We are welded... but not inverted..
A strong pull to the side will not allow an SGS hook to intentionally
release, but yes a TOST can release under any directional pull.
I say intentional release, not inadvertant release.

BT

"Bruce" wrote in message
...
Anecdotes make poor proof of thesis.

However - you are correct that the ultimate cause of the accident was poor
maintenance of the hook.
But - the failure mode is one the Tost/Ottfur does not have.
They cannot rotate in a horizontal plane around the mounting bolt.

If yours is welded on - good, if it is inverted - better. If not, as on
the Cessnas - your daily checks should include whether there is enough
friction to prevent rotation around the mount bolt.

If it does rotate it will back release. It is unlikely to do this at a
peaceful, stable moment in the tow.

One near miss - does someone have to die before we accept there is a risk?

This means there are at least two situations where the Schweizer hook is
unsafe. The other is failure to release under high lateral angle - which
can be overcome by inverted mounting. ref -
http://www.jdburch.com/Towstudy.htm

The Tost is safer - if you have the option I can't see why you would fit
an obsolete design that is no longer in production and is known to be
unsafe under circumstances that have killed a number of pilots - time to
move on.

Bruce

BT wrote:
"

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)

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