According to an NTSB press release:

Washington, DC - The National Transportation Safety Board today issued an urgent safety recommendation to the Federal Aviation Administration (FAA) in which it asked the agency to prohibit further flight of a type of a small airplane that has been involved in six in-flight structural breakups since 2006. The recommendations apply to the Zodiac CH-601XL, a low-wing, fixed-gear, single- engine, two-seat general aviation airplane designed by Zenair, Inc. In its urgent safety recommendation, the Board cited four accidents in the United States and two in Europe in which the CH-601XL broke up in-flight killing a total of ten people. Aerodynamic flutter - a phenomenon in which the control surfaces of the airplane can suddenly vibrate, and if unmitigated, can lead to catastrophic structural failure - is suspected in all of the accidents.

The CH-601XL was certified as a Special Light Sport Aircraft (S-LSA) by the FAA in 2005. This type of certification does not require that the FAA approve the airplane’s design. Instead, the airplane model is issued an airworthiness certificate if the manufacturer asserts that the plane meets industry accepted design standards and has passed a series ground and flight tests.

The Safety Board’s urgent recommendation to the FAA is to prohibit further flight of the Zodiac CH-601XL until they can determine that the airplane is no longer susceptible to aerodynamic flutter. The Safety Board’s investigations of the accidents that occurred in the U.S. point to a problem with the design of the flight control system, which makes the airplane susceptible to flutter.

This is not a hoax, people. The recommendation letters from the NTSB to the FAA and ASTM are available online, as well.

I plan to keep flying my Zodiac unless and until the FAA or AMD issue orders to ground the aircraft. I do keep on top of my aileron cable tensions per the AMD service bulletin - though the NTSB letters reveal those tensions were developed on the CH2000 Alarus, not the Zodiac - and make sure there's tension on the cables during preflight; keep the airspeed within the green arc unless the air's absolutely glass smooth; and slow to maneuvering speed in anything more than slight turbulence. I believe these steps will minimize the risk of flutter until a permanent fix can be found.

I do hope that Zenair and AMD will, finally, extend the testing they did for the Europeans to the 1320-pound USA version as well, and put this matter to rest once and for all.

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Comment by Mark Ertz on May 3, 2009 at 11:38pm
Not a Hoax, a market miss leader. My serial number in over six Thousand plus. I have 300 plus hours on my a/c. No Flutter. Just increase cable tension as the AD from europe recommends and end of story. All the FBOs, Factory fixed freaks and piper & cessna programed minds are off base again. This is an attempted to kill a great production line. Basically, they do not know how to deal with what they do not understand. Me and my airplane are free spirits and independent. If the other guys cannot gets a part of the action ($) they dog you. These guys would have grounded the Wright Brothers. They would have stopped Lindbrgh from flying ove the Atlantic. Worry about the TSA not the NTSB. The NTSB have their hands full in the Terminals and they are over their heads with the airlines. Fly Free and be Happy..........
Comment by Dave Gray on April 19, 2009 at 2:47am
Chris Heintz's engineering diploma (Masters) specialized in flutter and the Concord. I suspect that is the reason that the FAA has not supported the NTSB'S recommendation.
Comment by Phill Barnes on April 19, 2009 at 1:36am
That link again. see if it works this time.

Comment by Phill Barnes on April 19, 2009 at 1:26am
Please click on this link and if you click on the links in my post under the aileron pushrod pics, you will see aileron balance weights and wing tips added to the zodiac xl in Brazil.

Phill Barnes
Comment by Bob Pustell on April 18, 2009 at 10:44pm
I am in the very beginning of building my XL, so will not be doing wings or ailerons for a while. I hope the factory or some creative/talented soul out there comes up with a good balance weight setup. That, combined with staying on top of cable tension (which should be done on any airplane) should take care of things. The other option might be push-pull tubes instead of cables to control the ailerons, maybe............
Comment by Jake Reyna on April 17, 2009 at 12:08pm
Steve, I think you're on the right track. Since we are the manufacturers of experimental aircraft we have the ability to alter/modify a design. I wouldn't suggest we change the structure or alter spars, etc., but dealing with aileron flutter is as you say an easy fix.

I was wondering if gap sealing the aileron, thereby supporting the entire bottom out to the end of the aileron, if that would act as a damper and reduce the possibility of flutter, along with the benefits associated with gap sealing

Has anybody gap sealed their ailerons? If so, have you experienced any flutter?
Comment by Larry Hursh on April 14, 2009 at 9:08pm
Thanks for the clarification Jay. I can understand it now. There for a minute, I was thinking my government was starting to censor my postings (maybe sooner than we think....). Thanks again,
PS - Who in their right mind would want to give such a nice guy as you any problems? (these nuts are everywhere I might add). I think I live near a couple here
Comment by Jay Maynard on April 14, 2009 at 9:00pm
Larry, that's my choice, not the site's. I do that (and do so on my other blogs, too) because, as an Internet celebrity, I attract folks who follow me around and make irrelevant comments about me personally rather than sticking to the subject of the post. I make a policy of approving any comment that's on-topic.
Comment by Larry Hursh on April 14, 2009 at 8:57pm
Since WHEN does ANY messages from ANYONE need to be "approved" before people can see it??? WHO SAYS SO??? If this is a fact, then I'm on the WRONG WEBSITE!
Comment by John Cange on April 14, 2009 at 8:56pm
It'd be interesting to know if there is flutter in ailerons without the piano hinges as well. As stiff as mine are, I can't imagine any flutter. I don't know if there's a design problem or not, but it's going to be hard for Zenith to ignore the NTSB findings.

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