As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
(CAN) THE FLIGHT CREW REPORTED A FIRE IN THE TAIL PIPE OF NR4 ENGINE AFTER START DURING PUSHBACK FROM THE GATE. THE ENGINE WAS SECURED AND BOTH FIRE BOTTLES DETONATED. THE ENGINE WAS REPLACED AND THE AIRCRAFT WAS RETURNED TO SERVICE.INITIAL TEARDOWN INDICATED A POSSIBILITY OF INSUFFICIENT BLADE TIP CLEARANCE ON THE FIRST TURBINE.