What happened
On October 6, 2007, at approximately 13:00 UTC, a private leisure flight was being initiated at the Maillen ULM airfield. The operation involved a Motorized Delta Plane, registered OO-A8 86, which was used to tract a second delta plane for takeoff. To facilitate the launch, the second aircraft was positioned on a trailer, with the pilot connected to the towing aircraft via a cable.
As the takeoff sequence commenced, intense vibrations caused a variometer, which had been secured to the central bar of the delta plane via a collar, to become loose. This instrument pivoted on the bar and became entangled with a small connecting rope attached to the trailer. As the aircraft gained altitude, the entanglement caused the trailer to be lifted into the air, reaching a height of approximately 15 meters. The sudden added weight of the ascending trailer caused the delta plane to lose stability and crash to the ground. The pilot sustained several fractures during the impact.
The investigation
The investigation focused on the mechanical setup used during the takeoff and the stability of the equipment attached to the aircraft. Investigators examined the attachment method of the flight instrument and the physical connection between the aircraft and the trailer. The inquiry established that the primary failure originated from the unsecured variometer on the central bar.
Findings
- The variometer was not sufficiently tightened to the central bar.
- Vibrations during takeoff caused the instrument to pivot and snag the trailer's connecting rope.
- The weight of the lifted trailer disrupted the aircraft's flight path and led to the loss of control.
Safety action
Following the accident, a recommendation was directed toward the Federation of Delta Plane flying. The federation was advised to notify its members regarding the specific hazards associated with having equipment attached to the central bar when utilizing a trailer for takeoff procedures.