What happened
On January 6, 2022, a Schleicher ASK 16, registration HB-2033, was performing a private VFR flight from Grenchen to Wangen-Lachen. Following a period of snowfall and low cloud cover earlier in the day, the pilot had paused at Wangen-Lachen to wait for better weather. After a two-and-a single-hour break, the pilot returned to the aircraft to fly back to Grenchen.
During the pre-flight inspection, the pilot removed approximately 1 to 2 cm of accumulated snow from the airframe. After a successful engine run-up, the pilot commenced the takeoff roll on runway 26. While the aircraft initially accelerated normally, reaching a ground speed of 70 km/h after approximately 200 meters, the pilot noted that the subsequent acceleration felt abnormal. The aircraft eventually lifted off at a ground speed of 83 km/h after a total roll of 380 meters.
Upon rotation, the aircraft entered a slight right turn and remained at an altitude of only a few meters above the ground. Unable to climb out of the ground effect, the aircraft drifted approximately 100 meters past the shoreline and impacted the surface of the lake. The aircraft sustained heavy damage to the propeller, landing gear, engine cowling, fuselage, and wings, as well as water damage to the engine. The pilot, who was the sole occupant, sustained one minor injury and was rescued by a nearby boat shortly after the incident.
The investigation
Investigators examined the aircraft, engine, and propeller, finding no pre-existing technical defects that could have contributed to the accident. While water ingress prevented a post-accident engine test, GPS data and pilot testimony indicated the engine functioned normally throughout the flight. The investigation focused on the discrepancy between the expected takeoff performance and the actual flight path.
Findings
- The aircraft's takeoff mass was approximately 660 kg, well within the maximum allowable limit of 750 kg.
- The engine performance remained consistent, as the pilot reported no unusual noises and did not alter the throttle setting during the incident.
- Residual moisture on the wing surfaces likely increased the required takeoff speed beyond the standard 70 km/h, leading to a loss of climb performance.
- The aircraft was unable to overcome induced drag to climb out of the ground effect, resulting in the forced landing.