NTSB Identification: FTW04LA148.
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Accident occurred Sunday, May 23, 2004 in Altus, OK
Probable Cause Approval Date: 09/29/2004
Aircraft: Bruce Moore Skybolt, registration: N25BM
Injuries: 2 Uninjured.
NTSB investigators may not have traveled in support of this investigation and used data provided by various sources to prepare this aircraft accident report.
The pilot was performing aerobatic maneuvers when he noticed the fabric on the top right wing was separating and departing the airplane. The pilot reduced the engine power, airspeed, and altitude, and then returned to the airport. Examination of the airplane revealed the wing rib stitching had failed, and approximately 5 feet of the top right wing fabric and approximately 3 feet of the top right wing lower fabric was separated. According to a fabric manufacturer technical bulletin, "When light weight fabric is installed on an aircraft with a high horsepower engine and inadequate fabric forming structural spacing, coating fatigue cracks develop very rapidly...We recommend fabric weighing less than 2.4 [ounces] per [square yard] be used only on aircraft with engines up to 145 [horsepower]." The fabric covering weight on the airplane was 1.7 ounces per square yard, and the airplane was equipped with a 300-horsepower engine.
The National Transportation Safety Board determines the probable cause(s) of this accident to be: The partial in-flight separation of the wing fabric and rib structure due to an inadequate material installed by the airplane builder. Full narrative available
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