An improperly manufactured steel bolt that sheared off in flight has been cited as the likely cause of a June 2010 helicopter crash near Midlothian that killed a CareFlite pilot and mechanic during a routine post-maintenance flight.
The National Transportation Safety Board has not issued a final report on the investigation, but agency documents show that the crash inquiry quickly centered on a fractured drive pin, similar to an everyday bolt.The bolt was one of two that anchor the complex mechanism that operates the helicopter's rotor blades, transmitting the pilot's flight commands to the blades that control the aircraft.Bell Helicopter, which manufactured both of the drive pins used in the Bell Model 222 helicopter's rotor control assembly, has already reached out-of-court settlements with the victims' families.Dallas attorney Jon Kettles declined to disclose financial details of the settlements, but said once the likely cause of the accident became clear Bell officials quickly agreed to compensate the families."We were able to get it settled in about six months, completely independent of the NTSB investigation," said Kettles, an aviation lawyer and licensed air transport and helicopter pilot.Bell had already taken steps to collect all the other pins made at the same time, in 1999, and Kettles said the company told him it was considering redesigning the pin to prevent a recurrence."To Bell's credit, when they have a failure like this I believe they're upfront about finding why it occurred and taking steps to prevent another occurrence," Kettles said. "I felt comfortable they were doing what they needed to do to prevent it from happening again."A Bell spokesman said the company would not comment on the crash investigation or the settlement with the families.The crash killed CareFlite's chief pilot, Guy del Giudice, 44, of Fort Worth and mechanic Stephen Durler, 23, of Dallas. The safety board documents give no indication that either man's actions contributed to the accident.Safety board investigator Tom Latson could not be reached for further comment on the investigation. The safety agency investigators typically compile factual records on accidents and then forward them, often without any opinion, to the board in Washington to make a ruling on the cause.The crash occurred about 2 p.m. on June 2, 2010, just eight minutes after the helicopter lifted off from Grand Prairie Municipal Airport on a post-maintenance check-out flight. The investigation and eyewitness accounts showed something had gone terribly wrong with the two-blade main rotor system, which broke off of the aircraft.The helicopter's rotor mast broke off in two places, where it attaches to the rotor blades and farther down where it connects to the swashplate, the control mechanism. The safety board documents say there were no signs of pre-existing cracks in the mast.Instead, the post-crash examination indicated that the fractures were caused by massive stress on the metal mast. Further investigation found the suspect bolt had sheared off in flight, leaving one of the rotor blades uncontrollable and almost instantaneously resulting in extreme forces that tore the rotor assembly and the tail boom off the helicopter.The bolt that sheared off, according to Bell records obtained by the safety board, was one of two made in the same batch in 1999. The second was discarded, but no reason was recorded in the detailed manufacturing records that aircraft manufacturers are required to keep.The safety board document shows that agency investigators and engineers, working with Bell, examined the remaining portion of the sheared bolt and found abnormal, brittle characteristics in the heat-treated, high-strength steel, including pre-existing microscopic cracks.Newly manufactured bolts like those used in the aircraft were then tested by Bell at the safety board's direction. One of those pins was purposely heat-treated at less than the required 900 degrees. It subsequently fractured in a strength test and upon close examination using an electronic microscope showed similar characteristics to the pin that failed on the doomed helicopter.The bolts are made of very strong, high-grade steel and then coated with cadmium. But if the heat treatment is improperly performed, the steel can become more brittle and more likely to snap rather than bend when put under high stress.CareFlite turned over the helicopter's maintenance records after the accident, Kettles said, and there was no indication of any pre-existing problem with the aircraft or improper maintenance work. The safety board documents indicate that all the required safety inspections of the aircraft's components had been conducted.CareFlite had recently purchased the 1980s vintage Bell 222 and planned to use it as a backup aircraft. Maintenance crews had removed the rotor assembly and controls from the crash aircraft and swapped them with those from another aircraft, putting the newer rotor assembly on the aircraft that was to get the most use.Maintenance records show that Durler, the mechanic, did everything right but couldn't have known about the faulty bolt manufactured in a Bell factory a decade earlier, Kettles said."This is a good example of how [the safe operation of] every aircraft out there is relying on thousands of people," Kettles said. "It's a reminder there's an awful lot of people that have got to do their job right."Bob Cox, 817-390-7723Twitter: @bobcoxict
Read the NTSB report on the Careflite helicopter crash
June 15, 2010: Copter crash evidence points to mechanical failure
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