B727 FLC DEPLANES THEIR PAX WHEN AN APU TORCH IS NOTED. GND CREW AT FIRST THOUGHT IT WAS A WHEELWELL FIRE SO CREW CALLED CFR. BOTH AIR-CONDITIONING PACKS HAD BEEN OPERATING; ONE ILLEGALLY.

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SMOKE IN CABIN CAUSED BY AIR-CONDITIONING PACK OVERHEAT. BOARDED PAX WERE DEPLANED. PACK WAS IN USE BECAUSE OF IMPROPER PLACARDING OF SYS BY MAINT. PACK SHOULD NOT HAVE BEEN TURNED ON. HAD THE REQUIRED NOTIFICATION BEEN IN PLACE ON THE PANEL; THE PROB WOULD NOT HAVE OCCURRED. SUPPLEMENTAL INFO FROM ACN 368293: TURNED OFF PWR. THEN THE SMOKE CEASED. SMOKE SEEMED TO BE COMING FROM THE APU. CALLBACK CONVERSATION WITH RPTR ON ACN 368285 REVEALED THE FOLLOWING INFO: PIC RELATED THE SCENARIO IN THIS FASHION: THE SO HAD COME ON BOARD THE ACFT; THE PAX WERE BEING LOADED. ONE AIR CONDITIONING PACK WAS OPERATING. THE GND CREW WAS WORKING ON THE ACFT'S LOGBOOK ON THE JETWAY ENTRY. THE LOGBOOK HAD AN ENTRY REGARDING AN MEL'ED ITEM; THE FLOW MULTIPLIER UNIT ON THE APU. THIS UNIT; WHEN OPERATING; ENHANCES THE FLOW OF AIR TO THE APU WHEN BOTH AIR CONDITIONING COMPRESSORS ARE OPERATING BUT NOT WHEN ONE IS OPERATING. THE SO DID NOT KNOW THAT THE UNIT WAS INOP SINCE THERE WAS NO PLACARD REFING THIS ON THE PANEL; SO HE TURNED ON THE SECOND AIR-CONDITIONER. THE APU OVERHEATED; STARTED A SHUTDOWN AND TORCHED. THE GND CREW THOUGHT THAT THERE WAS A WHEELWELL FIRE AND SOMEONE IN THE CREW HAD GND CTL CALL THE CFR VEHICLES.