Ron Lee wrote:

Congrats on a safe landing. Do keep us informed on actual cause.

I don't think that it will ever be possible to say absolutely, but
after a day of discussions on the COZY and canard-aviators mailing
list, and a ton of email from many experts (Burt Rutan and Mike
Melvill, both of whom I work for, included), the consensus (with which
I agree) is that the prop bolt torque was low, causing bolt failure.

For Mike Regish, yes, the bolts were safety wired, but as Bob Moore
points out, with a wood core prop that doesn't necessarily mean diddly
:-).

.... I also have a Catto three blade prop on an RV-6A. The
"undertorqued" option seems unlikely since you no doubt can
properly torque bolts.

You know, however smart, qualified, and wonderful a person may or may
not be, mistakes can be made. I know that I make them at least my
fair share. I might have screwed up in my torqueing technique; I
might have had one or two bolts that were bottomed out; I might have
had them loosen due to temperature/humidity changes; or who knows what.

Is there a chance that a change in humidity from your normal
location caused a change in torque?

Well, I've been out here in the desert for over a year now, but it's
possible that even when I THOUGHT I was testing the REAL torque, I
wasn't, since I didn't loosen them and retighten them - I just pushed
on the torque wrench.

I will heretofore be checking torque at every oil change, rather than
only at the condition inspection.

Finding the prop could answer a lot of questions.

It could, but this is the classic needle in the haystack. No roads
nearby at all. To me, it's not even remotely worth the effort to find.

--
Marc J. Zeitlin
http://www.cozybuilders.org/
Copyright (c) 2006