Date: 202004
Local time of day: 1201-1800
Location: ZZZ.Airport, US
Flight conditions: VMC
Light: Daylight
Aircraft: Q400
Operator: Air Carrier
Operating under: Part 121
Flight plan: IFR
Mission: Passenger
Flight phase: Climb
Airspace: Class B ZZZ
Aircraft component: Pressurization Control System
Component problem: Failed
Reporter organization: Air Carrier
Reporter function: First Officer; Pilot Not Flying
Reporter qualification: Flight Crew Multiengine; Flight Crew Instrument; Flight Crew Air Transport Pilot (ATP)
Second reporter function: Pilot Flying; Captain
Anomaly: Aircraft Equipment Problem Critical; Deviation / Discrepancy - Procedural FAR; Deviation / Discrepancy - Procedural Published Material / Policy
Detector: Person Flight Crew
When detected: In-flight
Result: Air Traffic Control Provided Assistance; Flight Crew Diverted; Flight Crew FLC Overrode Automation; Flight Crew Landed in Emergency Condition; General Flight Cancelled / Delayed; General Maintenance Action
Contributing factors: Aircraft; Procedure
Primary problem: Aircraft

Narrative: Flight was filed ZZZ to ZZZ1. This was the fourth day flying with the same Captain. It was our third leg of the day and our second on [this] aircraft. Weather in both locations was clear with light winds out of the north. We pushed from the gate in ZZZ early with 13 passengers. Because of the light load; I pitched to 15 degrees on takeoff to avoid any chance of over-speeding the flaps. On the initial climb; I accelerated to 230 and continued. Through 5;000 ft.; I noted a creaking sound in the airframe and mentioned it to the Captain. Around the same time; he noted the pressurization panel. The cabin differential and cabin altitude were pegged to zero while the cabin showed a slight descent. Rapidly approaching 10;000 ft.; we noted that if we weren't pressurized; we should get a Master Warning chime through 9;800 ft. There was no warning chime. The caution panel remained dark. We began to wonder if it was the gauges that had failed. We discussed this for a moment and agreed to bring Maintenance into the situation. The Captain called Maintenance on SATCOM; and I took over ATC and continued to fly.Reaching FL200; we leveled and set cruise power. I had AUX2 turned down so I could focus on flying and ATC; so I didn't hear the Captain's conversation with Maintenance directly. Shortly after leveling; the Captain asked me to request 15;000 ft. while still on the call. The concern then was a potential overpressurization since we didn't know what the cabin differential was. I told ATC that we needed a descent to 15;000 ft. for a potential pressurization issue. We were cleared: 'Descend and maintain 16;000. Expect lower shortly.' The controller followed up by asking if we needed any assistance. I responded; 'Not at this time.' I set the alerter for 16;000; pressed ALT SEL; verified ALT SEL with the Captain while he was still on the call; and started a descent.The call with Maintenance was completed shortly after starting down; and the Captain recapped the conversation with me. Maintenance was fine with us continuing to ZZZ1 at a lower altitude. He asked for my thoughts on it. I asked if we had performance for it; and he said Maintenance checked with Dispatch and we were fine at the lower altitude. We agreed to reassess the situation at the lower altitude and make a decision from there. Shortly after; the Captain asked 'How are you feeling? I think I'm feeling a little lightheaded.' I responded; 'Yeah; I think my fingers are tingling a little. How about we go down to ten?' We agreed; and I told ATC that we needed 10;000 ft. Once we were cleared; I switched to IAS mode and reduced power to flight idle. The autopilot responded aggressively; so I disconnected it momentarily to establish the descent and reengaged it once we were stable. We used oxygen during the descent and discontinued use reaching 10;000 ft. The Captain asked the flight attendants what conditions were in the back: if the flight attendants were experiencing any symptoms; if the passengers were experiencing any symptoms; if they noticed any abnormalities or heard any hissing noises? Meanwhile; I was handed off to Approach. The Captain and I circled back. He informed me that the flight attendants had reported physiological symptoms that were commensurate with our own--starting in the descent. I don't recall any complaints from passengers; and there were no abnormal noises in the cabin. I reported that we were level at 10;000 ft. talking to [Approach] with a correct altimeter setting.At that point; we were approaching the Valley west of ZZZ2. The Captain noted that we were still at least 130 miles from ZZZ1. We both came to the conclusion that we didn't know what was wrong with the plane; specifically; and we didn't know why we weren't feeling right. Neither of us were comfortable with continuing to a higher-density airport at a lower altitude under the current circumstance. We agreed that a diversion to ZZZ2 was the best course of action. The Captain began coordinating with Dispatch; the flight attendants; and addressed the passengers. I advised ZZZ2 Approach that we needed to plan a diversion to ZZZ2; needed delay vectors; and a lower altitude. We were given present heading; 8;000 ft.; expect visual [Runway] XXL. ATC asked if we required assistance. I repeated; 'Not at this time.' By now; ZZZ2 was off of our right wing; so I slowed to 200 