What happened
On July 25, 2020, a TL 96 ultralight aircraft departed from Wesel-Römerwardt airfield for a flight to Marl-Lohmühle. The aircraft was carrying two occupants. During the arrival phase of the flight, while the pilot was on the right downwind leg of the circuit, the aircraft's emergency recovery system deployed. Witnesses observed that the parachute subsequently detached from the aircraft.
Following the deployment, the aircraft entered a rotation and plummeted into a residential building. The impact caused a fire in two apartments and resulted in 3 fatalities, including a woman residing in the house. The aircraft was destroyed in the crash.
The investigation
The BFU examined the wreckage and the components of the recovery system. Investigators recovered the engine, propeller hub, and various airframe components from the attic of the building, while other parts of the wing and landing gear were found in the surrounding area. The parachute was located 175 meters away from the crash site.
Technical analysis focused on the steel connection cables that attached the recovery system to the aircraft. The investigation included laboratory testing of the cables at the University of Stuttgart, which determined that the cables had failed due to brittle fractures. The study also examined the propeller, finding evidence of structural issues related to the adhesive bonding of the aluminum and composite components.
Findings
- The primary cause of the accident was the detachment of the emergency recovery system from the aircraft.
- The steel connection cables failed due to brittle fractures, with evidence of high transverse pressure and impact-like loading.
- The installation of the cables involved variations in length and potentially uneven distribution of loads due to the configuration of the connectors.
- Investigation of the propeller revealed that the surface preparation (sanding) used for the structural adhesive was not professional, leading to interface corrosion and potential structural weakness.
- The recovery system's connection cables were selected by the aircraft's importer/maintainer rather than the manufacturer.