This just in – The NTSB has issued an unusual request to FAA to immediately ground the Zenair CH601XL, a special light sport aircraft (S-LSA) . NTSB identified 6 fatal accidents involving in-flight breakups and resulting in 10 fatalities since 2006. Two of the breakups occurred outside the U.S.
This is a sobering development in the burgeoning LSA market and one that the “special” designation was hoping to address. “Special” means that the aircraft are built in a factory to ASTM consensus design standards (originally American Society for Testing and Materials). This organization was chosen as a simple, less expensive and extensive alternative to FAA certification. A cynic might say that we should stick with tried and true methods. Of course, if that were the case airplanes might not have been invented and I point out that there have been some spectacular failures in FAA-certificated aircraft. Several of the aircraft were kits so there’s a mix between the factory vs. homebuilt and it appears that if the designer’s specs are not followed exactly, bad things can happen.
We need to learn more. NTSB pointed to flutter and control forces as areas of interest. According to NTSB, “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.”
The NTSB does not have the authority to ground the aircraft but the FAA does. Six breakups in seemingly routine flight does not instill confidence so it’s time to get to the facts – quickly and unemotionally.
The safety record of S-LSA aircraft has been reasonable up to this point with no particular aircraft failure modes. ASF has tallied many landing accidents but this seems to relate to pilot skill as opposed to hardware issues.
This a setback for Zenair, and their family of owners and pilots. We encourage a thorough and timely investigation to resolve this.