As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
AIRCRAFT WAS FIREFIGHTING WHEN PILOTS HEARD A LOW FREQUENCY RUMBLE. AIRCRAFT RETURNED TO BASE FOR TROUBLESHOOTING. AFTER TROUBLESHOOTING AMTS FOUND 1 EA. 2ND STAGE N1 BLADE HAD BROKEN OFF AT THE ROOT. ENGINE IS BEING RETURNED TO THIS REPAIR STATION FOR FURTHER INVESTIGATION. ENGINE MANUFACTURE HAS BEEN NOTIFIED AND WILL PARTICIPATE IN THE INVESTIGATION.