Pilatus B4-PC 11 tow rope release leads to tree collision at Buttwil Flugplatz

On October 20, 1984, a Pilatus B4-PC 11 experienced an unexpected tow rope release during an aerotow launch at Buttwil Flugplatz, Switzerland. The incident occurred at approximately 40 meters above ground level, leaving insufficient altitude for the pilot to return to the airfield. The pilot attempted to gain speed by descending along the terrain but collided with tree tops, resulting in significant damage to the aircraft. The pilot sustained a severe concussion and multiple contusions. The official investigation identified the unintentional release of the tow rope at low altitude as the primary cause, with contributing factors including challenging wind conditions and a slack rope situation.