ACR MLG RETURN LAND WHEN BOTH ENGINE AND APU FIRE WARNINGS ACTIVATED DURING ICB.

Narrative

JUST AFTER LIFTOFF FROM YAK; THE FIRE BELL SOUNDED AND ALL 3 FIRE LIGHTS (ENGS 1 & 2 AND APU) ILLUMINATED. CEILINGS WERE VARIABLE 600' TO 1500' WITH VIS 2 1/2 MI IN FOG AND RAIN AND A 10-15 KT WIND OUT OF THE NE. WE IMMEDIATELY TURNED DOWNWIND; REMAINING IN VMC; AND LANDED UNEVENTFULLY. THE PROB PROVED TO BE RAINWATER ENTERING VARIOUS CONTROL ELECTRONICS BOXES IN THE E&E BAY. THE WATER MOST LIKELY ENTERED THROUGH THE FORWARD ENTRIES AND MAIN CARGO DOOR AREA DURING TURNAROUNDS AT STATIONS WHERE IT WAS RAINING. THE WATER SEEPS INTO THE SMOKE VENT/GRILLE IN THE FORWARD GALLEY AREA AND THEN DOWN TO THE ELECTRONICS BAY. WATER ACCUMULATES IN A DRAIN PAN ESPECIALLY DESIGNED FOR ISOLATING WATER INTRUDING INTO THE E&E BAY BUT THE DRAINS WERE PLUGGED WITH DIRT AND DEBRIS; ALLOWING THE DRAIN PAN TO FILL (AND OVERFLOW AT ACFT ROTATION). WE SUBMITTED A RECOMMENDATION TO OUR COMPANY TO INSPECT THE DRAIN PANS MORE FREQUENTLY; PARTICULARLY SINCE PRECIPITATION IS THE NORM AT THE ARPTS WE SERVE DURING THE WINTER SEASON. SUPPLEMENTAL INFO FROM ACN 97124: WE NOTED THAT THE #2 ENG OVERHEAT LIGHT WAS ALSO ON. WE RETARDED THE THROTTLE TO FLT IDLE PER THE FLT HANDBOOK BUT DID NOT SHUT DOWN THE ENG SINCE I SUSPECTED THIS WAS AN ELECTRICAL MALFUNCTION RATHER THAN AN ACTUAL OVERHEAT OR FIRE. DUE TO HIGH WORKLOAD I DID NOT BRIEF THE PAX OR F/A'S.