Ron Wanttaja wrote:
You're right, I don't think they can formally take action against the
Experimental Amateur-Built Zenairs. And if they do, it wouldn't last
long.... the "manufacturer" of the aircraft can "correct the
condition" any way they see fit.

Here's the notice online, which in turn contains links to safety letters to
the FAA and ATSM International:

http://www.ntsb.gov/Pressrel/2009/090414a.html

The very first item NTSB recommends in the FAA letter
(http://www.ntsb.gov/recs/letters/2009/A09_30_37.pdf)
to the FAA is:

"Prohibit further flight of the Zodiac CH-601XL, both special light sport
aircraft and experimental, until such time that the Federal Aviation
Administration determines that the CH-601XL has adequate protection from
flutter. (A-09-30) (Urgent)"

I don't think the authors of that NTSB safety letter quite understand
experimental certificates and their ramifications. For example, there is at
least one builder who pointed out on the Matronics Zenith mailing list that
he built his aircraft using push rods, not cables.