What happened
On September 24, 2009, at 10:53 AM, an Aviasud Sirocco microlight, identified by number 68ADW, crashed shortly after departing from runway 04 at the Annecy-Tessy airfield. While climbing toward the downwind leg, the pilot broadcasted a distress message indicating the aircraft was falling. Witnesses observed the left wing half folding upward, causing the aircraft to descend vertically. The aircraft subsequently struck the ground and collided with two vehicles parked in a nearby lot. The pilot was killed, and the aircraft was destroyed.
The investigation
The investigation focused on the structural integrity of the aircraft's wing assembly. Examination of the wreckage revealed significant deterioration of the airframe. Specifically, fraying was noted on the wing fabric of the left wing. Investigators determined that the failure originated at the wingtip, where the marginal tube was no longer properly secured to the leading edge. This instability allowed the tube to pivot around its attachment to the rear spar until the connection failed. The resulting aerodynamic forces caused the wing section to collapse toward the fuselage and rearward, leading to the failure of the spars. While the wing half remained attached to the bracing wires, it pivoted upward during the descent.
Findings
- The primary cause of the accident was the decision to operate an aircraft in a known state of disrepair.
- The aircraft was in a state of advanced age and deterioration.
- The pilot had performed several maintenance tasks since acquiring the aircraft in October 2008, including wing repairs, but the structural integrity of the wing assembly was compromised.
- The failure of the marginal tube at the wingtip initiated a chain of structural collapses involving the spars.