ADs State Accident May Have Been Caused By Wing-Structure Break-Up

As a result of an investigation into the September 14 crash of a Zodiac CH 601 XL, the Dutch CAA has released an emergency Airworthiness Directive grounding the type, effective October 24, 2008:

"On the 14th of September 2008 a fatal accident occurred with a Micro Light Aircraft, Type Zodiac CH 601 XL. There are indications that break-up of the wing structure was the cause of the accident. Based on the preliminary findings of the accident investigation of the Dutch Safety Board, the Civil Aviation Authority of the Netherlands declares the aircraft not airworthy until further notice."

In response to the action taken by the Dutch CAA, Zenair Europe issued a press release, and its own Airworthiness Directive:

"On Saturday October 25, Zenair SARL was informed by a Dutch Zodiac XL owner that the Dutch CAA had issued an emergency Airworthiness Directive the previous day, calling for the immediate grounding of all Zodiac XL in the Netherlands, effective immediately.

"This came as a complete surprise to Zenair Europe, Zenair Ltd, and Zenith Aircraft Co., as none of us had been previously contacted by the Dutch authorities. We were further surprised that the basis for the NL-CAA action was a preliminary accident report that offers no new findings regarding the Zodiac XL design. Rather it makes allusion to various other accidents and suggests that the 'calculated strength' of the design is 'probably too optimistic'.

"Zenair is eager to discuss the basis for these statements with the Dutch CAA and is keenly awaiting the return of CAA staff from their seasonal holiday. In the mean time, we note that no past accident investigations involving the CH 601 XL has ever found fault with the basic design; two accidents (2006 & 2008) are still being researched by the NTSB in the USA - completed design analysis in each case, however, has already found the design's engineering to be sound. We can also note that the Zodiac XL is not approved in Europe just on 'calculate strength', but on 'demonstrated strength' as well (extensive load-testing).

"To help appease possible concerns among neighboring countries, Zenair has taken the initiative of issuing a mandatory bulletin of its own. This AD (No. ZE-2008-01) addresses an important issue that may have contributed to the accident currently being investigated in Holland. We hope to share our thoughts on the issue with the Dutch CAA as soon as we may, and look forward to assisting with the on-going investigation in any way that we can.

"We believe that everyone concerned here has a common goal: to quickly find the solution(s) that will permit the Zenair CH 601 XL to once again be deemed 'airworthy' by the CAA in the Netherlands."

In its own Airworthiness Directive, Zenair calls for immediate mandatory inspection of all control cables and their tension; inspection of both ailerons for any type of deformation of the skins at the piano hinge and root rib area; and inspection of the rear spar attachment area at the wing root, looking for deformation or loose rivets.

"Under certain conditions, loose control cables can lead to flutter of control surfaces in some types of aircraft; Flutter has been experienced in the Zodiac CH 601 XL aircraft as reported by two pilots. The actions outlined in this directive are to eliminate the possibility of flutter in this aircraft design when the aircraft is flown within its design parameters," Zenair said.

At least one Zodiac aircraft has been involved in a suspicious in-flight breakup accident in the United States in the past two years. As ANN reported, a Zodiac S-LSA manufactured by Aircraft Manufacturing & Development Co. experienced an in-flight breakup while cruising approximately 8 nautical miles south of Yuba City, CA on November 4, 2006.

A witness to that accident told the NTSB the airplane's engine was "missing" and its power was "on and off." Seconds later the witness heard the sound of an explosion and observed the center section of the airplane falling straight down. The NTSB has not issued a Probable Cause report on the crash.

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