ASW 24 stalls in turnback after low-altitude aerotow release

An ASW 24 crashed during a CG-hook aerotow at Dunstable; the pilot was fatally injured and the glider destroyed. After liftoff the glider climbed high behind the tug and oscillated. Below ~15 m AGL the tow rope detached for undetermined reasons. The glider continued climbing to ~25 m AGL, then entered a steep left turn (~60° bank) to return. At that bank the stall speed rose to ~105 km/h; the glider stalled, spun, and struck the ground nose-first at the western boundary. AAIB cited the low-altitude turnback and the destabilising CG-hook aerotow configuration.

1. West Run aerotow takeoff: ASW 24 (1991 build, SN 24132, 1,351 total launches) on a CG-hook aerotow from the West Run at Dunstable Airfield, ~50 m tow rope. Northerly breeze gave a 5-10 kt crosswind from the right; clear visibility, broken cloud above 1,000 ft. Pilot 47 yo, BGA Sailplane Pilot's Licence and Basic Instructor, ~131 h total (26 on type), 18.75 h and 53 launches in the previous 12 months (Green currency on the BGA barometer). Twenty-fifth launch in this glider, all aerotow.
2. CG-hook only, known destabilising: G-CHBB had a CG hook only (no nose hook). The BGA Managing the Flying Risk document lists CG-hook-only aerotow as an additional risk factor for tug-upset situations due to the pitch-up moment from the hook geometry being below the glider's CG. The pilot had completed 24 prior aerotows in this glider on the CG hook; AAIB found no operational factor (distraction etc.) contributing to the initial vertical instability observed on the accident flight.
3. Tow rope detaches below 15 m AGL: While the glider was still below the tug's profile and at below ~15 m AGL, the tow rope detached from the glider. AAIB could not determine the mechanism and considered three credible scenarios: hook back-release (slack rope after the glider caught up to the tug), inadvertent operation of the release handle, or a deliberate release. The tow release was tested in acceptable technical condition; calendar overhaul interval had no mandatory backstop and launch life was within limits.
4. Startle/surprise likely: AAIB: for an unintentional release (back-release or inadvertent operation), the pilot would likely have experienced startle and/or surprise on realising the tow had separated. Startle responses impair pilot performance for ~0.3-1.5 s; surprise can produce delayed or incomplete application of planned responses. Pilots commonly self-brief 'land ahead' from below ~90 m AGL on aerotow, but executing that plan under startle/surprise is not assured.
5. Climb to ~25 m, steep left turnback: After separation from the tug, the glider continued climbing to ~25 m AGL (60 ft maximum recorded) then entered a steep left turn. CCTV imagery showed the bank angle exceeded 60° during the turn. At 60° bank the ASW 24's stalling speed rises from ~67 km/h level to ~105 km/h. Groundspeed entering the turn was ~105 km/h and reduced through the turn, with the tailwind component increasing as the glider rotated.
6. Stall and autorotation in steep turn: The combination of tight bank and reducing airspeed put the glider into an unsustainable flight regime. The left wing dropped, the nose yawed left, and the glider autorotated into an incipient spin. The 1994 flight-test evaluation noted the ASW 24 has 'relatively gentle' stall characteristics for the class but 'will drop a wing if provoked' and start to spin if back-pressure is held.
7. Nose-first ground impact, fatal: Glider struck the ground nose-first near the western boundary of the airfield; aircraft destroyed (severe structural damage; airbrakes found extended only as a result of ground impact). Pilot fatally injured. BGA archive: 40 reported aerotow failures below ~90 m AGL in the 10 years to August 2023 — of 22 land-ahead cases, no fatalities; this accident was the only fatal launch failure in that dataset. AAIB safety message: from below ~90 m AGL on aerotow, landing ahead offers the greatest probability of a successful outcome; turning back proved unachievable here.