Commercial Fixed Wing
Flight Crew Air Transport Pilot (ATP); Flight Crew Instrument; Flight Crew Multiengine
Flight Crew Last 90 Days 60; Flight Crew Total 2100; Flight Crew Type 600
Aircraft Equipment Problem Critical; Deviation / Discrepancy - Procedural MEL / CDL; Deviation / Discrepancy - Procedural Published Material / Policy; Flight Deck / Cabin / Aircraft Event Other / Unknown
Air Traffic Control Provided Assistance; Flight Crew Landed in Emergency Condition; Flight Crew Returned To Departure Airport; General Flight Cancelled / Delayed; General Maintenance Action
Aircraft
We had MEL'd Pack 2 the night before for being unable to control cabin temperature (too hot). This occurred the following morning- we were on arrival into ZZZ. We were given a descent to cross a fix around; if I remember correctly FL180. We began our descent. In the descent I noticed the Cabin Altitude was high; around 9;100 ft. I pointed this out to the Captain. Altitude kept climbing. Captain told me to get ready. Shortly thereafter the alarms sounded; we donned our O2 masks; I pulled and began running the QRH. The Captain assumed control of the radios and after making an announcement for the Flight Attendant to sit down; initiated an [expedited] descent to 10;000 ft. I was able to get some control back through manual mode. We were given direct the field. Upon reaching 10;000 ft. we removed our masks and somewhat went back to a normal arrival; with checklists/etc. We were given priority handling in. Landed safely and went to our gate. Captain wrote up aircraft.
Pilot reported a loss of pressurization that resulted in a diversion.