Flight History
On Saturday, 7 December 1963, at 15:35, a Piper Cub J3C (registration HB-OGC) departed from Beromünster airfield with a pilot and one passenger for a short private flight in the vicinity. The high fog layer was only about 80-100 metres above ground, with isolated patches hanging lower in the south and west. The pilot did not refuel, despite being warned that the fuel indicator showed approximately 15 litres remaining. The aircraft had flown 100 minutes since last refuelling.
Shortly after takeoff, while turning onto the crosswind leg at about 60 metres above ground, the pilot entered cloud patches. Unable to regain visual contact with the ground within a reasonable time, he decided to climb through the fog layer. After about 4-5 seconds he emerged into sunlight.
He then flew south, hoping to find clear conditions at Kägiswil, but observed that the fog extended beyond Kägiswil and Sarnen. With limited fuel, he attempted to reach Engelberg. Shortly after entering the Engelberg valley, the fuel indicator approached zero, and the pilot decided against continuing to Engelberg (still over 10 km away). After circling near Dallenwil, he identified the Alp Gibel near Niederrickenbach as a suitable landing area. During the approach glide, the engine began to misfire. The aircraft touched down at 16:05, the landing gear was torn off by uneven terrain, and after about 70 metres of sliding, the aircraft came to rest on its belly.
Investigation
The investigation was completed with the delivery of the investigation report on 13 May 1964. The aircraft was a two-seat, strut-braced shoulder-wing monoplane of mixed construction, powered by a 65 hp Continental A-65 engine. It was not certified for instrument flight. The maximum takeoff weight was 550 kg; the weight at the time of the accident was about 480 kg. The centre of gravity remained within limits. Cruising speed was about 110 km/h. The fuel tank capacity was 45 litres; fuel consumption in cruise was about 17 litres per hour. Fuel quantity was indicated by a cork float with a rod protruding through the tank cap; at 15 litres the rod extended about 7 cm.
Weather reports indicated a closed high fog layer with cloud base at 700-800 m above sea level and top at 1000-1200 m. The fog extended into the pre-alpine valleys. At the accident site, conditions were: at 500 m: +2°C, 85% humidity; at 1000 m: -2°C, 100% humidity; at 1500 m: +2°C, 50% humidity.
Findings
At the accident site, the fuel indicator was near its lower stop. On 18 December 1963, an investigator found about 5-8 litres remaining in the tank; the indicator appeared normal and functional. On 29 January 1964, when the fuel tank was removed at Basel airport, about 15 litres were found, and the cork float was heavily worn and loosely attached to the indicator rod. It could not be determined whether fuel had been added or the indicator altered in the interim.
Conclusion
The investigation concluded that the emergency landing in unsuitable terrain became necessary because the pilot undertook a visual flight in weather that did not offer sufficient safety, and with an insufficient fuel reserve under those conditions.
Both occupants remained uninjured. The aircraft was heavily damaged during touchdown and subsequent sliding; additional damage occurred during recovery. Ground damage was minor.
A similar accident was noted (reference 1962/42 HB-OWS).