Introduction
On 1 November 1980, a Piper PA-28-180, registered HB-OLI, operated by the Flugplatzverein Zweisimmen and owned by the Motorfluggruppe Obersimmental, departed from Zweisimmen Airfield on a private VFR flight to Ascona. The aircraft was occupied by two pilots (Pilot X and Pilot Y) and two passengers. The accident occurred during the initial climb phase near Mannried, a locality within the municipality of Zweisimmen, Bern.
Flight History
At 0800 hours, the two private pilots met at Zweisimmen Airfield. Pilot Y had observed fair weather from his home in Lenk and contacted the Zurich flight weather center, but no duty forecaster was available. He did not seek further weather information, confident that good weather would persist. Pilot X had not obtained any weather data that day. Upon arriving at the airfield, the pilots noted a high fog layer with a base approximately 200 m above ground. After refueling and preparing the aircraft, they waited in a restaurant. At around 0900, they returned to the airfield, noting that the fog was still present but that sunlight was visible toward St. Stephan. They drove to a tea room in St. Stephan to wait for the fog to lift.
When the sun began to shine in St. Stephan, the group returned to the airfield. The fog had not fully dissipated, but its base had risen slightly. The pilots assessed that a departure from Runway 35, followed by a turn and a climb toward St. Stephan and Lenk, would be feasible. Pilot Y filed a flight plan for Ascona, listing a departure time of 1040 hours and an estimated flight time of one hour. Initially, he listed himself as pilot and X as passenger, but shortly before departure he swapped the names. Pilot X wanted to be the responsible pilot, as he was familiar with the destination airfield. It was agreed that Y would handle radio communications.
The aircraft took off from Runway 35 at 1050 hours. The takeoff was normal. During the initial climb, Pilot X retracted the flaps at 90 mph and switched off the booster pump. According to Pilot X, Y then said "gimmer ne" (give me), after which X released the controls and raised his hands, and Y took over. Y vehemently denied this. The subsequent flight was described by X: near the Manneberg, he asked Y if he should fly ahead because it was unclear if fog was behind the mountain. Y was holding the controls stiffly, and the aircraft banked about 15° to the right. X then resumed control and initiated a 30° bank turn. Suddenly, Y pulled the control column fully back. X shouted and pushed forward. During this maneuver, the aircraft briefly entered fog. X intended to land on Runway 17 of Zweisimmen, but Y strongly pulled the controls to the left, and the aircraft flew toward a hillside. Due to proximity and low speed, X could not turn back toward the airfield. He performed a landing uphill, with the aircraft in a banked attitude and engine throttled back.
Pilot Y suffered a severe concussion and external injuries, resulting in retrograde amnesia; he could not recall the flight after passing south of the Manneberg. The other occupants sustained minor injuries.
Findings
- Both pilots held valid private pilot licenses and were qualified for VFR flight, but they did not hold instrument flight or radiotelephony endorsements.
- No pre-existing medical conditions were identified for either pilot.
- The aircraft was airworthy, and no pre-existing technical defects were found that could have influenced the accident. Weight and balance were within limits. The flaps were retracted at impact.
- Weather at the accident site: high fog, base around 1000 m AMSL, top around 1500 m AMSL; visibility 1–2 km; wind variable around 3 knots; temperature 4°C, dew point 3°C, QNH 1024 hPa. En route weather to Ascona included fog with top around 1300 m AMSL, visibility in Visp 2–5 km, and cloudy conditions south of the Alps with bases 1500–2000 m AMSL. The GAFOR Switzerland charts indicated closed conditions for several routes.
- The fog base at the accident site at the time of the investigation (early afternoon) was approximately 1120 m AMSL, about 40 m above the wreckage and 187 m above the airfield. According to witnesses, the fog had not changed significantly since morning.
- Pilot Y stated that before takeoff he could clearly see the rocky areas in the Schlattwald forest, located about 400 m above the airfield. However, a witness at the sawmill near Mannried reported that he could not see the Schlattwald ridge due to fog.
- According to the standard traffic pattern for Zweisimmen, after departure from Runway 35, a right-hand turn is to be executed.
Cause
The accident was attributed to insufficient visibility.
Contributing factors: insufficient flight preparation, inappropriate flight technique, and low pilot experience.