Narrative:

When climbing through FL240 we noticed our cabin altitude was climbing rapidly. We quickly received a 'cabin altitude' caution message (cabin altitude is at 8500 ft). The first officer ran the QRH cabin altitude message checklist (for the caution message). Meanwhile cabin altitude continued to rise toward 10000 ft within about 30 seconds after the initial 'cabin altitude' caution message. I donned my oxygen mask while the first officer ran the checklist. He was not able to finish the checklist before we received a triple chime and a master warning 'cabin altitude' message (cabin altitude at 10000 ft). I then called for the cabin altitude immediate action item checklist. The first officer donned his oxygen mask; established crew communication and proceeded with the new cabin altitude master warning message checklist. I declared an emergency with ATC and requested a lower altitude. ATC immediately turned me toward ZZZ and gave me an altitude of 12000 ft. I performed an emergency descent of approximately 6000 FPM. Before reaching 12000 ft; ATC assigned us 10000 ft. Upon reaching 10000 ft the first officer and I removed our oxygen masks. The first officer called the flight attendant to check on her; and the status of our passenger. Once we knew they were ok; I xferred the controls to the first officer; I then made a PA to inform the passenger of the situation; and to let them know that we were returning to ZZZ; and that it was safe for them to remove their oxygen masks. ATC continued to give us lower altitudes and assigned us an ILS approach to runway 27L in ZZZ. We finished the QRH checklists; descent and approach checklists; and briefed the approach to ZZZ. At this point we were still 10 mins out of ZZZ. I had time to call my dispatch; maintenance department; and operations to inform them of our situation. The cabin altitude was erratic in manual mode; and would not stabilize. It fluctuated up and down by thousands of feet. I switched it to automatic mode around 5000 ft AGL and the cabin pressure stabilized at 1100 ft. The first officer then xferred the controls back to me. We made a normal landing without complications. As a safety precaution I had the fire trucks follow us to the gate since the oxygen canisters had been used and the burning smell was apparent in the flight deck.

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Original NASA ASRS Text

Title: CRJ200 CABIN PRESSURIZATION BECAME UNCONTROLLABLE. FLT CREW PERFORMED EMER DESCENT AND RETURNED FOR LNDG.

Narrative: WHEN CLBING THROUGH FL240 WE NOTICED OUR CABIN ALT WAS CLBING RAPIDLY. WE QUICKLY RECEIVED A 'CABIN ALT' CAUTION MESSAGE (CABIN ALT IS AT 8500 FT). THE FO RAN THE QRH CABIN ALT MESSAGE CHKLIST (FOR THE CAUTION MESSAGE). MEANWHILE CABIN ALT CONTINUED TO RISE TOWARD 10000 FT WITHIN ABOUT 30 SECONDS AFTER THE INITIAL 'CABIN ALT' CAUTION MESSAGE. I DONNED MY OXYGEN MASK WHILE THE FO RAN THE CHKLIST. HE WAS NOT ABLE TO FINISH THE CHKLIST BEFORE WE RECEIVED A TRIPLE CHIME AND A MASTER WARNING 'CABIN ALT' MESSAGE (CABIN ALT AT 10000 FT). I THEN CALLED FOR THE CABIN ALT IMMEDIATE ACTION ITEM CHKLIST. THE FO DONNED HIS OXYGEN MASK; ESTABLISHED CREW COM AND PROCEEDED WITH THE NEW CABIN ALT MASTER WARNING MESSAGE CHKLIST. I DECLARED AN EMER WITH ATC AND REQUESTED A LOWER ALT. ATC IMMEDIATELY TURNED ME TOWARD ZZZ AND GAVE ME AN ALT OF 12000 FT. I PERFORMED AN EMER DSCNT OF APPROX 6000 FPM. BEFORE REACHING 12000 FT; ATC ASSIGNED US 10000 FT. UPON REACHING 10000 FT THE FO AND I REMOVED OUR OXYGEN MASKS. THE FO CALLED THE FLT ATTENDANT TO CHK ON HER; AND THE STATUS OF OUR PAX. ONCE WE KNEW THEY WERE OK; I XFERRED THE CTLS TO THE FO; I THEN MADE A PA TO INFORM THE PAX OF THE SIT; AND TO LET THEM KNOW THAT WE WERE RETURNING TO ZZZ; AND THAT IT WAS SAFE FOR THEM TO REMOVE THEIR OXYGEN MASKS. ATC CONTINUED TO GIVE US LOWER ALTS AND ASSIGNED US AN ILS APCH TO RWY 27L IN ZZZ. WE FINISHED THE QRH CHKLISTS; DSCNT AND APCH CHKLISTS; AND BRIEFED THE APCH TO ZZZ. AT THIS POINT WE WERE STILL 10 MINS OUT OF ZZZ. I HAD TIME TO CALL MY DISPATCH; MAINT DEPT; AND OPS TO INFORM THEM OF OUR SIT. THE CABIN ALT WAS ERRATIC IN MANUAL MODE; AND WOULD NOT STABILIZE. IT FLUCTUATED UP AND DOWN BY THOUSANDS OF FEET. I SWITCHED IT TO AUTO MODE AROUND 5000 FT AGL AND THE CABIN PRESSURE STABILIZED AT 1100 FT. THE FO THEN XFERRED THE CTLS BACK TO ME. WE MADE A NORMAL LNDG WITHOUT COMPLICATIONS. AS A SAFETY PRECAUTION I HAD THE FIRE TRUCKS FOLLOW US TO THE GATE SINCE THE OXYGEN CANISTERS HAD BEEN USED AND THE BURNING SMELL WAS APPARENT IN THE FLT DECK.

Data retrieved from NASA's ASRS site as of January 2009 and automatically converted to unabbreviated mixed upper/lowercase text. This report is for informational purposes with no guarantee of accuracy. See NASA's ASRS site for official report.