Flight Crew Multiengine; Flight Crew Instrument; Flight Crew Air Transport Pilot (ATP)
Flight Crew Last 90 Days 116; Flight Crew Type 941
Aircraft Equipment Problem Critical; Deviation / Discrepancy - Procedural Published Material / Policy; Flight Deck / Cabin / Aircraft Event Other / Unknown
Flight Crew Returned To Departure Airport; General Flight Cancelled / Delayed; General Maintenance Action
Aircraft
Shortly after reaching cruise altitude at FL 330; we noticed a pressurization issue. The cabin was at 8;900 ft.; the cabin rate was +100 and the pressure differential was 6.8. We descended to FL 310 and the cabin stabilized at 8;700 ft. Notable in this incident was there was no indication on the EICAS of any problem; no warnings; cautions; alerts or status messages. The only indication was the displayed cabin altitude; cabin rate and pressure differential at the bottom of the CRT that displays engine indications. These three items are displayed in a fairly small font and what caught our eye was the cabin altitude was displayed in yellow instead of white. With all the other items displayed on the multiple screens in a 787; it was mostly luck we noticed the cabin altitude. After discussion with [Technical Support Maintenance Control] and Dispatch and further research into our issue by [Technical Support Maintenance Control]; no solution was found. [Technical Support Maintenance Control] said he could see all 4 cabin air compressors functioning normally and the outflow valves were 100% closed. He speculated we had a large air leak via a duct somewhere in the pressurization system. It was obvious to me we needed to descend and return to ZZZ. I mentioned this and [Technical Support Maintenance Control] and Dispatch agreed. We coordinated with ATC a descent to 20;000 and a clearance back to ZZZ. A fuel jettison was accomplished to bring our landing weight below the max allowable landing weight. The return flight and landing were uneventful.
B787 Captain reported an air turnback after loss of pressurization control.