As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
(CAN) HELICOPTER WAS STARTED FOR A GROUND RUN. IT WAS NOTED THAT DURING THE GROUND RUN, MAIN ROTOR BLADES STARTED TO TURN. THEN THE MAIN ROTOR BLADES STARTED TO DEACCELERATE WITH NO THROTTLE ADJUSTMENT. WE ARE TROUBLESHOOTING THE OBSERVATION DEFECT.