Aerotow Regulations and Rope Specifications

[Markus Graeber]

I am in the process of writing up some regulations for aerotowing to
standardize operations and ensure safe procedures for us here in
Colombia. The civil aviation authorities don't know a thing about the
intricacies of aerotowing so we are on our own with how we want to go
about it. Hence the desire to implement something that resembles best
bractices across the gliding world.

I have been reviewing information/regulations from Germany, the US,
the UK, Australia and New Zealand as well as manufacturer information
and manuals. The result of this excercise so far has been that there
are some considerable differences across countries even with such
basic things as aerotow rope requirements.

As far as a general guide is concerned I ran into the newly published
book "Aerotowing Gliders" by John Marriot (http://www.amazon.com/
Aerotowing-Gliders-towing-gliders-emphasis/dp/1456775154/ref=sr_1_1?
s=books&ie=UTF8&qid=1325720610&sr=1-1) which after a first quick read
looks like a good basis for general operating procedures.

As far as aerotow investigations and rope requirements are concerned I
had, among other things, a good look at

http://www.negevgliding.com/safety/airtow.pdf
http://www.dg-flugzeugbau.de/Data/TN-DG/service-infos/2004-54-e.pdf
http://www.dg-flugzeugbau.de/sollbruchstelle-d.html (http://
translate.google.com/translate?sl=de&tl=en&u=://www.dg-flugzeugbau.de
%2Fsollbruchstelle-d.html&act=url)
http://www.dg-flugzeugbau.de/flugzeugschlepp-d.html (http://
translate.google.com/translate?sl=de&tl=en&u=http://www.dg-
flugzeugbau.de/flugzeugschlepp-d.html&act=url)

In addition and since I have years of past aerotow experience in the
US I looked again at the regulations in the FARs:

------------------------

FAR 91.309

Minimum Strength = 80 percent of the glider maximum certificated
operating weight
Maximum Strength = twice the maximum certificated operating weight

Note: Maximum certificated operating weight can be found in the glider
POH and may be the Maximum certificated gross weight at takeoff.

If the towrope has a breaking strength more than twice the maximum
certificated operating weight of the glider being towed, a safety link
has to be installed at the point of attachment of the glider and the
tow plane with the following breaking strength requirements.

Safety Link (Weak Link) Requirements

Safety link (Weak Link) at the glider end:

Minimum Strength = 80 percent of the glider maximum certificated
operating weight
Maximum Strength = twice the maximum certificated operating weight

Safety link (Weak Link) at the tow plane end:

Strength Requirements = Greater, but not more than 25% greater
than that of the safety link on the glider end, and not more than
twice the maximum certificated operating weight of the glider

------------------------

My conclusions that have come out of this so far are:

Aerotow, especially of single seater light wing loading gliders,
should only be done with a nose hook (and not a CG hook) to avoid the
danger of the rapid onset of kiting that will not break your standard
glider weak link but stall the tow plane (see UK tests described in
http://www.negevgliding.com/safety/airtow.pdf).

Weak links at both ends of the rope to protect the glider but also the
tow plane in case the rope gets caught e.g. in a tree or power line
after glider release when close to the ground (I ran into several
accident reports where this happened, especially after a tow emergency
at low altitude). Interestingly enough the UK requires a weak link at
the tow plane end to protect the tow plane with an additional glider
end weak link being optional while the Germans only explicitely
require a glider end weak link according to the glider manual.

I have a personal distaste for the US arangement of using ropes as
weak links since it is not easy to tell which rope has which diameter/
is made of which material to then indirectly deduct the rope weak link/
aerotow rope strength (if no weak links are used). In addition, rope
wear can quickly become an issue limiting weak link/rope strength.
Coming originally from a winching background for me there is nothing
simpler than teaching and checking the weak link color required for a
specific glider, no second guessing, no hidden rope wear reducing the
weak link/rope strength.

Now to the recommended weak link strengths: The US idea of having a
slightly stronger weak link on the tow plane end seems to be a
sensible idea to have the weak link fail first on the glider end to
protect the glider from getting entangled with the rope which could
happen if it breaks on the tow plane end. However, the specific US
weak link strength requirements do not make much sense and e.g. in the
case of the Diamond DA-40 contravene what the aircraft manual permits
(http://www.diamond-air.at/fileadmin/uploads/files/after_sales_support/
DA40-180/Airplane_Flight_Manual/Supplements/60101e-o1-r1.pdf):

DA-40 Manual states: Weak link of max. 899 lbf (400 daN) on tow plane
end required, on glider side optional according to glider manual, 750
kg/1653 lb max glider weight on tow, tow rope min breaking load 2248
lbf (1000 daN)

If I use the requirements of FAR 91.309 to determine weak link
strengths I could use between 80% and 200% of max gross weight of the
glider for the glider end but it would be limited to just below the
strength of the tow plane end weak link. So if the DA-40 manual limits
me to 899 lbf (400 daN) on the tow plane end my glider weak link has
to be less than that, best case 898 lbf (399 daN). The best I can do
now for max gross weight is a minimum of 80% of the glider's max gross
weight for the glider end weak link which would get me at the most
1122.5 lbs/509 kg for the glider. In short the FARs would not allow me
to tow any modern 2 seater with a DA-40 even though the DA-40 manual
explicitely allows for up to 1653 lb/750 kg gliders.

Now considering the UK tests mentioned earlier it seems to me like a
really bad idea to use a tow rope with no weak links approaching twice
the max gross weight as allowed by the FARs.

Research done in Germany suggests (see above links to documents on the
DG website) that weak links of no more than 661 lbf/300 daN are
necessary on the glider end even though most glider handbooks specify
the same weak link strength for aerotow as for winch launching (which
involves much higher forces).

So the quick summary of my take so far on all this with regards to
aerotow ropes is:

- Minimum aerotow rope breaking load of 2248 lbf (1000 daN)
- General purpose length of aerotow rope for standard daily ops of 50m/
165 feet
- Use of 2 weak links, one on the glider end, one on the tow plane end
- Weak links with the Tost reserve setup, 899 lbf (400 daN) on the tow
plane end, 661 lbf/300 daN on the glider end

Looking forward to comments, suggestions, experiences etc. Thanks in
advance,

Markus Graeber
Aeroclub de Colombia
Gliding Colombia/Vuelo a Vela Colombia

[BobW]

On 1/4/2012 6:11 PM, Markus Graeber wrote:
> I am in the process of writing up some regulations for aerotowing to
> standardize operations and ensure safe procedures for us here in
> Colombia. The civil aviation authorities don't know a thing about the
> intricacies of aerotowing so we are on our own with how we want to go
> about it. Hence the desire to implement something that resembles best
> bractices across the gliding world.
>
> I have been reviewing information/regulations from Germany, the US,
> the UK, Australia and New Zealand as well as manufacturer information
> and manuals.

