FLT CREW OF B747-200 EXPERIENCE INABILITY TO CTL CABIN ALT ON DEP FROM INC. DECLARE EMER; DUMP FUEL; RETURN TO RKSI.

Narrative

CLBING THROUGH APPROX FL220; THE CABIN ALT WARNING SOUNDED AND DECOMPRESSION WARNING LIGHT ILLUMINATED. THE CABIN WAS CLBING AT 500 FPM; THE CABIN DIFFERENTIAL WAS 4.0 AND STEADY; AND THE CABIN ALT WAS (AT ITS HIGHEST) 11000 FT. THE DECOMPRESSION EMER PROC WAS INITIATED; THE PRESSURIZATION CONTROLLER WAS CHANGED TO MANUAL MODE AND THE OUTFLOW VALVES WERE CLOSED. NO DOORS INDICATED OPEN. THE CABIN CONTINUED CLBING. AN EMER WAS DECLARED WITH THE INCHEON CTLR AND A CLRNC WAS OBTAINED AFTER MANY REQUESTS (DUE TO THE LANGUAGE BARRIER) ALTHOUGH AN EMER DSCNT HAD ALREADY BEEN INITIATED. A VECTOR BACK TO THE ARPT WAS RECEIVED; AND A DUMPING AREA WAS ASSIGNED BY ATC. FUEL DUMPING WAS COMMENCED AT 10000 FT AND APPROX 190000 LBS OF FUEL WAS DUMPED. COORD WITH MY COMPANY DISPATCHER WAS ACCOMPLISHED THROUGH USE OF ACARS SYS. ACFT LANDED UNEVENTFULLY AT THE MAX ALLOWABLE GROSS WT OF 630000 LBS. IT IS BELIEVED THAT A GND AIR CONNECTION VALVE FAILED TO CLOSE AFTER STARTING ENGS (DUE TO NO APU AIR AVAILABLE); THEREFORE; THE ACFT WAS ONLY ABLE TO PARTIALLY PRESSURIZE. THIS LENT ITSELF TO THE SLOW AND INSIDIOUS NATURE OF THIS EVENT. I ASSUME THAT MECHANICAL FAILURE OF THE VALVE WAS AT FAULT.