Flight Crew Multiengine; Flight Crew Instrument; Flight Crew Air Transport Pilot (ATP)
Flight Crew Last 90 Days 110; Flight Crew Total 12200; Flight Crew Type 6500
Distraction; Troubleshooting; Time Pressure
Aircraft Equipment Problem Critical
Flight Crew Landed in Emergency Condition; Flight Crew Returned To Departure Airport
Aircraft
While climbing thru FL270; a CABIN ALTITUDE warning occurred. At the time of occurrence we were operating with only the right pack. We did not get a bang or loud noise indicating a rapid decompression. The FO (First Officer) was the flying pilot. We immediately put on our oxygen masks. After a brief moment; we established crew communication. We [coordinated] with Center for a cabin altitude problem and started a descent to initially to 12;000 feet then down to 10;000 feet as required. Due to fogging of both of our eye shield portion of the full face oxygen mask; made reading the checklist and cabin altitude and rate display unreadable (after the post flight crew debrief; the FO revealed his mask was not fogged but he still had difficulty reading). The FO did an outstanding job doing an immediate descent from memory. While descending; notified Center our intention to return to ZZZ and received a heading direct back ZZZ. Shortly after initiating the decent; we turned on the left pack but did not feel any change of cabin pressure. During our level off at 10;000; the CABIN ALTITUDE warning extinguished. We took off our oxygen mask and used regular headsets for the remainder of the flight. We checked with each other; whether we had any physiological problems and determined we were both fine. We heard an unusual air hissing noise which could not be located. We requested an ILS to XXL with fire trucks assistance. After clearing the runway; notified ground control. We taxi back to ramp nine. After shutdown and secure gave a brief report to the fire crew. Gave a full debrief to maintenance at the aircraft.
B757-200 Captain reported a pressurization malfunction which resulted in an immediate descent; and a return to the departure airport.