As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
AFTER TAKEOFF WITH HEATER SELECTED ON, SPARKS WERE SEEN COMING OUT OF THE HEATER VENTS. THE HEATER WAS SHUT OFF AND AIRCRAFT RETURNED TO BASE WITHOUT FURTHER INCIDENT. HEATER REMOVED AND INSPECTED. DURING INSPECTION, A CRACK ABOUT 3 INCHES LONG WAS SEEN 6 INCHES FROM EXIT END. TIME SINCE LAST HEATER DECAY TEST WAS 45.7 HEATER HRS. LAST HEATER O/H RECORDED WAS 10-15-80. NO RECORD OF WHAT HEATER OVERHAUL INVOLVED IS AVAILABLE.