Towpilot fatality in Oregon

On Sep 5, 10:12*am, GARY BOGGS wrote:
The NTSB said that the bent tow hook mount was inconsistent with the
crash. *It is also very hard for me to imagine that a tow rope would
be strong enough to bend the tow hook mount.

Sorry about the lawyer comment. *I hope it's not true.

FWIW, when I was a new instructor, I allowed one student to get a
little too far behind the PIO curve on tow (this well above 1,000
feet) and we swung rapidly from low and right to high and left. Ka-
thwang - there was a God awful jerk and I saw the towplane (an L-19)
diving away. We'd actually broken the tow hitch from the towplane
(it remained connected by the release cable). The mounting plate was
pretty mangled. Luckily, I wasn't mangled by the towpilot, who gave
me a well-deserved dressing down behind the hangar.

Not saying this is or isn't related to the Oregon crash, but it is
possible to do a significant amount of damage to the tow hitch if you
let enough slack develop and don't handle the recovery well...

Originally Posted by Papa3

On Sep 5, 10:12*am, GARY BOGGS wrote:
The NTSB said that the bent tow hook mount was inconsistent with the
crash. *It is also very hard for me to imagine that a tow rope would
be strong enough to bend the tow hook mount.

Sorry about the lawyer comment. *I hope it's not true.

FWIW, when I was a new instructor, I allowed one student to get a
little too far behind the PIO curve on tow (this well above 1,000
feet) and we swung rapidly from low and right to high and left. Ka-
thwang - there was a God awful jerk and I saw the towplane (an L-19)
diving away. We'd actually broken the tow hitch from the towplane
(it remained connected by the release cable). The mounting plate was
pretty mangled. Luckily, I wasn't mangled by the towpilot, who gave
me a well-deserved dressing down behind the hangar.

Not saying this is or isn't related to the Oregon crash, but it is
possible to do a significant amount of damage to the tow hitch if you
let enough slack develop and don't handle the recovery well...

I suspect that in this case they were probably using the standard 1/4" polypropylene ropes with a theoretical rated breaking load of 1,000lbs. Even after a few tows off an asphalt runway I would think that it would be hard put to transmit a load much over 1,200 lbs even with the biggest snatch imaginable. Perhaps in your case you were towing with a much stronger rope with no weak link?

Gary, You say "NTSB said that the bent tow hook mount was inconsistent with the crash" - as I can't see the report listed on the NTSB's monthly summaries, I can only hope you are taking directly to the NTSB investigator rather than adding to the speculation with third-hand information.

I accept your apology regarding the lawyer comment, but I must emphasize the effect of that type of comment would have on those affected by this accident. Perhaps we should stick to verifiable first hand facts when adding to the discussion?

OGP

FWIW, when I was a new instructor, I allowed one student to get a
little too far behind the PIO curve on tow (this well above 1,000
feet) and we swung rapidly from low and right to high and left. Ka-
thwang - ....


Oh, man, how many instructors have stories like that? When i was a new
instructor, I was flying with an "experienced" student on a 20+ knot
wind day. On short final, he was getting slow below the tree line and I
said "keep your speed up". The next thing I know, the stick goes forward
to the stop. we hit on the skid (2-33) bounce back into the air and I
recover after that. Ever since, I keep my hand MUCH closer to the stick
near the ground when a student is flying.

Tony

I haven't had time to read all the posts on this thread, but none of those
I have read has given any real information on what actually happened.

I was involved in some testing of tow-plane accident scenarios many years
ago. I'm not suggesting that what happened in Oregon was this sort of
accident but nor do I know that it was not. For what it is worth,
herewith my recollections of those tests:

Whilst I was Chief Instructor at Booker Gliding Club, we conducted two
series of test on the phenomenon variously referred to as “Kiting”, “Winch
Launching behind the Tow-Plane” and “Sling-Shot Accident”, one in 1978 and
one in 1982; my memory of them is quite vivid.

