Accident Overview
On June 7, 1976, at approximately 1459 hours local time, a Schleicher K 8 B glider (registration HB-818) crashed near Chlei Gigi, about 2 kilometers east-southeast of Wolfenschiessen, Canton Nidwalden, Switzerland. The accident occurred during a ridge-soaring flight that began earlier that afternoon.
Flight Sequence
The pilot, who held a student pilot license with a limited solo authorization, departed Buochs airfield at 1439 hours under tow. The tow was released at the northwest flank of Buochserhorn at an altitude of approximately 1000–1100 meters above sea level (m/M). Using ridge lift, the glider climbed to the summit elevation of 1807 m/M and joined a colleague flying another K 8. The two pilots had agreed to fly together toward the Walenstöcke area, with the less experienced pilot (the accident pilot) flying behind.
After receiving a signal from the lead pilot—a roll of the glider and a hand gesture pointing toward Haldi—the flight proceeded southward along the east side of the Engelberg valley. The accident pilot followed, positioned slightly left, about 100 meters behind and 20 meters lower.
Near the north side of Chlei Gigi, the pilot detected lift and turned left into the area. Immediately, he saw a cable directly ahead. The glider passed just under a cable that sloped downward to the right; the right wingtip, approximately 1 meter from the end, struck the cable. The impact tore off a large section of the outer right wing, which remained hanging on the cable. The cockpit canopy also detached. The glider subsequently crashed at an elevation of about 1640 m/M.
Damage and Injuries
The pilot suffered serious injuries. The glider was destroyed.
Pilot Information
The pilot, born in 1958, began flight training on March 21, 1976, in Buochs. He had passed the theoretical and practical examinations for a glider pilot license but had not yet completed the required 20 solo flights. On May 27, 1976, he received a temporary authorization valid for 30 days, permitting solo flights without instructor supervision. His total flight experience recorded in his logbook was 18 hours and 42 minutes with 68 landings, of which 6 hours and 37 minutes and 10 landings were on the accident aircraft type. He had performed 19 flights solo. No evidence of medical impairment was found.
Aircraft Information
The Schleicher K 8 B HB-818 was certified for flight. Examination revealed no pre-existing technical defects that could have influenced the accident. Weight and center of gravity were within prescribed limits.
Weather and Obstacle Information
At the accident time, weather was characterized by a high-pressure system. Cloud cover was 1/8 cumulus at 2000 m/M, visibility 20–30 kilometers. Surface wind was northerly at 5–10 knots; at 1500 m/M, northeast at 10 knots. Temperature at ground was 20°C with a dew point of 7°C; at 1500 m/M, the temperature was 8°C and dew point 7°C. QNH was 1017 hPa. Sun azimuth was 245° with an elevation of 50°.
The entire east side of the Engelberg valley was marked with red hatching on the Swiss aeronautical obstacle chart (AIP MAP 4), indicating a zone with numerous and high obstacles. The transport cable struck had a maximum ground clearance of 55 to 60 meters. According to prevailing guidelines, such a cable did not require marking or special inclusion on the obstacle chart.
Regulatory Context
Swiss visual flight rules (Art. 60) generally prohibited flight below 150 meters above ground except during takeoff and landing, or with special authorization. However, ridge soaring with gliders (Art. 83) permitted a minimum height of 60 meters above ground, provided that no groups of people, herds, or wildlife were overflown and that the pilot had verified before flight that no collision hazard with any obstacle existed; additionally, a horizontal distance of at least 60 meters from the slope was required.
Assessment and Probable Cause
The investigation determined that the pilot had failed to check for obstacles along the intended flight route, particularly essential in mountainous terrain. By studying the obstacle chart, he could have obtained necessary information. He flew at approximately 60 meters above ground without verifying collision safety, indicating unfamiliarity with relevant regulations.
The probable cause was stated as:
- Inadequate flight preparation
- Non-observance of minimum flight altitude
Additionally, the pilot's very limited flight experience likely contributed to the accident.