History of Flight
On June 26, 2022, about 1938 Alaska daylight time, a Bell UH-1B helicopter, registration N9970F, operated by Northern Pioneer Helicopters LLC as a Title 14 Code of Federal Regulations Part 133 external load flight, was destroyed in an accident near Clear, Alaska. The pilot sustained fatal injuries. The helicopter was stationed at Clear Airport (Z84) to support wildland firefighting operations. The flight's purpose was to longline equipment to firefighters on the ground.
Numerous witnesses reported that after a normal liftoff, the helicopter hovered with the longline fully extended while maneuvering to hook up to the external load when a loud “snap” or “bang” was heard. One witness stated that the helicopter “bucked” and the pilot attempted to regain control as it descended. The helicopter rolled to the right, entered a nose-low descent, impacted the ground, and burst into flames.
A witness video captured the final seconds. The recording showed the helicopter hovering with a 125-foot longline fully extended, the hook about 15 feet above ground. As the pilot maneuvered to hook up, a loud mechanical noise was heard, followed by a shudder through the airframe, an extreme roll to the right past 90°, and a nose-low descent. During the descent, the transmission (with rotor head and blades attached) and the tail boom separated from the fuselage before ground impact.
Aircraft Information
The accident helicopter was a Bell UH-1B, equipped with a Lycoming T53-L-13B engine (serial number LE-18935) capable of 1,400 horsepower. The engine featured a five-stage axial and single-stage centrifugal compressor, an external annular combustion chamber, and two-stage turbines. The power shaft drove the reduction gearbox through the output shaft.
Wreckage and Impact Information
The helicopter impacted the asphalt on the north ramp area of Clear Airport (Z84) on its left side in a nose-low attitude and was largely consumed by postcrash fire. The transmission, with rotor head and blades still attached, was found about 30 feet from the main wreckage.
Examination of the left seat collective control found it attached to the torque tube. Neither cyclic control was located. Both right-side anti-torque pedals had been liberated from their supports; both left-side pedals remained attached and connected to their bell crank. Tail rotor drive system continuity was established through all five sections. The drive shafts had separated from both ends of the intermediate 42° gear box, which rotated smoothly and had a magnetic drain plug free of debris.
A postaccident examination of the airframe, including the annunciator panel, lateral and collective servos, hydraulic pump, tail rotor, and KAFlex drive shaft, revealed no pre-accident mechanical malfunctions or anomalies that would have precluded normal operation.
The NTSB Materials Laboratory examination found the transmission case fractured on the right side near the aft support. The forward pylon support legs were fractured through rivets attaching the isolation mount pad. The aft left support leg fractured at the lower attachment bracket for the friction damper, and the aft right support leg fractured at its lower end. The main transmission and pylon structure likely separated due to overstress. The aft isolation mounts and friction dampers showed evidence of substantial upward overtravel.
The engine came to rest on its left side with significant thermal damage. Visual examination of the compressor inlet and power turbine blades showed no damage. No pre-accident mechanical malfunctions or anomalies were found that would have precluded normal engine operation.
Medical and Pathological Information
An autopsy by the State of Alaska Medical Examiner's Office determined the pilot's cause of death as blunt force injuries of head, torso, and extremities due to the helicopter crash; the manner of death was accident. The medical examiner reported a gray-white area of the heart consistent with a remote posterior myocardial infarct, two venous grafts, and 75% stenosis of sections of coronary arteries. Toxicology testing detected rosuvastatin and metoprolol in cavity blood and urine; these are non-impairing medications used for cholesterol and blood pressure.
Additional Information
The source mentioned a similar accident involving pilot-induced oscillations from loss of hydraulic assist on a Bell UH-1H helicopter, but no direct link to this accident was established.