The safety agency published a report December 1 detailing important preliminary findings from the ongoing investigation of the crash that seriously injured the pilot and two passengers, and left three other passengers with minor injuries. The pilot told investigators that the helicopter began an uncontrolled spin to the right about 30 minutes into the flight operated by Paradise Helicopters, and a passenger reported seeing an object fall away from the helicopter, which continued its spinning descent until it impacted lava-covered terrain.
Investigators found the tail boom had separated at the main attachment point, and some fasteners were not found. The NTSB learned from Bell that the absent (upper left) attachment point fastener set carries the highest tension load of the four attachment fittings connecting the tail boom to the fuselage. Investigators determined that failure of the upper left attachment did not immediately cause separation, as the other three attachment points shared the increased load. Fatigue cracks were found near the lower-left attachment fitting.
“Based on preliminary analysis of the fatigue crack growth on the lower-left attachment fitting, it is possible that the fatigue crack grew over multiple takeoffs and landings,” the agency wrote. “However, this analysis is ongoing, and the results of the analysis, once completed, will be shared with the FAA and the Transportation Safety Board of Canada.”
Investigators found that the boom attachment fittings had been torque-checked as prescribed, and that no additional maintenance had been done since the last verification. The NTSB noted that while the investigation is ongoing, “given the findings thus far during the investigation, we are concerned that there may be additional Bell 407 helicopters with missing or fractured tail boom attachment hardware, and the potential for catastrophic failure warrants immediate and mandatory action. The NTSB concludes that any tail boom attachment hardware or fittings that is not installed properly or is fractured is a safety hazard because it can result in an inflight separation of the tail boom, which is catastrophic. Therefore, the NTSB recommends that the FAA and Transport Canada require operators of Bell 407 helicopters to conduct an immediate torque check of the tail boom attachment hardware, as well as a visual inspection of the tail boom attachment fittings for evidence of cracks and fractures, and report findings to their respective regulatory authority.”