MD-11
Flight Crew Multiengine; Flight Crew Air Transport Pilot (ATP); Flight Crew Instrument
Aircraft Equipment Problem Critical; Deviation / Discrepancy - Procedural Published Material / Policy
Air Traffic Control Provided Assistance; Flight Crew Returned To Departure Airport; General Flight Cancelled / Delayed; General Maintenance Action
Aircraft
Climbing out of ZZZZ to ZZZZ1 we were clear to unrestricted FL340. Empty of cargo we got to cruise level quick. We observed a pressure differential message and a rise 8.5 to 9.2 and up; as well as the cabin altitude rapidly climbing above schedule 7;000 ft quick; 8;000 ft and 9;000 ft at that point I told everybody; ' put the oxygen mask on' and verify the outflow valve. Quickly after that we got the level 3 ' cabin altitude' warning. I pulled the QRH and read to comply with the rest of the procedure for level 3 cabin altitude while the Captain was at the controls and the radios. I selected the cabin pressure on manual and turn the knob slowly and fast and there was no response. Since we had no control of the cabin altitude that kept on climbing; the Captain on the radio requested a descend to 10;000 feet follow by the wads and requested land back in ZZZZ with runway in use and weather. We recycle the air system controller and try the cabin pressure controller knob again no response. Then set on auto for the landing in ZZZZ Runway XXR + 3;000 meters visibility night conditions. After landing I verified the outflow open and pressure differential. We parked on apron. During the flight we were asked by the controller if we where having an emergency; The Captain answered: 'no; but we were experiencing a pressurization problem and we needed to descend'. On the ground the mechanic showed us the lower pressure relief valve stuck clogged with insulation. I am not sure how to prevent this event from occurring again; but next time I get a clearance to climb unrestricted and I am close to another heavy aircraft; climbing on the departure maybe request a vector. But that was the furthest on my mind; because of night flying and terrain the only thing I could think about at that moment was climbing at a good rate.
Pilot reported uncontrollable cabin altitude; resulting in an Air Turn Back and precautionary emergency landing.