Airplanes used were, for the first series, a Beagle Terrier (a side by
side, two place, high wing, tail-dragger), fitted with an Ottfur Glider
hook for towing (very similar to the Tost hook, dissimilar to the
Schweitzer hook) with a 160 hp Lycoming engine; for the second series of
tests a PA18-180 with a Schweitzer hook was used. Gliders used were a
Schleicher Ka 8b and ASK 13. Tow rope initially used was a heavy (4000 lb
breaking strain) rope with a thinner rope weak link at the glider end
(nominally 900 lb, but a well worn specimen could break at as little as
200 – 300 lbs – laboratory tests, not opinion), the second series of test
used the same heavy duty rope with “Mity” links at each end, 1100 lbs at
the Tow-Plane end and 900 lbs at the Glider end – these links use metal
shear pins, one under load and a second unloaded, which takes over if the
first one fails. This eliminates failure due to fatigue and means that
the links always fail at close to their nominal load even after some time
in service – again laboratory tested, not just subjective opinion. Rope
length was around 180 feet in all cases.

I was the Glider Pilot on all tests; Tow-Plane Pilot was Verdun Luck (then
my deputy Chief Instructor) for the first series of tests and Brian
Spreckley (then Manager of Booker GC) for the second. The object of the
tests was to try to reproduce the “Kiting” under controlled circumstances,
with a view to developing a Tow-Plane release mechanism that would
automatically release the glider if it got dangerously high above the
Tow-Plane. All tests were conducted at about 4000 feet agl.

First test: Terrier Tow-Plane and ASK 13 on nose-hook. At about 4000
feet I took the glider progressively higher above the tow-plane,
eventually reached about 100 feet above tow-plane (i.e. rope angle more
than 45 degrees above horizontal). At about this point, the tow pilot,
who had been using progressively more back stick, ran out of back stick
and the Tow-Plane began to pitch nose down but not excessively violently.
I released at that point. It took a very positive control input on my part
to achieve the displacement, we both felt it was something unlikely to
occur accidentally, even with an inexperienced glider pilot, and there was
plenty of time for either party to release if it did occur.

Second test: Terrier Tow-Plane and ASK 13 on C of G hook. I pitched the
glider about 25 – 30 degrees nose up – the weak link broke immediately!
Tow pilot reported a sharp jerk, but no significant change to flight
path.

Third test: Terrier Tow-Plane, K 8b on C of G hook. I pitched the glider
about 25 degrees nose up. The glider continued to pitch up fairly rapidly
(as at the start of a winch launch) and substantial forward movement of
the stick only slightly slowed the rate of pitch. The glider achieved
about 45 degrees nose up, speed increased rapidly from 55 knots to about
75 knots and the glider was pulled back towards level flight (again as at
the top of a winch launch). I released at that point. The entire
sequence of events occupied a VERY short period of time (subsequently
measured as 2 - 3 seconds). The Tow Pilot reported a marked deceleration
and start of pitching down which he attempted to contain by moving the
stick back; this was followed immediately by a very rapid pitch down
accompanied by significant negative “G”. The tow-plane finished up about
70 degrees nose down and took about 400 feet to recover to level flight.
We both found the experience alarming, even undertaken deliberately at
4000 feet. Our conclusion was that the combination of the initial pitch
down and the upward deflection of the elevator caused the horizontal
stabilizer/elevator combination to stall and the abrupt removal of the
down-force it provided caused the subsequent very rapid pitch-down and
negative “G”.

Our first conclusion was that, in the event of this sequence occurring
accidentally as a result of an inadvertent pitch up by the glider pilot,
there was effectively no chance that either the glider pilot or tow-pilot
would recognise the problem and pull the release in the available time.

Attempts to produce a tow-plane hook that would release automatically were
unsuccessful for reasons that became apparent later.

