AN ACR WDB SUFFERS A SLOW LOSS OF CABIN PRESSURE. THE FLC FAILS TO NOTE THIS UNTIL THE ALT WARNING ALERT AND RED CAUTION LIGHT TELLS THEM THAT SOMETHING IS WRONG.

Narrative

AFTER 1 HR CRUISE AT FL330 CREW OBSERVED CABIN ALT WARNING HORN AND LIGHT (RED). PERFORMED LOSS OF PRESSURIZATION EMER CHKLIST AND REQUESTED IMMEDIATE DSCNT. ATC PROVIDED IMMEDIATE CLRNC TO FL190. IMMEDIATELY PRIOR AND DURING DSCNT; OBSERVED CABIN RATE OF CLB AT +200 FPM. CABIN OUTFLOW VALVE POS FULLY CLOSED. AUTO; STANDBY; AND MANUAL MODES OF CABIN PRESSURE CTL COULD NOT CLOSE CABIN CTL VALVE ANY MORE; VALVE INDICATED FULLY CLOSED. ALL 3 PACK PRESSURES; TEMPS; AND FLOW INDICATIONS NORMAL. DSNDING THROUGH FL200; OBSERVED CABIN RATE INDICATING 200 FPM DSCNT. CABIN SLOWLY REPRESSURIZED; AND REQUESTED 17000 FT CRUISE ALT. DSNDED CABIN TO 4000 FT AND CONTINUED APPROX 1 HR TO DEST. NO OBVIOUS STRUCTURAL FAILURE; IE; NOISE; DOOR WARNING; OR PACK FAILURE WAS OBSERVED. LOSS OF CABIN PRESSURIZATION WAS SO GRADUAL THAT NO EAR EQUALIZATION DISCOMFORT WAS NOTICED. DURING CRUISE AT 17000 FT AND DSCNT TO LNDG; AIR FLOW INTO CABIN WAS VERY WEAK; IE; NO FLOW AT EYEBALL OUTLETS AND OUTFLOW VALVE REMAINED ALMOST COMPLETELY CLOSED. DURING EVENT; SVCS OF A DEADHEADING COMPANY PLT WERE VALUABLE IN OBSERVING/COLLECTING CABIN DATA. CRM WAS UTILIZED TO GREAT ADVANTAGE FOR SAFE OUTCOME.