Date: 201211
Local time of day: 1801-2400
Location: ZZZ.ARTCC, US
Flight conditions: VMC
Light: Night
Aircraft: B737-500
Operator: Air Carrier
Operating under: Part 121
Mission: Passenger
Flight phase: Climb
Airspace: Class A ZZZ
ATC / advisory: Center ZZZ
Aircraft component: Pressurization System
Reporter organization: Air Carrier
Reporter function: Captain
Reporter qualification: Flight Crew Air Transport Pilot (ATP)
Second reporter function: Pilot Flying; First Officer
Anomaly: Aircraft Equipment Problem Critical
Detector: Person Flight Crew
When detected: In-flight
Result: Air Traffic Control Provided Assistance; Flight Crew Returned To Clearance; Flight Crew Requested ATC Assistance / Clarification; Flight Crew Overcame Equipment Problem
Contributing factors: Aircraft
Primary problem: Aircraft

Narrative: Climbing out on departure through FL280; the Cabin Altitude Warning horn went off. We donned oxygen masks; established communication; and ran the Abnormal Pressurization Checklist. I asked for a descent from Center; telling them we had a pressurization problem. We got to FL250 and then had to get a vector until we could get further descent. I tried to contact Dispatch to see if they wanted us to return to our departure airport. It took several minutes to get their answer. As we were only about 100 miles out; I asked to return to our departure airport; and as we were getting vectored back; Dispatch said they wanted us to continue since the masks had not dropped and no emergency was declared. We asked Center for vectors back to our destination and they turned us back west. We continued to our destination at 10;000 FT; and arrived uneventfully with 5;400 LBS of fuel. I checked with the flight attendants en route and they reported nothing abnormal in the cabin.


Second narrative: Climbing through FL290; the Cabin Altitude Warning horn sounded. We immediately donned our oxygen masks and accomplished the Cabin Altitude Warning Horn/Abnormal Pressurization memory items and checklist. While the pilot not flying coordinated with ATC and the rest of the crew; I immediately took a 30-degree turn to the south (ATC directed for traffic) and started an expeditious descent. Due to traffic; we were required to level off at FL220 momentarily and then quickly continued a descent to 10;000 FT MSL. The cabin altitude displayed 12;000 FT MSL and was rising approximately 500 FT per minute. After completing the Abnormal Pressurization Checklist; the pressurization did not appear to stabilize and we noted while descending through FL180 the cabin altitude had risen to 13;500 FT while the cabin VSI indication continued to show a 500 FT per minute climb. Descending through 12;000 FT MSL; the pressurization 'bumped' and stabilized in less than a minute. After coordination with Dispatch; the decision was made to continue at 10;000 FT MSL. The flight landed on time without further incident. The passengers were unaware that anything out of the ordinary had taken place. This was our second leg in this aircraft. The logbook indicated that this aircraft had previous pressurization problems. We discussed the possibility of this happening when we initially took the aircraft so it was not a complete surprise and we were ready. The excellent simulator training I have received here in the past prepared us for this; and I feel both the Captain and I did a very good job getting this aircraft safely on the ground without any injuries or even any passenger discomfort. I believe if we had delayed our descent even just a few moments at a minimum that the passenger oxygen masks would have deployed.


Synopsis: B737-500 flight crew had a Cabin Altitude Warning horn activation during climb out at FL290. Flight crew responded as per the checklist.