Background
On 4 June 2006, a regional glider competition took place at Hausen am Albis airfield, about 15 km south of Zurich. A Maule M-7-235 motorplane (registration HB-KDM) was assigned to tow an ASW 27 glider (HB-3269). During a morning briefing, a standard departure procedure was established: the start coordinator would give three commands—"auflinieren" (line up), "Seil ausziehen" (pull the cable), and "Seil ist straff" (cable taut) as takeoff clearance. An abort command was mentioned but not defined.
Sequence of Events
At approximately 14:45, the glider pilot prepared for departure on runway 27. Assistant A pulled the tow cable from the winch, hooked it to the glider, and moved to the right side. The glider pilot extended and retracted the air brakes; with brakes retracted, the wheel brake was inactive. He then set the flaps for takeoff.
Assistant B lifted the left wing to horizontal, signaling readiness. The coordinator then transmitted "Delta Mike, Seil ausziehen." The tow plane rolled forward slowly. As the cable tautened, it jerked, causing the unbraked glider to roll forward. The tow pilot stopped, leaving the cable slack, and the glider overran it with its main wheel.
The coordinator, unaware of the overrun, gave takeoff clearance: "Maule Delta Mike, das Seil ist straff." The tow pilot heard this but noticed a glider being pushed off the runway and stopped, announcing "Wir warten noch schnell." The glider pilot heard the waiting call.
The two assistants saw the overrun and believed the tow pilot had stopped for that reason. They moved in front of the glider's wings to push it back. The coordinator saw them and, inferring the cable was overrun, called "Stopp" over the radio. The tow pilot did not hear this command; when the runway cleared, he applied full throttle.
At that moment, the assistants were directly in front of the wing leading edges. The glider's wings struck them as it began to roll. Assistant A rolled backward, but Assistant B fell onto his back and struck his head on the pavement, sustaining serious injuries. Neither pilot noticed the collision. They completed the takeoff and later landed after being informed of an interruption.
Injuries and Damage
One ground assistant suffered serious head injuries. No other persons were injured. The glider and tow plane were undamaged.
Probable Cause
The accident was caused by the wings of the glider striking two assistants as a result of an inappropriate departure procedure.