N473TTBell 47G-3B-1 · 1968

On June 14, 2020, about 2030 central daylight time, a Bell 47G, N473TT, was substantially damaged when it was involved in an accident near Burnett Heliport (59TN), Atoka, Tennessee. The pilot and two passengers were not injured. The helicopter was operated as a Title 14 Code of Federal Regulations Part 91 personal flight.

According to the pilot, on the day of the accident, he was providing short (7- to 8-minute) nonrevenue passenger flights. The pilot had completed eight flights uneventfully. The pilot had added 20 gallons of fuel (10 gallons to each tank) to the helicopter before the eighth flight, for a total of about 39 gallons. During the ninth flight, when the helicopter was about 1.5 miles north of 59TN and was descending through 900 ft mean sea level, the engine lost all power. The pilot performed an autorotation to a field; during touchdown, the main rotor blade struck the tailboom, which severed the aft 20 inches of the tailboom, including the tail rotor, from the airframe.

Postaccident examination of the accident site revealed that the helicopter came to rest upright in the field. All major components of the helicopter were found.

The engine showed no evidence of a preimpact malfunction, and all components were present. The hydraulic pump was removed for access to the drive so that the crankshaft could be turned. One spark plug was removed in each cylinder for a compression check, and the crankshaft was rotated using a tool inserted in the pump drive pad. Continuity of the crankshaft, camshaft, and valve train was confirmed. A borescope inspection of the cylinders found no anomalies. Both magnetos rotated normally, and the timing was within normal limits. All ignition leads and spark plugs appeared to be completely functional. The air filter and induction system inspection indicated no obstruction to air flow. The throttle had a normal operating range.

The fuel line to the carburetor appeared to have collapsed, and about 4 ounces of fuel drained from the system after disconnecting the line. The fuel line was inspected using a borescope, and no light passed through the fuel line. The borescope was then pushed through the fuel line, and no contaminates were found. Both the left and right fuel tanks tested normal for 100LL fuel with no contamination. The fuel sample obtained from the fuel supply system on the support truck was determined to be uncontaminated.

The fuel line was subsequently examined by the National Transportation Safety Board’s Materials Laboratory. No blockages were observed; the interior of the hose appeared undamaged and intact; and no evidence of kinks, creases, or material creep was observed on the exterior of the fuel line.