Date: 202102
Local time of day: 1201-1800
Location: ZZZ.ARTCC, US
Flight conditions: Marginal
Light: Daylight
Aircraft: Citation V/Ultra/Encore (C560)
Operator: Fractional
Operating under: Part 135
Flight plan: IFR
Mission: Passenger
Flight phase: Climb; Initial Climb
Airspace: Class A ZZZ
ATC / advisory: Center ZZZ
Aircraft component: Pressurization System
Component problem: Failed
Reporter organization: Fractional
Reporter function: Pilot Flying; Captain
Reporter qualification: Flight Crew Instrument; Flight Crew Air Transport Pilot (ATP); Flight Crew Multiengine
Human factors: Physiological - Other; Situational Awareness; Time Pressure; Human-Machine Interface
Second reporter function: Pilot Not Flying; First Officer
Anomaly: Aircraft Equipment Problem Critical; Deviation / Discrepancy - Procedural Published Material / Policy
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 Requested ATC Assistance / Clarification; Flight Crew Returned To Departure Airport
Contributing factors: Aircraft
Primary problem: Aircraft

Narrative: During our initial climb-out we noticed the rate of climb on the pressurization gauge was acting erratic with various climb and descent rates. As ATC continued to assign higher altitudes we both noticed that the cabin altitude was climbing but the differential rate needle was not increasing like normal. As we climbed through 10;000 feet the cabin altitude needle started to decrease and the differential rate needle started to increase. After leveling off at 23;000 feet everything appeared to be stable. The cabin altitude was decreasing below 9;000 feet after nearly getting up to 10;000 feet and the differential rate needle started to increase between 5 and 6 psi showing that cabin was pressuring like normal. After ATC clear us to 25;000 feet I then requested climb to 27;000 feet because of the moderate chop/turbulence at 25;000 feet. Once we reached 27;000 feet we proceeded with running the cruise checklist. Moments after completing the checklist our pressurization rate of needle showed a descent of 6;000 feet depressurizing the cabin; triggering the cabin high altitude annunciater and the master warning lights. At that time we both donned our oxygen mask; performed abnormal checklist and asked ATC for a lower altitude because of our depressurization issue. Once we reached a safe altitude we removed our oxygen masks and decided to return back to our departure airport.Although I believed this incident was handled safely; declaring an emergency would have been the right thing to do. Anytime an emergency checklist is used or a return to field situation arise should trigger one to declare an emergency regardless of the severity. By doing so helps the pilot in handling the emergency more effectively.


Second narrative: Upon initial climb out we felt our ears straining and popping so I as Pilot Monitoring looked at the pressurization gauge; and it was fluctuating between climbs and descents. We continued to monitor it and it stabilized acted as normal as we climbed through about 10;000 to 11;000 feet. The cabin needle stabilized just below 10;000 (cabin altitude) feet and started a slow descent down to 9;000 (cabin altitude) feet. As we climbed into the Flight levels up to our cleared altitude of 23;000 feet; it appeared stable at 9;000 feet; and the differential needle pushed to a higher differential as its design to do.ATC then cleared us to our filed altitude of 29;000 feet. As we continued the climb; the pressurization continued to operate normally; with the differential increasing and the cabin altitude slowly descending just below 9;000 feet. The Pilot in Command asked me to asked ATC for 25;000 feet as a level off altitude. We leveled there and were getting continuous moderate turbulence at 25;000 feet so we requested 27;000 feet as our final. We climbed up to 27;000 feet. We leveled off; and shortly after running the cruise checklist; we both felt high pressure in our ears; and I instantly saw the cabin needle jump up too a 6;000 foot a minute climb and then the Red Cabin above 10;000 foot annunciator illuminated and as well the master warning. We then both put on our mask and made sure oxygen was 100% and notified ATC that we were having an issue and needed to descend. The decision was made to return to our point of departure. ATC cleared us direct to the field and we descended down to 6;000 feet. We ran through the abnormal checklist for the cabin above 10;000 foot annunciator. Once were low enough to safely remove the oxygen masks we did. We did not declare an emergency. We continued without any further incident and landed safely.


Synopsis: A Flight Crew reported a loss of pressurization then returned to their departure airport and landed safely.