The National Transportation Safety Board says that ASTM design standards used by the Federal Aviation Administration as the basis for certificating its light sport aircraft are “deficient,” according to a report by John Croft in Flight International magazine.
Along with asking the FAA to ground one particular LSA model, Zenith’s Zodiac CH-601XL, the NTSB is asking ASTM to bolster requirements to reduce the potential for aerodynamic flutter, minimize inadvertent over-controlling of the aircraft through stick forces, and ensure accurate airspeed indications, Croft wrote. The NTSB action followed its suspicions that flutter and other related factors in six CH-601XL crashes killed 10 people since 2006.
Zenith has said it believes that wing flutter will not occur if the control cables are properly adjusted. It commented that each accident discussed in the NTSB grounding request occurred under different circumstances. “Some of the accidents are still being investigated and what caused those accidents has not been determined,” a Zenith spokesman said.
The FAA granted the first airworthiness certificates in its then-new LSA category in 2005. The category marked a sharp departure from regulatory practice, with the FAA adopting airworthiness standards written by a consensus committee system in which it was not a leader, but a minor participant. The process, governed by ASTM International, is a model the FAA may replicate in other emerging aviation categories such as unmanned and suborbital vehicles and, perhaps eventually, even in commercial aviation.