What happened
On August 13, 2011, a Glaser-Dirks/DG 505 Elan Orion glider departed from the Uelzen airfield for a maintenance test flight following the installation of a new accelerometer. At an altitude of approximately 1,700 m, the pilot unhooked from the tow plane and began performing aerobatic maneuvers. After several successful figures, the pilot attempted an inverted loop. During this maneuver, the pilot experienced concerns regarding the aircraft's controllability and subsequently attempted to test the pitch and roll functions.
At an altitude of approximately 600 m, the pilot initiated a descent. While the aircraft successfully transitioned into an inverted flight position, the pilot found that the elevator had become blocked when attempting to return to level flight. The aircraft could only be controlled to a pitch angle of approximately 30° to 45°. Unable to recover a horizontal flight path, the pilot deployed an emergency parachute at roughly 400 m altitude.
Following the pilot's egress, the glider entered a series of oscillations and loops before entering a vertical dive in an inverted position. The aircraft crashed into a forest northeast of the airfield, resulting in heavy damage to the airframe. The pilot landed nearby and sustained minor injuries.
The investigation
The BFU examined the wreckage and the cockpit controls. Investigators found that the rear headrest could be folded forward, a position that physically blocked the control stick. The tether intended to prevent the headrest from moving forward was found to be improperly secured; it was attached to the tubular frame with a loose knot, and the tether was excessively long.
Furthermore, the investigation reviewed the aircraft's maintenance records. While the manufacturer had issued a Technical Communication (TM 348/20, 843/28) in 2008 requiring a modification to the headrest tether system to prevent such interference, there was no record of this modification being performed on the involved aircraft. Additionally, the aircraft's documentation had not been updated with recent service instructions.