Narrative:

While cruising at FL390; approximately ten minutes following level off; the first officer and I experienced an abnormal cabin pressure warning horn. We immediately donned oxygen masks and established inter-cockpit communications. The cabin altitude indicated 12;000 ft with a 500 to 700 FPM climb rate. Packs were verified in the auto position and the bleed switches were on. No other annunciator lights were illuminated. A descent was coordinated with center and quickly initiated. During the descent; we continued to attempt to correct the malfunction by attempting to manually close the outflow valve though it already indicated closed. We additionally placed the packs to high and activated the recirc fan. Descending through approximately FL300; the cabin altitude began to descend and control of the pressurization system regained. We leveled at FL200; and assessed that the cabin altitude was below 10;000 ft and descending.at this point we removed our oxygen masks; evaluated the aircraft systems; and determined our ability to continue or possibly diverting. We then informed the flight attendants of the situation. They informed us that the supplemental oxygen masks had not deployed; an indication the cabin altitude did not exceed 14;000 ft; and that the passengers were completely unaware of the pressurization problem. I established verbal communication with dispatch to allow them to review our situation and fuel state. Based on the current ability to hold pressurization; lack of passenger issues; destination weather; and fuel state we determined; we could safely continue to our destination at FL200 and still have the required fuel reserves. The remainder of the flight was otherwise uneventful and the flight was met by the aircraft maintainers who were briefed on the nature and indications of the malfunction. Maintenance control was also briefed. A logbook entry was made and aircraft turned over to maintenance for evaluation.

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Original NASA ASRS Text

Title: A B737-700 flight crew reported abnormal cabin pressure in cruise at FL390. They donned masks and ran the procedure; and after descending to FL200 regained control of the cabin; allowing them to continue to destination at that altitude.

Narrative: While cruising at FL390; approximately ten minutes following level off; the First Officer and I experienced an Abnormal Cabin Pressure Warning horn. We immediately donned oxygen masks and established inter-cockpit communications. The cabin altitude indicated 12;000 FT with a 500 to 700 FPM climb rate. Packs were verified in the auto position and the bleed switches were on. No other annunciator lights were illuminated. A descent was coordinated with Center and quickly initiated. During the descent; we continued to attempt to correct the malfunction by attempting to manually close the outflow valve though it already indicated closed. We additionally placed the packs to high and activated the recirc fan. Descending through approximately FL300; the cabin altitude began to descend and control of the pressurization system regained. We leveled at FL200; and assessed that the cabin altitude was below 10;000 FT and descending.At this point we removed our oxygen masks; evaluated the aircraft systems; and determined our ability to continue or possibly diverting. We then informed the flight attendants of the situation. They informed us that the supplemental oxygen masks had not deployed; an indication the cabin altitude did not exceed 14;000 FT; and that the passengers were completely unaware of the pressurization problem. I established verbal communication with Dispatch to allow them to review our situation and fuel state. Based on the current ability to hold pressurization; lack of passenger issues; destination weather; and fuel state we determined; we could safely continue to our destination at FL200 and still have the required fuel reserves. The remainder of the flight was otherwise uneventful and the flight was met by the aircraft maintainers who were briefed on the nature and indications of the malfunction. Maintenance Control was also briefed. A logbook entry was made and aircraft turned over to maintenance for evaluation.

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.