What happened
On July 12, 2020, at approximately 12:21 UTC, a Schempp-Hirth Ventus cM glider departed from Linz-Ost Airport (LOLO) via a tow-assisted takeoff. The aircraft was connected to the towplane using a center-of-gravity coupling rather than a standard nose coupling.
Shortly after takeoff, the glider began to oscillate significantly behind the towplane. The pilot attempted to correct the aircraft's position, but the glider repeatedly climbed above and dropped below the towplane's flight path, a phenomenon that occurred three times in total.
As the towplane reached an altitude of approximately 50 meters above ground level, the pilot initiated a right-hand turn to avoid high-voltage power lines, following standard departure procedures for the airfield. At this moment, the glider was in a high, nearly stalled state. In an attempt to stabilize the aircraft, the pilot deployed the air brakes. This maneuver caused the towline's weak link to break, leading to a rapid loss of airspeed. The glider subsequently experienced a stall on the right wing and plummeted into the Danube River. The pilot sustained severe injuries.
The investigation
The SUB investigation reconstructed the flight path using eyewitness accounts and physical evidence. The investigation examined the aircraft's technical condition, the pilot's experience, and the environmental factors present at the time of the accident. The investigation also reviewed the aircraft's configuration, specifically noting the use of the center-of-gravity coupling.
Findings
- The glider was properly registered and maintained, with no pre-existing technical defects found.
- The pilot held all necessary valid licenses, though flight experience on this specific aircraft type was low.
- Meteorological conditions were suitable for VFR flight.
- The aircraft's weight and center of gravity were within permissible limits.
- The primary cause of the accident was the oscillatory motion (pendulum effect) of the glider during the tow operation.
- A contributing factor was the low altitude of the glider during the occurrence of the instability.