Pilatus B4 tow release incident at Buttwil airfield results in crash landing
On March 22, 1972, a Pilatus B4 experienced an unexpected tow release shortly after takeoff at Buttwil Airfield in Switzerland. The glider, piloted by a licensed glider pilot with limited recent flying experience, climbed steeply to about 50 meters before descending at a steep angle and crashing. The pilot sustained serious injuries, and the glider was destroyed. The investigation noted that the tow rope likely released automatically due to slack, leading to the incident. Weather conditions were favorable at the time of the accident.
- Aerotow takeoff roll: The Pilatus B-4 glider began an aerotow launch behind a Piper tug from grass runway 34 at Buttwil, with the initial ground roll and liftoff reported as normal.
- Pilot recency and type: The pilot had not flown for the previous 90 days, had never flown from Buttwil, and this was his first flight on the Pilatus B-4 without a formal type-specific checkout.
- No rope-break training: During his glider training the pilot had not practiced rope-break or cable-break exercises, leaving him untrained for an unexpected low-altitude tow release.
- Automatic tow release: At about 10–15 m above ground, after strong rolling/pendulum motions of the glider, the tow rope automatically released from the B-4, likely due to excessive slack activating the release mechanism.
- Steep climb after release: Following the unexpected tow release, the pilot pulled the glider up into a steep climb instead of maintaining speed and preparing for an immediate landing.
- Low-altitude stall: The steep climb at low height led to the glider stalling or ‘abschmieren’ at about 40–50 m above ground and pitching nose-down in a steep descent toward the ground.
- Crash - serious injury: The glider descended at a steep angle and crashed into soft, slightly swampy terrain about 90 m west of the north end of runway 34, seriously injuring the pilot and destroying the aircraft.