As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
DURING PRACTICE AUTOROTATION, ENGINE POWERSHAFT TO KFLEX POWERTRAIN ADAPTER CAME LOOSE BY BACKING OUT, DURING OPERATION MAIN ROTOR WAS NO LONGER POWERED BY ENGINE. BOLT PIN NAS1225-4N IS A BOLT WITH A SMALL CIRCLE OF PLASTIC ON THREADS FOR LOCKING. EMERGENCY LANDING, NO DAMAGE.