Double Release Failure

On Sep 7, 7:05*pm, ZZ wrote:
It is likely that the probability of an ACTUAL double release failure on
tow is what ever positive number is closest to zero. Of course that
doesn't mean that Mr.Murphy can't serve one of these up.

I would be interested in hearing any accounts of actual, non-instructor
induced double release failures which required either a landing on tow
or purposely breaking he rope to end the problem.

I would also be interested in any opinions regarding practicing landing
on tow to prepare oneself for this unlikely event. (I know that this is
or was a required maneuver in some European countries...but is it worth
the risk?)

Paul
ZZ

It's probably worth mentioning that 'release failure' can also be an
uncommanded release. I've had a couple of those when the wing runner
didn't fully insert the Tost ring set into the hook but it somehow
partially engaged only to release on it's own later. Examination
showed nothing wrong with the hook.

I recall the story of a woman in a 1-26 who had the red ball come off
in her hand due to the steel cable breaking off inside the ball. She
looked at it for a moment, then reached under the panel and pulled on
the remaining cable activating the release. Cool head.

I've flown several training gliders which required an unusual amount
of pulling motion to effect a release - the usual 2" tug wouldn't do
it. Many pilots checking out in the glider would report a 'release
failure' and I'd have to say "pull further". The take home is that
you need to make sure you've fully actuated the release.

Final note: The FAA and NTSB seem to be taking a serious look at
release mechanisms, ring sets and weak links. If there's an accident
investigation, it probably isn't wise to be found to be using a chain
link in instead of a Tost ring set or a weak link at variance from
that specified in the POH.

I've been informed that the weak link, Tost hook and ring set are part
of a gliders airworthiness certificate documentation and substitutions
are judged to be an unauthorized modification from a regulatory and
enforcement perspective. Most JAR 22 gliders specify a weak link
strength + or - 10% (read your POH) for both aero tow and winch which
effectively requires a metal link made by Tost or equivalent. Rope
weak links can't meet that strength tolerance.