As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
ASH 2940 YYZ. CREW DECLARED AN EMERGENCY ON DESCENT. CREW REPORTED THAT ON APU START UP THERE WAS AN APU FIRE WARNING INDICATION AND THE APU FIRE BOTTLE WAS ACTIVATED. CONTRACT MX INSPECTED THE APU AREA BUT FOUND NO SIGNS OF ACTUAL FIRE. THE APU FIRE EXTINGUSHING SYSTEM WAS DEFERRED, TREATING THE APU AS INOPERATIVE. MX REPLACED FCU.