What happened
The FAA’s narrative, in sentence case. The FAA writes it in capitals and removes private details.
Helicopter was in cruise flight on an estimated heading of 325° and at 2000?MSL (about 450?AGL) indicating 125 KTS of airspeed when it experienced an un-commanded left yaw of the helicopter. Assuming an engine problem, the pilot reduced power to try to diagnose the situation, reducing airspeed to 100 KTS. He looked over his engine instruments and everything appeared to be normal. Oil pressure was in the green, ng was around 85 percent, trq 35 percent, N2/NR 100 percent, and airspeed still 100 KTS with a slight decent rate caused by the reduction in power. The pilot brought power back into cruise to see how the engine would react. As the pilot pulled up on the collective to get back to cruise power the helicopter yawed to the left and the nose tucked simultaneously. At this point he thought the engine had quit and the pilot entered a power-on autorotation and emergency decent and landed the helicopter
As the FAA filed it
HELICOPTER WAS IN CRUISE FLIGHT ON AN ESTIMATED HEADING OF 325° AND AT 2000?MSL (ABOUT 450?AGL) INDICATING 125 KTS OF AIRSPEED WHEN IT EXPERIENCED AN UN-COMMANDED LEFT YAW OF THE HELICOPTER. ASSUMING AN ENGINE PROBLEM, THE PILOT REDUCED POWER TO TRY TO DIAGNOSE THE SITUATION, REDUCING AIRSPEED TO 100 KTS. HE LOOKED OVER HIS ENGINE INSTRUMENTS AND EVERYTHING APPEARED TO BE NORMAL. OIL PRESSURE WAS IN THE GREEN, NG WAS AROUND 85 PERCENT, TRQ 35 PERCENT, N2/NR 100 PERCENT, AND AIRSPEED STILL 100 KTS WITH A SLIGHT DECENT RATE CAUSED BY THE REDUCTION IN POWER. THE PILOT BROUGHT POWER BACK INTO CRUISE TO SEE HOW THE ENGINE WOULD REACT. AS THE PILOT PULLED UP ON THE COLLECTIVE TO GET BACK TO CRUISE POWER THE HELICOPTER YAWED TO THE LEFT AND THE NOSE TUCKED SIMULTANEOUSLY. AT THIS POINT HE THOUGHT THE ENGINE HAD QUIT AND THE PILOT ENTERED A POWER-ON AUTOROTATION AND EMERGENCY DECENT AND LANDED THE HELICOPTER