As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
(CAN) DURING TAKEOFF FOR A PRACTICE, NR 2 ENGINE BACKFIRED. THE LOAD OF WATER WAS JETTISONED, THE ENGINE WAS SHUTDOWN AND THE PROPELLER WAS FEATHERED. THE AIRCRAFT RETURNED TO BASE. UPON INVESTIGATION BY MAINTENANCE CREW, A BROKEN LOW TENSION IGNITION LEAD WAS FOUND. THE LEAD WAS REPLACED. THE AIRCRAFT WAS RETURNED TO SERVICE.