“partially ejected from the helicopter” and killed.
The Investigation Investigators found two of the three main-rotor Starflex arms separated at nearly right angles to the blades and the tail boom broken in two places, all damage consistent with impact forces. The third main-rotor blade was “daggered into the ground.”
Flight control continuity was confirmed to the main- and tail-rotor systems. The hopper of the PSD machine was empty, its payload having been used up during the flight. The bottom of the fuel tank was crushed and breached, but with the heli- copter resting on its side, about 20 gal. remained in the tank. The engine’s axial compressor was free
of foreign object debris, and the axial com- pressor/gas generator was easily rotated by hand. Sheared front-support bolts bound
the freewheel shaft, preventing rotation of the free turbine.
Electrical connections were secure, and all other fuel, oil, and air lines were tight and correctly safetied. However, the main fuel line between the firewall and the hydromechanical unit (HMU), which includes the fuel shutoff valve, was found loose with no safety wire installed. Data downloaded from the digital engine-control unit after it was returned to the engine manufacturer recorded a fault for “P3 drift or engine flameout,” with rap- idly decreasing N1 (low-pressure compres- sor) speed. The operator’s director of maintenance reported that on Feb. 14, about six weeks before the accident, the Forest Service had requested verification of the weight and balance of all the helicopters used on its contracts. To provide this information, the operator had to empty each helicopter of fuel to determine its basic empty weight,
which in turn necessitated disconnecting the main fuel line from the HMU. The technician who’d reconnected the
line after the weighing operation on this helicopter was “confident that he had torqued and secured the line,” but no frag- ments of safety wire were found inside the cowling. On Feb. 23, the helicopter failed to start,
which was addressed by replacing “the engine’s igniters and/or igniter box.” No other anomalies were observed during the 25 hours it had flown since being refueled, except a brief flickering of the fuel-pressure light that the pilot reported a few days before the accident. This was resolved by briefly turning on the boost pump. The pilot was instructed to monitor the situation and report any recurrence. A follow-up inspection confirmed that the fuel lines of all the operator’s other heli- copters were correctly torqued and safety-wired.
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70 ROTOR MARCH 2023
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