As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
(CAN) AT SCHEDULED MAINT - AD 2004-21-05 - HEATER DECAY TEST REQUIRED. THE DECAY TEST PASSED. FUNCTION CHECK OF THE FAILED SWITCH IS NOT REQUIRED BY THE AD BECAUSE OF THE PN ON SWITCH. NORMAL PRACTICE IS TO FUNCTION CHECK THIS SWITCH AS IT IS REMOVED TO CARRY OUT THE DECAY TEST. THE SWITCH WAS FOUND FAILED ON IN THE NORMALLY OPEN POSITION. THIS ALLOWED THE HEATER TO OPERATE BUT COULD HAVE CAUSED A PROBLEM ALLOWING THE HEATER TO OPERATE WITH A FAILED COMBUSTION AIR SOURCE.