These tests were repeated a few years later with a PA18 – 180 as the
tow-plane, Brian Spreckley flying it. The third test described above was
repeated and photographed from a chase plane using a 35 mm motor drive
camera on automatic (this took a frame every half second – video
camcorders of small size were not readily available then). The photo
sequence started with the glider in a slightly low normal tow position and
starting to pitch up, the second frame has the glider about 30 degrees nose
up and about 20 feet higher than previously in the third frame it is about
45 degrees nose up and has gained another 30 feet or so, the tow-plane is
already starting to pitch down, in the fourth frame the glider is about
100 feet higher than its original position and the climb is starting to
shallow, the tow-plane is about 50 degrees nose down, the final frame
shows the tow-plane about 70 degrees nose down and the glider almost back
in level flight , almost directly above it (that was about the point that
I pulled the release).

Sufficiently alarmed by events, Brian Spreckley had been trying to pull
the release in the tow-plane earlier and found that it would not operate
until my releasing at the glider end removed the tension from the rope.
Subsequent tests on the ground showed that the Schweitzer hook fitted to
the tow-plane, whilst perfectly satisfactory under normal loads, was
jammed solid by the frictional loads when subject to a pull of around 700
lbs with a slight upwards component – not something that a normal
pre-flight check would reveal.

We solved that problem on our tow-planes by replacing the bolt that the
hook latches onto with a small roller bearing. So far as I know no one in
the UK has tested the Schweitzer hook as fitted to a glider, but I would
not be surprised if it exhibited the same characteristics at high loads.

The photo sequence also showed that at no time was the glider at an angle
greater than 30 degrees above the tow-plane’s centre-line. However, of
course once the glider has pitched up, the wings generate considerable
extra lift and that extra lift provides extra load on the rope. With a
large, heavy glider it is easy to exceed weak link breaking strains and
with a lightweight machine the tension can easily rise to 700 lbs or so.
With that much load on the rope, quite a small upward angle provides
enough of a vertical component to produce the results described.

That of course is the reason that attempts to produce a hook that released
if a certain angle was exceeded were unsuccessful. The, quite small, angle
between the rope and the fuselage centreline needed to trigger the “Kiting”
when the glider is pitched significantly nose-up is not much greater than
the amount of out of position commonly experienced in turbulent
conditions. We did build an experimental hook and tried it, but, set to
an angle that prevented “Kiting” it occasionally dumped an innocent glider
in turbulence, and set to an angle that prevented that, it didn’t prevent
the “Kiting”. What was needed was a hook that responded to the vertical
component of the load, not the angle at which it was applied, and that
problem we decided was beyond us (at least in a form robust and fool-proof
enough to be attached to the rear end of a tow-plane).

Our conclusions for preventing “Kiting” we

Don’t aerotow gliders, especially lightweight, low wing-loading gliders,
on C of G hooks intended for winch launching (I think the JAR 22
requirement for nose hooks to be fitted to new gliders for aerotowing was
at least in part a result of these tests).

Don’t use short ropes. The speed at which things happen varies directly
with the length of the rope.

Don’t let inexperienced pilots fly at anywhere near aft C of G.

Don’t let inexperienced pilots fly solo in turbulent conditions.

Replace or modify all Schweitzer hooks fitted to tow planes. (So far as I
know there are none on gliders in the UK, so that question never arose).

We did also modify our PA18’s so that instead of the release cable ending
at a floor-mounted lever, it went round a pulley where that lever used to
be, and then all the way up the side of the cockpit, anchored at the roof.
This meant that grabbing any point on the wire and pulling it in any
direction could operate the release; considerably easier than finding a
floor mounted lever when being subject to about minus two “G”. We never
regarded this modification as being likely to prevent a worst-case
scenario, because, as stated earlier, it was the opinion of all involved,
that in a real “Kiting” incident, there was no realistic hope that either
pilot would respond in time.

Are any of the pictures still around? I would love to see them. I'm
sure others would too.

Gary Boggs

Originally Posted by GARY BOGGS

Are any of the pictures still around? I would love to see them. I'm
sure others would too.

Gary Boggs

I think they were posted on the BGA website once?

