Narrative:

We were cruising at FL370 and I was the first officer (first officer) and PF (pilot flying.) while in cruise; I noticed the cabin altitude increasing. After pointing this out; the crew felt the pressure changing and heard a whistling noise as if someone had opened a window or door. The cabin altitude passed 10;000 feet and continued to climb. The ca (captain) instructed me to put on the O2 mask and begin a descent. The ca then informed ATC. The crew accomplished the rapid cabin depressurization and emergency descent checklists. The ca then notified the flight attendant (flight attendant) of the situation and told her to put her O2 mask on as well just in case the aircraft continued to lose pressure. The oxygen masks in the cabin were not deployed as the cabin pressure never exceeded 14;000 feet and the ca elected not to manually deploy the masks as the cabin altitude was slowly decreasing.the cabin pressure reached 12;000 feet by the time the descent was initiated. The ca elected to divert to [a nearby alternate] as it was close and a [company] serviced station. The planned alternate was over 150 nm away. The ca elected to descend to 10;000 feet and get the aircraft safely on the ground sooner than later as we did not know the cause of the pressurization failure.the crew safely landed the aircraft with no injuries to crew or passengers. Auto pressurization mode fail.thanks to the training department about the job they do on preparing the pilots.

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Original NASA ASRS Text

Title: EMB-145 First Officer reported descending to a lower altitude and diverting to a nearby alternate airport due to loss of cabin pressure.

Narrative: We were cruising at FL370 and I was the FO (First Officer) and PF (Pilot Flying.) While in cruise; I noticed the cabin altitude increasing. After pointing this out; the crew felt the pressure changing and heard a whistling noise as if someone had opened a window or door. The cabin altitude passed 10;000 feet and continued to climb. The CA (Captain) instructed me to put on the O2 mask and begin a descent. The CA then informed ATC. The crew accomplished the Rapid Cabin Depressurization and Emergency Descent checklists. The CA then notified the FA (Flight Attendant) of the situation and told her to put her O2 mask on as well just in case the aircraft continued to lose pressure. The oxygen masks in the cabin were not deployed as the cabin pressure never exceeded 14;000 feet and the CA elected not to manually deploy the masks as the cabin altitude was slowly decreasing.The cabin pressure reached 12;000 feet by the time the descent was initiated. The CA elected to divert to [a nearby alternate] as it was close and a [company] serviced station. The planned alternate was over 150 nm away. The CA elected to descend to 10;000 feet and get the aircraft safely on the ground sooner than later as we did not know the cause of the pressurization failure.The crew safely landed the aircraft with no injuries to crew or passengers. Auto pressurization mode fail.Thanks to the training department about the job they do on preparing the pilots.

Data retrieved from NASA's ASRS site and automatically converted to unabbreviated mixed upper/lowercase text. This report is for informational purposes with no guarantee of accuracy. See NASA's ASRS site for official report.