NTSB recommends grounding US 601XLs

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 Larry Hursh on April 14, 2009 at 8:55pm
As my EAA Tech Advisor (also will be my DAR) was looking over my wings before I put the top skins to them, he made mention to be about my airlerons being so big and not having any counter-balances on them. I've been keeping up with all the advisories that Zenith puts out and are saving them in a file for my Advisor to read. This way, he will know that I am concerned about any updates that might be issued, but the fact that I am safety conscience. I expect to read about this on Zenith's website within the next day or so. I certainly hope Zenith officially notifies (via certified letter) each and every one of us that hold plans with serial numbers and are building/flying this aircraft. In my humble opinion, if you say "to hell with it, no government is telling me not to fly my plane", you are only fooling yourself. Sure you probably did build it right, BUT if the ailerons have a design flaw, and you insist on flying it, then WHO is the biggest fool? It won't be me. I fully expect Zenith to take action on this - they have to............
Comment by Stephen R. Smith on April 14, 2009 at 8:49pm
I think we know reasonably well that the problem is control flutter due to loose cables. Ever since the control cable issue came out a few months ago I have kept my cables tight and have told everyone else I know flying a 601XL in my area to do the same.

Frankly I don’t want anymore weight in my plane. I feel the risk of flutter is low for me because I don’t fly fast (anymore) and I do pay attention to the cables.

I do know of one 601 pilot who experienced aileron flutter on a high-speed pass. He pulled power and it went away before anything bad happened. He did say it was a frightening phenomenon. His cables WERE very loose at the time.

For what it is worth I have had my airplane up to 181 MPH – really – I have the GPS track to prove it. I did it only once about 18 months ago. I never saw any point in doing it again. Nothing bad happened. May cables were tight at the time.

I was planning to leave for Sun-N-Fun this Saturday. I sure as heck don’t want to get stuck thousands of miles from home because I have been grounded. Sure puts a damper on my plans.

Steve

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