I sent out requests for answers to various knowledgeable individuals in advance of publishing the article above. These are the answers I have so far:

Other questions to ask are regarding:

the mass of the rope / fittings
stiffness of the rope
aerodynamic fairings on ropes (covers over the carabineers)

These factors may play a part in knotting. Knotting may be something that is important such as the Tocumwal fatality with knotted rope around a side wire, or knotting of a rope through barrel release (many of the systems have evolved with this in mind, the Dragonfly pilots have this release on the tug end and have the longest of bridles, they are very particular about the rope that they use in this area). Also, look at aerodynamic fairings on ropes (covers over the carabineers), when employed correctly may play a role in reducing the risk of capturing a wire.

More on the Tocumwal aerotow accident in a later article.

Snap link: http://ronstan.thomasnet.com/item/stainless-steel-hardware/stainless-steel-carbine-hooks/rf652?&seo=110

Ronstan RF652 hook is typical and has previously been used in Australian competitions, only with long leaders (in front of the release) to mitigate risk of the hook catching a part of the bridle or glider wires.

How do these stainless steel hooks compare with the light weight non locking aluminum carabineers? At 2.4 oz. they are 0.7 ounces heavier than the light weight carabineers linked to above, or 40% heavier.

What is "...single standard chain link used as the weak link tow ring?" You take a chain and cut every second link, leaving you with (usually some rough welded edged) rings.

The bridle was a non recommended type, non conforming because it is not the mandated non stretch type (such as spectra/dyneema).

Actually this is what the HGFA tow manual says:

"3. 3.1 - Bridle Construction

Bridles should be constructed from pre-stretched rope. This is necessary to avoid injury to the pilot in the event of a weak link break or release under tension. A bridle that can stretch under tow will spring back toward the pilot if the load is suddenly released."

"Do we have reports of incidents of "heavier" rings or locking carabineers hitting pilot's in the face and causing injury?"

This is a very real risk and there was an instance of injury in Deniliquin by a rope type bridle. This risk is mitigated in Australia by mandated low stretch bridles and low mass releases. Horse panic type releases such as illustrated in the Canadian tow manual are not recommended. Safety glasses are recommended. Vecrtan / spectra barrel type releases are fine in this regard.

"It is my experience that very few if any pilots wear hook knifes, or wear them in places that make it easy to get to their bridles to cut them. What is the percentage of pilots who do this?"

I know of one person only who does not wear a hook knife.

That would be me? :-)