OGP

At 20:10 06 September 2009, OregonGliderPilot wrote:

GARY BOGGS;705095 Wrote:
Are any of the pictures still around? I would love to see them. I'm
sure others would too.

Gary Boggs

I think they were posted on the BGA website once?

OGP

I have looked in the BGA website, but can't find these photos. If you
have access to the BGA Instructors Manual there is a graphic in Section 17
which shows the sequence of events. It shows that if the glider gets too
high and kites on a belly hook, the tug can be pulled into a stalled and
near vertically downwards attitude within 3 seconds! There is a note
saying that it takes at least 800 feet to recover from this!

At about the time I started gliding in the early 1980s, I remember there
were three or four such accidents to tugs in one year in the UK, all
unfortunately fatal. Also from memory I think most of them involved K18s
fitted only with belly hooks. This type is particularly prone to kite.

As a result of these and the Booker experiments, the standard towing
position was moved down a bit and glider pilots were briefed to release if
they started to get significantly too high or lost sight of the tug
altogether. Also tug rope releases where improved to make them more
accessible to the pilot, and there was a recommendation that all new
gliders should be fitted with nose hooks for aerotowing.

The main danger of getting too high is shortly after take off, when the
combination is still accelerating and the glider's wings are making more
and more lift due the increasing airspeed. The glider pilot needs to keep
easing the stick forward so that the glider does not get much higher than
the top of the tug's tail fin. It is probably a good idea to trim well
forward for this stage of the launch. If a tug upset does occur at this
stage of the launch there is almost no chance of the tug pilot being able
to recover before hitting the deck.

Derek Copeland

The graphic in the BGA Instructors Manual was based on the photos mentioned
(as was an Australian Safety Poster from around that time). The Ka18
isn't particularly prone to the accident, it's just that the small
number imported into the UK all only had C of G Hooks, no nose hooks, but
were quite often aerotowed with low experience pilots. The problem can
arise with anything aerotowed on a C of G Hook. When we bought two used
Ka18's from Dunstable at around that time we did not allow them on site
until nose-hooks were fitted.

There were never as many as three or four such fatals in one year in the
UK, but a year with two such accidents was enought to start us on the
tests described, as Booker was the busiest aerotow operation in the UK at
that time and I wanted to try to ensure we never had one.

The standard towing position was not moved down, it remained unchanged.
To go to a lower towing position (or worse still to trasit to "low-tow")
would put the glider close to, or in, the turbulent prop wash and wake of
the tow-plane, and getting bounced around by that is one of the possible
causes of the momentary, inadvertant, pitch-up that can cause the
accident.

As in almost all phases of flight the glider should be trimmed for as
close to zero forward or back pressure on the stick as can be pre-set.
Having to hold a substantial back-pressure on the stick would be
un-helpful.

In the last sentance delete the word "almost".


At 11:00 07 September 2009, Derek Copeland wrote:
At 20:10 06 September 2009, OregonGliderPilot wrote:

GARY BOGGS;705095 Wrote:
Are any of the pictures still around? I would love to see them.
I'm
sure others would too.

Gary Boggs

I think they were posted on the BGA website once?

OGP

I have looked in the BGA website, but can't find these photos. If you
have access to the BGA Instructors Manual there is a graphic in Section
17
which shows the sequence of events. It shows that if the glider gets too
high and kites on a belly hook, the tug can be pulled into a stalled and
near vertically downwards attitude within 3 seconds! There is a note
saying that it takes at least 800 feet to recover from this!

At about the time I started gliding in the early 1980s, I remember there
were three or four such accidents to tugs in one year in the UK, all
unfortunately fatal. Also from memory I think most of them involved K18s
fitted only with belly hooks. This type is particularly prone to kite.

As a result of these and the Booker experiments, the standard towing
position was moved down a bit and glider pilots were briefed to release
if
they started to get significantly too high or lost sight of the tug
altogether. Also tug rope releases where improved to make them more
accessible to the pilot, and there was a recommendation that all new
gliders should be fitted with nose hooks for aerotowing.

