What happened
On April 8, 2017, a self-built ASW 24 E glider with a retractable engine departed from Bremgarten airfield via a self-launch. During the takeoff roll on runway 05, witnesses observed the engine running with an unsteady, stuttering rhythm. The air traffic controller noted that the aircraft achieved only marginal altitude gain before turning into the right downwind leg of the runway.
While on the downwind leg, the aircraft was observed by the crew of another aircraft to pull up steeply before stalling. Ground witnesses also saw the glider descend in a steep dive. The aircraft struck the grounds of a biogas plant, where it caught fire. The impact caused a fire in the facility's wood chip stockpile. The pilot sustained fatal injuries, and the aircraft was destroyed.
The investigation
The BFU investigation focused on the technical state of the aircraft and the legality of its operation. The aircraft carried a Spanish experimental registration, but the investigation established that it was being operated in Germany without a valid flight permit. The Spanish aviation authorities confirmed that neither a provisional nor a final certificate of airworthiness had been issued, as the owner had not completed or documented the required testing process.
Investigators examined the modifications made to the airframe. Approximately two years prior to the accident, a non-aviation-certified Aixro XF 40 Wankel engine had been installed. This installation included a custom-built engine mount rather than a part from the original manufacturer. Additionally, a second fuel tank had been installed roughly three weeks before the accident. Because there was no documentation or installation plans for these modifications, the aircraft's weight and balance could not be verified.
Findings
- The aircraft was an experimental build with significant unauthorized modifications, including a non-certified engine and a custom engine mount.
- The aircraft was being operated in Germany without the necessary flight authorization or airworthiness certification.
- The engine experienced irregular performance during takeoff, which was noted by witnesses as a stuttering motion.
- There was a lack of technical documentation regarding the installation of the engine, the custom mount, and the secondary fuel tank, making it impossible to determine the aircraft's center of gravity.