<Snip of excellent research summary...>

> So the quick summary of my take so far on all this with regards to
> aerotow ropes is:
>
> - Minimum aerotow rope breaking load of 2248 lbf (1000 daN)
> - General purpose length of aerotow rope for standard daily ops of 50m/
> 165 feet
> - Use of 2 weak links, one on the glider end, one on the tow plane end
> - Weak links with the Tost reserve setup, 899 lbf (400 daN) on the tow
> plane end, 661 lbf/300 daN on the glider end
>
> Looking forward to comments, suggestions, experiences etc. Thanks in
> advance,
>
> Markus Graeber
> Aeroclub de Colombia
> Gliding Colombia/Vuelo a Vela Colombia

Hello Markus,

Seems like a great "good news/bad news" situation you're faced with...the good
news of having a blank sheet of paper & the bad news being (non-bureaucratic)
you have to do all the filling in of it. I hope the Powers That Be eventually
see fit to buy into your conclusions/suggestions...

Off-the-cuff thoughts follow...
- "Real" (as in metallic, testable, precision-made) weak links at both ends
seem to me to be eminently sensible & much preferred over "knots in rope"
sort of weak links. While only Tost (so far as I'm aware) makes these, anyone
with access to spec-ed metal, standard machine tools, and a pull tester could
easily "roll their own." Hence, spec-ing such doesn't necessarily build
"whiney" up-front costs. IM(U.S.-based)O, the U.S. FAA approach of specifying
*only* breaking strengths probably has worked as well as it has mainly because
historically the U.S. has been primarily an aero-tow operation. Kinda-sorta
related, personally I wouldn't winch launch without a "metal-spec" weak link
at the glider end.
- I think you're right to "ignore DA-40-like" plane-specific special cases in
any spec-ing you do. Let plane manufacturers rule out/self-limit any newer
models they roll out. It probably won't be in our lifetimes
non-manufacturer-spec-ed acceptable towplanes (e.g. Pawnees and Super Cubs in
the U.S.) vanish. Don't self-create problems for your country/self.
- Avoid the "over specification" swamp. For example, don't specify max/min
rope length or strength. (Well, OK, maybe some motherhood words about an
aerotow rope having to be stronger than either weak link, just to satisfy the
lawyer crowd.) On the winch side, if some bubba wants to build a monster winch
using chain as the cable, a glider-end weak link should adequately protect the
glider and its educated, qualified and current pilot (and passenger, if any),
which I would suggest is the proper/sufficient goal. Let education and "the
market" address all the other glider-launching, safety-related issues.

You should get some interesting feedback!

Regards,
Bob W.

[Bill D]

A careful reading of the US FAR's shows 91.309 is not the only
applicable rule addressing aero tow weak links. 91.9 require all
aircraft to be operated in accordance with their Approved Flight
Manuals (POH) - if one was published as part of the airworthiness
documentation. JAR-22 gliders and most other modern glider have such
AFM's which specify an aero tow weak link. Seen in this light, 91.309
is a historical accident which has become a "catch all" for gliders
without an AFM specified weak link, (eg, Schweizers).

Taken together, 91.309 and 91.9 mean that the AFM specified weak link
it to be used at the glider end and a weak link at the tow plane end
must be stronger than the glider end link but not more than 25%
stronger. FAA FSDO inspectors I've discussed this with agree with
this interpretation.

AFAIK, no one in the US is actually operating in accordance with the
above rules since they think it would be a hassle to be switching weak
links for every glider. Fortunately, Tost makes hardware which makes
it somewhat easier. It wouldn't surprise me to see an NPRM clarifying
the above.

