Narrative:

The event occurred due to a malfunction of the cabin pressure system; indication system; or both. Other items that contributed to the event were the QRH procedures that didn't seem to address the possibility of indications of high cabin altitude at low MSL altitudes; and the local weather conditions. We were climbing out at approximately 21;000 ft when the cabin altitude warning came on. The captain and I donned our oxygen masks and established communications. I leveled the aircraft off; and initiated a descent while the captain talked to ATC and got a clearance down to 11;000 ft initially and then went to the QRH for the cabin altitude/emergency descent procedure. The masks in the cabin had automatically dropped and we instructed the flight attendant's to use the oxygen. The captain ran through the QRH procedures; but we couldn't control the cabin altitude. As we were descending we noticed the cabin altitude was fluctuating around 16;000 and 13;000 ft but was not coming down any further. We were approximately 50 miles outside of ZZZ heading directly towards the airport and decided to make our diversion there. We continued to descend with ATC clearance down to 9;000 ft but the cabin altitude would not come down farther; and it stabilized indicating 16;900 ft. We decided to keep our masks on based on the indications of the cabin altitude and contacted ZZZ approach for clearance to the ILS. ZZZ was landing runway 28 with light snow and reported RVR of 5500FT. We got vectors for the ILS 28 and entered IMC at approximately 6000 ft MSL; we were cleared for the approach and continued inbound. The captain continued to review the QRH procedure for loss of pressurization/manual pressurization to see what steps if any we should accomplish after landing. We were handed over to tower and we completed the before landing checklist. We broke out of the clouds at approximately 400FT AGL and saw the runway and continued in for landing. After we landed the captain was no longer positive we had been cleared to land and asked me if I remembered hearing the clearance. I thought we had been cleared; but I couldn't honestly recall as I had been focused entirely on the approach and landing. We called tower and they did not say anything about landing without clearance; only inquiring about braking action and giving taxi instructions to the ramp; so we assumed we had been cleared. We cleared the runway and continued to the ramp; but the cabin altitude still indicated 16;900 ft and nothing we did would change it. At the ramp the captain talked to the flight attendants and saw that no one appeared to be suffering from any effects of high altitude as the cabin still indicated; so he decided to remove his mask and see if he noticed anything. After a period of time with no ill effects; I also removed my mask so it was easier to communicate. We could still not get the cabin altitude indication to come down and the captain called maintenance control to see if they had any ideas. In the process of sitting there; the ground personnel attempted to open the cabin door from the outside; but it was jammed. While waiting on ideas from maintenance control; the aft lav smoke warning sounded; on the captain's instructions I called back to the flight attendant's and had the aft flight attendant check the lav for smoke or fire and the forward flight attendant stow his jumpseat in case we had to make an evacuation. The aft flight attendant didn't smell or see any smoke in the lav; but we instructed him to keep a watch as I ran the QRH procedure and pulled the associated circuit breakers. The captain continued to talk to maintenance control; but nothing maintenance control instructed us to do was working. After approximately 15-20 minutes with the captain on the phone with maintenance control I saw the cabin altitude indication change immediately from 16;900 ft to negative 3;900 feet. With the captain's permission I put the manual cabin altitude control to up and the selector to full increase. As the cabin altitude came up to local elevation the aft lav smokewarning went out; and the flight attendant was then able to open the forward cabin door. All the ground personnel had left to work other flights; so I went outside and into the terminal to get a jetbridge driver; and then we deplaned the passengers. I am not sure if we had an actual loss of cabin pressure or if it was just an indicating issue or both. I never felt any symptoms of hypoxia but I donned my mask immediately after the warning. I did feel quite a lot of pressure changes in my ears during the descent however. The high cabin altitude indications after descending below 10;000 ft and continuing after landing were very confusing as they didn't make any sense; and the QRH procedure didn't seem to offer a solution for having a high cabin altitude after descending. The cabin altitude warning and aural tone sounded; as well as the aft lav smoke warning later on the ground. We donned oxygen masks; initiated an emergency descent; ran the QRH procedures; diverted to ZZZ; and then contacted maintenance control when we were unable to solve the issue on the ground. Review the QRH procedure for cabin altitude; to include steps to accomplish if the cabin altitude still indicates high altitudes after descending below 10;000 ft. Indications of high cabin altitude at low MSL altitudes is unexpected and confusing during an emergency; and having something outlined in the QRH procedure would help solve this.callback conversation with reporter revealed the following information: the reporter stated that the cabin pressure monitoring computer displays cabin altitude; differential pressure and deploys passenger oxygen masks at the appropriate time. The CRJ700 has no visual indication of outflow valve position. The reason for the on ground difficulties was traced to the outflow valve being closed with the aircraft being slightly pressurized. The outflow valve was closed during the initial phase of the emergency and also produced the pressure surges the crew sensed. The lav smoke detector was triggered by the passenger oxygen generators and the lack of air flow in the cabin.

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Original NASA ASRS Text

Title: CRJ700 CREW AND PAX EXPERIENCE CABIN PRESSURE; PAX OXYGEN MASK; AND LAVATORY SMOKE DETECTOR ANOMALIES; POSSIBLY AS A RESULT OF FAILURE OF THE CABIN ALT MONITORING COMPUTER.

