What happened
On 19 July 2020, a Grob G103 Twin Astir II, registered F-CFKS, departed Bourges airport for a local flight. After a towed takeoff and climbing to approximately 2,700 m, the pilot maintained an altitude above 2,000 m for roughly two hours.
At approximately 17:42, the aircraft's flight path became abnormal. The glider began experiencing altitude oscillations with a period of about 17 seconds. Over the next seven minutes, the aircraft's path became increasingly erratic, characterized by tight turns and maneuvers resembling successive stalls or incomplete loops. During this period, the aircraft's altitude gradually decreased. At 17:50, the glider struck a row of trees before impacting the ground at high speed. The pilot was fatally injured.
The investigation
The BEA analyzed flight data from the FLARM and OGN systems, alongside wreckage examination and witness statements. Investigators evaluated three primary scenarios regarding the aircraft's flight path: voluntary aerobatics, a blocked control surface, and a "stick free" condition (where the pilot is no longer actively controlling the aircraft).
Examination of the wreckage showed no mechanical failures in the flight control linkages or pitch controls. The aircraft was within its weight and balance envelope, though it had a slightly forward center of gravity. Witnesses on the ground reported seeing the aircraft performing failed loops at low altitude, but noted the maneuvers did not appear to be intentional aerobatics.
Findings
Investigators concluded that the pilot most likely suffered an in-flight incapacitation, which prevented him from maintaining control of the aircraft. Once the pilot ceased active control, the glider entered a divergent phugoid mode—a natural longitudinal oscillation. This resulted in the observed pattern of alternating climbs and dives, which eventually led to the uncontrolled maneuvers and the final impact.
While the exact cause of the incapacitation could not be definitively determined via autopsy, the investigation noted that the pilot's long-duration flight at high altitudes (up to 2,700 m) may have led to moderate hypoxia. The pilot's age and known medical history, including a previous fainting episode and cardiovascular abnormalities, were identified as potential contributing risk factors.