Aerotow Regulations and Rope Specifications

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

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?

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

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.

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.

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."

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."

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

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

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.