Synopsis
On 12 August 2011, at approximately 17:40, an Aero AT-3 R100 aircraft, registration HB-SRA, made an emergency landing in Worbboden, Worb/BE, Switzerland, due to an engine stoppage caused by fuel shortage. The aircraft subsequently collided with obstacles, sustaining heavy damage. Both occupants were uninjured.
History of the Flight
The aircraft was operated by Alp-Air Bern AG and owned by Alp-Aircraft GmbH. Earlier that day, the flight instructor had filled the aircraft with 34 gallons of gasoline, and the fuel on board was recorded as 70 litres based on the fill level. A trainee pilot conducted a solo navigation flight of 2 hours 29 minutes, with intermediate landings at Ecuvillens and Wangen-Lachen. After returning to Bern-Belp Airport, the flight instructor and another trainee flew four circuits, consuming 26 minutes of flying time. The remaining fuel was measured at 30 litres using a dipstick.
At approximately 16:00, the flight instructor met another trainee pilot for a planned training flight of about 40 minutes. The trainee measured the fuel level with a dipstick and estimated it between 22 and 25 litres, confirmed by the flight instructor. After pre-flight checks, the aircraft took off from runway 32 at 17:02. The flight proceeded to the Kirchberg area for simulated aerodrome circuits. After three simulated approaches, the return flight began. Shortly before entering the control area, the engine began to stutter and lose power. The flight instructor attempted various throttle positions without success, and the engine quit completely. At 17:39:30, the flight instructor declared an emergency landing.
Due to insufficient altitude to diagnose the problem, the flight instructor focused on landing. A first field was rejected due to a high-voltage line. A second field in Worbboden was chosen. After extending flaps and closing the fuel valve, the aircraft touched down slightly diagonally. During rollout, it struck a field of sunflowers, causing the aircraft to turn right and come to a halt after about 25 meters. Both occupants exited unassisted; no fire occurred.
Aircraft Information
The Aero AT-3 R100 (serial number 051, manufactured 2009) is a two-seat, low-wing, piston-engine training aircraft with fixed tricycle landing gear. It is powered by a Rotax 912 S2 engine. The maximum take-off and landing mass is 582 kg. The airframe had 2365 landings at the time of the accident.
Meteorological Information
The weather at Bern-Belp Airport at 15:50 UTC (17:50 local time) was overcast with base at 8000 feet, visibility over 10 km, wind from 280 degrees at 7 knots, temperature 22°C, dewpoint 9°C, QNH 1015 hPa. Over the accident site, wind was from the western sector at 5 to 10 knots. Visibility was 60 km in the region. Lighting conditions were daylight.
Causes
According to the investigation, the accident resulted from an emergency landing with subsequent collision with obstacles because the engine stopped in flight due to lack of fuel. Contributing factors included:
- Insufficient design of the fuel quantity indication system.
- Incorrect manufacturer information regarding tank contents.
- The fuel quantity being too tight for this flight mission.