Date: 201901
Local time of day: 1801-2400
Location: ZZZ.Airport, US
Flight conditions: VMC
Light: Night
Aircraft: Cessna Citation Sovereign (C680)
Operator: Fractional
Operating under: Part 91
Flight phase: Climb
ATC / advisory: Center ZZZ
Aircraft component: Pressurization Control System
Component problem: Malfunctioning
Reporter organization: Fractional
Reporter function: Captain; Pilot Not Flying
Reporter qualification: Flight Crew Multiengine; Flight Crew Instrument; Flight Crew Air Transport Pilot (ATP)
Human factors: Training / Qualification
Second reporter function: First Officer; Pilot Flying
Anomaly: Aircraft Equipment Problem Critical; Deviation / Discrepancy - Procedural Published Material / Policy
Detector: Person Flight Crew
When detected: In-flight
Result: Flight Crew Overcame Equipment Problem; General Physical Injury / Incapacitation
Contributing factors: Aircraft; Human Factors
Primary problem: Aircraft

Narrative: Enroute; we experienced a CABIN ALTITUDE amber CAS message that caused us to defer the AUTO function of the cabin pressurization system.  The system was not reacting appropriately to the schedule when in HI ELEV mode and displayed the message inappropriately; we thought; given the information in the Operations Manual and the QRH. MX shared with us an identical account by a crew on a different tail number. While the SIC was delivering a forgotten box to our inbound passenger and fielding questions from a charter crew looking for assistance in getting their passengers to their destination after an AOG; I completed the deferral and began to tackle another possible MX issue. With that resolved; I began to review the Operations Manual procedures regarding the use of Manual Mode of the pressurization system. The SIC soon joined me in the cockpit where I reviewed with him the procedures and asked that he peruse the OM [Operations Manual] to make sure I didn't miss or misconstrue anything. I briefed the SIC of the Note (in the FS PTM) regarding placing the CABIN ALT Toggle Switch into either UP or DOWN for more than 6 seconds 'causes a pronounced and startling change in the rate of cabin climb or descent'. The OM [Operations Manual] doesn't note this; however; elsewhere; it notes a 'dramatic' change in rate. Since we were at 9;000 MSL for takeoff we briefed not climbing out at an excessive rate so as to be able to keep up with the cabin altitude adjustment. We were also aware of the fact that we didn't wanted to delay a normal climb from the airport. We discussed that we were unaware of how the Manual Mode would react and the effort it was going to take to adequately control the cabin. The SIC expressed some reservation conducting the flight given the lack of training in the actual operation of the Manual Mode. After takeoff; given the climb rate of the jet and the need to immediately control the cabin down to below airport elevation; I found it difficult to set an acceptable rate. Frustrated; I found myself controlling the Manual Mode into the 'startling and dramatic' range and the cabin went to a below sea level range. I managed to get it back to a positive climb rate as we continued our climbout. As we were passing FL250; I felt that the cabin was at lower altitude than normal and began to raise the cabin. It was difficult to adjust the rate up beyond the current climb rate with short toggle applications. I directed the Pilot Flying to manage the radios as I maintained attention to the system. We were passing FL275 for FL290 when the Pilot Flying asked to return to FL270. ATC cleared us back to that altitude. We were thinking a stable altitude and power setting would ease control of the system. Once again; I controlled it into the 'startling and dramatic' range. The cabin climbed dramatically setting off the red CABIN ALTITUDE message. The Pilot Flying pushed the nose over to begin a descent and we donned the masks. I believed we could simply get to FL270 and regain control of the cabin instead of an emergency descent. The Pilot Flying descended to FL260 and leveled off since I was asking why he was descending.  The cabin rise and call to ATC to get a return to FL270 by the Pilot Flying couldn't have happened together at a worse time. The two of us were working separate issues at that precise time and I feel that it divorced us of the greater picture if not for a brief span of time. At FL260; I informed ATC that we were trying to manage a pressurization issue and asked to descend to 17;000. Once at 17;000 [feet] we felt we had stabilized the cabin and continued to [destination].Do this in the sim. Startling and dramatic doesn't even describe how fast the rate changes. While I felt like I didn't get close to the six seconds of input I wonder if repeated attempts close together pushed it towards that threshold. The SIC and I discussed the flight after we landed. While I felt informed about the procedures and he felt 'untrained' we should have reached out to the Fleet Director for additional information and advice.


Second narrative: The Captain is seeing and hearing that I'm not happy about the decision to MEL this item; but is not taking my thoughts and opinions into consideration.On departure; my ears immediately began popping; and I saw that the Captain was having difficulty controlling the rate of cabin climb with the cherry picker. A few minutes later climbing through FL180; I felt tremendous pressure in my ears and pain behind my eyes. I looked at the cabin climb rate and it was maxed out at 9999 FPM. A short while later; things stabilized and it seemed like he got it under control. We leveled off at FL270. A few seconds later; I once again felt sharp pain in my ears and eyes; and the climb rate was maxed out once again. Now; we instantly had a RED cabin altitude CAS message; and the cabin altitude was around 13;500 ft. I donned my O2 mask; and my training kicked in. I initiated an emergency descent. The Captain; however; had his hand on the controls and was applying back pressure while instructing me to level off. I wasn't understanding at the time why he was arresting the descent; and it caused an enormous amount of stress and anxiety in the cockpit (for me at least). Apparently he got the cabin alt back down to an acceptable level; but I wasn't aware of this. We only descended 1;000 feet below our assigned altitude and advised ATC of our pressurization issue. We flew the rest of the way at 17;000 feet; and had no further operational issues. Upon arriving to my hotel room; I my ears were completely blocked and ringing; I had pressure behind my eyes and my vision was blurred.We should have never been instructed to MEL this item without some sort of training on how to run the system in manual. This was a flight for [Flight Test] pilots only! I want to make sure this never happens to anyone again. We were both completely unprepared for how sensitive the system would be in manual; and the consequences of not performing this procedure correctly. I am frustrated with [Company] for allowing this to happen. I am also frustrated with my Captain for not respecting my 22 years and 10;000 hours of flight time; by downplaying my concerns. I'm lastly disappointed with myself for not trusting my gut and being more assertive by refusing to do the flight.


Synopsis: CE680 flight crew reported difficulty controlling the cabin pressure using the manual backup system; and the FO reported pain in his eyes and ears as a result of the pressure fluctuations.