A FOKKER 100 IN CRUISE AT FL330 DECLARED AN EMER AND MADE AN EMER DSCNT DUE TO LOSS OF CABIN PRESSURIZATION.

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CRUISING AT FL330 IN IMC ICING CONDITIONS AND MODERATE TURB WITH ANTI-ICE ON. WHILE TALKING ON INTERPHONE WITH FLT ATTENDANT ABOUT ADVISABILITY OF SITTING DOWN AND BUCKLING UP; WE RECEIVED AN UNEXPECTED CABIN ALT WARNING WITH TRIPLE CHIME. A QUICK GLANCE REVEALED CABIN ALT ABOVE 10000 FT AND CLBING AT ABOUT 800 FPM. ANXIOUS TO AVOID PAX MASK PRESENTATION; ELECTED EMER DSCNT TO 10000 FT. DECLARED EMER AND RECEIVED APPROPRIATE CLRNC. NOW FACED WITH 2 CONFLICTING NEEDS. RAPID DSCNT REQUIRES IDLE PWR AND ICING CONDITIONS AND STILL RAPIDLY CLBING CABIN REQUIRES INCREASED PWR. EXPERIMENTED BRIEFLY WITH PWR INCREASE WHICH CAUSED AUTOSPD BRAKE RETRACTION AND RAPID ACCELERATION THROUGH CLACKER SPD. RECOVERED SMOOTHLY. SOMETIMES THINGS SEEM TO SNOWBALL. LEVEL AT 10000 FT; ANTI-ICE WORKED NORMALLY AND CABIN STABILIZED IN COMFORTABLE DSCNT. DISCUSSED CIRCUMSTANCES; POS AND FUEL ON BOARD WITH DISPATCH AND MUTUALLY DECIDED TO CONTINUE TO ATL. FMC PREDICTED ARR WITH COMFORTABLE RESERVES AT CRUISE ALT OF 10000 FT. REMAINDER OF TRIP UNEVENTFUL EXCEPT FOR IMC WITH ICING CONDITIONS AND FREQUENT MODERATE CHOP. ADVISED MAINT OF ALL PARTICULARS INCLUDING OVERSPD FOR APPROPRIATE INSPECTION -- WHICH REVEALED NO DAMAGE. CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO: THE RPTR STATED THE ACFT CABIN STARTED TO CLB AT FL330 AND THEN STABILIZED WHEN REACHING 10000 FT. THE RPTR SAID A LOG ITEM WAS MADE ON THE PRESSURIZATION SYS AND OVERSPD CHK THAT WAS REQUIRED. THE RPTR STATES THAT MAINT COULD FIND NOTHING WRONG WITH THE PRESSURIZATION SYS AND CLRED THE ITEM. THE RPTR STATES THAT 1 WK AFTER THIS INCIDENT THE RPTR AGAIN OPERATES THE SAME AIRPLANE AT FL330 WITH NO ICING CONDITIONS AND THE CABIN PRESSURE IS NORMAL UNTIL THE AIRFOIL ANTI-ICE IS SWITCHED ON AND THE PNEUMATIC DUCT PRESSURE DROPS ABNORMALLY. THE RPTR SAID THAT MAINT DID NOT RPT THE FIX FOR THIS PROB.