Bell 47G accident near North Las Vegas, Nevada, August 28, 2019

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

During the flight before the accident, the pilot of the helicopter observed that the engine would not produce adequate power to keep the rotor rpm within the green arc of the tachometer, and witnesses reported hearing backfiring from the engine. The pilot sought the assistance of an acquaintance to help him perform maintenance on the helicopter. The acquaintance told the pilot that he was a commercial pilot with 3,000 hours of flight experience in helicopters, and 300 hours in the accident helicopter make and model. After performing maintenance on the helicopter, they relocated the helicopter to a helipad and boarded the helicopter for flight. The pilot lifted the helicopter to a hover but soon began to have difficulty maintaining control and transferred the flight controls to the passenger. The passenger acknowledged that he had the flight controls. Shortly thereafter, the passenger lost control of the helicopter and it drifted backward into a fuel cart and rolled onto its left side. A postaccident interview and review of Federal Aviation Administration records revealed that the passenger did not possess a pilot certificate. Examination of the airframe revealed no preaccident mechanical malfunctions or failures that would have precluded normal operation. Examination of the engine revealed that the No. 1 cylinder inner and outer intake valve springs were fractured and collapsed, which was likely the cause of the low engine and rotor speed on the previous flight.

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.