Introduction
On 6 June 1970, a Piper PA-18 "Super Cub" (registration HB-OYM) sustained heavy damage in an accident at Courtelary aerodrome, Switzerland. The pilot, who was uninjured, had been performing glider towing flights for the Groupe de vol à voile de Bienne.
Aircraft and Pilot Information
The aircraft, built in 1965, was powered by a Lycoming O-320-A2B engine producing 150 hp and equipped with a Sensenich M74DM propeller. It had accumulated 1,087 flight hours and 8,679 landings, with its last 50-hour check performed on 30 October 1969 after 992 hours. The pilot, born in 1941, held a private pilot license issued 29 November 1967 and a professional pilot license issued 11 March 1970. He had a total of 260 flight hours and 1,200 landings, including 90 hours and 520 landings on the Piper PA-18. On the day of the accident, the pilot had flown 3 hours and performed 24 landings, all on towing flights.
Flight Sequence
The accident occurred at 1748 local time after the pilot's 25th flight of the day. After releasing the tow rope, he turned for the final approach to runway 06. Feeling too high, the pilot initiated a sideslip with flaps extended 15° and the stabilizer set slightly nose-up for landing. He reported an indicated airspeed of 60 mph, below the recommended approach speed of 70 mph specified in the owner's manual. As he neared the runway threshold, the pilot observed an irregular bise wind of 10 knots with possible gusts up to 20 knots. Two to three meters above the ground, he attempted to recover from the sideslip but stated that the aircraft did not respond, despite having pulled the control stick fully aft. The aircraft touched down left wheel first approximately 2–3 meters before the start of the grass runway, skidding slightly to the right. After touchdown, witnesses noted damage to the aircraft.
Weather Conditions
Meteorological reports indicated 7/8 cloud cover, wind from 050–080° at 10–15 knots, visibility 20 km, light turbulence from the bise, and possible gusts to 20 knots. The sun elevation was 023° with an azimuth of 279°.
Damage and Findings
The pilot remained uninjured. The aircraft sustained heavy damage, including distorted landing gear and fuselage. No third-party damage occurred. Post-accident inspection found slack control cables, but this was attributed to the fuselage deformation, and no evidence of pre-existing structural issues was discovered.
Discussion and Conclusion
The investigation noted that the pilot had the appropriate certifications and was well-trained on the aircraft. It suggested that fatigue may have possibly contributed to the accident. The sideslip maneuver, with flaps extended, requires sufficient airspeed; the recommended approach speed for the Piper Super Cub is 70 mph. The pilot's reported speed of 60 mph was insufficient, especially in the existing turbulent conditions. Near the ground, speed likely decreased further, rendering the controls ineffective. Recovery would have required increasing speed by diving slightly and applying power, but altitude was insufficient. The pilot's intention to achieve a very short landing to reach the glider park located at the start of the runway may have influenced his decision. The official conclusion attributed the accident to the pilot waiting too long to recover the aircraft while flying in a sideslip at insufficient speed with flaps extended.