What was found
DEBRIEFED CREW AFTER RETURN TO THE FIELD, APU FIRE BOTTLE HAS BEEN DISCHARGED. 1/27AIR TURN BACK. THE CREW DECLARED AN EMERGENCY AND RETURNED TO THE GATE DUE TO APU FIRE WARNING AND INDICATION. THE PILOT DISCHARGED THE BOTTLE, AND TWO PSUS WERE DEPLOYED ON THE PASSENGER CABIN. AC TOWED FROM THE GATE TO PEMCO HANGAR. UPON INVESTIGATION, AN APU EXHAUST DUCT CLAMP WAS NOT SECURED. JC 29-4981-1-2500 WAS PERFORMED DURING C CHECK FOR INSPECTION OF EXHAUST DUCT CONDITION SO, THE EXHAUST WAS REMOVED DURING C CHECK VISIT BY PEMCO PERSONNEL. CURRENTLY, PEMCO PERSONNEL ARE WORKING ON AIRCRAFT.