NTSB -- NTSB ASKS FAA TO PROHIBIT FUTHER FLIGHT OF LIGHT SPORT AIRPLANE TIED TO IN-FLIGHT BREAKUPS

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NTSB PRESS RELEASE / SAFETY RECOMMENDATION

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National Transportation Safety Board

Washington, DC 20594

FOR IMMEDIATE RELEASE: April 14, 2009

SB-09-15

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NTSB ASKS FAA TO ‘PROHIBIT FUTHER 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)

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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

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

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NTSB Media Contact: Peter Knudson/Keith Holloway

(202) 314-6100

peter.knudson@xxxxxxxx or hollowk@xxxxxxxx

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http://www.ntsb.gov/recs/letters/

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The complete recommendation letter is available on the Web

at the URL indicated above.

The letter is in the Portable Document Format (PDF) and can

be read using the Acrobat Reader 5.0 or later from Adobe

(http://www.adobe.com/prodindex/acrobat/readstep.html).

An archive of recommendation letters is available at

http://www.ntsb.gov/recs/letters/letters.htm.

Electronic versions of letters may or may not include

enclosures; however, related publications, accident

briefs, and aviation accident synopses may be found

on the NTSB website.

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