National Transportation Safety Board
> Washington, DC 20594
>
> FOR IMMEDIATE RELEASE: April 14, 2009
> SB-09-15
>
> ************************************************************
>
> NTSB ASKS FAA TO ‘PROHIBIT FURTHER FLIGHT’ OF LIGHT
> SPORT AIRPLANE TIED TO IN-FLIGHT BREAKUPS
>
>
> (Safety Recommendation A-09-30{urgent}through A-09-37 and A-
> 09-38 through A-09-40)
>
>
> ************************************************************
>
> 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.
>
> “The NTSB does not often recommend that all airplanes of a
> particular type be prohibited from further flight,” said NTSB Acting
> Chairman Mark V. Rosenker.  “In this case, we believe such action
> will save lives. Unless the safety issues with this particular Zodiac
> model are addressed, we are likely to see more accidents in which
> pilots and passengers are killed in airplanes that they believed
> were safe to fly.”
>
> The Board also found that the stick force gradient - a measure of
> the force applied to the control stick and the increase in lift that
> results -  was not uniform throughout the range of motion,
> particularly at high vertical accelerations or Gs.  The lessening of
> the gradient at high Gs could make the airplane susceptible to
> being inadvertently over-controlled by the pilot, which could create
> a condition in which the airplane is stressed beyond its design
> limits leading to an in-flight structural failure.
>
> In addition, problems with the airspeed indication system were
> identified.  Errors with the correlation between the actual airspeed
> of the airplane and that shown on the instruments in the cockpit
> could result in the airplane being piloted at airspeeds exceeding
> design limits, which could compromise the plane’s structural
> integrity. While the airspeed indication issue has not been linked
> to any accidents, the Safety Board believes that this is a safety-of-
> flight issue that should be corrected.
>
> The date, location and circumstances of the six accidents the
> Board cited in which the CH-601XL suffered in-flight structural
> failures are as follows: On February 8, 2006, near Oakdale,
> California, a CH-601XL crashed after its wings collapsed (two
> fatalities). On November 4, 2006, a CH-601XL broke up in flight
> while cruising near Yuba City, California (two fatalities). On
> February 5, 2008, a CH-601XL crashed near Barcelona, Spain,
> after its wings folded up during a descent shortly before landing
> (two fatalities). On April 7, 2008, a CH-601XL broke up in flight
> near Polk City, Florida (one fatality). On September 14, 2008, a
> CH-601XL crashed in the Netherlands (two fatalities).  On March 3,
> 2009, a CH-601XL broke up in flight while cruising near Antelope
> Island, Utah (one fatality).
>
> In addition to the urgent recommendation to the FAA on
> prohibiting further flight of the Zodiac CH 601XL, the Safety Board
> issued the following seven additional recommendations to the
> FAA: 1) make a comprehensive evaluation of the wing and aileron
> system on the Zodiac CH 601XL to identify design and/or
> operational changes that will reduce the potential for flutter; 2)
> notify owners of Zodiac CH-601XLs of any design and/or
> operational changes to the CH 601XL and require them to
> implement the changes; 3) work with ASTM International to
> incorporate standards for light sport airplanes that would reduce
> the likelihood of encountering in-flight flutter; 4) evaluate the stick
> force gradient at the aft center of gravity and  especially at the
> higher Gs, and notify pilots of such effects; 5) develop standards
> on stick force characteristics for light sport airplanes that minimize
> the possibility of pilot’s inadvertently over-controlling the airplane;
> 6) ensure that the pilot’s airspeed indicator accurately reflects the
> Plane’s velocity and update pilot operating handbooks (POHs)
> accordingly; and 7) work with ASTM International to ensure
> standards for light sport airplanes result in accurate airspeed
> indications and appropriate documentation in new airplane pilot
> operating handbooks.
>
> The Board’s investigations have identified several areas in which
> the design standards for light sport airplanes were deficient.  ASTM
> International provides the standards that are developed by industry
> working groups.  The NTSB has asked the ATSM to take the
> following actions:  1) Add requirements to ensure the standards for
> light sport airplanes reduce the potential for aerodynamic flutter to
> develop; 2) develop standards on stick force characteristics for light
> sport airplanes that minimize the possibility of pilot’s inadvertently
> over-controlling the airplane; and 3) ensure standards for light
> sport airplanes result in accurate airspeed indications and
> appropriate documentation in new airplane pilot operating
> handbooks.
>
> Safety recommendation letter to the Federal Aviation
> Administration: http://www.ntsb.gov/recs/letters/2009/A09_30_37.pdf
> Safety recommendation letter to ATSM International:
> http://www.ntsb.gov/recs/letters/2009/A09_38_40.pdf
>
> -30-
>
> NTSB Media Contact: Peter Knudson/Keith Holloway
> (202) 314-6100
> This e-mail address is being protected from spambots. You need JavaScript enabled to view it or This e-mail address is being protected from spambots. You need JavaScript enabled to view it