Fatal crash Arizona

Don's suggestion that there is a rigid rule about turn back heights in the UK is a surprise to me (I am an instructor). Select the least bad option at the time. Prepare students for it by (at an earlier stage) saying 'from here I would..'. Later asking 'if the tow fails here, where would you go?'

In most circumstances from 200 foot I would turn back.

Quite right, individual clubs may have had a minimum turn back height as
advice or even a rule, the BGA has not. I write as the ex-National Coach
who produced the BGA Instructor's Manual.

At 02:47 19 July 2014, waremark wrote:
Don's suggestion that there is a rigid rule about turn back heights in
the
=
UK is a surprise to me (I am an instructor). Select the least bad option
at=
the time. Prepare students for it by (at an earlier stage) saying 'from
he=
re I would..'. Later asking 'if the tow fails here, where would you go?'

In most circumstances from 200 foot I would turn back.

On Saturday, May 3, 2014 at 10:27:10 PM UTC-6, Waveguru wrote:
Premature termination of the tow at 100ft. Did not complete the turn back to the runway.

http://www.kathrynsreport.com/2014/0...izona.html?m=1

Boggs

A really scary comment in the NTSB final report: "Postaccident examination of the glider's release system revealed that it was missing a spring, which likely resulted in the cable not engaging in the detent and caused the premature release from the tow line." http://www.ntsb.gov/_layouts/ntsb.av...04X34426&key=1

It was a bumpy day. I took off about 10 minutes of Bob and hit strong turbulence and sink over the last few hundred yards of the runway. My 200 foot countdown took much longer than usual, but, as I continued on tow, finally got up and found a good thermal and left the area, unaware of the crash that had occurred behind me.

Bob was a very experienced jet pilot with thousands of hours, but had just gotten into gliding and had only recently purchased the glider. Having his glider release itself because of a faulty release mechanism in turbulence only 100 ft. AGL and only desert trees ahead, our newbe pilot made the unfortunate fatal decision to turn back and spun in.

When was the last time YOU had your release checked by a professional???

On 9/9/2016 3:58 PM, Bob T wrote:
Snip

A really scary comment in the NTSB final report: "Postaccident examination
of the glider's release system revealed that it was missing a spring, which
likely resulted in the cable not engaging in the detent and caused the
premature release from the tow line."
http://www.ntsb.gov/_layouts/ntsb.av...04X34426&key=1

It was a bumpy day. I took off about 10 minutes of Bob and hit strong
turbulence and sink over the last few hundred yards of the runway. My 200
foot countdown took much longer than usual, but, as I continued on tow,
finally got up and found a good thermal and left the area, unaware of the
crash that had occurred behind me.

Bob was a very experienced jet pilot with thousands of hours, but had just
gotten into gliding and had only recently purchased the glider. Having his
glider release itself because of a faulty release mechanism in turbulence
only 100 ft. AGL and only desert trees ahead, our newbe pilot made the
unfortunate fatal decision to turn back and spun in.

When was the last time YOU had your release checked by a professional???


"Right on!" regarding "known-good release health."

Philosophical agreement aside...if (big "if") the release was an original
Aerotek release, I've a hard time getting my head around the NTSB's "missing
spring" possibility (though if it happens, it must be possible).

So far as I'm aware, every Zuni left the factory with a clone of Dick
Schreder's dirt-simple HP release (used in every HP I've examined, including
up to HP-16's and one HP-18).

The original release uses a single spring, easily visible (assuming the
cockpit-side of the release wasn't subsequently enclosed by some sort of
doghouse). But more to the point, without the spring the original release
simply doesn't *work* properly - as in, requiring active, precise-and-fiddly,
action (on-the-rope-connnector-person's-part), to make a tension-holding
connection. I know because I tried both my HP-14 and Zuni (S/N 3)releases
sans-spring, on the ground, just out of curiosity. As it was, even with a
properly functioning release, part of my pre-launch routine was describing to
(almost!) every rope-connecting-person how to connect the rope (a task Joe
Pilot could not assist with from within the cockpit). Whereas having "Joe
Average Connector Person" make a successful connection with a functioning
spring is "verbally trivial" from Joe Pilot's perspective, I doubt I could
have talked through J.A.C. Person into making a(n apparently) secure
connection in the absence of a spring. Memory says that doing so requires two
hands, one with access to the interior/cockpit side of the release.

Now if the spring failed or somehow came loose, I'd expect an immediate back
release the instant the rope lost tension for any reason.

Bob W.

Go to the accident docket and read the MATERIALS LABORATORY FACTUAL REPORT.
My conclusion is that the pawl spring had been missing for some time.

Ernst

On 9/12/2016 8:34 AM, Ernst wrote:
Go to the accident docket and read the MATERIALS LABORATORY FACTUAL
REPORT. My conclusion is that the pawl spring had been missing for some
time.

Ernst


I found the 7-page Factual Report, which includes the statement, "A detailed
examination report for the glider release mechanism is contained in the
Materials Laboratory factual report located in the public docket."

I've been unable to find the "Materials Laboratory factual report." Pointer
help will be Seriously Appreciated!

Meanwhile, I'm still finding it hard to believe the accident aircraft was
successfully operated for ~26 hours without the release spring, though I can
believe the (light-in-tension) spring *might* leave very little in the way of
witness marks on the I.D. of the pawl's through hole.

Thanks very much.

Bob W.

