NTSB Seeks FAA Grounding of Zodiacs

An urgent safety recommendation has been issued by the National Transportation Safety Board (NTSB) urging the FAA to prohibit further flight of the Zodiac CH-601XL. The aeroplane is sold both in a kit version by Zenith Aircraft and as an S-LSA manufactured by Aircraft Manufacturing & Design. According to the NTSB, the Zodiac CH-601XL has a propensity to experience aerodynamic flutter due to a significant issue with the design of the aircraft. During aerodynamic “flutter”, the control surfaces of the aeroplane can vibrate rapidly, leading to the possibility of massive structural failure, such as has occurred six times over the past three years.

The NTSB has cited four accidents in the US (two of which were experimental amateur-built aeroplanes) and two in Europe, in which CH-601XL aircraft broke up in flight, killing a total of 10 people.

The FAA has reportedly advised the American Society for Testing and Materials (ATSM) to conduct a review of its Light Sport Aircraft (LSA) standards regarding aerodynamic flutter. It has also been found that the stick force gradient was not standardised, and was lesser at high-g, making the aircraft susceptible to over-control by the pilot, which could lead to over-stressing the design limits and result in in-flight structural failure.

“The NTSB does not often recommend that all airplanes of a particular type be prohibited from further flight,” explained NTSB Acting Chairman Mark 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 Zodiac XL was introduced in 2001 as Zenith’s first entry for the Sport Pilot/LSA category and the model was replaced with the Zodiac CH-650 last year.

Matthew Heintz, manager of Zenair in Canada, has said that the company is in the process of evaluating the NTSB’s report and says that if there is a problem with the aircraft, they want to fix it. However, Zenair has absolute confidence in the aircraft. Heintz has also added that two independent firms have been conducting flutter analyses on the design and, so far, no aerodynamic flutter has been found.

Despite the recent concern, insurance availability for the aircraft has apparently not changed, as the industry is taking a “wait and see” approach.  While the FAA is looking into concerns raised over all versions of the Zodiac CH-601XL, it apparently has no plans to call for the grounding of the type in the immediate future, despite the NTSB’s recommendation.

New Zealand CAA Issues CAN For Zenith and Zenair CH601 Aircraft

The New Zealand CAA has issued a Continuing Airworthiness Notice regarding the Zenith and Zenair CH601 series “in the interests of aviation safety.”

A CAN contains non-regulatory information and guidance that does not meet the criteria for an Airworthiness Directive (AD). The inspections and practices described in this CAN must still be carried out in accordance with the applicable NZCAR Parts 21, 43 and 91. CAA’s CANs are advisory only and are not mandatory.

The CAN is applicable to “All Zenith and Zenair CH601 series aircraft” and advises operators of Zenith and Zenair CH601 series aircraft that there have been six in-flight structural breakups of Zodiac CH601 XL aircraft since 2006. It appears that aerodynamic flutter was the likely cause of four of the accidents in the USA and at least two in Europe.

The aircraft manufacturer believes flight control flutter will not occur if the control cables are correctly adjusted. On the 28th of October 2008, Zenair Europe issued SB No. ZE-2008-01 on behalf of Zenair Ltd, requiring the inspection of all control cables for correct tension to prevent aerodynamic flutter.

The CAA will continue to monitor the situation closely but in the interim it is advising owners of Zenith and Zenair CH601 series aircraft to exercise all possible caution in operating their aircraft. In particular the CAA recommends they avoid flight in severe turbulence, high speeds and/or severe manoeuvres and says that aerobatics should not be attempted.

The NZ CAA recommends the review of documents available from http://www.zenithair.com/