Narrative:

It was a routine flight that was normal until top of descent. Prior to descending from our cruising altitude center advised us that the ride in the descent had moderate turbulence until flight level 250; and issued the clearance to descend to FL250. Once I initiated the descent I set a fairly steep descent rate to try and expedite our descent through the rough air. After a short period of time; probably less than 1 minute after initiating the descent; I noticed that the cabin altitude was climbing; and the cabin psi was decreasing. I verbalized the abnormality to the first officer and continued to monitor the cabin pressure. It was a very gradual loss of pressure and the cabin rate was showing between 600 and 800 ft per minute climb. I waited around 60 seconds to see if the cabin pressure would stabilize or not. Cabin altitude continued to climb at 600 to 800 ft per minute. So I initiated a steeper descent; and called ATC to tell them we were losing cabin pressure and we needed lower. He initially cleared us to FL190; I replied that we needed to descend to 10;000. I then called the flight attendant to adviser her that we were slowly losing cabin pressure and that masks might drop. I also told her; that we were already descending and that everything else was ok; but if the masks did drop to go ahead and use them. We were now descending though about 25;000 - 28;000 and I turned my attention back to the cabin pressure problem. Around this point the cabin altitude reached 10;000 and we received the aural warning for cabin pressure. We received clearance to descend to 11;000; and we were advised that ATC had declared an emergency for us. I ran the QRH for loss of cabin pressure; which directed us to use the oxygen masks and make an emergency descent. We were already descending at about 4;500 ft per minute at maximum speed and speed brakes open. With that descent rate and our altitude somewhere in the 20;000 range; still holding a cabin pressure of less than 11;000 ft; but [we were] still losing cabin pressure at 600 to 800 ft per minute. I elected not to slow the aircraft to 250 KTS to extend the landing gear. We were about 1 minute from being low enough that the passenger oxygen masks wouldn't drop; and 2 to 3 minutes from being level at 10;000 ft. I estimated that first slowing the plane to make a steeper descent with the landing gear out would be about equal in time if the 4;500 ft per minute descent was continued. A frequency change with a new controller got us clearance to 10;000. Even though several altitude clearances were issued that were above the requested 10;000; we never got close to reaching the cleared altitude before a lower one was issued. For most of the descent I was trying to troubleshoot possible causes for the pressurization problem. While I'm not exactly sure in what order or at what time or altitude; I know that I rechecked the set altitude in the pressurization controller that was set properly at 900 ft. I also recycled the engine bleeds and packs. I tried advancing the thrust levers to increase bleed pressure. I verified that all monitored doors were closed on the doors page. I started the APU and used the APU bleed air for the packs. I also tried moving the pressurization controlled to the manual mode. Everything I tried had no effect on the loss of cabin pressure. Our altitude and cabin pressure caught up to each other at 12;100 ft. We leveled off at 10;000 ft and the cabin pressure stabilized at 10;000 ft as well. I don't know for a fact; but I suspect the emergency ram air valve opened because the cockpit temperature got very cold. Adjusting the temperature control to almost maximum; (I didn't use maximum temperature so the packs wouldn't overload or overheat and possibly exacerbate our pressurization problem;) the cockpit temperature was around 8 degrees celsius. In an effort to get to warmer air we continued our descent to 2;500 ft. We had approximately 50 miles left to our destination airport; so I decided it best continue to the original destination. We used the next few minutes to get caught up on things like the arrival briefing and in-range checklist. We also answered some ATC questions about souls; fuel; and if we needed further assistance. There were no other known abnormalities and we completed a normal approach and landing. The passenger masks were never deployed; manually or automatically. Contract maintenance troubleshot the pressurization problem and determined that there was something wrong with the controller and subsequent tries to pressurize the plane on the ground all failed.

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Original NASA ASRS Text

Title: EMB145 Captain experiences a loss of cabin pressure as a normal descent is initiated from FL300. The cabin is climbing at up to 800 FPM and all attempts to control the rate are ineffective. The masks do not drop and the flight continues to destination. Maintenance determined there was something wrong with the controller and subsequent tries to pressurize the plane on the ground all failed.

