AN ACR MLG HAD AIR CONDITIONING SMOKE IN THE CABIN ON THE GND.

Narrative

THIS PROB WAS CAUSED BY SPILLED HYD FLUID DRAINING FROM A SMALL VENT JUST IN FRONT OF THE APU INTAKE. THE COPLT OR I COULD NOT SMELL OR SEE ANYTHING IN THE COCKPIT. AFTER THE FLT ATTENDANT CALLED AND TOLD ME THERE WAS AN ODOR AND HAZE IN THE CABIN; I LOOKED BACK FROM THE COCKPIT AND COULD SEE A SLIGHT HAZE IN THE CABIN. WE HAD JUST STARTED THE APU AND TURNED ON THE AIR CONDITIONING PACKS. I SHUT THE PACKS OFF AND THE FLT ATTENDANT INFORMED ME THE SMOKE DETECTORS IN THE AFT LAVATORY HAD SOUNDED. I CALLED FOR MAINT AND THE COPLT TOLD ME OF PREVIOUS WRITE-UPS CONCERNING AIR CONDITIONING PACKS CAUSING SMOKE. I SAW NO NEED TO EVAC; AS THERE WAS A LET UP IN THE HAZE AFTER SHUTDOWN OF THE PACKS. I TOLD THE FLT ATTENDANT TO OPEN THE REAR DOORS TO VENT ACFT. THE MECH FOUND HYD FLUID DRIPPING FROM A DRAIN AND BEING INGESTED INTO THE APU. IT WAS THEN SHUT DOWN. SMOKE/HAZE CLRED AND ACFT WAS DISPATCHED APU INOP. AN EXTENSIVE INSPECTION WAS DONE TO FIND SOURCE OF HYD FLUID; BUT NO LEAKS FOUND. FLUID PROBABLY SPILLED DURING PREVIOUS MAINT ON ACFT. JUST AFTER TKOF; THE FLT ATTENDANT INFORMED ME THAT THE AFT LAVATORY SMOKE DETECTORS HAD SOUNDED AGAIN; BUT NO ODOR OR HAZE OR SMOKE WAS SEEN. THIS LASTED ONLY A MIN OR SO AND STOPPED. I JUDGED THIS TO BE ONLY A SMALL AMOUNT OF HYD FLUID RESIDUAL IN AIR CONDITIONING SYS; AND WITH NO FURTHER PROB; WE PROCEEDED TO CVG. A SINGLE PAX WAS UPSET AND WISHED TO RETURN TO STL AND LAND. THE FLT ATTENDANT EXPLAINED THE NATURE OF THE PROB AND THAT THERE WAS NO DANGER.