What happened
On September 22, 2013, a Fläming Air FA 01 Peregrine SL ultralight aircraft was engaged in a multi-leg flight starting from Stendal. After a stop in Ballenstedt and a subsequent leg to Oehna, the pilot began the return flight to Stendal at 16:15 local time. Prior to departure from Oehna, the pilot had confirmed to witnesses that sufficient fuel was on board.
At 17:04, the pilot contacted Stendal tower to report an intention to land. Approximately four minutes later, the pilot notified the flight leader of an ongoing problem. Shortly thereafter, emergency services were notified of an aircraft crash on the southeastern outskirts of Stendal. The aircraft had collided with a treeline at an altitude of approximately 15 meters, causing the wings to separate from the fuselage before the wreckage impacted a meadow. The impact resulted in two fatalities and the total destruction of the aircraft.
Witnesses near the site reported seeing the aircraft flying at a very low altitude with unusual engine noises and observed the aircraft performing several oscillations around its longitudinal axis before the collision.
The investigation
The BFU investigation focused on the mechanical state of the engine and the fuel system. Investigators examined the engine's carburetors at the manufacturer's facility, which found no defects capable of causing engine failure. The investigation also utilized video footage from a Samsung Galaxy Tab carried on board, which captured the pilot switching fuel tanks from the right to the left tank.
Technical analysis of the fuel gauges and tank sensors was conducted to determine if the pilot had been accurately informed of the remaining fuel levels. The fuel system utilized plastic floats that changed electrical resistance to indicate levels on analog instruments.
Findings
While the carburetors were found to be in good working order, the investigation identified a critical issue with the fuel level indication. The BFU discovered a functional restriction in the movement of the left tank sensor arm specifically when the fuel level reached the half-tank mark. This mechanical limitation caused the fuel gauge to fluctuate erratically during the tank switchover, potentially obscuring the true fuel state from the pilot. Although the aircraft's takeoff weight and center of gravity were within limits, the unreliable indication contributed to the pilot's inability to accurately monitor fuel reserves during the final leg of the flight.