Narrative:

While turning final I could feel a huge pressure change in my ears; I looked at the pressurization gauges and the cabin was climbing at 4;000 FPM. Within seconds the cabin was then descending at 1;500 FPM which matched the aircraft rate of descent. We thought that we had lost pressurization. The first officer switched the pressurization mode selector to standby; but that did not stabilize the pressurization. I noticed that pressure differential gauge showed that we would be landing with greater than the allowable 0.125 positive pressure differential; however I believed that that gauge may be giving an inaccurate reading as the cabin rate of descent continued to match the aircraft rate of descent.with less than 2 minutes to landing I focused on pilot not flying duties required for approach and landing and no longer worried about the pressurization. After landing I taxied clear of the runway and now realized there was still something wrong with the pressurization. I elected to keep the aircraft away from the gate and troubleshoot the pressurization problem. The cabin altitude showed zero; the cabin differential was 7.5; and the airport elevation was 2;300. The cabin rate of climb was still changing from a 500 FPM descent to a 1;000 FPM climb. The QRH gave no guidance.I contacted dispatch to inform them of the problem and receive guidance from maintenance. Maintenance control had us bring the cabin altitude up by using the manual mode to control the outflow valve. Once we got the cabin differential to zero; we continued to the gate and passengers deplaned. Maintenance control believes that the outflow valve may have frozen in flight causing the problem.I considered a go-around so that we could troubleshoot the pressurization problem; but multiple factors led to my decision to continue to a landing including crew fatigue and lack of familiarity with the surrounding terrain. In training we practice certain emergencies (rapid depressurization at altitude; for instance); but at times there are the scenarios that have never been seen in the simulator and we must make decisions based on the knowledge that we have and the time/fuel constraints given.

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Original NASA ASRS Text

Title: After considering all factors; a B737-300 flight crew turning final approach elected to land ASAP rather than go around to assess a cabin pressurization problem.

Narrative: While turning final I could feel a huge pressure change in my ears; I looked at the pressurization gauges and the cabin was climbing at 4;000 FPM. Within seconds the cabin was then descending at 1;500 FPM which matched the aircraft rate of descent. We thought that we had lost pressurization. The First Officer switched the pressurization mode selector to standby; but that did not stabilize the pressurization. I noticed that pressure differential gauge showed that we would be landing with greater than the allowable 0.125 positive pressure differential; however I believed that that gauge may be giving an inaccurate reading as the cabin rate of descent continued to match the aircraft rate of descent.With less than 2 minutes to landing I focused on pilot not flying duties required for approach and landing and no longer worried about the pressurization. After landing I taxied clear of the runway and now realized there was still something wrong with the pressurization. I elected to keep the aircraft away from the gate and troubleshoot the pressurization problem. The cabin altitude showed zero; the cabin differential was 7.5; and the airport elevation was 2;300. The cabin rate of climb was still changing from a 500 FPM descent to a 1;000 FPM climb. The QRH gave no guidance.I contacted Dispatch to inform them of the problem and receive guidance from Maintenance. Maintenance Control had us bring the cabin altitude up by using the manual mode to control the outflow valve. Once we got the cabin differential to zero; we continued to the gate and passengers deplaned. Maintenance Control believes that the outflow valve may have frozen in flight causing the problem.I considered a go-around so that we could troubleshoot the pressurization problem; but multiple factors led to my decision to continue to a landing including crew fatigue and lack of familiarity with the surrounding terrain. In training we practice certain emergencies (rapid depressurization at altitude; for instance); but at times there are the scenarios that have never been seen in the simulator and we must make decisions based on the knowledge that we have and the time/fuel constraints given.

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.