What happened
On the afternoon of September 21, 2011, a flight student and a flight instructor assistant prepared for training flights at Landshut-Ellermühle airfield. Due to a delay in their arrival, the flight preparations began later than originally planned. At 18:16, the Rans S6 Coyote II departed from runway 07. Shortly after takeoff, witnesses observed the aircraft banking heavily to the left at an altitude of approximately 60 meters before entering a steep descent.
Despite attempts to recover the aircraft before impact, the ultralight crashed into a harvested field near the airfield. The aircraft sustained heavy damage, and the two occupants sustained serious injuries.
The investigation
The BFU examined the aircraft, the engine, and the fuel system following the accident. The investigation focused on the engine's performance and the condition of the fuel tanks. Technical inspections of the Rans S6 Coyote II revealed that the control surfaces and the airframe were intact, with no mechanical failures found in the steering systems. However, investigators discovered water present in the wing tanks and the additional fuselage tank.
Testing of the engine confirmed that introducing even small amounts of water (10 ml) into the float chambers caused the engine to fail within 10 to 15 seconds. The investigation also noted that the aircraft's additional fuselage tank modification lacked an effective way to drain accumulated liquids.