What happened
On July 21, 2000, a Vogt LO 100 Zwergreiher glider was performing a training flight as part of an aerobatic competition at the Landau-Ebenberg glider field. The flight began with a tow takeoff, and after unhooking at 1,200 meters, the pilot commenced a series of aerobatic maneuvers, including a loop and a 45-degree downward bank followed by a half-roll.
During the pull-out phase following the downward roll, the right wing of the aircraft structurally failed. The fuselage, along with the left wing and tail section, entered a spin and crashed onto a paved surface. The pilot managed to exit the aircraft at an altitude between 80 and 100 meters and landed safely via an emergency parachute, sustaining only minor abrasions and bruises.
The investigation
The BFU investigation examined the wreckage and the aircraft's maintenance history. Debris from the right wing, including the aileron and leading edge, was found scattered approximately 300 meters from the main wreckage. An accelerometer recovered from the wreckage recorded a peak acceleration of +7.2 g.
Investigators reviewed the aircraft's technical specifications, noting that while the design required a load factor of 6.0 for symmetrical recovery, the aircraft's takeoff weight was a critical factor. The investigation also looked into a previous landing accident in June 199lar, which had caused damage to the fuselage and tail, though the wings had been inspected and cleared at that time. The investigators could not definitively determine if any internal damage to the spar remained from that previous incident.
Findings
Several contributing factors were identified that likely led to the structural failure:
- Excessive takeoff weight: The total takeoff mass was 280 kg, which exceeded the maximum allowable mass of 245 kg specified for aerobatic flight.
- Pilot error: The pilot may have committed a control error during the aerobatic maneuvers.
- Potential structural weakness: The possibility of undetected internal damage to the wing spar from a previous accident could not be ruled out.
- Atmospheric conditions: The presence of unquantified gusts during the flight may have contributed to the load on the wing.
While the recorded 7.2 g acceleration was within the ultimate safety factor of the design, the combination of the overweight condition and the high-load maneuvers likely exhausted the remaining structural margin.