A321
Flight Crew Multiengine; Flight Crew Air Transport Pilot (ATP); Flight Crew Instrument
Time Pressure; Workload
Aircraft Equipment Problem Critical; Deviation / Discrepancy - Procedural Published Material / Policy; Deviation / Discrepancy - Procedural Clearance
Air Traffic Control Provided Assistance; Flight Crew Requested ATC Assistance / Clarification; Flight Crew Returned To Departure Airport; Flight Crew Overcame Equipment Problem; General Maintenance Action; General Flight Cancelled / Delayed
Aircraft
We were climbing in the high teens; we had just done the transition standard on the altimeters. Somewhere around FL200-FL210 the Captain noticed the Cabin Altitude blinking. The cabin altitude was increasing as the aircraft was climbing. I believe the cabin altitude was around 9;600 feet. I asked ATC for an immediate level off which was granted and we did. However; the cabin altitude was still climbing. The ECAM popped up descent message. We began to run the QRC and I asked ATC for an immediate descent down to 10;000 feet. We did not state PAN PAN or Emergency. We decided not to because as soon as we started descending the cabin altitude began to lower as well. ATC asked if we wanted to declare an emergency and we decided it was not necessary. The ECAM went away and the cabin altitude descended normally. We then got radar vectors; slowed the plane down; dropped the gear and added flaps as well as turned on the APU so we could burn fuel. We were 3 - 4000 lbs over max landing weight so we circled around about 30 miles west of ZZZ. Once we got under the max landing weight we landed on Runway XX uneventfully. The Captain did an amazing job of staying calm and professional. He let the passengers know what was happening once we had leveled off The passengers and flight attendants were all calm. ATC was very helpful in obliging our requests. One interesting thing about the event is that once we returned to the gate one of the mechanics made the statement that the plane has had a history of pressurization issues. The forward cargo door seal had been replaced not too long ago so maybe it was that? I'd like to know what caused the problem.
On departure; climbing through 20;000 feet I noticed a pulsing cabin pressure 9;400. Leveled off at 21;000 feet and as leveling the cabin altitude reached 10;000 [feet] and received ECAM warning that our cabin altitude reached 10;000 feet. Requested descent to 10;000 and completed Emergency Descent Checklist. Cabin altitude started coming down immediately. By level off at 10;000 feet it was back to normal. No passengers were out of their seats and flight attendants sat down immediately when I told them to at top of descent. There were no injuries. We proceeded back to ZZZ and landed normally on Runway XX.
A321 flight crew reported an uneventful air return initiated during climb due to loss of cabin pressurization system.