Citing six recorded in-flight breakups leading to 10 fatalities since 2006, the NTSB has asked the FAA to ground the Zodiac 601XL. Previously available as a kitplane, it was certified as a light sport aircraft in 2005. It is based on an original configuration created by designer Chris Heinz, of Switzerland, in the early 1970s. The NTSB said the design of the 601XL is susceptible to aerodynamic flutter, leading to structural failure. Acting chairman of the safety agency said, "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 NTSB wrote that ASTM International, the agency that administers design standards for light sport aircraft, should establish requirements for light-sport designs that address the potential for aerodynamic flutter-and also standards for stick-force characteristics that would minimize the chance of pilots over controlling.