What was found
(CAN) THE ACFT WAS TRANSPORTING BACK TO BASE FIREFIGHTERS THAT HAD BEEN WORKING A FOREST FIRE WHEN THE PILOT NOTED ENGINE FLUCTUATIONS FOLLOWED BY A LOSS OF MAIN ROTOR SPEED. HE RETARDED BOTH ENGINES TO IDLE AND HE MADE AN AUTOROTATION IN A FIELD. THE HELO TOUCHED DOWN WITH A SLIGHT YAW AND ROLLED OVER. THERE WERE NO INJURIES TO THE 9 ON BOARD. OFFER OF ASSISTANCE HAS BEEN MADE, MFG WILL INVESTIGATE TO ESTABLISH ROOT CAUSE AND SUPPLEMENT THE REPORT ONCE THE INFORMATION IS AVAILABLE.