Bill D


On Jan 4, 6:11*pm, Markus Graeber > wrote:
> I am in the process of writing up some regulations for aerotowing to
> standardize operations and ensure safe procedures for us here in
> Colombia. The civil aviation authorities don't know a thing about the
> intricacies of aerotowing so we are on our own with how we want to go
> about it. Hence the desire to implement something that resembles best
> bractices across the gliding world.
>
> I have been reviewing information/regulations from Germany, the US,
> the UK, Australia and New Zealand as well as manufacturer information
> and manuals. The result of this excercise so far has been that there
> are some considerable differences across countries even with such
> basic things as aerotow rope requirements.
>
> As far as a general guide is concerned I ran into the newly published
> book "Aerotowing Gliders" by John Marriot (http://www.amazon.com/
> Aerotowing-Gliders-towing-gliders-emphasis/dp/1456775154/ref=sr_1_1?
> s=books&ie=UTF8&qid=1325720610&sr=1-1) which after a first quick read
> looks like a good basis for general operating procedures.
>
> As far as aerotow investigations and rope requirements are concerned I
> had, among other things, a good look at
>
> http://www.negevgliding.com/safety/airtow.pdfhttp://www.dg-flugzeugbau.de/Data/TN-DG/service-infos/2004-54-e.pdfhttp://www.dg-flugzeugbau.de/sollbruchstelle-d.html(http://
> translate.google.com/translate?sl=de&tl=en&u=://www.dg-flugzeugbau.de
> %2Fsollbruchstelle-d.html&act=url)http://www.dg-flugzeugbau.de/flugzeugschlepp-d.html(http://
> translate.google.com/translate?sl=de&tl=en&u=http://www.dg-
> flugzeugbau.de/flugzeugschlepp-d.html&act=url)
>
> In addition and since I have years of past aerotow experience in the
> US I looked again at the regulations in the FARs:
>
> ------------------------
>
> FAR 91.309
>
> * * Minimum Strength = 80 percent of the glider maximum certificated
> operating weight
> * * Maximum Strength = twice the maximum certificated operating weight
>
> Note: Maximum certificated operating weight can be found in the glider
> POH and may be the Maximum certificated gross weight at takeoff.
>
> If the towrope has a breaking strength more than twice the maximum
> certificated operating weight of the glider being towed, a safety link
> has to be installed at the point of attachment of the glider and the
> tow plane with the following breaking strength requirements.
>
> Safety Link (Weak Link) Requirements
>
> Safety link (Weak Link) at the glider end:
>
> * * Minimum Strength = 80 percent of the glider maximum certificated
> operating weight
> * * Maximum Strength = twice the maximum certificated operating weight
>
> Safety link (Weak Link) at the tow plane end:
>
> * * Strength Requirements = Greater, but not more than 25% greater
> than that of the safety link on the glider end, and not more than
> twice the maximum certificated operating weight of the glider
>
> ------------------------
>
> My conclusions that have come out of this so far are:
>
> Aerotow, especially of single seater light wing loading gliders,
> should only be done with a nose hook (and not a CG hook) to avoid the
> danger of the rapid onset of kiting that will not break your standard
> glider weak link but stall the tow plane (see UK tests described inhttp://www.negevgliding.com/safety/airtow.pdf).
>
> Weak links at both ends of the rope to protect the glider but also the
> tow plane in case the rope gets caught e.g. in a tree or power line
> after glider release when close to the ground (I ran into several
> accident reports where this happened, especially after a tow emergency
> at low altitude). Interestingly enough the UK requires a weak link at
> the tow plane end to protect the tow plane with an additional glider
> end weak link being optional while the Germans only explicitely
> require a glider end weak link according to the glider manual.
>
> I have a personal distaste for the US arangement of using ropes as
> weak links since it is not easy to tell which rope has which diameter/
> is made of which material to then indirectly deduct the rope weak link/
> aerotow rope strength (if no weak links are used). In addition, rope
> wear can quickly become an issue limiting weak link/rope strength.
> Coming originally from a winching background for me there is nothing
> simpler than teaching and checking the weak link color required for a
> specific glider, no second guessing, no hidden rope wear reducing the
> weak link/rope strength.
>
> Now to the recommended weak link strengths: The US idea of having a
> slightly stronger weak link on the tow plane end seems to be a
> sensible idea to have the weak link fail first on the glider end to
> protect the glider from getting entangled with the rope which could
> happen if it breaks on the tow plane end. However, the specific US
> weak link strength requirements do not make much sense and e.g. in the
> case of the Diamond DA-40 contravene what the aircraft manual permits
> (http://www.diamond-air.at/fileadmin/uploads/files/after_sales_support/
> DA40-180/Airplane_Flight_Manual/Supplements/60101e-o1-r1.pdf):
>
> DA-40 Manual states: Weak link of max. 899 lbf (400 daN) on tow plane
> end required, on glider side optional according to glider manual, 750
> kg/1653 lb max glider weight on tow, tow rope min breaking load 2248
> lbf (1000 daN)
>
> If I use the requirements of FAR 91.309 to determine weak link
> strengths I could use between 80% and 200% of max gross weight of the
> glider for the glider end but it would be limited to just below the
> strength of the tow plane end weak link. So if the DA-40 manual limits
> me to 899 lbf (400 daN) on the tow plane end my glider weak link has
> to be less than that, best case 898 lbf (399 daN). The best I can do
> now for max gross weight is a minimum of 80% of the glider's max gross
> weight for the glider end weak link which would get me at the most
> 1122.5 lbs/509 kg for the glider. In short the FARs would not allow me
> to tow any modern 2 seater with a DA-40 even though the DA-40 manual
> explicitely allows for up to 1653 lb/750 kg gliders.
>
> Now considering the UK tests mentioned earlier it seems to me like a
> really bad idea to use a tow rope with no weak links approaching twice
> the max gross weight as allowed by the FARs.
>
> Research done in Germany suggests (see above links to documents on the
> DG website) that weak links of no more than 661 lbf/300 daN are
> necessary on the glider end even though most glider handbooks specify
> the same weak link strength for aerotow as for winch launching (which
> involves much higher forces).
>
> So the quick summary of my take so far on all this with regards to
> aerotow ropes is:
>
> - Minimum aerotow rope breaking load of 2248 lbf (1000 daN)
> - General purpose length of aerotow rope for standard daily ops of 50m/
> 165 feet
> - Use of 2 weak links, one on the glider end, one on the tow plane end
> - Weak links with the Tost reserve setup, 899 lbf (400 daN) on the tow
> plane end, 661 lbf/300 daN on the glider end
>
> Looking forward to comments, suggestions, experiences etc. Thanks in
> advance,
>
> Markus Graeber
> Aeroclub de Colombia
> Gliding Colombia/Vuelo a Vela Colombia

[John Roche-Kelly]

Hi Markus

https://www.gliding.co.uk/bgainfo/clubmanagement/documents/aer
otownotes.pdf

for the British Gliding Association handbook. I am sure that the
BGA would be more than happy to help you develop your own
national equivalent.

Best wishes

John Roche-Kelly
Norfolk Gliding Club

[John Cochrane[_2_]]

