Small Transport; Low Wing; 2 Turbojet Eng
Flight Crew Air Transport Pilot (ATP); Flight Crew Instrument; Flight Crew Multiengine
Flight Crew Last 90 Days 55; Flight Crew Total 2748; Flight Crew Type 930
Aircraft Equipment Problem Critical; Deviation / Discrepancy - Procedural Published Material / Policy
Flight Crew Overcame Equipment Problem
Aircraft
Slow decompression event noted. Flight from ZZZZ to ZZZ.  Thirty eight (38) minutes prior to planned crossing of ZZZZZ Intersection; windshield bleed valves were turned on; cabin defog was turned to high; and windshield bleed air was turned to the low setting. Cabin pressure held at about 8.5 PSI or 8;000 foot cabin. At approximately XA:0X clearance was given to cross ZZZZZ Intersection at 12;000 feet. This required a descent of 2;500 FPM. Descent was immediately initiated. A minute later descending through FL380; the cabin altitude greater than 10;000 feet annunciator illuminated. There were no noises; air pressure changes or other events noted by either the pilot or copilot. COVID masks and head sets were removed and quick donning oxygen masks were donned by both crew immediately and set to 100% oxygen with pressure support. Oxygen mask mike switch was switched to oxygen masks. Immediate descent was initiated; thrust levers set to idle; speed brakes activated; igniters activated. Cabin pressure reading did not rise above 11;000 feet during descent. Maximum descent was recorded as 5;000 feet/minute. Checklist was followed. Communication with ATC was attempted multiple times; but reported unreadable by ATC. Switched to main mike and reported descent due to loss of pressure. Formal emergency not declared due to adequate control of aircraft; cabin pressure stability; no obvious hull breach as well as adequate fuel to arrive at destination at lower altitudes. Pilot was wearing oxygen saturation monitor during the entire event; with saturations reaching a nadir of 93%. After reaching 12;000 feet; requested 10;000 feet and was granted. Masks removed; air conditioner activated to dehumidify the cabin due to excess moisture. From 10;000 feet to surface cabin pressure followed outside pressure. Uneventful approach and landing. Aircraft is currently in maintenance for evaluation.
Corporate Captain reported a slow and manageable cabin decompression event.