SB-5E V-tail flutter on low ridge pass — tail section tears away

An SB-5E V-tail was destroyed and the pilot seriously injured on a solo ridge flight along Cross Fell (UK). After two low passes behind the windward edge of the summit at about 30 m AGL, the second at 85-95 kt ground speed, between the rough-air limit and VNE, the V-tail entered divergent flutter and tore away within about three seconds. The glider pitched nose-down and fell vertically below the summit. The cockpit placard and ASI had carried an incorrect rough-air limit, 10 kt too high since import, and formal ridge training was limited.

1. Solo ridge flight on visit: 15 yo pilot (69 h total, 2 h on type) visiting a club near Penrith with a group from his home club; launched by winch and climbed via thermal to ~3 000 ft to transit to the Cross Fell ridge.
2. Limited formal ridge training: Pilot had check flights with the CFI but no formal in-flight ridge instruction; practical ridge knowledge had been passed informally from another 15 yo in the group.
3. Incorrect Rough Air placard: Cockpit placard and ASI markings carried a Rough Air speed limit 10 kt higher than the correct value; the error had been replicated since the glider's import in 1981.
4. Low pass at 85-95 kt ground speed: On a second low pass behind the windward edge of the summit at ~100 ft AGL, ground speed was 85-95 kt — between the Rough Air limit and VNE.
5. V-tail divergent flutter: Video shows both V-tail surfaces oscillating, ruddervators lagging the fixed structure. Amplitude grew over ~3 s.
6. Tail section tears away: Whole tail section broke from the fuselage, remaining only by twisted control rods. Glider pitched nose-down with the right wing first.
7. Vertical impact below summit: Aircraft fell vertically below summit level and impacted ~170 m NW of the Cross Fell trig point. Aircraft destroyed; pilot seriously injured. AAIB also notes design features more susceptible to flutter than current standards.