On Jan 4, 7:11*pm, Markus Graeber > wrote:
> I am in the process of writing up some regulations for aerotowing to
> standardize operations and ensure safe procedures for us here in
> Colombia. The civil aviation authorities don't know a thing about the
> intricacies of aerotowing so we are on our own with how we want to go
> about it. Hence the desire to implement something that resembles best
> bractices across the gliding world.
>
> I have been reviewing information/regulations from Germany, the US,
> the UK, Australia and New Zealand as well as manufacturer information
> and manuals. The result of this excercise so far has been that there
> are some considerable differences across countries even with such
> basic things as aerotow rope requirements.
>
> As far as a general guide is concerned I ran into the newly published
> book "Aerotowing Gliders" by John Marriot (http://www.amazon.com/
> Aerotowing-Gliders-towing-gliders-emphasis/dp/1456775154/ref=sr_1_1?
> s=books&ie=UTF8&qid=1325720610&sr=1-1) which after a first quick read
> looks like a good basis for general operating procedures.
>
> As far as aerotow investigations and rope requirements are concerned I
> had, among other things, a good look at
>
> http://www.negevgliding.com/safety/airtow.pdfhttp://www.dg-flugzeugbau.de/Data/TN-DG/service-infos/2004-54-e.pdfhttp://www.dg-flugzeugbau.de/sollbruchstelle-d.html(http://
> translate.google.com/translate?sl=de&tl=en&u=://www.dg-flugzeugbau.de
> %2Fsollbruchstelle-d.html&act=url)http://www.dg-flugzeugbau.de/flugzeugschlepp-d.html(http://
> translate.google.com/translate?sl=de&tl=en&u=http://www.dg-
> flugzeugbau.de/flugzeugschlepp-d.html&act=url)
>
> In addition and since I have years of past aerotow experience in the
> US I looked again at the regulations in the FARs:
>
> ------------------------
>
> FAR 91.309
>
> * * Minimum Strength = 80 percent of the glider maximum certificated
> operating weight
> * * Maximum Strength = twice the maximum certificated operating weight
>
> Note: Maximum certificated operating weight can be found in the glider
> POH and may be the Maximum certificated gross weight at takeoff.
>
> If the towrope has a breaking strength more than twice the maximum
> certificated operating weight of the glider being towed, a safety link
> has to be installed at the point of attachment of the glider and the
> tow plane with the following breaking strength requirements.
>
> Safety Link (Weak Link) Requirements
>
> Safety link (Weak Link) at the glider end:
>
> * * Minimum Strength = 80 percent of the glider maximum certificated
> operating weight
> * * Maximum Strength = twice the maximum certificated operating weight
>
> Safety link (Weak Link) at the tow plane end:
>
> * * Strength Requirements = Greater, but not more than 25% greater
> than that of the safety link on the glider end, and not more than
> twice the maximum certificated operating weight of the glider
>
> ------------------------
>
> My conclusions that have come out of this so far are:
>
> Aerotow, especially of single seater light wing loading gliders,
> should only be done with a nose hook (and not a CG hook) to avoid the
> danger of the rapid onset of kiting that will not break your standard
> glider weak link but stall the tow plane (see UK tests described inhttp://www.negevgliding.com/safety/airtow.pdf).
>
> Weak links at both ends of the rope to protect the glider but also the
> tow plane in case the rope gets caught e.g. in a tree or power line
> after glider release when close to the ground (I ran into several
> accident reports where this happened, especially after a tow emergency
> at low altitude). Interestingly enough the UK requires a weak link at
> the tow plane end to protect the tow plane with an additional glider
> end weak link being optional while the Germans only explicitely
> require a glider end weak link according to the glider manual.
>
> I have a personal distaste for the US arangement of using ropes as
> weak links since it is not easy to tell which rope has which diameter/
> is made of which material to then indirectly deduct the rope weak link/
> aerotow rope strength (if no weak links are used). In addition, rope
> wear can quickly become an issue limiting weak link/rope strength.
> Coming originally from a winching background for me there is nothing
> simpler than teaching and checking the weak link color required for a
> specific glider, no second guessing, no hidden rope wear reducing the
> weak link/rope strength.
>
> Now to the recommended weak link strengths: The US idea of having a
> slightly stronger weak link on the tow plane end seems to be a
> sensible idea to have the weak link fail first on the glider end to
> protect the glider from getting entangled with the rope which could
> happen if it breaks on the tow plane end. However, the specific US
> weak link strength requirements do not make much sense and e.g. in the
> case of the Diamond DA-40 contravene what the aircraft manual permits
> (http://www.diamond-air.at/fileadmin/uploads/files/after_sales_support/
> DA40-180/Airplane_Flight_Manual/Supplements/60101e-o1-r1.pdf):
>
> DA-40 Manual states: Weak link of max. 899 lbf (400 daN) on tow plane
> end required, on glider side optional according to glider manual, 750
> kg/1653 lb max glider weight on tow, tow rope min breaking load 2248
> lbf (1000 daN)
>
> If I use the requirements of FAR 91.309 to determine weak link
> strengths I could use between 80% and 200% of max gross weight of the
> glider for the glider end but it would be limited to just below the
> strength of the tow plane end weak link. So if the DA-40 manual limits
> me to 899 lbf (400 daN) on the tow plane end my glider weak link has
> to be less than that, best case 898 lbf (399 daN). The best I can do
> now for max gross weight is a minimum of 80% of the glider's max gross
> weight for the glider end weak link which would get me at the most
> 1122.5 lbs/509 kg for the glider. In short the FARs would not allow me
> to tow any modern 2 seater with a DA-40 even though the DA-40 manual
> explicitely allows for up to 1653 lb/750 kg gliders.
>
> Now considering the UK tests mentioned earlier it seems to me like a
> really bad idea to use a tow rope with no weak links approaching twice
> the max gross weight as allowed by the FARs.
>
> Research done in Germany suggests (see above links to documents on the
> DG website) that weak links of no more than 661 lbf/300 daN are
> necessary on the glider end even though most glider handbooks specify
> the same weak link strength for aerotow as for winch launching (which
> involves much higher forces).
>
> So the quick summary of my take so far on all this with regards to
> aerotow ropes is:
>
> - Minimum aerotow rope breaking load of 2248 lbf (1000 daN)
> - General purpose length of aerotow rope for standard daily ops of 50m/
> 165 feet
> - Use of 2 weak links, one on the glider end, one on the tow plane end
> - Weak links with the Tost reserve setup, 899 lbf (400 daN) on the tow
> plane end, 661 lbf/300 daN on the glider end
>
> Looking forward to comments, suggestions, experiences etc. Thanks in
> advance,
>
> Markus Graeber
> Aeroclub de Colombia
> Gliding Colombia/Vuelo a Vela Colombia

In addition to the technical advice given by others, let me offer
tactical advice.

Keep the regulation as simple as possible. Develop a separate set of
"best practices" which are good advice but not codified into legally
binding regulation.

The US 80% - 200% has been in the regulations since time immemorial --
at least the 1940s. Regulations don't adapt to advances in technology
and technique. The 80Z%-200% contravenes what's written in many
operating handbooks for example.

Nosehooks are another example. OK, write a best practices that it's
better to airtow with nosehooks. But don't put that in regulations!
Many of us have been airtowing with belly hooks for a long time, and
it's simply not legal to retrofit others with nosehooks. (If the
manufacturer doesn't have an approved kit, and you have a fully legal
repair station, etc.) You can end up unintentionally grounding half
your fleet.

