Narrative:

During intermediate level off at FL270 with the captain flying; the cabin altitude warning sounded. Per our procedures; we donned our oxygen masks and attempted to establish communications. We confirmed that the cabin alt was; indeed; above 10;000 ft and climbing rapidly (approx 1;900 FPM). It is worth noting that no other indications of malfunctions were displayed such as the automatic fail light. I confirmed that the pressurization and pneumatic panels were properly configured and returned my efforts to trying to communicate with the captain using the overhead speaker. Finally; using hand signals; we agreed to get a clearance from ATC for a lower altitude and beginning a descent to 10;000 ft. Because the captain was having difficulty communicating with his oxygen mask on while initiating an emergency descent; I contacted ATC before completing the QRH procedures. At first; ATC cleared us only to fl 250. I reiterated to them that we needed 10;000 right away. Finally after having little success getting our requested altitude. I declared an emergency and notified ATC that we would be descending to 10;000. At that point; we received a clearance to 10;000. Strangely; soon after we received clearance to 10;000; we received another clearance to 13;000 ft. During communications with ATC; I had to stop working on the checklist ; which allowed the cabin to continue climbing to the point where the passenger oxygen masks deployed. The overriding issue during this emergency was the extreme difficulty in communicating both with each other on the flight deck and with ATC. As I worked the QRH; I was able to gain control over the outflow valve using man AC and dc mode. I elected to control the cabin with man dc because of its slower response while still effecting very large fluctuations in the cabin rate of descent. Quickly; I was able to stabilize the cabin rate of descent at -500 FPM. I then made an announcement over the PA; briefly explaining what had happened and that we would be returning to our departure airport. I made a point to mention that connecting flight information would be available after we landed just to take some of the urgency and alarm out of my message. Around the same time; the head flight attendant called and mentioned that the passenger oxygen masks had dropped. I told her that we did; in fact; have a problem with the pressurization system and to have the passengers use the masks. I also told her that we would be landing in roughly 25 minutes and that it would be a normal landing. The maximum altitude of the cabin was 14;300 during the event. Continuing with our descent to 10;000; I finished the QRH procedures and read them aloud to the captain. Once we reached 10;000; we took off our masks and set up the aircraft for an overweight landing. A smooth landing at 125;000 pounds was made. After we blocked in; maintenance control told me that they had replaced the auto controller and outflow valve the day prior and that most likely it had failed again. I believe more realistic training in non-normal/emergency cockpit communications (using the masks with speakers) with multiple distractions would be helpful in making events like this go smoother in the future. I feel that I may have been able to arrest the rapid cabin altitude climb if I would been able to focus on the pressurization panel without having to coordinate communication with ATC at the same time. Overall; I believe the captain and I reacted to this situation very well in light of and in spite of the difficulties we had communicating. We improvised and got the situation turned around and stabilized very quickly.

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Original NASA ASRS Text

Title: A B737-400 suffered a failed pressurization controller; initiated an emergency descent; and returned to departure airport for an uneventful overweight landing.

Narrative: During intermediate level off at FL270 with the Captain flying; the cabin altitude warning sounded. Per our procedures; we donned our oxygen masks and attempted to establish communications. We confirmed that the cabin alt was; indeed; above 10;000 FT and climbing rapidly (approx 1;900 FPM). It is worth noting that no other indications of malfunctions were displayed such as the AUTO FAIL light. I confirmed that the pressurization and pneumatic panels were properly configured and returned my efforts to trying to communicate with the Captain using the overhead speaker. Finally; using hand signals; we agreed to get a clearance from ATC for a lower altitude and beginning a descent to 10;000 FT. Because the Captain was having difficulty communicating with his oxygen mask on while initiating an emergency descent; I contacted ATC before completing the QRH procedures. At first; ATC cleared us only to FL 250. I reiterated to them that we needed 10;000 right away. Finally after having little success getting our requested altitude. I declared an emergency and notified ATC that we would be descending to 10;000. At that point; we received a clearance to 10;000. Strangely; soon after we received clearance to 10;000; we received another clearance to 13;000 FT. During communications with ATC; I had to stop working on the checklist ; which allowed the cabin to continue climbing to the point where the passenger oxygen masks deployed. The overriding issue during this emergency was the extreme difficulty in communicating both with each other on the flight deck and with ATC. As I worked the QRH; I was able to gain control over the outflow valve using MAN AC and DC mode. I elected to control the cabin with MAN DC because of its slower response while still effecting very large fluctuations in the cabin rate of descent. Quickly; I was able to stabilize the cabin rate of descent at -500 FPM. I then made an announcement over the PA; briefly explaining what had happened and that we would be returning to our departure airport. I made a point to mention that connecting flight information would be available after we landed just to take some of the urgency and alarm out of my message. Around the same time; the head Flight Attendant called and mentioned that the passenger oxygen masks had dropped. I told her that we did; in fact; have a problem with the pressurization system and to have the passengers use the masks. I also told her that we would be landing in roughly 25 minutes and that it would be a normal landing. The maximum altitude of the cabin was 14;300 during the event. Continuing with our descent to 10;000; I finished the QRH procedures and read them aloud to the Captain. Once we reached 10;000; we took off our masks and set up the aircraft for an overweight landing. A smooth landing at 125;000 LBS was made. After we blocked in; Maintenance Control told me that they had replaced the auto controller and outflow valve the day prior and that most likely it had failed again. I believe more realistic training in non-normal/emergency cockpit communications (using the masks with speakers) with multiple distractions would be helpful in making events like this go smoother in the future. I feel that I may have been able to arrest the rapid cabin altitude climb if I would been able to focus on the pressurization panel without having to coordinate communication with ATC at the same time. Overall; I believe the Captain and I reacted to this situation very well in light of and in spite of the difficulties we had communicating. We improvised and got the situation turned around and stabilized very quickly.

Data retrieved from NASA's ASRS site as of April 2012 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.