Narrative:

While en route to lga from atl while climbing through FL250, our large transport lost pressurization. The problem was discovered when the second officer noticed the cabin pressurization showing a climb in excess of 2000 FPM. The second officer was unable to control the cabin manually, therefore I contacted center for an altitude of 10000', squawked 7700 and began a rapid descent in order to ensure a safe level of pressure in the cabin, and returned to atl for maintenance. The apparent cause of this loss of pressurization was a failure of the outflow valve. In my opinion, there is not way to preclude this type of incident from occurring since the failure of a mechanical device such as an outflow valve cannot be forecast. Cooperation and coordination by ATC was excellent.

Related reports:

Google
 

Original NASA ASRS Text

Title: ACR LGT EXPERIENCES LOSS OF PRESSURIZATION WHILE CLIMBING THROUGH FL250 ON TRIP FROM ATL TO LGA. FLT CREW OPTS TO DECLARE EMERGENCY AND LAND BACK AT ATL.

Narrative: WHILE ENRTE TO LGA FROM ATL WHILE CLBING THROUGH FL250, OUR LGT LOST PRESSURIZATION. THE PROB WAS DISCOVERED WHEN THE S/O NOTICED THE CABIN PRESSURIZATION SHOWING A CLB IN EXCESS OF 2000 FPM. THE S/O WAS UNABLE TO CONTROL THE CABIN MANUALLY, THEREFORE I CONTACTED CENTER FOR AN ALT OF 10000', SQUAWKED 7700 AND BEGAN A RAPID DSCNT IN ORDER TO ENSURE A SAFE LEVEL OF PRESSURE IN THE CABIN, AND RETURNED TO ATL FOR MAINT. THE APPARENT CAUSE OF THIS LOSS OF PRESSURIZATION WAS A FAILURE OF THE OUTFLOW VALVE. IN MY OPINION, THERE IS NOT WAY TO PRECLUDE THIS TYPE OF INCIDENT FROM OCCURRING SINCE THE FAILURE OF A MECHANICAL DEVICE SUCH AS AN OUTFLOW VALVE CANNOT BE FORECAST. COOPERATION AND COORD BY ATC WAS EXCELLENT.

Data retrieved from NASA's ASRS site as of July 2007 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.