The US National Transportation Safety Board says ASTM design standards used by the US Federal Aviation Administration as a basis for certificating its light sport aircraft are "deficient".

Along with asking the FAA to ground one particular LSA model, the Zenith Zodiac CH 601 XL, the NTSB is requesting that ASTM bolster requirements to reduce the potential for aerodynamic flutter, minimise inadvertent overcontrolling of the aircraft through stick forces and ensure accurate airspeed indications. The action follows revelations that flutter and other related factors are suspected in six CH 601 XL crashes that killed 10 people in Europe and the USA since 2006.

Zenith says it continues to believe that wing flutter will not occur on the model if the control cables are adjusted properly. Further, the company says 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," Zenith adds.

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 in commercial aviation.

Source: Flight International