What happened
On July 23, 2012, a towing operation commenced at the Leverkusen (EDKL) airfield for a private flight. The flight involved an Avions Pierre Robin DR 400 RP acting as the tow aircraft and an Alexander Schleicher ASK 21 glider. The pilots had agreed upon a towing altitude of approximately 500 meters.
According to the glider pilot, the takeoff and initial climb proceeded normally. However, during the outbound leg, the tow aircraft suddenly entered a descent. The glider pilot noted that he had to apply back pressure on the elevator to maintain position and follow the tow aircraft. Immediately following this, the pilot of the DR 400 RP instructed the glider pilot to "release." The glider pilot complied, observing the tow aircraft rapidly losing altitude.
Witnesses on the ground observed the tow aircraft in a high angle of attack during a left turn, noting that the tow rope was sagging and the glider was positioned higher than the tow plane. Another witness reported seeing the tow aircraft bank to the left and enter a nearly vertical dive. The glider landed safely at the airfield without damage or injury to its pilot. The tow aircraft struck the ground near a forest edge, resulting in a post-impact fire. The pilot of the DR 400 RP sustained fatal injuries, and the aircraft was destroyed.
The investigation
The BFU examined the aircraft, the flight data from the glider's FLARM device, and witness testimonies. The investigation confirmed that both pilots were appropriately licensed and experienced for the operation. The aircraft were properly registered and maintained, with the tow aircraft's weight and balance within limits.
Analysis of the FLARM data showed that the separation of the aircraft occurred approximately 42 seconds after takeoff at an altitude of about 150 meters. While the investigation could not determine the exact cause of the aircraft's subsequent dive, the BFU noted that the pilot's command to release, combined with the sudden descent, suggested a potential technical issue, such as a loss of engine power.
Findings
- The pilot of the DR 400 RP lost control of the aircraft and was unable to recover from the uncontrolled flight state.
- There was no evidence that the glider's position or flight path caused the instability of the tow aircraft.
- A potential engine power loss was considered a possible contributing factor due to the sudden descent and the instruction to release the tow rope.
- The high degree of destruction to the tow aircraft prevented a detailed technical examination of the engine or airframe components.