Mini Nimbus clips a treetop crossing a ridge too low in weak lift
A Mini Nimbus pilot was slightly injured and the glider destroyed when it crossed a ridge too low above Schänis and a wing caught a treetop. Working weak ridge lift that only rose close to the forested slope, the pilot had been drawn in very low along the Chüemettler. About two hours into the flight, at ~1300 m, he turned right to cross the ridge; too low, the left wing caught a fir treetop ~22 m up, snapping about 1.5 m off it, and the glider fell in a left spiral into the forest ~50 m on. Mass and CG were in limits and no defect was found. Cause: flying below the minimum height for ridge soaring.
- Aerotow ridge soaring: The pilot aerotowed from Mollis and then spent about two hours soaring in weak thermals and ridge lift near the Chüemettler ridge.
- Weak ridge lift: Weak thermals and hang wind meant usable lift was only available close to the forested slope, encouraging flight very near the terrain.
- Low ridge height: The glider was flying relatively low, around 1300 m MSL, as it approached the Chüemettler ridge above Schänis.
- Low-altitude ridge crossing: While relatively low, the pilot decided to cross the Chüemettler ridge by turning right over the crest.
- Wing hits treetop: During the right turn over the ridge, the left wing struck the top of a fir tree about 22 m above ground, breaking off roughly 1.5 m of the treetop.
- Spiral into forest: Following the treetop strike, the glider entered a left spiral and descended uncontrolled into the forest about 50 m further on.
- Crash - minor injury: The glider crashed in the forest, destroying the aircraft and causing minor injuries to the pilot.