Accident Sequence
Approximately three minutes after takeoff, an air traffic controller received a garbled transmission with an emergency locator transmitter signal in the background. Witnesses reported seeing the helicopter in level flight at about 300 feet above a hill when the tail section detached. The helicopter subsequently entered a spin, rolled inverted, and descended into trees.
Examination Findings
The tail boom section aft of boom station 167 was recovered 650 feet from the main wreckage. This section included the upper and lower vertical fin, the tail rotor gear box, and the tail rotor hub and blades. Examination of the separated area revealed fatigue cracks.
Maintenance and Reporting Background
In response to reports of tail boom cracking, the manufacturer issued an Alert Service Bulletin in 1987 recommending an inspection of the tail boom every 100 hours. The operator had complied with this bulletin. The manufacturer and the FAA certification office were aware of a few reports of tail boom cracking but were not aware of over 220 Service Difficulty Reports concerning cracks in Bell 206L tail booms. A doubler had been added to the failed area on recent production models, but no modification was developed to add a doubler to older models.