Narrative: It was a routine flight that was normal until top of descent. Prior to descending from our cruising altitude Center advised us that the ride in the descent had moderate turbulence until flight level 250; and issued the clearance to descend to FL250. Once I initiated the descent I set a fairly steep descent rate to try and expedite our descent through the rough air. After a short period of time; probably less than 1 minute after initiating the descent; I noticed that the cabin altitude was climbing; and the cabin PSI was decreasing. I verbalized the abnormality to the First Officer and continued to monitor the cabin pressure. It was a very gradual loss of pressure and the cabin rate was showing between 600 and 800 FT per minute climb. I waited around 60 seconds to see if the cabin pressure would stabilize or not. Cabin altitude continued to climb at 600 to 800 FT per minute. So I initiated a steeper descent; and called ATC to tell them we were losing cabin pressure and we needed lower. He initially cleared us to FL190; I replied that we needed to descend to 10;000. I then called the Flight Attendant to adviser her that we were slowly losing cabin pressure and that masks might drop. I also told her; that we were already descending and that everything else was OK; but if the masks did drop to go ahead and use them. We were now descending though about 25;000 - 28;000 and I turned my attention back to the cabin pressure problem. Around this point the cabin altitude reached 10;000 and we received the aural warning for cabin pressure. We received clearance to descend to 11;000; and we were advised that ATC had declared an emergency for us. I ran the QRH for loss of cabin pressure; which directed us to use the oxygen masks and make an emergency descent. We were already descending at about 4;500 FT per minute at maximum speed and speed brakes open. With that descent rate and our altitude somewhere in the 20;000 range; still holding a cabin pressure of less than 11;000 FT; but [we were] still losing cabin pressure at 600 to 800 FT per minute. I elected not to slow the aircraft to 250 KTS to extend the landing gear. We were about 1 minute from being low enough that the passenger oxygen masks wouldn't drop; and 2 to 3 minutes from being level at 10;000 FT. I estimated that first slowing the plane to make a steeper descent with the landing gear out would be about equal in time if the 4;500 FT per minute descent was continued. A frequency change with a new Controller got us clearance to 10;000. Even though several altitude clearances were issued that were above the requested 10;000; we never got close to reaching the cleared altitude before a lower one was issued. For most of the descent I was trying to troubleshoot possible causes for the pressurization problem. While I'm not exactly sure in what order or at what time or altitude; I know that I rechecked the set altitude in the pressurization controller that was set properly at 900 FT. I also recycled the engine bleeds and packs. I tried advancing the thrust levers to increase bleed pressure. I verified that all monitored doors were closed on the doors page. I started the APU and used the APU bleed air for the packs. I also tried moving the pressurization controlled to the manual mode. Everything I tried had no effect on the loss of cabin pressure. Our altitude and cabin pressure caught up to each other at 12;100 FT. We leveled off at 10;000 FT and the cabin pressure stabilized at 10;000 FT as well. I don't know for a fact; but I suspect the emergency ram air valve opened because the cockpit temperature got very cold. Adjusting the temperature control to almost maximum; (I didn't use maximum temperature so the packs wouldn't overload or overheat and possibly exacerbate our pressurization problem;) the cockpit temperature was around 8 degrees Celsius. In an effort to get to warmer air we continued our descent to 2;500 FT. We had approximately 50 miles left to our destination airport; so I decided it best continue to the original destination. We used the next few minutes to get caught up on things like the Arrival Briefing and In-Range Checklist. We also answered some ATC questions about souls; fuel; and if we needed further assistance. There were no other known abnormalities and we completed a normal approach and landing. The passenger masks were never deployed; manually or automatically. Contract Maintenance troubleshot the pressurization problem and determined that there was something wrong with the controller and subsequent tries to pressurize the plane on the ground all failed.

Data retrieved from NASA's ASRS site as of July 2013 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.