Experimental Planes Need Safety Retrofit, NTSB Says
A seventh crash now under investigation appears to have been caused by the aerodynamic flutter identified by NTSB last spring. Owners of factory-built Zodiac CH-601XLs have been directed to make structural modifications, but owners who built theirs from a kit are not required to make the same changes.
The latest fatal accident of an amateur-built Zodiac CH-601XL to be investigated by the National Transportation Safety Board occurred on Nov. 7, when one of the planes broke up in flight near Agnos, Ark., and the pilot was killed. Both wings of his plane separated from its fuselage in flight, the agency said.
The Zodiac CH-601XL can be bought as a completed aircraft (one that is classified as a special light sport aircraft) manufactured by Aircraft Manufacturing and Design, LLC or built by amateurs from a kit available from its designer, Zenith Aircraft Company (in which case it is classified as an experimental aircraft), according to NTSB. The agency said it asked the FAA to ground both types of the plane seven months ago after linking six accidents involving them to aerodynamic flutter, where a plane’s control surfaces and wings can suddenly oscillate and bring about structural failure. Those six accidents killed 10 people. “Preliminary investigation of the November 6 accident in Arkansas reveals a failure mode similar to that seen in the earlier crashes,” NTSB said Friday.
The FAA replied in July that they lacked "adequate justification to take immediate certificate action to ground the entire fleet," NTSB said. But on Nov. 7, a day after the most recent accident, the FAA issued a Special Airworthiness Information Bulletin strongly recommending that all owners and operators of Zodiac CH-601XL/CH650 airplanes comply with this Safety Alert/Safety Directive
issued by Aircraft Manufacturing and Design, LLC. The directive requires owners of special light sport aircraft models to make structural modifications to the airplane and add aileron counter-balances before they fly the aircraft again. Zenith “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,” NTSB said. "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 no modifications are required on the amateur-built planes," NTSB Chairman Deborah A.P. Hersman said. "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."