"

We had a world class pilot write off an ASW20 in December. The schweizer
hook turned 180 degrees and sold him the rope at 50 feet... An anthill
saw to the rest.


How can a tow hook on the tow plane rotate (turn) 180 degrees, do you mean
it was mounted "inverted"?
And if mounted upright or inverted, the SGS hook, if properly installed and
maintained would not just, "sell him the rope".
Just because it was "inverted" means nothing.. they are all "inverted" when
installed on the glider.
Something was not maintained.

I noticed once between flights and I was out of the cockpit that the tow
plane end of the rope (hook) seemed to be almost "1/2" way to the release
point.
I reset it, did a tow and got out and looked again. It had moved again on
it's own. So now I start looking to see what would have happened to cause
that.
The release cable rides in a plastic casing inside the Pawnee, zip tied to
fuselage formers.

Some ties had aged and broke, the cable was free to sag. So bouncing in
turbulence on the way down, the cable bounced in the aft fuselage, no
"pressure" on the hook and it was pulling the release lever.

There is more to towing than inspecting the rope and the release system...
Check ALL of the airplane and it's parts.
The SGS hook failure is no different than if TOST springs were broken and
not caught on preflight inspection or checked during the day.
No different than a weak link failure.. No different than the engine
coughing and the tow purposefully releasing the rope.

Had a Stearman blow a jug, the glider pilot saw the puff of smoke and then
saw the rope release within a second of the puff.
Those are the chances you take... don't blame the hook, blame the preflight.

BT (Pawnee Tow Pilot on an SGS Upright Hook)