Twin Astir outlands after flying with its spoilers unknowingly open
A Grob Twin Astir met heavy rotor-wave sink after an aerotow near Franconia and kept descending after release; the two occupants were unhurt and the tail boom was substantially damaged. The pilot then found the spoilers had been left open, closed them, and turned for a nearby airport. Choosing to fly the pattern rather than go straight in, he was too low on downwind to clear the trees and landed in a field, ground-looping in tall grass. The undetected open spoilers were the main cause, with the decision to fly the circuit 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.