What was found
DURING REMOVAL OF FWD DRAIN MAST, FOUND THAT THE 2 AFT HOLES OF PANEL 193AL THAT ATTACHES DRAIN MAST TO PANEL ARE DAMAGED. PANEL IS DELAMINATED AND FILLER IS MISSING LEAVING A 6 INCH BY 4 INCH HOLE, DELAMINATED AREA IS 6 BY 10 INCHES. REMOVED FWD DRAIN MAST, NEW DRAIN MAST IS LOB WITH HARDWARE, WIRES ARE CAPPED OFF, ACP TEMP REPAIR WITH TAPE TO COVER HOLE FOR MAINT FERRY. FOUND FWD DRAIN MAST FROZEN AFTER LANDING IN DENVER. SHUT OFF WATER SUPPLY TO FWD AND MID CABIN LAVATORY SINKS AND GALLEYS. MAST ASSY (PCN 752-3200 ON EXP C3561 PRECAUTIONARY). NEW DRAIN MAST IS LOB WITH HARDWARE PCN 160-7432. REPLACED DRAIN MAST.