On Monday, September 12, 2016 at 8:09:10 PM UTC-7, Bob Whelan wrote:

...I've been unable to find the "Materials Laboratory factual report." Pointer
help will be Seriously Appreciated!

The Docket Management System (DMS) has many good detail photos of broken aircraft. It is (or should be) every detail designer's go-to resource:

http://dms.ntsb.gov/pubdms/search/hi...docketID=58737

Thanks, Bob K.

On 9/12/2016 9:21 PM, Bob Kuykendall wrote:
On Monday, September 12, 2016 at 8:09:10 PM UTC-7, Bob Whelan wrote:

...I've been unable to find the "Materials Laboratory factual report."
Pointer help will be Seriously Appreciated!

The Docket Management System (DMS) has many good detail photos of broken
aircraft. It is (or should be) every detail designer's go-to resource:

http://dms.ntsb.gov/pubdms/search/hi...docketID=58737

Thanks, Bob K.


Many thanks!

Just to (sorta) complete the train of thought in my (bemused) posts preceding
this one. The photos of the release mechanism from the accident aircraft seem
to (pretty much) match my (oldish) memories of how it functions, the "pretty
much" exception being I remembered the hook retraction spring as a simple
tension spring (and not the dual-sided, probably custom-bent) coil type. It
was THAT spring force to which I referred when writing I couldn't understand
how the hook could have sensibly functioned in its absence. That force serves
dual purposes: 1) maintaining the hook cover against the back side of the
opening slot while in flight (while also allowing a back release in the event
of loss of rope tension combined with a Big Bow), and 2) (by
through-transmittal of the hook-opening-cover force) retracting the entire
hook mechanism after the pawl is released from the flat-plate/cable-hook
detent by the pilot pulling the release knob/cable.

As for the report's claimed missing pawl spring...I must be getting dense in
my old age, since I'm still puzzled by the intended function and line of force
of that implicated piece of (missing?) hardware. Using Figure 8 by way of
illustrating my puzzlement, it seems to me such a spring could either serve to
decrease or increase the pawl's contact force against the hook plate.
Decreasing the contact force would appear to be counter-productive, while
increasing it (arguably) might have served to make the incomplete contact
condition shown in Figure 9 even more likely.

In any event, my current working hypothesis is the hook likely back released
(as intended, for better or for worse) from a bow in the rope (gusty sink
being reported in that vicinity by the previously-towed pilot) at an
unfortunate/ugly towing-location, followed by loss of control. Having had two
such back releases during gnarly tows (one nearly too low to warrant an
attempted return, above head-high sagebrush, but fortunately not occurring
until later that same tow), I can relate. Whether or not the incomplete
contact condition between pawl and cable hook detent (shown in Figure 9) was a
contributor, I have no idea.

Back to the hook design - what am I missing? Thanks!

Bob W.

On Tuesday, September 13, 2016 at 10:34:20 AM UTC-4, BobW wrote:
As for the report's claimed missing pawl spring...I must be getting dense in
my old age, since I'm still puzzled by the intended function and line of force
of that implicated piece of (missing?) hardware.
Back to the hook design - what am I missing? Thanks!

Bob W.

If I understand correctly, the missing spring pushes the pawl
in the direction opposite of pulling the release knob.
Otherwise, the pawl is not secured in the "latched" position,
except by a bit of friction with the hook plate (from the
spring that is present and any rope tension).

Do I understand correctly??

On 9/13/2016 9:26 AM, Dave Nadler wrote:
On Tuesday, September 13, 2016 at 10:34:20 AM UTC-4, BobW wrote:
As for the report's claimed missing pawl spring...I must be getting dense
in my old age, since I'm still puzzled by the intended function and line
of force of that implicated piece of (missing?) hardware. Back to the
hook design - what am I missing? Thanks!

Bob W.

If I understand correctly, the missing spring pushes the pawl in the
direction opposite of pulling the release knob. Otherwise, the pawl is not
secured in the "latched" position, except by a bit of friction with the
hook plate (from the spring that is present and any rope tension).

Do I understand correctly??


Quite possibly. I suppose such a spring fairly might be considered the
"suspenders" to the hook-retract-spring's "belt." It's not obvious from the
photos (Figure 1 shows it best), but installed-geometry, plus gravity, in the
pawl's as-installed position/angle work "against" the pawl remaining
detent-seated...i.e. the pawl pivoting by itself (no other physical contacts)
would tend to flop its "business end" *away* from the detent due to the longer
cable-attach arm's length compared to the detent-engagement arm's length
(unequal length teeter-totter).

Nonetheless, whether the absence of a compression spring between the pawl and
receptacle/pawl-spring-housing was a crucial element in this accident is
debatable; it would take very little force on the rope to rotate the cable
hook from the barely-engaged position (Figures 9) to the fully engaged
position (Figure 8). Once there, further testing definitely required to
determine whether the design would be more or less prone to back-releasing in
the absence of the pawl spring, in the presence of a rope bow...

That said - and since a number of these hooks have been installed into the
noses of German-built ships originally entering the USA with only a CG hook -
owners of ships with these hooks SHOULD (and easily can) VERIFY the
presence/absence of such a compression spring by checking to see if the pawl
is positively forced against the rotating piece of the cable hook throughout
its rotation range. Positive engagement = spring-present. (Note that the
spring itself is hidden in the hook's assembled state...and might easily
escape unnoticed in the event of the hook being disassembled for any reason.)

Bob W.