What happened
On April 22, 2006, at approximately 09:26 UTC, an L-13 Blanik glider was performing a routine aero-tow departure from Kapfenberg Airfield (LOGK) in Austria. The glider was being towed by a HK 36 TTC Super-Dimona motor glider as part of a seasonal check flight for a club member.
During the climb, at an altitude of approximately 20 to 30 meters, the pilot of the towing aircraft experienced engine problems and radioed an urgent instruction to release the tow cable. The glider pilot immediately disconnected the cable. The towplane was able to land safely back at the airfield. However, the glider continued forward past the end of the runway. The pilot then attempted a steep right-hand turn to return to the landing strip. During this maneuver, the right wingtip struck the ground, causing the wing to break and the aircraft to impact the ground violently. The pilot in the front seat sustained fatal injuries at the scene, while the instructor in the rear seat was seriously injured. The glider was destroyed.
The investigation
The SUB investigation reconstructed the flight sequence using eyewitness accounts, statements from the towplane pilot, and the instructor in the glider. The investigation examined the maintenance and operational history of both aircraft, the fuel levels in the towplane, and the flight conditions.
Investigators found that the towplane pilot had performed 13 successful tow starts earlier that day and was nearing exhaustion. While the towplane's fuel gauge indicated more than half a tank, the investigation revealed that the actual fuel remaining in the system was only approximately 0.75 liters. The investigation also looked into the procedures for emergency releases and the club's operational practices regarding pilot fatigue and fuel verification.