Date: 201509
Local time of day: 0601-1200
Location: ZZZ.Airport, US
Flight conditions: VMC
Weather elements / visibility: 10
Light: Daylight
Aircraft: Citationjet (C525/C526) - CJ I / II / III / IV
Operator: Air Taxi
Operating under: Part 135
Flight plan: IFR
Mission: Passenger
Flight phase: Descent
Airspace: Class A ZZZ
ATC / advisory: Center ZZZ
Aircraft component: Pressurization Outflow Valve
Component problem: Malfunctioning
Reporter organization: Air Taxi
Reporter function: Pilot Flying; Captain
Reporter qualification: Flight Crew Air Transport Pilot (ATP)
Human factors: Other / Unknown
Second reporter function: First Officer; Pilot Not Flying
Anomaly: Aircraft Equipment Problem Less Severe
Detector: Automation Aircraft Other Automation; Person Flight Crew
When detected: In-flight
Result: Air Traffic Control Issued New Clearance; Flight Crew Overcame Equipment Problem; Flight Crew Took Evasive Action; General Maintenance Action
Contributing factors: Human Factors; Aircraft
Primary problem: Human Factors

Narrative: This was a charter flight with 2 passengers. Our cruise altitude was FL430. When Center gave us our descent for landing we experienced a loss of cabin pressure. Around FL320 we started an emergency descent and communicated that with Center. At 10;000 feet the emergency was over and we asked for the RNAV GPS approach. The weather was clear with 10 miles visibility. The landing was uneventful the passengers were safe. The aircraft was taken for repair at the [maintenance center]. The outflow valve was replaced; we then flew it to home base at FL410 without incident.


Second narrative: We were descending from FL450 to the low 30's (don't recall the exact assigned altitude); Captain was the PF; I was working the radios. Around the time of level-off; the cabin began to climb uncontrollably. I took off my headset and glasses to put on my mask. Headset and glasses back on; I then pulled out the checklist and opened it to the correct page in anticipation of the captain asking me to go through it. I asked about it a few times but got no response. He was talking to ATC and asking for a vector and lower altitude - he seemed tied up with that so I began going through the checklist to make sure we weren't overlooking something important and I checked on the 2 passengers. (Since the cabin had stabilized at about 14;000 ft they seemed to be handling it ok - not even strapping the masks on their heads; and instead just placing them over their mouth & nose and removing them to talk with me to let me know they were ok). At this point; I realized that the captain was continuing the descent. He still couldn't hear me talking through the mask; so since the cabin was stable; rather than troubleshoot the mask communications; I took the mask straps off my head so that I could communicate with just my headset (I kept the mask in my lap and placed it over my nose & mouth when I wasn't talking on the headset). We were descending through the mid 20's; and I don't remember the exact query; but I got the impression from the controller that he didn't know what we were doing or why. I got back on the radios and advised him that we had lost cabin pressurization and needed to get lower. The rest of the flight was uneventful. What I didn't realize until yesterday was that when the captain jumped on the radios while I was putting on my mask; he had NOT declared an emergency as his first contact with ATC even though he had decided to continue the descent and dialed in a lower altitude. The captain's report to our 135 operator stated that we had declared an emergency; which we had; but I had not yet pieced together the various clues that [ATC wasn't aware of our situation] until I got back on the radios - and we had already descended well below our last assigned altitude.(Looking back; my first clue should have been that the captain was repeatedly asking for a heading and altitude; and the controller was not immediately cooperating and; in fact; sounded a little perplexed. My second clue should have been when the controller asked if we were declaring an emergency.)My lesson in hindsight: I needed to verify with the captain that we had [had advised ATC of our situation] or received a lower altitude while I was 'off the air' putting on my mask and again when I was checking on the passengers. I shouldn't have assumed that just because he had taken over the radios that he had also coordinated with ATC and advised them of what we were doing and why.


Synopsis: CE525 flight crew experienced a pressurization anomaly during descent to FL320. The flying Captain continued the descent without advising ATC while the First Officer had his headset off while donning his oxygen mask. Eventually ATC was advised and the descent was continued to 10000 feet with the cabin never exceeding 14000 feet.