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?