TMetzinger
Final Approach
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.
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.