John Cochrane

[Markus Graeber]

Thanks all, especially the BGA Aerotowing Guidance Notes linked to by
John is very good stuff (by the same author as the mentioned book), I
hadn't seen those yet even though we use quite a few BGA publications
as a reference here. Just to clarify the situation, I am not going to
write any legally binding regulations for the civil aviation
authorities here (Aerocivil). The idea is a common sense set of rules
for the federation level and a very specific set of rules for the
club's operation based on the equipment and operating environment we
have. Since we control these rules ourselves (much like the BGA does
in the UK as well as the AU GFA and NZ GN as largely selfgoverning
gliding organisations) it will be easy for us to change them quickly
if needed.

In addition, gliders here in Colombia are in practical terms treated
like experimentals in the US so we can pretty much do as we please as
long as we can reasonably assure it's safe to fly. If for example I
want to install a nose hook I don't have to worry about STCs from the
FAA/EASA, if I can dig up install instructions based on solid
engineering I can just go ahead and install it. One example is the 2
LAK 12s we have in the club. They are known for lacking a bit of
rudder so the owners got together and developed a slight extension to
improve rudder effectiveness. Both LAKs also came without CG hooks so
in order to get them ready for our winch launch operation I just
organized the factory drawings for the CG hook install with the
necessary specifications for the belly reinforcement. The actual
install with the factory information is not that big of a deal if you
have a good A&P around that has experience with fibreglass, no
artificial legal barriers to worry about.

Here, like all over the world, but sadly sometime more so, people have
a habit of just improvising and out of convenience ingnore what should
be common sense. Hence the need to be very specific, at least at the
club level, based on a general set of reference rules. In addition,
the club has a professional pilot school that is now starting to
implement glider training into the general power pilot curriculum so
we have to make every effort to develop a sound set of rules we can
point to that can safe our ass and the school's certification when
that accident that shouldn't happen eventually does.

Hence my desire to make the best out of the situation and, free from
any governmental tight jacket, develop a set of rules based on best
practices and the latest research/developments. So for starters I
would for example have no problem mandating that the school needs to
replace the Schweizer aerotow hook on our PA-18 with a Tost for use
for aerotow training while resticting the use of the Schweizer hook on
our private C-180 to glider pilots with a certain aerotow experience
level until it is replaced by a Tost. Taking into account the UK tests
and fatal accidents that have happened due to the inability to trigger
the release of a Schweizer hook under high loads I find it a bit mind
boggling that these hooks are still legal in many countries and not
being phased out on a mandatory basis. All the club's gliders have
dedicated aerotow hooks so the only thing that needs to be done for
now is mandating their use for aerotow to limit the risk of kiting. If
someone eventually brings in a glider with a CG hook only (e.g. an ASW
20) we could then deal with it on a case by case basis on the
federation or club level.

As far as the aerotow ropes are concerned I am considering requiring a
minimum rope strength (e.g. 1000 daN) and and weak links on both ends
that comply with the max limits in the respective airplane's manual, I
don't really see any valid excuse for not making that relatively small
investment into proper safety equipment. On top of that would then be
the recommendation to use a 400 or 500 daN weak link on the tow plane
side not exceeding any limits imposed by the manufacturer while
recommending 300 daN for most gliders or 400 daN for Open Class
gliders with a take off weight of more than 600 kg (having in mind
recent research and DG's weak link recommendation of half the glider's
take-off weight).

Keep it coming,

Markus Graeber

[kirk.stant]

On Jan 5, 10:58*am, Markus Graeber > wrote:
> Thanks all, especially the BGA Aerotowing Guidance Notes linked to by
> John is very good stuff (by the same author as the mentioned book), I
> hadn't seen those yet even though we use quite a few BGA publications
> as a reference here. Just to clarify the situation, I am not going to
> write any legally binding regulations for the civil aviation
> authorities here (Aerocivil). The idea is a common sense set of rules
> for the federation level and a very specific set of rules for the
> club's operation based on the equipment and operating environment we
> have. Since we control these rules ourselves (much like the BGA does
> in the UK as well as the AU GFA and NZ GN as largely selfgoverning
> gliding organisations) it will be easy for us to change them quickly
> if needed.
>
> In addition, gliders here in Colombia are in practical terms treated
> like experimentals in the US so we can pretty much do as we please as
> long as we can reasonably assure it's safe to fly. If for example I
> want to install a nose hook I don't have to worry about STCs from the
> FAA/EASA, if I can dig up install instructions based on solid
> engineering I can just go ahead and install it. One example is the 2
> LAK 12s we have in the club. They are known for lacking a bit of
> rudder so the owners got together and developed a slight extension to
> improve rudder effectiveness. Both LAKs also came without CG hooks so
> in order to get them ready for our winch launch operation I just
> organized the factory drawings for the CG hook install with the
> necessary specifications for the belly reinforcement. The actual
> install with the factory information is not that big of a deal if you
> have a good A&P around that has experience with fibreglass, no
> artificial legal barriers to worry about.
>
> Here, like all over the world, but sadly sometime more so, people have
> a habit of just improvising and out of convenience ingnore what should
> be common sense. Hence the need to be very specific, at least at the
> club level, based on a general set of reference rules. In addition,
> the club has a professional pilot school that is now starting to
> implement glider training into the general power pilot curriculum so
> we have to make every effort to develop a sound set of rules we can
> point to that can safe our ass and the school's certification when
> that accident that shouldn't happen eventually does.
>
> Hence my desire to make the best out of the situation and, free from
> any governmental tight jacket, develop a set of rules based on best
> practices and the latest research/developments. So for starters I
> would for example have no problem mandating that the school needs to
> replace the Schweizer aerotow hook on our PA-18 with a Tost for use
> for aerotow training while resticting the use of the Schweizer hook on
> our private C-180 to glider pilots with a certain aerotow experience
> level until it is replaced by a Tost. Taking into account the UK tests
> and fatal accidents that have happened due to the inability to trigger
> the release of a Schweizer hook under high loads I find it a bit mind
> boggling that these hooks are still legal in many countries and not
> being phased out on a mandatory basis. All the club's gliders have
> dedicated aerotow hooks so the only thing that needs to be done for
> now is mandating their use for aerotow to limit the risk of kiting. If
> someone eventually brings in a glider with a CG hook only (e.g. an ASW
> 20) we could then deal with it on a case by case basis on the
> federation or club level.
>
> As far as the aerotow ropes are concerned I am considering requiring a
> minimum rope strength (e.g. 1000 daN) and and weak links on both ends
> that comply with the max limits in the respective airplane's manual, I
> don't really see any valid excuse for not making that relatively small
> investment into proper safety equipment. On top of that would then be
> the recommendation to use a 400 or 500 daN weak link on the tow plane
> side not exceeding any limits imposed by the manufacturer while
> recommending 300 daN for most gliders or 400 daN for Open Class
> gliders with a take off weight of more than 600 kg (having in mind
> recent research and DG's weak link recommendation of half the glider's
> take-off weight).
>
> Keep it coming,
>
> Markus Graeber

