CEN11FA337 · Bell OH-58C

The helicopter was being used for agricultural spraying of a wheat field. It had just taken off from a support truck for another spraying circuit when the support truck workers heard a noise, looked in the direction of the helicopter, and saw the helicopter spinning without its tail boom attached. The terrain in the area of the accident site consisted of rolling hills. At the top of a hill along the route of flight, several spray nozzles from the helicopter’s spray boom were found on the ground. The main wreckage of the helicopter was located about 250 feet further along the route of flight. The tail rotor and the aft section of the tail boom were found between the spray nozzles and the main wreckage. Examination of the wreckage revealed evidence that the main rotor blade had struck the tail boom severing it from the helicopter. Further examination found no preimpact defects of the helicopter, its engine, control system, or drive system. Data downloaded from an on-board global positioning system (GPS) showed that the helicopter took off from the support truck and headed in a westerly direction and accelerated to about 52 miles per hour. The GPS track passed over the location where the spray nozzles were found. The recorded altitude from the GPS was below the elevation of the surrounding terrain. Therefore, the altitude information from the GPS was not accurate enough to use for flight analysis. Based on the available information, it is likely that the pilot inadvertently flew the helicopter into the rising terrain, which resulted in the main rotor blades flexing downward and severing the tail boom. Once the tail boom was severed, the pilot would not have had any anti-torque control and would not have been able to prevent the helicopter from spinning uncontrollably.

Verbatim NTSB analysis and probable cause from the NTSB dataset