Enstrom 280 accident near Hayden, Idaho, June 24, 2020

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

Shortly after takeoff on an instructional flight, a helicopter was maneuvering at a low altitude when the engine rpm “skyrocketed,” and the engine lost total power; the flight instructor (who was at the controls) reported hearing “backfiring” at the time, although the engine was still running. The flight instructor then had to maneuver the helicopter to avoid nearby power lines, but the helicopter impacted terrain. The main rotor blades struck the tailboom, and the helicopter subsequently spun around about 180° before coming to rest. A postcrash fire then ensued, which consumed most of the helicopter. Additionally, the student pilot stated to a witness after the accident that the helicopter was losing power. An engine examination revealed that detonation had occurred in two of the four engine cylinders. (Detonation in a piston engine occurs when the fuel-air mixture in a cylinder detonates or explodes prematurely instead of being ignited by spark plugs and burning evenly and smoothly, as occurs with normal combustion.) Furthermore, damaged spark plugs were observed in one of the detonated cylinders as well as another cylinder. The combined effects of the detonation and damaged spark plugs likely caused the loss of engine power. Because the loss of power occurred at a low altitude, the flight instructor likely did not have enough altitude to adequately establish a steady-state autorotation to avoid the helicopter’s impact with terrain.

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.