Towing Accident Rate vs GA?

On Jan 27, 2:03*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

Amazing the NTSB overlooked the tow hook installation and completely
disregarded the most likely probable cause - that the tug had an
unrecoverable upset caused the glider being out of position.

This report, and one for a tow fatal at Peoria, AZ, seem to show that
NTSB is completely unfamiliar with the tug upset scenario.

The combination of a 2-33 which requires considerable forward stick
pressure to maintain position on tow, a distracted glider pilot, and a
****ty tug tow hook was a sure set up for another dead tow pilot.

Andy

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

The following extracts come from multiple years of SSF(Soaring Safety
Foundation) Safety Reviews. See the reports for more details on each
of the
accidents.

http://www.soaringsafety.org/prevention/reports.html

The SSF does not know how many hours or flights were flown by gliders/
tow
planes so the following is raw data and not statistics.

ACCIDENTS INVOLVING TOW PLANES

2009
During FY09, one accident involving tow aircraft occurred resulting in
fatal
injuries to the pilot. The tow-plane was towing a Schweizer glider
when it
crashed shortly after takeoff.

2008
During FY08, one accident involving tow aircraft occurred resulting in
no
injuries to the pilot. As noted above, tow-plane was involved in a mid-
air
collision with the glider it had just released.

2007
During FY07, one accident involving tow aircraft occurred resulting in
fatal
injuries to the pilot. As noted above, the glider released after
noticing a
problem with the towplane. The towplane departed the right side of
the
runway and crashed while attempting to avoid trees.

2006
During FY06 only a single accident directly involved a towplane. As
noted
below, the towplane was preparing to launch when it was struck by a
landing
glider. The pilot of a Piper Pawnee (PA-25-235) was uninjured when
the
airplane was struck by a landing Grob 103 glider. The glider pilot
received
minor injuries while the passenger was uninjured. *NTSB SEA06LA163A
and
SEA06LA163B.

2005
During 2005, three accidents involving tow aircraft occurred during
the
landing phase of flight. One commercially rated and two privately
rated
pilots received no injuries as a result of these accidents, but all
three
airplanes were substantially damaged during the event.

2004
During 2004, five accidents involving tow aircraft occurred during
the
take-off phase of flight. As a result of these accidents, two pilots
were
fatally injured, two pilots received no injuries, and one pilot and
one
passenger received minor injuries. Additionally, two tow aircraft
were
destroyed and three were substantially damaged during these events.

2000-2003
Not available on the above SSF link.

1999
During 1999, four accidents involving tow aircraft were reported to
the
National Transportation Safety Board. Two of these accidents occurred
in-flight while the remaining events were divided between the takeoff
and
landing phases of flight. As a result of these accidents, two pilots
were
fatally injured and two aircraft were destroyed.

1998
During 1998, three accidents involving tow aircraft occurred during
the
takeoff phase of flight. As a result of these accidents, one pilot
was
fatally injured and two pilots received minor injuries. Additionally,
two
tow aircraft were substantially damaged and a third was destroyed.