Duke 60
Flight Crew Instrument; Flight Crew Commercial; Flight Crew Multiengine
Flight Crew Last 90 Days 200; Flight Crew Total 1700; Flight Crew Type 40
Aircraft Equipment Problem Critical
Air Traffic Control Provided Assistance; Flight Crew Requested ATC Assistance / Clarification; Flight Crew Overcame Equipment Problem; General Maintenance Action
Aircraft
Upon reaching FL210; I noticed a hissing noise from the back of the cabin near the door. The cabin pressure was decreasing so I immediately initiated a descent and notified ATC. I was asked if I wanted to [request priority handling] and at that time; the cabin pressure was beginning to correct itself; so I said no. I just asked to continue the flight at 11;000 ft. to be safe just in case it happened again.
Pilot reported a pressurization problem and advised ATC.