Duo Discus T propeller hub fatigue sheds blade; aileron damage forces outlanding

A Schempp-Hirth Duo Discus T sustainer suffered a propeller blade detachment near Droxford (UK); no injuries, outlanding without further damage. The pilot started the engine at ~760 m to cross the Solent. After ~5 min at ~920 m a bang and severe vibration signalled blade departure. The blade embedded in the left wing root, damaging the aileron control circuit. The pilot shut the engine, briefly handed controls to the passenger to secure loose items, then landed in an into-wind stubble field needing minimal aileron. Investigators cited metal fatigue in the propeller hub blocks — a known Technoflug issue with a redesigned hub available.

1. Engine started at ~760 m to cross water: While cruising in poor soaring conditions en route Halton to Bembridge, the pilot deployed and started the self-sustaining engine at about 760 m AMSL to prepare for crossing the Solent.
2. Known propeller hub fatigue issue: The propeller hub blocks had a known fatigue-cracking issue since 2006; the manufacturer issued Technical Notes and added a daily hub check in 2011. A redesigned hub was available from 2013.
3. Blade departs after 5 min at ~920 m: After about 5 minutes of engine running at around 920 m AMSL, a loud bang and severe vibration occurred as one of the five propeller blades detached due to failure of two hub block segments.
4. Blade embeds in left wing root: The departing blade embedded in the left wing root and damaged the aileron circuit; the adjacent blade was also struck, and the engine moved on its mounts under the out-of-balance forces.
5. Engine off; loose items secured: The pilot switched the ignition off and let the damaged propeller stop, briefly handing control to the passenger, also a pilot, while securing loose items thrown around by the vibration.
6. Field selected for minimal aileron: Returning to the controls, the pilot felt a restriction in aileron movement. He selected a nearby into-wind stubble field ~10-12 km away needing minimal aileron, and stowed the engine.
7. Successful outlanding, no injuries: The glider landed in the stubble field without further damage. Damage was limited to the propeller, fuselage marks, and the wing-root/aileron area; crew and passenger were unharmed.