On Feb 1, 1:07*pm, "kirk.stant" wrote:
On Feb 1, 9:07*am, Gilbert Smith wrote:



Darryl Ramm wrote:
On Jan 27, 1:03*am, bumper wrote:
From the NTSB report,

"Examination of the tow airplane tail hook assembly revealed that the
mounting plate was bent upward and the
heads of two connecting bolts were in contact with the base of the
rudder. The tail hook was intact and remained attached to the mounting
plate. The hook was in the locked position, closed around the tow
ring. The release cable remained attached to the hook and was
continuous to the cockpit release handle. Functional testing of the
tail hook assembly revealed no anomalies, and the assembly functioned
appropriately."

I'm really surprised at the above part of the NTSB report - - my take
is a bit different. I visited the yard where the wreckage was stored,
some weeks after the accident, as I happened to be there on other
business. I was not allowed to take pictures but did examine the
wreckage and in particular, the tow hook assembly. I'm not an expert
on aviation wreckage examination, I am trained in auto accident
investigation.

There were two Schweizer tow hooks mounted to a flat plate, with an
additional mounting hole for a third hook, all side-by-side ( I
understand multiple tow hooks are sometimes used for banner towing.)
The multiple hook mounting plate was attached to the aircraft via what
looked to be an alluminum bar, guessing 1/4" thick by 1.5" wide and
extending back maybe 8" from the rudder post spring mount . . . you
would be correct if you concluded this bar offered minimal resistance
to vertical loads without bending. As the NTSB says, the bar was bent
upwards and had impacted the lower part of the rudder, deforming
bending the bottom bow of the rudder up in the process. Though this
jammed the rudder, given the low altitude and nose down attitude pre-
crash, the jammed rudder probably was not causal.

The upward bend and position of the tow hooks inserted a significant
amout of slack in the tow release cable forward of the hook. This
slack, along with the new geometry or position of the tow hook with
respect to the release cable (i.e. now would be pulling upward on the
release toggle instead of forward as necessary to release the hook),
looked to me like it would have been impossible to release the tow
hook/s from the cockpit, even with no load on the hook. Otherwise the
hook appeared to be functional, just not by the cable (note that I did
not touch or try to operate the hook by hand - - I was only allowed to
look, not touch).

From what I saw, I believe the tow hook installation was inadequate
and unsafe. If it was causative, it was doubtless not the only cause
of this accident, though. It may well be that even if the mount had
been designed with the cutomary strength common in tow planes (rather
than just being adequate for banner towing) that a kiting glider would
still have resulted in the same tragic outcome.

I'm posting this as I think the NTSB overlooked and/or glossed over
the role the bent tow hook mount may have played, and in doing so
missed an opportunity for us to learn from this. As we know even a
properly installed upright Schweizer hook can be difficult to release
with upward loading. If the mount is inadequate (that aluminum bar
comes to mind) and bends up easily, unless the Bowden cable is
installed in such a way that the cable stays in line with the hook
(i.e. perpendicular to the release toggle) *and, unless there's a way
for the release lever or mechanism in the cockpit to take up any extra
slack that my be induced by the bent mount, I'd say there's no hope of
releasing whatsoever - - even if the tuggie is right on it.

bumper

I guess this largely depends on what exact post-crash functional
testing of the release mechanism that the NTSB did. Did they test with
the tow hook loaded up with a rope at appropriate (high) angles?

Does anybody know if the aluminum (or could it be duralium - either
way it sounds surprisingly weak to bending) mount was a part of a kit
or was custom fabricated? Was it installed via a 337 for glider towing
or banner towing only? (There are no STC for tow hooks on Pawnees
AFAIK so it would have been a 337).

Especially if others are flying with a similar setups we need to try
hard to help prevent another tow release accident. Maybe this is
something the SSA could followup on with the NTSB folks involved. Its
a tragedy that the tow pilot was killed, and I'd hate to see something
missed even if there are other impairment factors here.

When aerotowing I get towed mostly behind Pawnees that have
retractable tow ropes and rope guillotines. That big handle is going
to work if needed. The soaring community is dependent on towplanes and
all our great tow pilots who support us and its very sad to see
accidents like this happening.

Darryl

There is a simple test: tie the tow rope to a tree, work the tow plane
up to full power, then pull the release. I bet there are a lot of
PA18s and the like which fail this test today.

Another test is to tie the rope to something above the tail of the
towplane to simulate the angle you might get in an upset and try
activating the release. *What you are trying to simulate is the force
of the towring on the moving arm of the Schweitzer. *We tried it on
our Pawnee and I was surprised that it wasn't as hard to do as I
thought it would be - even with the tail ballasted to add tension to
the rope. * But it did take a hefty pull.

This is a GOOD thing to demonstrate and let all your tow-pilots
practice before the season starts!

Better solution is to invert the release (there is a 337 for that mod)
or go to a Tost.

I too have had an upset - fortunately a minor one - when a solo
student botched a soft release in a 2-33 during a pattern tow. *Pulled
the tail up on my Pawnee, but he released before I could get to the
release handle and the upset was only about 10 degrees or so. *Got my
attention, though!

Kirk
Icing up in St Louis...

I fly a towplane with the release on the floor and you push down on
the handle to release. The one upset I had was luckily at around 1500
feet when the glider kited. The negative g plastered me against the
ceiling and I physically could not reach down far enough to affect a
release.