Narrative:

During climbout; and at approximately 33;500 ft; the cabin altitude warning horn sounded. We completed the memory items and requested a descent from ATC. The cabin altitude was 11;000 ft. We initially requested FL250. As we descended; the aircraft began to pressurize. The cabin descended at 1;000 ft per minute and was soon below 10;000 ft. At 25;000 pressure altitude the cabin was maintaining 5;000 ft. There were no indications of a pressurization controller or pack malfunction. When the situation was stabilized; we did notice that the duct pressure on the right side was near zero; and the pressure on the left side was near 50. We continued without further incident. The passenger oxygen masks did not deploy. There were no complaints from any of the passengers or flight attendants relating to abnormal pressurization.upon arrival; I mistakenly contacted the dispatcher responsible for the next leg of our flight; rather than the leg we just completed. I also contacted operations to request maintenance. Company maintenance met us at the gate. The problem was explained to them and MEL options were discussed. They proceeded to contact maintenance control to work a solution. Maintenance control and I completed a pressurization incident form via phone. The aircraft was taken out of service; and a spare aircraft was provided. En route to our next destination; I received a message to contact dispatch upon landing. During the discussion that followed; I realized that I was not clear enough with the dispatcher that we had a cabin pressurization problem. They were unaware of the event.

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Original NASA ASRS Text

Title: B737-300 Captain experiences a cabin altitude warning horn approaching FL350. A descent is initiated and upon reaching FL250 cabin altitude has descended to 5;000 FT. There were no indications of a pressurization controller or pack malfunction; but the duct pressure on the right side was near zero.

Narrative: During climbout; and at approximately 33;500 FT; the Cabin Altitude Warning horn sounded. We completed the memory items and requested a descent from ATC. The cabin altitude was 11;000 FT. We initially requested FL250. As we descended; the aircraft began to pressurize. The cabin descended at 1;000 FT per minute and was soon below 10;000 FT. At 25;000 pressure altitude the cabin was maintaining 5;000 FT. There were no indications of a pressurization controller or pack malfunction. When the situation was stabilized; we did notice that the duct pressure on the right side was near zero; and the pressure on the left side was near 50. We continued without further incident. The passenger oxygen masks did not deploy. There were no complaints from any of the passengers or flight attendants relating to abnormal pressurization.Upon arrival; I mistakenly contacted the Dispatcher responsible for the next leg of our flight; rather than the leg we just completed. I also contacted Operations to request Maintenance. Company Maintenance met us at the gate. The problem was explained to them and MEL options were discussed. They proceeded to contact Maintenance Control to work a solution. Maintenance Control and I completed a pressurization incident form via phone. The aircraft was taken out of service; and a spare aircraft was provided. En route to our next destination; I received a message to contact Dispatch upon landing. During the discussion that followed; I realized that I was not clear enough with the Dispatcher that we had a cabin pressurization problem. They were unaware of the event.

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.