Bell 47D1 accident near Zelienople, Pennsylvania, October 31, 2021

The NTSB's narrative final · quoted from the NTSB record

The pilot receiving instruction and the flight instructor picked up the helicopter following maintenance and performed a brief instructional flight. The instructor disembarked while the helicopter’s engine continued to run, and the pilot subsequently departed for a solo flight to the home airport. Shortly after departure, the engine “sputtered,” and there was a “drop” in both the engine and main rotor rpms. The pilot performed a 180° turn back toward the departure airport, and when he leveled the helicopter, engine and rotor rpm “returned.” However, soon after, the helicopter lost total engine power. The pilot entered autorotation and maneuvered the helicopter for a “flat” open area but lacked the altitude and rotor rpm to reach it. He landed on sloped terrain, which resulted in the destruction of the main rotor blades and substantial damage to the landing gear and tailboom. Initial examination of the wreckage by Federal Aviation Administration inspectors revealed a fragmented engine accessory case. Examination of the accessory case fragments revealed that the fracture surface features were consistent with overstress due to impact. Other than the fractured accessory case, the initial wreckage examination revealed no evidence of mechanical anomalies. The helicopter’s owner blocked access to the wreckage, and no further examination of the helicopter could be performed. Weather conditions reported in the area at the time of the accident was conducive to the development of serious carburetor icing at a glide power setting. It is possible that carburetor ice may have developed during the time the helicopter was operating on the ground while the instructor disembarked; however, the pilot’s use of carburetor heat was not determined, and other reasons for the loss of engine power could not be ruled out due to the lack of a more extensive examination of the helicopter. Therefore, the reason for the loss of engine power could not be determined based on the available information.

The complete narrative as the NTSB published it. The NTSB's docket holds the report as a PDF and any photographs, statements and other documents from the investigation.