Markus,

About the Schweizer tow hooks on towplanes: While the Tost is without
a doubt a better solution, and safer, we have been using the Schweizer
in the US for a long time with few problems. Unless you fly a fleet
of early trainers, the pitch up problem is probably more theoretical
than real (for that matter, it would still be a problem with the Tost
at low altitude, since you still have to release and recover!). That
being said, one relatively simple fix is to invert the Schweizer
release on the towplane, so the arm releases from the bottom (like on
the glider). That way, upwards tension on the towrope caused by
kiting is taken by the fixed arm and pivot, avoiding the problem of
the towrope tension jamming the release arm. There is a 337 for this
mod on Pawnees - Turf Soaring in Arizona developed it and they could
help if interested.

Regardless of the type of tow hook, a good briefing for both the tow
pilot and glider pilot on the causes and consequences of this type of
upset is essential!

Cheers,

Kirk

[Mike the Strike]

On Jan 5, 11:45*am, "kirk.stant" > wrote:
> On Jan 5, 10:58*am, Markus Graeber > wrote:
>
>
>
>
>
>
>
>
>
> > Thanks all, especially the BGA Aerotowing Guidance Notes linked to by
> > John is very good stuff (by the same author as the mentioned book), I
> > hadn't seen those yet even though we use quite a few BGA publications
> > as a reference here. Just to clarify the situation, I am not going to
> > write any legally binding regulations for the civil aviation
> > authorities here (Aerocivil). The idea is a common sense set of rules
> > for the federation level and a very specific set of rules for the
> > club's operation based on the equipment and operating environment we
> > have. Since we control these rules ourselves (much like the BGA does
> > in the UK as well as the AU GFA and NZ GN as largely selfgoverning
> > gliding organisations) it will be easy for us to change them quickly
> > if needed.
>
> > In addition, gliders here in Colombia are in practical terms treated
> > like experimentals in the US so we can pretty much do as we please as
> > long as we can reasonably assure it's safe to fly. If for example I
> > want to install a nose hook I don't have to worry about STCs from the
> > FAA/EASA, if I can dig up install instructions based on solid
> > engineering I can just go ahead and install it. One example is the 2
> > LAK 12s we have in the club. They are known for lacking a bit of
> > rudder so the owners got together and developed a slight extension to
> > improve rudder effectiveness. Both LAKs also came without CG hooks so
> > in order to get them ready for our winch launch operation I just
> > organized the factory drawings for the CG hook install with the
> > necessary specifications for the belly reinforcement. The actual
> > install with the factory information is not that big of a deal if you
> > have a good A&P around that has experience with fibreglass, no
> > artificial legal barriers to worry about.
>
> > Here, like all over the world, but sadly sometime more so, people have
> > a habit of just improvising and out of convenience ingnore what should
> > be common sense. Hence the need to be very specific, at least at the
> > club level, based on a general set of reference rules. In addition,
> > the club has a professional pilot school that is now starting to
> > implement glider training into the general power pilot curriculum so
> > we have to make every effort to develop a sound set of rules we can
> > point to that can safe our ass and the school's certification when
> > that accident that shouldn't happen eventually does.
>
> > Hence my desire to make the best out of the situation and, free from
> > any governmental tight jacket, develop a set of rules based on best
> > practices and the latest research/developments. So for starters I
> > would for example have no problem mandating that the school needs to
> > replace the Schweizer aerotow hook on our PA-18 with a Tost for use
> > for aerotow training while resticting the use of the Schweizer hook on
> > our private C-180 to glider pilots with a certain aerotow experience
> > level until it is replaced by a Tost. Taking into account the UK tests
> > and fatal accidents that have happened due to the inability to trigger
> > the release of a Schweizer hook under high loads I find it a bit mind
> > boggling that these hooks are still legal in many countries and not
> > being phased out on a mandatory basis. All the club's gliders have
> > dedicated aerotow hooks so the only thing that needs to be done for
> > now is mandating their use for aerotow to limit the risk of kiting. If
> > someone eventually brings in a glider with a CG hook only (e.g. an ASW
> > 20) we could then deal with it on a case by case basis on the
> > federation or club level.
>
> > As far as the aerotow ropes are concerned I am considering requiring a
> > minimum rope strength (e.g. 1000 daN) and and weak links on both ends
> > that comply with the max limits in the respective airplane's manual, I
> > don't really see any valid excuse for not making that relatively small
> > investment into proper safety equipment. On top of that would then be
> > the recommendation to use a 400 or 500 daN weak link on the tow plane
> > side not exceeding any limits imposed by the manufacturer while
> > recommending 300 daN for most gliders or 400 daN for Open Class
> > gliders with a take off weight of more than 600 kg (having in mind
> > recent research and DG's weak link recommendation of half the glider's
> > take-off weight).
>
> > Keep it coming,
>
> > Markus Graeber
>
> Markus,
>
> About the Schweizer tow hooks on towplanes: *While the Tost is without
> a doubt a better solution, and safer, we have been using the Schweizer
> in the US for a long time with few problems. *Unless you fly a fleet
> of early trainers, the pitch up problem is probably more theoretical
> than real (for that matter, it would still be a problem with the Tost
> at low altitude, since you still have to release and recover!). *That
> being said, one relatively simple fix is to invert the Schweizer
> release on the towplane, so the arm releases from the bottom (like on
> the glider). *That way, upwards tension on the towrope caused by
> kiting is taken by the fixed arm and pivot, avoiding the problem of
> the towrope tension jamming the release arm. *There is a 337 for this
> mod on Pawnees - Turf Soaring in Arizona developed it and they could
> help if interested.
>
> Regardless of the type of tow hook, a good briefing for both the tow
> pilot and glider pilot on the causes and consequences of this type of
> upset is essential!
>
> Cheers,
>
> Kirk

You might also want to revisit the pros and cons of high versus low
tow. Low tow seems likely to be safer for the tow pilot as kiting
upsets are less likely.

