Summary
On 20 June 1961, the pilot of Piper Cub HB-OIS intended to fly from Bern to Kloten and back. He was accompanied by his father and his 5-year-old niece. The flight proceeded without incident until reaching the area of Lakes Sempach and Hallwil, where poor visibility led the pilot to abort the onward journey and return. During the return flight, the pilot lost orientation, and because his passengers were experiencing discomfort, he decided to land in an open field.
The landing was uneventful on a field near Huttwil. After reorienting himself, the pilot resolved to fly back to Bern immediately. When the aircraft took off at 1530 local time, it had already reached the end of the chosen takeoff path. In the adjacent grain field, the aircraft made ground contact again, significantly reducing speed. The pilot maintained full throttle and continued across further fields until the landing gear collided with an uneven ground feature, causing the aircraft to overturn. The pilot and his father sustained minor injuries, while the child was unharmed. The aircraft suffered substantial damage.
Investigation
The Bureau for Aircraft Accident Investigations was notified at 1550 local time by the chief of Bern airport. The investigator arrived at the accident site to find conditions unchanged and began initial inquiries after contacting the cantonal police.
Pilot Information
The pilot was born in 1927. He began flight training on 23 October 1958 in Bern and received his private pilot license on 30 October 1959, valid until 13 February 1962, after repeating the exam due to insufficient performance. His total flight experience prior to the accident was 112 hours and 385 landings, of which about 10 hours and 20 landings occurred in the preceding three months. The pilot flew only the accident aircraft type. He had no prior accidents or reported violations. His last medical examination on 10 February 1961 found him fit. He began the flight well-rested, and no health issues were indicated.
Aircraft Information
The aircraft was a Piper J3-C, registered HB-OIS. It was a strutted high-wing monoplane with tandem seating, of mixed construction, built in 1944. The engine was a Continental C-85-12 (85 hp) built in 1947, with a metal McCauley CM 7176 fixed-pitch propeller. Owner and operator: "OIS"-Club. The aircraft was imported from U.S. military surplus in 1946 with unknown total flight hours. After arrival in Switzerland, it accumulated 1485 flight hours until a hangar fire in April 1956. Subsequently, the aircraft was rebuilt by three owners: fuselage, landing gear, and tail surfaces were original; wings were new. The engine, with 500 total hours, came from another crashed aircraft and underwent a major overhaul before installation. The airworthiness certificate was issued on 28 August 1958, valid until 27 August 1961. The last inspection by the Federal Air Office was on 25 October 1960. The last 100-hour check (by Alpar AG in Bern) occurred after 717 operating hours since rebuild, during which elevator and rudder bolts and the right tire were replaced.
The aircraft was equipped with a VHF radio (Mitchell Avigator). Fuel system had two wing tanks (2 × 40 liters).
Weight: empty weight (including radio) 402 kg; maximum payload 178 kg; maximum takeoff weight 580 kg. The pilot was aware of the maximum payload. Weight at Bern departure: empty 402 kg, fuel and oil about 46 kg, pilot 75 kg, passengers 70+20=90 kg, giving a takeoff weight of about 613 kg. Weight at Huttwil departure: empty 402 kg, fuel and oil about 26 kg, pilot 75 kg, passengers 90 kg, total about 593 kg. Thus, the aircraft was overloaded at both departures. The center of gravity remained within limits.
At the accident site, the aircraft was inverted opposite the takeoff direction. Both propeller blades were bent backward; the engine mount was kinked; the firewall and cowling were damaged; the air filter was torn off; the engine appeared not heavily damaged but required overhaul; cabin glazing was shattered; some fuselage tubes were bent; wings seemed undamaged but struts were partly kinked; the vertical fin and rudder were damaged; all control surfaces were attached and partially movable; the right landing gear was slightly deformed; wheels did not rotate freely.
Cockpit controls: master switch off; ignition off; throttle mid-position; mixture rich; fuel pump unlatched; carburetor heat off; fuel cock open to left tank (left tank ~20 L, right ~10 L); rear control stick removed; trim slightly nose-heavy.
Further examination of the landing gear revealed that the slight binding of both wheels was pre-existing, not caused by the accident. The brake linings were non-original, made by a co-owner and installed without the knowledge of the inspecting officer during rebuild. The material and dimensions deviated significantly from original; some elements jammed, and return springs were missing. Measurements showed constant brake drag requiring an average total force of 7.7 kg to overcome. The pilot was aware of this, stating he noticed that the aircraft was harder to push than others.
Meteorological Conditions
According to the Swiss Meteorological Institute, the general situation was high pressure with light east wind and hazy broken clouds over the Mittelland and adjacent pre-Alps. At Huttwil: total cloud cover 4/8 to 6/8, with 2/8 to 4/8 at 1500–1800 m; some cumulus above. Visibility 7–12 km, with lower values on the east side of Mount Napf due to weak blocking. Dense haze up to 1800 m reduced visibility to 10–15 km at 1500 m. Wind northeast 5–10 knots up to 1800 m, then veering to light southerly. Weak thermal turbulence. Temperature at 500 m: +24°C, humidity 60%; at 1500 m: +16°C, humidity 90%; at 4300 m: 0°C, humidity 40%. Pressure 7 mb above standard. At Zurich-Kloten, visibility at 1445 was 13 km, at 1515 was 11 km.
Terrain
The accident site was 1 km east of Huttwil, coordinates 632.200/218.200 at ~670 m. The pilot's takeoff direction was northwest, parallel to a shooting range. The used strip (mowed grain field) was 190 m long with a slight 1.5% upslope and uneven surface (transverse undulations), rather soft. Beyond the usable strip, five sections led to the overturn point: 1) 30 m grain (stalk height 80 cm); 2) 30 m cut hay; 3) 85 m short grass with a large broad depression about 1.70 m deep perpendicular to the takeoff roll; 4) 10 m dense grass 30 cm high; 5) 30 m grain (70 cm stalks). The boundary between the last grain field and the next section was a sharp step about 15 cm high that the gear could not overcome, causing the overturn.
Regulations
According to Article 24, paragraph 3, of the Implementing Ordinance to the Aviation Law of 5 June 1950, the required documents must be carried on board.