What happened
On May 22, 2018, an Arcus M sailplane, registered HB-2471, was engaged in a training flight at the Fricktal-Schupfart airfield (LSZI). Following an initial successful training flight and a subsequent debriefing regarding engine performance and takeoff distance, the pilot attempted a second takeoff.
During the takeoff roll on runway 25, the pilot failed to transition the wing flaps from a neutral or negative position to the required positive position (+2) at approximately 40 km/h, as mandated by the Aircraft Flight Manual (AFM). Because the crew was primarily focused on monitoring engine power and acceleration, this procedural step was missed. As the aircraft reached the point where lift was expected, it failed to become airborne. The pilot subsequently aborted the takeoff, causing the aircraft to overshoot the end of the runway and enter the tall grass, where it spun around its vertical axis.
The investigation
The investigation examined the takeoff procedures and the crew's workload during the critical phase of flight. The investigators reviewed the requirements set forth in the AFM regarding flap settings during takeoff. No technical malfunctions were reported or identified regarding the aircraft's mechanical systems.
Findings
- The failure to adjust the wing flaps to the positive position prevented the aircraft from achieving lift-off.
- At low speeds, aileron effectiveness is improved when flaps are in a neutral or negative position compared to a positive position; therefore, the AFM requires a specific transition during the takeoff roll.
- The pilot and instructor were heavily focused on monitoring engine performance and acceleration due to the relatively short runway length.
- This intense focus on engine and speed monitoring led to the omission of the flap adjustment procedure.
- The aircraft sustained minor damage to the wingtip wheels, hinges, and the left outer wing aileron flap after contacting the tall grass.
- There were no injuries to the crew or any third parties.