What happened
On August 26, 2007, at Iserlohn-Sümmern airfield, a Robin DR 400/180R towplane was engaged in training operations. Following a landing with its engine shut down, the pilot restarted the engine and prepared for a subsequent takeoff. During this period, a glider winch launch was also being conducted.
As the towplane was in its initial climb, it encountered the descending winch cable of a glider. Due to a prevailing wind from the right, the cable had drifted diagonally across the runway path. The left wing of the Robin DR 400/180R struck the cable, which severed the wing's torsion box up to the level of the main spar. This impact caused a severe deceleration and a leftward yaw, forcing the aircraft into a steep descent. The aircraft struck the ground in a conifer forest approximately 25 meters southwest of the runway end. The pilot sustained fatal injuries and died at the scene.
The investigation
The BFU investigation examined the sequence of events, the airfield's operational procedures, and the meteorological conditions. Investigators found that the aircraft was properly maintained, with its last annual inspection completed in June 2007. The pilot was highly experienced, with approximately 4,100 total flight hours.
Technical examination of the wreckage revealed no mechanical failures in the aircraft. The investigation also focused on the airfield's regulations, which prohibit simultaneous winch operations and powered flight. The investigation confirmed that the winch cable, made of Dyneema, had been cut by the impact, and the cable end was found near the winch station.