What happened
On November 16, 1968, a Cessna 150 (registration HB-CTE) attempted a takeoff from the Wangen-Lachen airfield in Switzerland. After accelerating down the paved runway, the aircraft briefly lifted off but failed to maintain altitude. The pilot attempted a second rotation near the end of the runway, but the aircraft lost lift and descended into the upper part of Lake Zurich, approximately 70 meters from the shore. The aircraft struck the water with significant force. The pilot and one passenger were able to exit the sinking aircraft and swim to the shore; both escaped without injury.
The investigation
The investigation examined the aircraft's condition, the pilot's experience, and the environmental factors present at the time of the accident. The aircraft, which had only 120 hours on the engine and airframe, was relatively new. Investigators inspected the engine and carburetor, finding no evidence of mechanical failure or technical defects. The investigation also reviewed the pilot's flight training and recent experience on the Cessna 150 type. Additionally, the physical state of the aircraft following the impact and the weather conditions—including light snowfall and temperatures near 0°C—were analyzed.
Findings
The investigation established that the aircraft suffered from insufficient lift during the takeoff sequence. While the pilot and witnesses noted a possible reduction in engine power, no mechanical cause for such a drop was found. Two primary contributing factors were considered:
- The presence of residual snow on the upper surface of the wings, as the pilot had only partially cleared the snow during pre-flight preparations. This could have significantly reduced the maximum lift coefficient and increased drag.
- The possibility of carburetor icing, given the cold, moist conditions and the fact that the carburetor heat was not applied during the initial stages of the takeoff roll.
Ultimately, the loss of lift was the decisive factor that prevented the aircraft from climbing and necessitated the emergency water landing.