What happened
On April 2, 2011, an ASK 21 glider, registration HB-1982, was being prepared for a check flight at Hausen am Albis airfield. The glider was being towed by a Varga 2180, registration HB-DCU. The takeoff was conducted on a grass runway, despite the availability of a paved runway.
During the takeoff roll, the tow aircraft experienced difficulty lifting its nose wheel, likely due to the soft surface of the grass. The pilot of the HB-DCU decided to abort the takeoff, reducing engine power and releasing the tow cable while steering the aircraft toward the paved runway. The glider, which had already lifted off the ground, was unable to follow the tow aircraft's sudden change in direction. The pilot of the HB-1982 attempted to land in a field beyond a nearby stream, but the glider's nose dipped, causing it to strike an embankment. The impact resulted in serious injuries to the pilot and heavy damage to the glider's fuselage.
The investigation
SUST examined the flight paths using Flarm collision warning data from both aircraft. The investigation focused on the runway conditions, the takeoff sequence, and the crew's decision-making. Investigators noted that a previous takeoff on the same grass runway had been sluggish, which could have served as a warning. Additionally, the investigation found that the glider's airspeed and altitude instruments had been covered with paper for the seasonal focus of the flight school, which prevented the pilot from detecting the impending stall during the emergency maneuver.
Findings
- The primary cause of the accident was the collision of the glider with an embankment because the grass runway was inadequate for the takeoff.
- The subsequent abort of the takeoff was executed inappropriately, leading to a loss of control of the glider.
- The crew of the HB-1982 failed to seek information from the previous flight crew regarding their takeoff performance on the grass runway.
- There was a lack of mental preparation among the glider crew for a potential takeoff abort.
- The glider may have been positioned too high in the tow.