What stops it being used, is it just the lack of STC for each type of
glider/tow-plane?

At 16:05 12 September 2009, sisu1a wrote:
Just out of curiosity, do the problems with releasing under high
load
that are known with the Schweizer hook extend also to the Tost hook?

Ed

No, Tost hooks are fine. The Polish hooks are great too. It's a real
shame the Mcfarlane replacement towhook is not able to be used on most
Schweizers & towplanes though. It has a roller bearing, hardened ways,
improved ring positioning and increased leverage. It looks much like a
Schweizer hook and mounts w/same bolt pattern, however it DOES release
under pressure.
http://www.mcfarlaneaviation.com/new.../march2007.htm

-Paul