SA-227 AC Metro III
Flight Crew Commercial; Flight Crew Instrument; Flight Crew Multiengine
Troubleshooting
Aircraft Equipment Problem Critical; Deviation / Discrepancy - Procedural Clearance
Flight Crew Requested ATC Assistance / Clarification; General Maintenance Action
Aircraft
We were in cruise at 16;000 ft when all of a sudden the cabin altitude went from near 0 to 2;000 ft per minute for a very short time and then re-pressurized. It did this two additional times; except on the third time it was a rapid depressurization and the cabin altitude continued to climb. We got the cabin altitude light on the MAP and immediately donned our oxygen masks and requested 10;000 ft MSL from Center. We worked through the QRH for cabin not pressurizing. We tried switching to the manual pressurization mode but it did not make a difference. We ended up turning the bleeds off and turned the cabin dump switch on before landing. Sudden depressurization of the aircraft; light on MAP The outflow valve could have potentially been stuck. It might have something to do with the very cold temperatures. Immediately don oxygen masks and descend to lower altitude; and then start troubleshooting the issue. Possibly periodic inspections of the pressurization system components.
SA-227AC First Officer reported that a pressurization problem resulted in an expedited descent.