JS1-C stall/spin on 3rd familiarization flight — turbulent thermals, low experience

After a stall and spin near Mont Crosin during a third type-familiarization flight, the pilot of a Jonker JS1-C was lightly injured and the aircraft heavily damaged. Total experience was about 104 hours with 2:42 hours on the demanding JS1-C type, all from the day before. CG sat close to the aft limit (within limits) and thermals were turbulent. While searching for lift, IAS dropped from 117 to 84 km/h in 10 s as altitude rose; the glider stalled and entered a spin at 250 m AGL. Recovery was attempted but height was insufficient before the glider struck a young forest.

1. 3rd type-familiarization flight: After ~4 minutes of aerotow from Courtelary (LSZJ) and release at 1502 m AMSL at 12:36, the pilot spent ~5 minutes searching for thermals near Mont Crosin in an altitude band of ±70 m without notable gain. This was her third familiarization flight on the JS1-C — a high-performance 18 m flapped single-seater with a jet sustainer; the previous two flights were the day before.
2. Low total experience: SUST-cited contributing factor. The pilot held an SPL licence obtained 30 September 2023 with ~104:59 h total flight time. Post-licence experience: ~28 h, of which ~11 h solo and ~13 h dual on two-seaters; plus ~11 h PIC on Arcus M from three flights in May 2024. Total time on JS1-C: 2:42 h — all on the previous day (15 June), including jet-sustainer handling on the second flight.
3. Demanding type, CG near aft limit: The JS1-C is a high-performance single-seater with flaps and a small jet sustainer. CG was within limits but close to the aft limit per SUST, which worsens stall behavior. The operator's rental policy required either 500 h glider experience OR specific familiarization training; the pilot was on the latter path.
4. Turbulent thermals: SUST-cited contributing factor. Wind 15 kt 190° gusting to 25 kt (Chasseral station 12:40-12:50); calculated wind 13 ± 5 kt from 210 ± 30°. Forecast for the Jura: slope ascendance with turbulence and broken/torn moderate thermals, confirmed by the pilot. SUST: conditions demanding for a low-experience pilot.
5. Training setup overwhelmed pilot: SUST analysis. SUST concludes the combination of low total experience, limited prior time on comparable demanding types, and the turbulent conditions led to a capacity overload in the final phase, which explains the inadvertent zoom and energy bleed. The pilot in charge of training was not formally instructor-qualified but was competent and knew the type well; SUST notes EASA does not legally require an instructor qualification for familiarization (as opposed to ab-initio) training.
6. Inadvertent zoom and energy bleed: From 12:41:03, IAS dropped from 117 to 84 km/h in 10 seconds while altitude rose — the JS1-C zoomed and bled energy. Variometer was showing 3-4 m/s sink before the stall, per the pilot.
7. Stall and spin entry at 250 m AGL: At 12:41:13 the glider stalled and entered a spin at ~1350 m AMSL (~250 m above ground). IAS continued to decay for ~4 seconds to ~80 km/h. The aft-of-centre CG (within limits) contributed to stall onset and spin behavior.
8. Recovery short of height: The pilot attempted spin recovery but could not complete it before ground impact at 12:41:28, after more than one turn. The emergency parachute was not deployed; it was still in the cockpit at the wreckage.
9. Young-forest impact: The JS1-C impacted a young-forest area at 1099 m AMSL. Left wing detached from fuselage; right wing leading edge heavily damaged with main spar broken at the fuselage. Forward cockpit very damaged, canopy shattered, panel disintegrated. ASI needle at 190 km/h at impact. The pilot self-extracted with light injuries; aircraft destroyed. No technical defect or in-flight disintegration found.