What happened
On December 26, 1975, a Cessna 150G, registration HB-CSH, departed from Triengen for a private VFR flight. The purpose of the flight was to provide a 15-year-old passenger with an aerial view of his home near Rothenburg. After departing, the aircraft climbed to approximately 300 meters and followed the northeastern shore of Lake Sempach.
Upon reaching Neuenkirch, the pilot executed a left turn toward the railway line between Sursee and Luzern. During this maneuver, the aircraft's speed and altitude were reduced. The flight path then transitioned into a wide left turn at an altitude between 15 and 30 meters to locate a specific farmhouse near Bärtiswil. While passing the property, the left wing of the aircraft struck a 16-meter-tall tree located roughly 60 meters from the house. Following the contact, the pilot applied full power and climbed directly back to Triengen, landing safely at 10:25 AM.
There were no injuries to the pilot or the passenger, though the aircraft sustained minor damage.
The investigation
The investigation examined the pilot's credentials, the aircraft's mechanical state, and the environmental conditions at the time of the incident. The pilot held a valid private pilot license with approximately 40 hours of total flight time. No medical or psychological issues were identified that would have impaired his ability to fly.
Technical inspections of HB-CSH revealed no pre-existing mechanical defects capable of causing the accident, and the aircraft's weight and center of gravity were within legal limits. Weather conditions involved a stratus cloud layer between 1500 and 1800 meters, visibility of 8–10 km, and light, variable winds. The ground was covered in fresh snow, which may have created diffuse lighting or glare from the sun.