Twin Astir spoilers left extended unnoticed — outlanding in rotor sink
A Grob Twin Astir made an off-field landing near Franconia (New Hampshire); occupants were uninjured and the tail boom was substantially damaged. An aerotow encountered turbulence and rotor-wave sink. After release the pilot noted heavy sink and turned back; the glider kept descending. He then noticed the spoilers had been left extended, retracted them, and tried to reach a diversionary airport. Entering the pattern rather than flying straight-in, on downwind he was too low to clear trees and landed in a field. The glider ground-looped in tall grass. NTSB cited the undetected spoiler deployment, with the downwind decision contributing.
- Aerotow near mountains: The Grob Twin Astir was being aerotowed to altitude near mountainous terrain in the Franconia, NH area.
- Turbulence and rotor-wave sink: On tow the glider encountered turbulence and rotor-wave activity; after release the pilot reported heavy sink ("some bad sink").
- Spoilers extended undetected: The spoilers were inadvertently left extended and the pilot did not detect their deployment, prolonging an excessive descent rate. The NTSB cites this as the probable cause.
- Spoilers retracted, diversion: After noticing the spoilers were extended, the pilot retracted them and attempted to reach a diversionary airport, but the glider continued to descend rapidly.
- Downwind approach decision: Rather than flying a straight-in approach to the diversionary airport, the pilot entered the traffic pattern. The NTSB cites this decision as a contributing factor.
- Insufficient altitude for trees: On the downwind leg the pilot realized he did not have enough altitude to clear nearby trees and elected to land in a field instead.
- Outlanding ground-loop: The glider landed in a nearby field, ground-looped when it contacted tall grass, and sustained substantial damage to the tail boom; both occupants were uninjured.