What happened
On September 9, 2015, a Comco Ikarus C42B ultralight aircraft was conducting a practical flight examination for a student pilot. The flight began at Rheinermark airfield, where the aircraft first flew to Münster Telgte before returning toward the original location. During the return leg, radar data indicated that the aircraft began a descent from approximately 2,100 ft AMSL.
As the aircraft approached the Iserlohn-Sümern airfield, it performed a left-hand turn at a very low altitude. Witnesses observed the aircraft flying over a wooded area adjacent to the airfield, where it entered a steep bank from an altitude of only 10 to 20 meters. The aircraft subsequently struck the ground, causing the airframe to be destroyed and resulting in one fatality (the examiner) and one serious injury (the student pilot).
The investigation
The BFU investigation focused on the flight parameters, aircraft weight, and the pilot's credentials. Investigators examined the wreckage and found no evidence of mechanical failure; the engine, carburetors, and spark plugs were all in functional condition. Radar data showed a continuous descent and a reduction in speed from 80 knots to approximately 60 knots prior to the impact, suggesting the crew was likely performing a simulated emergency landing maneuver.
Crucially, the investigation scrutinized the aircraft's weight and balance. While the official flight documentation listed weights that were within limits, the investigation revealed that the actual weights of the occupants were significantly higher than recorded. The examiner's weight was noted to be much higher than the 75 kg listed in the flight preparation documents.
Findings
- Overloading: The aircraft was significantly over its maximum takeoff weight. The investigation found that the actual weight of the occupants likely exceeded the legal limits, a practice the BFU noted is sometimes tacitly tolerated in certain ultralight operations.
- Aerodynamic Stall/Loss of Control: The combination of the aircraft being overloaded and the high load factor induced by the low-altitude turn increased the minimum stall speed. This caused the aircraft to enter an unrecoverable state at an altitude too low to permit corrective action.
- Operational Risks: The examiner was performing a simulated emergency landing maneuver at an altitude that left no safety margin for error. Furthermore, the examiner's appointment as a flight examiner had expired.
- Safety Culture: The BFU identified a deficiency in safety culture, noting that the practice of exceeding weight limits undermines the safety of ultralight flight training.