NTSB Identification: NYC96GA083.
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Accident occurred Thursday, April 04, 1996 in CHARLESTON, WV
Probable Cause Approval Date: 05/02/1997
Aircraft: Bell 206L-1, registration: N79SP
Injuries: 2 Fatal.

: NTSB investigators either traveled in support of this investigation or conducted a significant amount of investigative work without any travel, and used data obtained from various sources to prepare this public aircraft accident report.

Three minutes after takeoff, an ATC controller heard a garbled transmission with an ELT signal in the background. Witnesses observed the helicopter in level flight, about 300 feet above a hill, when a tail section separated from the helicopter, followed by the helicopter entering a spin, rolling inverted, and descending into trees. The tail boom section aft of boom station 167, which included the upper and lower vertical fin, the tail rotor gear box, and the tail rotor hub and blades, was found 650 feet from the main wreckage. Examination revealed fatigue cracks at the separated area of the tail section. Due to reports of tail boom cracking, an Alert Service Bulletin had been published by the manufacturer in 1987 recommending an inspection of the tail boom every 100 hours, which had been complied with by the operator. The manufacturer and the FAA certification office were aware of a few reports of tail boom cracking, and were not aware of over 220 Service Difficulty Reports that concerned cracks in the Bell 206L tail booms. A doubler was added to the failed area on recent production models; however, no modifications were developed to add a doubler to the failed area of the older models.

The National Transportation Safety Board determines the probable cause(s) of this accident to be:

the helicopter manufacturer's inadequate maintenance service bulletin inspection interval which failed to provide timely detection of preexisting fatigue cracks in the tail boom. Factors were: the manufacturer's failure to develop a modification of the failed area, and the failure of the FAA certification office to monitor and act upon the significant number of reports of tail boom cracking that were reported by industry.

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