Tost release failure

No amount of release checking will avoid a wrongly hooked on rope.
Standard reply is:
"My release was checked yesterday"




10:25:49 -0700 (PDT), "kirk.stant"
wrote:At 02:14 25 August 2012, Andreas Maurer wrote:
On Fri, 24 Aug 2012

Finally! I've been refusing to do release checks for years and get the
stink-eye everytime.
I've tried explaining that if you can hook up, then you have checked as
much as you can, but still get people saying "but what if it fails?".

Maybe one of you smart guys out there can explain the logic of a
separate
release check?


I can.

1. Three weeks ago we had an accident at an airfield close to us where
the pilot was very, very lucky.

He did a winch tow in an ASW-19. The small ring of the tow cable was
not put into the tow hook, but jammed between the Tost release and its
steel attachement structure, creating an extremely strong and
permanent connection. Mistake of the student pilot who did the hookup.

After the pilot had (thought he had) released at about 1200 ft, he
turned into left downwind. After passing the winch the tow cable went
tense and pulled the ASW-19 into a ballistic arc towards earth - the
emergency cutter on the winch didn't work either.
The pilot estimates that the remaining time till impact was about 5-10
seconds.

Only chance for the pilot was to apply aileron and turn towards the
winch (nose still being pulled into a dive), which fortunately worked.
He flew over the winch at an altitude of about 300 ft and then tried
an extremely tight turn in order to land next to the winch. Just as he
was on final, the tow cable got tangled in some bushes, the ASW-19 got
a nose-down impulse, impacted hard from about 25 ft and was damaged
very badly.
Fortunately, the pilot escaped unhurt - even those old Schleicher
gliders are built incredibly strong.

Time from first inkling of the problem till impact 37 seconds.
Time from noticing the problem (rapide nose-down impulse) till
possible bail-out, estimated by the pilot: None. Bailout not possible.


A release check would have prevented this accident (of course, the
next hookup might have resulted in the same mistake...).


2. I know of a number of incidents where it was possible to hook up
the tow cable, but release failed when it was attempted to release the
cable under tension (on of these cases happened to me in a Ka-8 when I
was a student pilot, fortunately the back release worked). Usual cause
was wrong ring on the tow cable and mechanical prblem in the glider
concerning the control cable to the Tost release.


Lections learned:
If you are the one who's doing the hookup:
- LOOK at the tow release when you put the ring in
- Check the ring if it fits perfectly (it should have just a little
play)
- Check the release mechanism under tension

- Check the emergency release of the winch. Often. We checked ours
imediately after we heard about the accident, and only one of two
emergency cutters worked (the other was stopped by very little dirt
that had collected in the mechanism during the last 6 months). We were
quite surprised how little dirt it takes to block the cutter (ours has
got a force of about one ton to cut our steel cable).

And, of course
- Never, never use rings that are not approved by Tost
- Never, never mess with a Tost release






Cheers
Andreas