Narrative: THE EVENT OCCURRED DUE TO A MALFUNCTION OF THE CABIN PRESSURE SYSTEM; INDICATION SYSTEM; OR BOTH. OTHER ITEMS THAT CONTRIBUTED TO THE EVENT WERE THE QRH PROCEDURES THAT DIDN'T SEEM TO ADDRESS THE POSSIBILITY OF INDICATIONS OF HIGH CABIN ALTITUDE AT LOW MSL ALTITUDES; AND THE LOCAL WEATHER CONDITIONS. WE WERE CLIMBING OUT AT APPROXIMATELY 21;000 FT WHEN THE CABIN ALT WARNING CAME ON. THE CAPTAIN AND I DONNED OUR OXYGEN MASKS AND ESTABLISHED COMMUNICATIONS. I LEVELED THE AIRCRAFT OFF; AND INITIATED A DESCENT WHILE THE CAPTAIN TALKED TO ATC AND GOT A CLEARANCE DOWN TO 11;000 FT INITIALLY AND THEN WENT TO THE QRH FOR THE CABIN ALTITUDE/EMERGENCY DESCENT PROCEDURE. THE MASKS IN THE CABIN HAD AUTOMATICALLY DROPPED AND WE INSTRUCTED THE FA'S TO USE THE OXYGEN. THE CAPTAIN RAN THROUGH THE QRH PROCEDURES; BUT WE COULDN'T CONTROL THE CABIN ALTITUDE. AS WE WERE DESCENDING WE NOTICED THE CABIN ALTITUDE WAS FLUCTUATING AROUND 16;000 AND 13;000 FT BUT WAS NOT COMING DOWN ANY FURTHER. WE WERE APPROXIMATELY 50 MILES OUTSIDE OF ZZZ HEADING DIRECTLY TOWARDS THE AIRPORT AND DECIDED TO MAKE OUR DIVERSION THERE. WE CONTINUED TO DESCEND WITH ATC CLEARANCE DOWN TO 9;000 FT BUT THE CABIN ALTITUDE WOULD NOT COME DOWN FARTHER; AND IT STABILIZED INDICATING 16;900 FT. WE DECIDED TO KEEP OUR MASKS ON BASED ON THE INDICATIONS OF THE CABIN ALTITUDE AND CONTACTED ZZZ APPROACH FOR CLEARANCE TO THE ILS. ZZZ WAS LANDING RUNWAY 28 WITH LIGHT SNOW AND REPORTED RVR OF 5500FT. WE GOT VECTORS FOR THE ILS 28 AND ENTERED IMC AT APPROXIMATELY 6000 FT MSL; WE WERE CLEARED FOR THE APPROACH AND CONTINUED INBOUND. THE CAPTAIN CONTINUED TO REVIEW THE QRH PROCEDURE FOR LOSS OF PRESSURIZATION/MANUAL PRESSURIZATION TO SEE WHAT STEPS IF ANY WE SHOULD ACCOMPLISH AFTER LANDING. WE WERE HANDED OVER TO TOWER AND WE COMPLETED THE BEFORE LANDING CHECKLIST. WE BROKE OUT OF THE CLOUDS AT APPROXIMATELY 400FT AGL AND SAW THE RUNWAY AND CONTINUED IN FOR LANDING. AFTER WE LANDED THE CAPTAIN WAS NO LONGER POSITIVE WE HAD BEEN CLEARED TO LAND AND ASKED ME IF I REMEMBERED HEARING THE CLEARANCE. I THOUGHT WE HAD BEEN CLEARED; BUT I COULDN'T HONESTLY RECALL AS I HAD BEEN FOCUSED ENTIRELY ON THE APPROACH AND LANDING. WE CALLED TOWER AND THEY DID NOT SAY ANYTHING ABOUT LANDING WITHOUT CLEARANCE; ONLY INQUIRING ABOUT BRAKING ACTION AND GIVING TAXI INSTRUCTIONS TO THE RAMP; SO WE ASSUMED WE HAD BEEN CLEARED. WE CLEARED THE RUNWAY AND CONTINUED TO THE RAMP; BUT THE CABIN ALTITUDE STILL INDICATED 16;900 FT AND NOTHING WE DID WOULD CHANGE IT. AT THE RAMP THE CAPTAIN TALKED TO THE FLIGHT ATTENDANTS AND SAW THAT NO ONE APPEARED TO BE SUFFERING FROM ANY EFFECTS OF HIGH ALTITUDE AS THE CABIN STILL INDICATED; SO HE DECIDED TO REMOVE HIS MASK AND SEE IF HE NOTICED ANYTHING. AFTER A PERIOD OF TIME WITH NO ILL EFFECTS; I ALSO REMOVED MY MASK SO IT WAS EASIER TO COMMUNICATE. WE COULD STILL NOT GET THE CABIN ALTITUDE INDICATION TO COME DOWN AND THE CAPTAIN CALLED MAINT CTL TO SEE IF THEY HAD ANY IDEAS. IN THE PROCESS OF SITTING THERE; THE GROUND PERSONNEL ATTEMPTED