly after takeoff, while the aircraft was flying at a low altitude and entering a right-hand turn with a bank angle of approximately 20 degrees, the pilot experienced heavy, unresponsive controls. As the aircraft began to roll uncontrollably to the right, the pilot released the tow rope. Witnesses observed the motor glider continuing to increase its bank angle until it struck a farmhouse. The impact, which involved hitting the roof of a building before the aircraft fell into a courtyard, resulted in the total destruction of the aircraft and one serious injury to the pilot.
The investigation
The BFU examined the wreckage and the control systems of the Schempp-Hirth Nimbus 3T. Due to the extreme destruction of the airframe, the technical examination of the control surfaces was difficult. Investigators inspected the ten L’Hotellier fasteners used to connect the control rods between the inner and outer wing sections for the left aileron. While nine of these fasteners showed signs of being forcibly opened during the impact, one specific fastener was found to be open but lacked visible signs of violent force.
Investigators also reviewed the pre-flight procedures. Before takeoff, the pilot and an assistant had performed a control surface check, with the assistant physically manipulating the surfaces while the pilot operated the cockpit controls. The investigation found that this specific method of testing only applied pressure to the control rods, which was insufficient to detect the underlying issue.
Findings
- The primary cause of the accident was the inadequate controllability of the motor glider due to an improperly connected left aileron control rod.
- The pre-flight control check was ineffective because it only subjected the pushrods to pressure, failing to reveal that the connection at the outer wing junction was not properly seated.
- Although the safety pin on the L’Hotellier fastener was correctly inserted, the locking ball had likely been placed only on or in front of the housing's notch rather than being fully engaged, creating a false sense of security.
- The pilot was unable to correct the increasing roll angle, leading to the fatal descent.