Another In-Flight Wing Seperation Reinforces Growing Concerns

As previously noted on ANN, another Zodiac CH-601 series (the subject of an NTSB grounding recommendation to the FAA  seven months ago, until a flight control problem could be corrected), was involved in another fatal accident last week.

On November 6, 2009, a Zodiac CH-601XL, an experimental amateur-built airplane, was destroyed as a result of an in-flight breakup near Agnos, Arkansas, killing the pilot -- who was the sole occupant. The debris field was scattered over an area more than 600 feet long. Both wings had separated from the fuselage in-flight.

In April 2009, the NTSB called on the FAA to ground the Zodiac CH-601XL after the Safety Board linked six accidents involving that aircraft model to aerodynamic flutter, a phenomenon in which the control surfaces and wings of the airplane can suddenly oscillate and lead to catastrophic structural failure. Those accidents killed a total of ten people. Preliminary investigation of the November 6 accident in Arkansas reveals a failure mode similar to that seen in the earlier crashes.

The Safety Board's urgent recommendation to the FAA was to "prohibit further flight of the Zodiac CH-601XL, both special light sport aircraft and experimental, until such time that the FAA determines that the CH-601XL has adequate protection from flutter." The FAA replied in July that they lacked "adequate justification to take immediate certificate action to ground the entire fleet." 

The Zodiac is available as a ready-to-purchase airplane (classified as a special light sport aircraft), which is manufactured by Aircraft Manufacturing and Design, LLC, and as an amateur-built plane from a kit (classified as an experimental aircraft) available from the designer, Zenith Aircraft Company.

On November 7, one day after the accident in Arkansas, the FAA issued a Special Airworthiness Information Bulletin strongly recommending that all owners and operators of Zodiac CH-601XL/CH650 airplanes comply with a Safety Alert/Safety Directive issued by the manufacturer, Aircraft Manufacturing and Design, LLC. The Safety Alert/Safety Directive requires all owners of special light sport aircraft models to make structural modifications to the airplane and add aileron counter-balances before further flight. Since the directives of the manufacturers of special light sport aircraft must be complied with, those aircraft not in compliance are effectively prohibited from further flight.

CH-601 XL File Photo

The designer, Zenith Aircraft Company, has asked the owners of the kit-built experimental airplanes to make the same modifications, but there is no requirement that the modifications be completed before further flight is attempted.

"We are pleased that the FAA and the manufacturer have acted on the safety-of-flight issues that we identified with the Zodiac special light sport airplane. We are troubled, however, that the no modifications are required on the amateur-built planes," said NTSB Chairman Deborah A.P. Hersman. "We are very concerned that a lack of required compliance may lead to more accidents like the one in
Arkansas, and others we've already seen," she said.

CH-601 XL File Photo

Zenith's Christ Hentz has recommended an aggressive series of upgrades, via an 'Upgrade Package'  to "over" correct potential issues in the aircraft. "The past two years have been challenging for the CH 601 XL community around the world. As we all know, a number of accidents have occurred over the span of a few years for which no common cause has been determined. This lack of a “smoking gun” has caused all kinds of conjectures and wild guesses as to probable cause, and each time a new 'theory' or 'solution' is proposed, I and numerous engineers spend long hours trying to validate or rebuke the latest round of speculation. To this date, after thousands of man-hours of investigations, multiple design reviews and an unheard-of amount of testing, the accidents in question still do not share a common cause. In offering this 'Upgrade Package' I have had to set aside my own professional opinion (that the design is sound) as well as legal counsel’s advice in order to provide builders, owners and pilots the 'fix' that they have been asking me for. With these upgrades (my '180º shift'), the safety margins of key airframe components have been dramatically increased…" said Heintz.

The Safety Board's investigation of the November 6 accident is on-going.

FMI: www.ntsb.gov, http://www.zenithair.com, www.zenithair.com/zodiac/xl/data/qa-chris-heintz-1a.pdf