Narrative:

[In cruise flight] FL310 we noticed the cabin altitude climbing above normal level. After reference of checklists etc we were still unable to control the cabin altitude from climbing. We descended to FL250 and subsequently descended to FL230. This stabilized the cabin altitude just below 8000 feet. The cabin continued to descend with our lower cruise altitude. We contacted dispatch; [maintenance] and after careful consideration of factors and available resources (checklists; weather; notams; fuel; aircraft state; maintenance; performance; passengers; crew) we elected (with dispatch and [maintenance] concurrence) to divert to [a suitable airport]. We continued a gradual early descent in order to lower the cabin altitude in a comfortable manner. No sops or fars violated. No discomfort issues with passengers or crew. ATC was notified of our condition. We made a normal uneventful approach and landing.

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Original NASA ASRS Text

Title: B757 flight crew reported diverting to an alternate after loss of automatic pressurization control.

Narrative: [In cruise flight] FL310 we noticed the cabin altitude climbing above normal level. After reference of checklists etc we were still unable to control the cabin altitude from climbing. We descended to FL250 and subsequently descended to FL230. This stabilized the cabin altitude just below 8000 feet. The cabin continued to descend with our lower cruise altitude. We contacted Dispatch; [Maintenance] and after careful consideration of factors and available resources (checklists; weather; NOTAMs; fuel; aircraft state; maintenance; performance; passengers; crew) we elected (with Dispatch and [Maintenance] concurrence) to divert to [a suitable airport]. We continued a gradual early descent in order to lower the cabin altitude in a comfortable manner. No SOPs or FARs violated. No discomfort issues with passengers or crew. ATC was notified of our condition. We made a normal uneventful approach and landing.

Data retrieved from NASA's ASRS site 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.