CRJ200 CREW MADE AN EMER DSCNT AFTER THE CABIN ALT WAS RISING RAPIDLY. THE CREW WAS DISPATCHED WITH 1 PACK MEL'ED INOP.

Narrative

R PACK WAS DEFERRED WHEN OUR FLT LEFT MSP. ACFT WAS DEICED AT MSP AND DEPARTED NORMALLY. DURING CLB THROUGH FL180; THE FLT CREW HEARD A LOW RUMBLING NOISE. ALL SYS PAGES WERE SCANNED; BUT THE SOURCE COULD NOT BE LOCATED. DISPLAY COOL MESSAGE ILLUMINATED. BEFORE THE CAPT COULD REACH FOR THE QRH; THE CABIN ALT MESSAGE ILLUMINATED AND CABIN ALT WAS SEEN TO BE RISING RAPIDLY. CAPT AND THE FO DONNED THEIR OXYGEN MASKS AND PERFORMED MEMORY ITEMS FOR AN EMER DSCNT. CAPT NOTIFIED ATC THAT AN IMMEDIATE DSCNT TO 10000 FT WAS NECESSARY. FLT WAS CLRED DOWN TO 11000 FT AND THEN SHORTLY AFTER TO 10000 FT. CREW CAME OFF OXYGEN MASKS (CABIN MASKS DID NOT AUTO-DEPLOY). CREW PERFORMED QRH PROCS FOR DISPLAY 'COOL' AND 'CABIN ALT' MESSAGES. CAPT NOTIFIED FLT ATTENDANT AND ATC. AN EMER WAS NOT DECLARED. BOTH MESSAGES CLRED AFTER QRH WAS COMPLETE AND CAPT ATTEMPTED TO NOTIFY DISPATCH; BUT WAS UNABLE. PLANE WAS CLBED TO 15000 FT BUT ONCE CONTACT WAS ESTABLISHED WITH DISPATCH AND MAINT CTL; CABIN ALT AGAIN BEGAN TO RISE. PLANE WAS AGAIN DSNDED TO 10000 FT AND DISPATCH AND MAINT CTL WERE ADVISED. DISPATCH COMPUTED NEW NUMBERS TO PROCEED TO CVG. ALL AGREED THAT THE FLT COULD SAFELY CONTINUE TO CVG AND THE FLT PROCEEDED UNEVENTFULLY. WHEN THE ACFT PARKED AT THE GATE; THE FUEL ON BOARD WAS 2200 LBS. MAINT MET THE PLANE AT THE GATE.