Mike

[Markus Graeber]

Thanks Kirk, good point, I had heard about inverting the Schweizer tow
hook many years ago while still flying in ABQ but somehow forgot about
it. We have to worry within the club about a PA-18 and a C-180, will
check with the shop what it would take to invert them and if/what the
legal ramifications in Colombia would be.

Markus

[John Roche-Kelly]

Low tow very tricky in a glider with only a CoG hook.

John
>
>You might also want to revisit the pros and cons of high versus
low
>tow. Low tow seems likely to be safer for the tow pilot as kiting
>upsets are less likely.
>
>Mike
>

[[email protected]]

On Jan 5, 3:38*pm, John Roche-Kelly >
wrote:
> Low tow very tricky in a glider with only a CoG hook.
>
> John
>
> NOT true. I've flown low tow with CG hooks for 35 years with no issues.
UH
>
>
>
>

[son_of_flubber]

On Wednesday, January 4, 2012 at 11:24:22 PM UTC-5, Bill D wrote:
> A careful reading of the US FAR's shows 91.309 is not the only
> applicable rule addressing aero tow weak links. 91.9 require all
> aircraft to be operated in accordance with their Approved Flight
> Manuals (POH) - if one was published as part of the airworthiness
> documentation. JAR-22 gliders and most other modern glider have such
> AFM's which specify an aero tow weak link. Seen in this light, 91.309
> is a historical accident which has become a "catch all" for gliders
> without an AFM specified weak link, (eg, Schweizers).
>
> Taken together, 91.309 and 91.9 mean that the AFM specified weak link
> it to be used at the glider end and a weak link at the tow plane end
> must be stronger than the glider end link but not more than 25%
> stronger. FAA FSDO inspectors I've discussed this with agree with
> this interpretation.
>
> AFAIK, no one in the US is actually operating in accordance with the
> above rules since they think it would be a hassle to be switching weak
> links for every glider. Fortunately, Tost makes hardware which makes
> it somewhat easier. It wouldn't surprise me to see an NPRM clarifying
> the above.


Has any clarity emerged since this was posted (in Jan 2012) on how to satisfy the POH specified weak link and 91.309 simultaneously?

I'd guess that a shiny new POH specified weak link of 1400-1700 lbs will break after the somewhat worn/used tow rope at my club... so inserting the weak link at the glider would not change the outcome in practice. Putting a stronger weak link at the tow plane would likewise not change the outcome.

The POH also calls for a 40 meter (131 foot) 'long' tow rope.

Do issues like this ever get resolved?

[Bill T]

A 130ft rope is a bit on the short side. We start with about 200ft before the eye splice at each end, plus weak links. The glider end wears out from "inflight whipping" and being dragged on landing. We'll shorten it a couple of times. Normally no shorter than 150ft, but by then the rest of the rope is about worn out.

BillT

[Pat Russell[_2_]]

> Do issues like this ever get resolved?

Some do. Some don't.

Nobody is pushing for this one to be resolved because current practice is more enlightened than the thinking behind the regulation.

FAR 91.309 was written as a result of research conducted with a winch.

[Bill D]

On Wednesday, May 20, 2015 at 5:27:57 AM UTC-6, Pat Russell wrote:
> > Do issues like this ever get resolved?
>
> Some do. Some don't.
>
> Nobody is pushing for this one to be resolved because current practice is more enlightened than the thinking behind the regulation.
>
> FAR 91.309 was written as a result of research conducted with a winch.

91.309 had nothing whatsoever to do with winches - it applies only to aero tow. It was written into the FAR's in the 1950's because none of the WWII surpluss gliders nor many of the subsequent Schweizer gliders offered weak-link guidance in their manuals.

European (JAR-22/CS-22 certificated) gliders do call out weak-links in their Approved Flight Manuals for both winch launch and aero tow and FAR 91.9 makes the use of those weak-links manditory.

[Bob Pasker]

The other question is who is responsible for compliance with the tow regs?

The glider pilot (who probably never sees the rope)?

The glider pilot (who only gets to see one end if the ground crew happens to show it to him)?

The ground crewmember (who has no regulatory responsibility)?

Separately, in ASI's operation procedures manual, section 4.1 says: "Tow ropes are typically set up with a combination of Schweizer and Tost rings. If weak links are desired they must be provided by the glider owner."

[Bob Pasker]

well shucks. corrected:

On Wednesday, May 20, 2015 at 11:58:12 AM UTC-4, Bob Pasker wrote:
> The other question is who is responsible for compliance with the tow regs?
>
> The TOW pilot (who probably never sees the rope)?
>
> The glider pilot (who only gets to see one end if the ground crew happens to show it to him)?
>
> The ground crewmember (who has no regulatory responsibility)?
>
> Separately, in ASI's operation procedures manual, section 4.1 says: "Tow ropes are typically set up with a combination of Schweizer and Tost rings. If weak links are desired they must be provided by the glider owner."

[kirk.stant]

On Wednesday, May 20, 2015 at 10:59:04 AM UTC-5, Bob Pasker wrote:
>
> > The TOW pilot (who probably never sees the rope)?

Bob, whatever makes you think the tow pilot never sees the rope? Aside from the fact that most tow pilots are also glider pilots, it's usually the tow pilot who preflights and attaches the towrope to his towplane at the start of operations, who checks it out during breaks in tows (usually by "snaking" it out behind his towplane), and who winds it up (or coils it) at the end of the day prior to storing it.

Some big operations (and races) may drop ropes and reattach a new one prior to each tow - but those are probably exceptions.

When I'm towing I often end up inspecting the tow rope several times a day - and often find knots and other problems before they become an issue - I consider it part of my job as a tow pilot.

