Accident Overview
On 9 September 1986 at 1440 local time, a Cessna F152 (registration HB-CGZ) operated by Flugsportgruppe Zürcher Oberland was performing a local flight from Flugfeld Speck-Fehraltorf. The pilot, a Swiss private pilot born in 1946, and his father as passenger were on board. After departing from runway 12, the aircraft failed to gain sufficient altitude and executed an emergency landing, colliding with railway infrastructure. The aircraft sustained heavy damage; both occupants were lightly or not injured. Third-party damage was limited to Swiss Federal Railways (SBB) installations.
Sequence of Events
The pilot had refueled the aircraft to approximately three-quarters full. Before takeoff, all checklist items were completed with no anomalies noted. During the takeoff roll, the pilot applied full throttle, reaching 2500 rpm and about 55 knots before lifting off. He then lowered the nose to accelerate, but reaching 65 knots took longer than expected. After reaching 65 knots and initiating a climb, the engine began to misfire intermittently. Speed decayed, and the pilot realized he would not clear the railway line ahead. He decided to perform an emergency landing before the railway tracks. The aircraft touched down but subsequently impacted the railway embankment.
Observers in the flight office noted that after lifting off, the aircraft gained only 5–10 meters of height in a nose-high attitude and entered a shallow left turn before disappearing behind houses. One observer radioed "Vollgas, Vorwärmung aus!" (full throttle, carburetor heat off) but noted no response. Another witness, located about 300 meters past the runway end and 200 meters left of the runway axis, reported the aircraft at 5–10 meters above a cornfield with engine sound noticeably quieter than normal but operating regularly without misfire.
Aircraft and Pilot
The pilot held a valid private pilot license with a total of 165 flying hours, 127 hours on type, and 1:29 hours in the preceding 90 days. The aircraft was a Cessna F152 (HB-CGZ), certified for VFR operations. The takeoff weight was 773.4 kg, exceeding the maximum allowable takeoff weight of 758 kg. The center of gravity was at 0.83 m, within the permissible range for 758 kg but slightly outside given the overweight condition.
Technical Findings
A technical examination of the aircraft revealed that the right main landing gear brake had a condition where the brake lining, which was riveted to the brake plate, protruded radially and contacted the periphery of the brake disc hub. This caused a slight braking effect on the right wheel. The engine had been run during a 100-hour inspection on the previous days; no evidence was found to explain the perceived lack of full power during takeoff. Witnesses with technical expertise opined that the engine did not deliver full takeoff power based on its sound, which was described as smooth but lower in power, similar to operation with carburetor heat on or on a single magneto. However, no specific mechanical cause was identified.
Environmental Conditions
Weather at the scene was reported as 3–5/8 cloud cover at 1,500 m and 6–8/8 at 3,000 m, visibility over 8 km, wind northeast at 10 knots gusting to 20 knots, temperature 16°–18°C, and QNH 1015 hPa. A witness at the airfield reported wind approximately 050° at 5–10 knots, temperature 18°C, little turbulence, and a dry, hard runway.
Probable Cause
The accident was due to an emergency landing on unfavorable terrain as a result of insufficient acceleration during takeoff. Contributing elements included a takeoff not aborted in time, an engine probably not delivering full power for an unknown reason, a slightly braked right main wheel, high takeoff weight, and low flight experience.