What happened
On July 17, 1971, a Smarard HB-SEC was preparing for a private flight from Zweisimmen military airfield to Bern-Belp. The flight was operated by a flight instructor accompanied by one passenger. Earlier that day, the pilot had been conducting glider towing and instructional maneuvers at the airfield.
As the aircraft reached a speed of approximately 90 km/h during the takeoff roll, a powerful gust of wind abruptly lifted the aircraft by 4 to 6 meters. Although the pilot managed to maintain the aircraft's attitude and prevent a stall or roll, the intensity of the wind prompted an immediate decision to abort the takeoff. The pilot applied the brakes and brought the aircraft to a stop at the end of the runway in a three-point attitude.
During the aborted takeoff, the aircraft overran the runway, breached a barbed-wire fence, and briefly lifted off the ground again before impacting the terrain. The aircraft veered to the right and slid sideways into a line of trees, where the left wing became lodged between the trunks. A small smoldering fire developed in the engine compartment but was extinguished using carbonated mineral water.
There were no injuries to the pilot or the passenger, though the aircraft sustained heavy damage.
The investigation
The investigation examined the meteorological conditions and the pilot's decision-making process. While the pilot had contacted Bern-Belp airport via telephone approximately 20 minutes before takeoff to inquire about weather conditions—receiving a report of good visibility and moderate winds—the local situation at Zweisimmen was rapidly deteriorating.
Investigators found no evidence of mechanical failure or technical defects in the aircraft. The pilot's training record and health were also found to be in good standing, with no prior incidents noted in his dossier.
Findings
- The local weather was extremely unstable due to the movement of a cold front following a period of foehn-like conditions. This resulted in unpredictable, heavy turbulence and wind gusts exceeding 30 knots from various directions.
- The pilot underestimated the rapid changes in meteorological conditions typical of the Alpine region.
- The decision to proceed with the takeoff under such critical weather conditions was incorrect.