The main danger of getting too high is shortly after take off, when the
combination is still accelerating and the glider's wings are making
more
and more lift due the increasing airspeed. The glider pilot needs to
keep
easing the stick forward so that the glider does not get much higher
than
the top of the tug's tail fin. It is probably a good idea to trim well
forward for this stage of the launch. If a tug upset does occur at this
stage of the launch there is almost no chance of the tug pilot being
able
to recover before hitting the deck.

Derek Copeland

I was a bit slimmer in those days, but I regularly flew Bill Dean's K18 at
Lasham, which only had a belly hook. It had also been fitted with a
castoring tail wheel, which made take offs and landings in a cross wind
quite 'interesting' as it was a taildragger. I remember that even with
the trim hard forward, you still had to push a bit to stop it climbing too
high on aerotow, as it basically wanted to do a winch launch. I agree that
the type became much easier to aerotow when fitted with a nose hook, and I
did fly the Booker ones and the one at Sandhill Farm as a visitor when so
fitted.

As an instructor, I would recommend setting the trimmer slightly too far
forward, rather than slightly too far back, for the early part of the
launch as this minimises the tendency to zoom too high. You can always
retrim when you get to a safe height.

After said aerotow accidents we were definitely instructed to aerotow in a
slightly lower position, just above the slip stream but definitely not in
it. If you are not sure where the correct position is, just move down a
bit until you feel a little bit of buffeting and then move back up a few
feet. You should definitely not be looking down at the tug. The
Australians generally use the low tow position below the wake.

Derek Copeland


At 14:15 07 September 2009, Chris Rollings wrote:
The graphic in the BGA Instructors Manual was based on the photos
mentioned
(as was an Australian Safety Poster from around that time). The Ka18
isn't particularly prone to the accident, it's just that the small
number imported into the UK all only had C of G Hooks, no nose hooks,
but
were quite often aerotowed with low experience pilots. The problem can
arise with anything aerotowed on a C of G Hook. When we bought two used
Ka18's from Dunstable at around that time we did not allow them on site
until nose-hooks were fitted.

There were never as many as three or four such fatals in one year in the
UK, but a year with two such accidents was enought to start us on the
tests described, as Booker was the busiest aerotow operation in the UK
at
that time and I wanted to try to ensure we never had one.

The standard towing position was not moved down, it remained unchanged.
To go to a lower towing position (or worse still to trasit to
"low-tow")
would put the glider close to, or in, the turbulent prop wash and wake
of
the tow-plane, and getting bounced around by that is one of the possible
causes of the momentary, inadvertant, pitch-up that can cause the
accident.

As in almost all phases of flight the glider should be trimmed for as
close to zero forward or back pressure on the stick as can be pre-set.
Having to hold a substantial back-pressure on the stick would be
un-helpful.

In the last sentance delete the word "almost".


At 11:00 07 September 2009, Derek Copeland wrote:
At 20:10 06 September 2009, OregonGliderPilot wrote:

GARY BOGGS;705095 Wrote:
Are any of the pictures still around? I would love to see them.
I'm
sure others would too.

Gary Boggs

I think they were posted on the BGA website once?

OGP

I have looked in the BGA website, but can't find these photos. If you
have access to the BGA Instructors Manual there is a graphic in Section
17
which shows the sequence of events. It shows that if the glider gets
too
high and kites on a belly hook, the tug can be pulled into a stalled
and
near vertically downwards attitude within 3 seconds! There is a note
saying that it takes at least 800 feet to recover from this!

At about the time I started gliding in the early 1980s, I remember
there
were three or four such accidents to tugs in one year in the UK, all
unfortunately fatal. Also from memory I think most of them involved
K18s
fitted only with belly hooks. This type is particularly prone to kite.

As a result of these and the Booker experiments, the standard towing
position was moved down a bit and glider pilots were briefed to release
if
they started to get significantly too high or lost sight of the tug
altogether. Also tug rope releases where improved to make them more
accessible to the pilot, and there was a recommendation that all new
gliders should be fitted with nose hooks for aerotowing.

