DG-400 self-launch interrupted by propeller-mount fatigue fracture; outlands in corn

A DG-400 sustained light damage when, during its initial climb from Jesenwang, the rear support plate of the propeller mast fractured by fatigue at both flanges; the pilot throttled to idle and outlanded in an 80 cm corn field ~2.4 km NW. On touchdown the right wing dipped deeper into the corn than the left and the glider ground-looped right. Pilot uninjured. Analysis: cracks initiated at the surface near washer prints; ~90-97% of each fracture face was fatigue, consistent with bending under propeller thrust. No prescribed inspection would have caught them. Investigators recommended a redesign and retrofit of the propeller-mast connection.

1. Private local self-launch from Jesenwang: The pilot self-launched the DG-400 motor glider at 12:30 from runway 25 at Jesenwang for a private local flight, in VFR weather with a light westerly wind.
2. Strong vibration before downwind turn: Initial climb normal; just before turning into the left downwind leg, the pilot felt strong vibration from the engine area; he throttled to idle and started a right U-turn back toward EDMJ.
3. Fatigue cracks in mast support plate: The rear support plate of the propeller mast fractured at both bolts in close succession, mainly from fatigue; pre-flight checks could not have detected this, as no inspection covered it.
4. Outlanding: corn field 2.4 km NW: Realising he could not safely reach EDMJ, the pilot picked an 80 cm tall corn field into wind, ~2.4 km NW of EDMJ, and landed with the engine still extended.
5. Right wing in corn; right ground-loop: At touchdown the right wing dipped deeper into the 80 cm grain than the left, dragging the glider into a right ground-loop around its vertical axis; light crop damage on the field.
6. No injuries; light engine/gear damage: The pilot was uninjured; the engine and landing gear sustained damage requiring major repair, but the structure remained intact. The damage was classified as light.