TO OPEN THE CABIN DOOR FROM THE OUTSIDE; BUT IT WAS JAMMED. WHILE WAITING ON IDEAS FROM MAINT CTL; THE AFT LAV SMOKE WARNING SOUNDED; ON THE CAPTAIN'S INSTRUCTIONS I CALLED BACK TO THE FA'S AND HAD THE AFT FLIGHT ATTENDANT CHECK THE LAV FOR SMOKE OR FIRE AND THE FORWARD FLIGHT ATTENDANT STOW HIS JUMPSEAT IN CASE WE HAD TO MAKE AN EVACUATION. THE AFT FLIGHT ATTENDANT DIDN'T SMELL OR SEE ANY SMOKE IN THE LAV; BUT WE INSTRUCTED HIM TO KEEP A WATCH AS I RAN THE QRH PROCEDURE AND PULLED THE ASSOCIATED CIRCUIT BREAKERS. THE CAPTAIN CONTINUED TO TALK TO MAINT CTL; BUT NOTHING MAINT CTL INSTRUCTED US TO DO WAS WORKING. AFTER APPROXIMATELY 15-20 MINUTES WITH THE CAPTAIN ON THE PHONE WITH MAINT CTL I SAW THE CABIN ALTITUDE INDICATION CHANGE IMMEDIATELY FROM 16;900 FT TO NEGATIVE 3;900 FEET. WITH THE CAPTAIN'S PERMISSION I PUT THE MANUAL CABIN ALT CONTROL TO UP AND THE SELECTOR TO FULL INCREASE. AS THE CABIN ALTITUDE CAME UP TO LOCAL ELEVATION THE AFT LAV SMOKEWARNING WENT OUT; AND THE FLIGHT ATTENDANT WAS THEN ABLE TO OPEN THE FORWARD CABIN DOOR. ALL THE GROUND PERSONNEL HAD LEFT TO WORK OTHER FLIGHTS; SO I WENT OUTSIDE AND INTO THE TERMINAL TO GET A JETBRIDGE DRIVER; AND THEN WE DEPLANED THE PASSENGERS. I AM NOT SURE IF WE HAD AN ACTUAL LOSS OF CABIN PRESSURE OR IF IT WAS JUST AN INDICATING ISSUE OR BOTH. I NEVER FELT ANY SYMPTOMS OF HYPOXIA BUT I DONNED MY MASK IMMEDIATELY AFTER THE WARNING. I DID FEEL QUITE A LOT OF PRESSURE CHANGES IN MY EARS DURING THE DESCENT HOWEVER. THE HIGH CABIN ALTITUDE INDICATIONS AFTER DESCENDING BELOW 10;000 FT AND CONTINUING AFTER LANDING WERE VERY CONFUSING AS THEY DIDN'T MAKE ANY SENSE; AND THE QRH PROCEDURE DIDN'T SEEM TO OFFER A SOLUTION FOR HAVING A HIGH CABIN ALTITUDE AFTER DESCENDING. THE CABIN ALT WARNING AND AURAL TONE SOUNDED; AS WELL AS THE AFT LAV SMOKE WARNING LATER ON THE GROUND. WE DONNED OXYGEN MASKS; INITIATED AN EMERGENCY DESCENT; RAN THE QRH PROCEDURES; DIVERTED TO ZZZ; AND THEN CONTACTED MAINT CTL WHEN WE WERE UNABLE TO SOLVE THE ISSUE ON THE GROUND. REVIEW THE QRH PROCEDURE FOR CABIN ALT; TO INCLUDE STEPS TO ACCOMPLISH IF THE CABIN ALT STILL INDICATES HIGH ALTITUDES AFTER DESCENDING BELOW 10;000 FT. INDICATIONS OF HIGH CABIN ALTITUDE AT LOW MSL ALTITUDES IS UNEXPECTED AND CONFUSING DURING AN EMERGENCY; AND HAVING SOMETHING OUTLINED IN THE QRH PROCEDURE WOULD HELP SOLVE THIS.CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO: THE RPTR STATED THAT THE CABIN PRESSURE MONITORING COMPUTER DISPLAYS CABIN ALT; DIFFERENTIAL PRESSURE AND DEPLOYS PAX OXYGEN MASKS AT THE APPROPRIATE TIME. THE CRJ700 HAS NO VISUAL INDICATION OF OUTFLOW VALVE POSITION. THE REASON FOR THE ON GROUND DIFFICULTIES WAS TRACED TO THE OUTFLOW VALVE BEING CLOSED WITH THE ACFT BEING SLIGHTLY PRESSURIZED. THE OUTFLOW VALVE WAS CLOSED DURING THE INITIAL PHASE OF THE EMER AND ALSO PRODUCED THE PRESSURE SURGES THE CREW SENSED. THE LAV SMOKE DETECTOR WAS TRIGGERED BY THE PAX OXYGEN GENERATORS AND THE LACK OF AIR FLOW IN THE CABIN.

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.