The main danger of getting too high is shortly after take off, when the
combination is still accelerating and the glider's wings are making
more
and more lift due the increasing airspeed. The glider pilot needs to
keep
easing the stick forward so that the glider does not get much higher
than
the top of the tug's tail fin. It is probably a good idea to trim well
forward for this stage of the launch. If a tug upset does occur at this
stage of the launch there is almost no chance of the tug pilot being
able
to recover before hitting the deck.

Derek Copeland

It was a Ka6 (also with CofG hook only) that was involved in the death
of the Dunstable tow pilot, and a Ka6 which nearly killed me around
the same time.

No kiting was involved in my case, the glider pilot gradually got too
high, which I was well aware of, and then increased speed in an
attempt to find the tow plane. With the tension removed from the rope
I assumed he had sorted it out (this is a BIG mistake), and when he
gave up and slowed down, the jerk on the rope snapped the tug 90 deg
nose down in a fraction of a second.

It took 400 ft to recover, which was below hedge height.

Chris Rollings wrote:

The graphic in the BGA Instructors Manual was based on the photos mentioned
(as was an Australian Safety Poster from around that time). The Ka18
isn't particularly prone to the accident, it's just that the small
number imported into the UK all only had C of G Hooks, no nose hooks, but
were quite often aerotowed with low experience pilots. The problem can
arise with anything aerotowed on a C of G Hook. When we bought two used
Ka18's from Dunstable at around that time we did not allow them on site
until nose-hooks were fitted.

There were never as many as three or four such fatals in one year in the
UK, but a year with two such accidents was enought to start us on the
tests described, as Booker was the busiest aerotow operation in the UK at
that time and I wanted to try to ensure we never had one.

The standard towing position was not moved down, it remained unchanged.
To go to a lower towing position (or worse still to trasit to "low-tow")
would put the glider close to, or in, the turbulent prop wash and wake of
the tow-plane, and getting bounced around by that is one of the possible
causes of the momentary, inadvertant, pitch-up that can cause the
accident.

As in almost all phases of flight the glider should be trimmed for as
close to zero forward or back pressure on the stick as can be pre-set.
Having to hold a substantial back-pressure on the stick would be
un-helpful.

In the last sentance delete the word "almost".


At 11:00 07 September 2009, Derek Copeland wrote:
At 20:10 06 September 2009, OregonGliderPilot wrote:

GARY BOGGS;705095 Wrote:
Are any of the pictures still around? I would love to see them.
I'm
sure others would too.

Gary Boggs

I think they were posted on the BGA website once?

OGP

I have looked in the BGA website, but can't find these photos. If you
have access to the BGA Instructors Manual there is a graphic in Section
17
which shows the sequence of events. It shows that if the glider gets too
high and kites on a belly hook, the tug can be pulled into a stalled and
near vertically downwards attitude within 3 seconds! There is a note
saying that it takes at least 800 feet to recover from this!

At about the time I started gliding in the early 1980s, I remember there
were three or four such accidents to tugs in one year in the UK, all
unfortunately fatal. Also from memory I think most of them involved K18s
fitted only with belly hooks. This type is particularly prone to kite.

As a result of these and the Booker experiments, the standard towing
position was moved down a bit and glider pilots were briefed to release
if
they started to get significantly too high or lost sight of the tug
altogether. Also tug rope releases where improved to make them more
accessible to the pilot, and there was a recommendation that all new
gliders should be fitted with nose hooks for aerotowing.

The main danger of getting too high is shortly after take off, when the
combination is still accelerating and the glider's wings are making
more
and more lift due the increasing airspeed. The glider pilot needs to
keep
easing the stick forward so that the glider does not get much higher
than
the top of the tug's tail fin. It is probably a good idea to trim well
forward for this stage of the launch. If a tug upset does occur at this
stage of the launch there is almost no chance of the tug pilot being
able
to recover before hitting the deck.

Derek Copeland