While the "plan" seems to be seriously flawed, and contributed to the
accident, it may not be the direct cause. Photos and videos clearly
show the right airbrake extended and the left retracted. This points
to a failure of the airbrake controls, which would be consistent with
what most witnesses reported (he veered off to the right after doing a
pull-up). There is an AD out on the DG-1000 airbrake control circuit.
These controls hookup automatically, so an assembly error is not
likely.

This is the most sensible of our current speculations.

Really, it makes no sense that anyone would plan to auto tow to 200
feet and do a 180 degree turn to landing. If they had planned to turn
around, they would have used the whole runway, and a much longer rope.
if they were using a 200 foot rope, the most sensible conclusion is
that they planned to land straight ahead over the tow car. So the turn
is likely unintentional.

I can well imagine that at 150 feet and 60 mph, you haul out spoilers
on a long-winged glider and only one side comes out -- and perhaps
stays out - you have a huge problem on your hands; possibly not
recoverable at all.

Reading accident reports, it seems the NTSB checks control systems
routinely, so we'll know pretty soon if this is the cause.

John Cochrane