What happened
On April 10, 1971, at approximately 16:45, a Ka-6 CR glider, registration HB-796, was involved in an accident in the Gurtentäli region, west of Bern. The pilot had departed from Bern Airport at 15:45 for a one-hour training flight via aero-tow. After releasing from the tow plane, the pilot reached an altitude of approximately 1,700 meters near the Längenberg ridge but subsequently descended to 1,250 meters as the flight progressed toward the Schwarzwasser bridge.
While attempting to return to the windward side of the ridge, the pilot encountered significant sinking air, which depleted the aircraft's altitude. This forced an unplanned off-field landing in the narrow, obstacle-dense Gurtentäli valley. During the approach, the pilot crossed a 16-kV power line and attempted to gain enough airspeed to clear a secondary 220/380 V telephone line. Finding insufficient energy to climb over the second obstacle, the pilot opted to fly beneath it. To avoid a utility pole located on the left, the pilot executed a sharp right turn, causing the right wingtip to strike the soft ground. The impact caused the left wing to tear through telephone wires, and the aircraft's nose struck the ground heavily.
The investigation
The investigation established that the pilot held a valid glider license with appropriate ratings for towing and passenger flights. The aircraft, a wooden single-seat high-wing glider, was also fully compliant with all airworthiness requirements. Investigators examined the structural failure of the fuselage and determined there were no pre-existing mechanical defects in the airframe.
Findings
- The primary cause of the accident was a delayed decision to land, which left the pilot with insufficient time to select a suitable landing site or execute a proper approach.
- The necessity for the emergency landing was caused by the pilot flying too far behind the ridge line, resulting in entrapment in sinking air currents.
- The wing strike was a direct result of an abrupt maneuver intended to avoid a utility pole during the final approach.