I get the feeling that your experiences with tow pilots has not left you with a very high opinion of the breed... ;^)

Kirk
Pawnee.__________________.LS6

[Bob Pasker]

thanks for the correction! i'm sure there's a broad range of tow rope inspections going on, but i've honestly never seen the tow *pilot* handle and inspect the rope, only the ground crew

on the hookup side of things, I've had all sorts of different experiences:

everything from the ground crew just grabbing the end rope and giving me hand signals to open/close the release knob

to handing me the glider end of the rope for my inspection, attaching the ring, and giving a glider-moving tug on the rope



On Wednesday, May 20, 2015 at 12:42:04 PM UTC-4, kirk.stant wrote:
> On Wednesday, May 20, 2015 at 10:59:04 AM UTC-5, Bob Pasker wrote:
> >
> > > The TOW pilot (who probably never sees the rope)?
>
> Bob, whatever makes you think the tow pilot never sees the rope? Aside from the fact that most tow pilots are also glider pilots, it's usually the tow pilot who preflights and attaches the towrope to his towplane at the start of operations, who checks it out during breaks in tows (usually by "snaking" it out behind his towplane), and who winds it up (or coils it) at the end of the day prior to storing it.
>
> Some big operations (and races) may drop ropes and reattach a new one prior to each tow - but those are probably exceptions.
>
> When I'm towing I often end up inspecting the tow rope several times a day - and often find knots and other problems before they become an issue - I consider it part of my job as a tow pilot.
>
> I get the feeling that your experiences with tow pilots has not left you with a very high opinion of the breed... ;^)
>
> Kirk
> Pawnee.__________________.LS6

[BobW]

On 5/20/2015 9:59 AM, Bob Pasker wrote:
> well shucks. corrected:
>
> On Wednesday, May 20, 2015 at 11:58:12 AM UTC-4, Bob Pasker wrote:
>> The other question is who is responsible for compliance with the tow
>> regs?
>>
>> The TOW pilot (who probably never sees the rope)?
In my club, a daily responsibility of the tow pilot prior to the day's first
tow is visually inspecting the entire length of the towrope. Decision to use
as-is, shorten, or discard (meaning: cut into "obviously too-short-for-towing"
lengths) is entirely the towpilot's responsibility.

>> The glider pilot (who only gets to see one end if the ground crew happens
>> to show it to him)?
Every tow, SOP is for the wing runner to show (and hand-to, if requested by
the glider pilot) the glider-end of the towrope to the glider pilot for his or
her inspection, after which the glider type can choose to launch, replace the
weak link or (very rarely) request the line be shortened or replaced prior to
the tow.

>> The ground crewmember (who has no regulatory responsibility)?
See above...

A host of obvious questions likely springs to each reader's mind, all centered
on the "burning question": How can anyone KNOW any of this does any good/meets
regulatory compliance/etc.?

FWIW, strictly my own personal conclusions as a self-interested glider
sort/engineer, and based on having done my own digging over time into these
sorts of questions, here's my take on things:

a) "Actual line safety," "legally-binding regulatory safety," and "known
regulatory compliance" are pretty much different things, with VERY fuzzy,
arguably smallish-to-largish overlapping subsets. Some of the fuzziness is due
to unavoidable, practical, realities...e.g. testing/methodology,
continuing-use vs. degradation testing, correlating visual degradation to
measurable strength, etc. Some is due to the inherent difficulties in trying
to define/describe/place hard/legal bounds on engineering problems. Some is, I
would bet, almost certainly due to bureaucratic hand-washing/disinterest/etc.

b) At least one (engineer) member of my club built a pull-to-failure test rig
(resides in the towplane hangar for any curious club member to "play with")
and (more than once) performed extensive parametric testing over the years, of
new and used tow ropes and weak link methodologies (e.g. separate links of
smaller-than-towrope diameters, knots in the rope, etc.). In large part the
club's daily procedures described above are derived from this testing, said
testing coupling at some level with regulatory guidelines.

c) A former (late) on-field glider FBO (CFIG, FAA designated examiner, A&P [w.
IA?], "engineer-head") had done his own independent pull-to-failure testing
along the lines of B) above...and interestingly came to essentially the same
conclusions as my (operationally independent) club, regarding "the best
method" to safely "meet the intent of regulations."

Strictly from personal engineering curiosity, I picked the brains of both men
once learning of their test efforts. My interest was in doing what I could to
reassure myself the club's towrope guidelines conveyed to every member,
weren't simply picked out of the air or otherwise "of dubious provenance." I
had zero interest in bringing "Philadelphia lawyer-ism" to the regulatory
question of "What's safe?"

Bottom line is in over 30 years of operations from the field - over which time
I've seen towrope/weaklink methods evolve and "reinvent a wheel" once or twice
- zero "entirely unforeseeable" towrope/weaklink issues come to mind, while I
*can* remember some unknown quantity of self-inflicted rope/link failures (aka
footshots from slack line training or PIC inattention). My conclusion?
Regardless of the fun-to-discuss, of-legal-implication issues surrounding how
"to best define & regulate" towrope/weaklink strengths, is that "for all
practical purposes" our gliderpilot derived, local towrope procedures, pretty
much "work acceptably" and have the benefit of simplicity.

In my mind, "If it ain't broke, don't fix it," applies on this front, though I
realize "Better is the enemy of good enough," might also be brought to the
discussion. Meanwhile, I'll bet Real Money that anyone "needing absolute
assurance" of towline/weaklink breaking strength on every given tow, is doomed
to the same unquantifiable disappointment as those arguing how many angels can
fit on the head of a pin. And, yes, I'm aware of Tost's metallic weaklinks,
and readily acknowledge their superiority for winch launching, while being
prepared to debate their "necessity" for aerotow.

YMMV,
Bob W.

[son_of_flubber]

On Wednesday, May 20, 2015 at 4:22:37 PM UTC-4, BobW wrote:
<500 words of tantalizing buildup and then no mention of the actual 'club procedures'>

[Bill T]

My club, the tow pilot inspect the rope and both links at the beginning of the day. The ground crew puts the rope away, another chance for inspection.
We use 3Ply Twisted Polypropylene , 7/16 " is the main rope 200ft, 5/16 weak link on the tow pilot end, 1/4" weak link on the glider end.
This works for all gliders except the Janus C which specifies in the POH a heavier weak link, it gets the 5/16" on both ends.

5/16" is to strong for the SGS 1-26, 1/4" works for the 1-26, Grob 103, 2-33 and most single seat glass with no water.

The main rope has an eye splice on each end. The weak links have eye splices with the tost or schweizer ring in the eye, a plastic tube over the 1/4" protects the ring from chaffing on the rope. Eye splices to swap the weak links are easy for the appropriate ring. Students can eye splice weak links before solo.

The ground crew presents the weak to the glider pilot before hook up. As slack goes out the glider pilot and ground crew watch for knots.
We will shorten the rope as needed for wear, down to about 150ft minimum. Normally by the time the rope is that short it is worn out from dragging, whipping and UV.
BillT