Narrative:

Normal ground ops and departure from ZZZ. MEL item lower recirc fan all other systems normal. After level off at FL330 entering ETOPS; pm noticed cabin altitude at 8600 ft.; steady increase at 100 ft./min. Cabin alt was amber; no other EICAS or cautions. Differential pressure was 6.5. Captain/pilot flying called dispatch/ [technical operations maintenance control]; unable to rectify issue; dispatch concur with air return. Relief pilot recalled to flight deck; pilot monitoring request clearance for return to ZZZ while [relief pilot] ran qrg divert checklist. Captain ran test checklist; briefed approach; flew normal landing.

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Original NASA ASRS Text

Title: Flight Crew reported loss of cabin pressurization control; resulting in an air turnback.

Narrative: Normal ground ops and departure from ZZZ. MEL item lower recirc fan all other systems normal. After level off at FL330 entering ETOPS; PM noticed cabin altitude at 8600 ft.; steady increase at 100 ft./min. Cabin alt was amber; no other EICAS or cautions. Differential pressure was 6.5. Captain/Pilot Flying called Dispatch/ [Technical Operations Maintenance Control]; unable to rectify issue; Dispatch concur with air return. Relief pilot recalled to flight deck; Pilot Monitoring request clearance for return to ZZZ while [Relief Pilot] ran QRG divert checklist. Captain ran TEST checklist; briefed approach; flew normal 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.