KIAS to allow time to set up and brief the approach and began a descent to 8;000 ft. During that time; the TRACON went through a shift change. I changed the destination in the EFB and requested performance for ZZZ2. I also set up the FMS for the RNAV XXL.Once each of us had everything taken care of; the Captain and I circled back to brief the approach. We acknowledged that [there] were several threats in front of us and outlined the visual approach backed up with the RNAV XXL. By this point; we were on a high downwind for XXL. We completed the descent and approach checklists and descended for the approach. We were left fairly high on the base turn; so I increased our descent rate until we were in a better place for the approach. The controller vectored us at a sharp angle for final and asked if we had the airport in sight. The Captain responded that we needed vectors to final; and we were given a sharp turn to intercept XXL then cleared for the visual approach. The FMS began overshooting the turn; so I disengaged the autopilot and made the corrections to get back on profile. We continued a stable approach to a normal landing. Once clear of the runway; we contacted [Operations] for a gate assignment; continued to the gate; and deplaned. After recounting the anomalies to maintenance personnel; the crew met in the back to debrief and discuss the events that had happened. No additional info needed for [this report].In the sequence of events that unfolded; it was interesting that there was no singular trigger that indicated that we were approaching a [critical situation]. Our expectation for depressurization or lack of pressurization was a CABIN PRESS annunciation associated with a Master Warning. That expectation wasn't realized; so we decided to bring Maintenance into the discussion. In the time that it took to address each level; with what seemed like appropriate action at that time; the situation escalated or more information was learned requiring a further escalation of action. I think CRM played a key role in being able to mitigate the rolling events that resulted in a diversion on an already short flight. From my perspective; it made a huge difference that the Captain had confidence in my ability to handle the airplane; our flight path; and communication with ATC. That allowed him to handle all of the communication with company and flight attendants all while keeping the passengers informed. I especially liked the fact that he continually asked for my input; opinion; and feelings on decisions. We established a collaborative environment in which we quickly assessed where we were; assigned expectations for the next few moments; completed those tasks individually; gathered information; and then circled back to evaluate and repeat the process. I also recognize that we both felt empowered; even for me from the right seat; to say I'm not comfortable with this and stop the operation. In retrospect; I am concerned that the trigger for the Master Warning failed in tandem with the instrumentation on the cabin pressure control panel. I feel like the warning system should be independent of the system itself. Given that; having the visual pressurization check on the after-takeoff flow and the cruise flow helps trap that threat. Going forward; if there's ever any question of pressurization; I would level at a lower altitude and assess the situation. In hindsight; because we hadn't received a Master Warning annunciation; we believed that we were in fact pressurized and sought additional input before making further decisions.


Second narrative: Operating flight; departing ZZZ to ZZZ1; our aircraft and aircrew were in good operating order. Ceilings and visibility departing ZZZ were unrestricted and we were about to finish the final leg of our 4 day trip. The First Officer was the pilot flying and the Captain was the pilot monitoring for this leg. Just prior to passing through 10;000 ft. on our climb-out the Captain checked the pressure indication control panel which indicated the cabin was pressurizing at a rate of about 500 fpm; which isn't unusual for a departure from a near sea level airport; combined with the high climb rate of our light aircraft. What did seem odd was the readings on the other two instruments; the differential gauge was pegged at zero; as was the cabin altitude gauge. These two instruments clearly were not in agreement with each other; or with the pressurization rate gauge. In talking with the First Officer as we climbed through 10;000 ft.; we thought that another way to confirm if we were pressurizing was if the Cabin Press master warning was triggered through 9;800 ft. Also we confirmed that the bleeds and packs were on with normal flow control setting. We did discuss that we were both experiencing popping ears and the First Officer thought he might have heard a creaking noise from the airframe. As we received no master warning; we thought we were probably pressurizing as the rate indicator showed; but possibly had faulty cabin differential and cabin alt gauges. At this point this Captain informed the First Officer that he was going to call Maintenance Control to help troubleshoot the gauges and to get a second opinion as to if we were in fact pressurizing as the crew had thought. The Captain handed the radios over to the First Officer.Maintenance Control informed this Captain that there was not anything they could guide the flight crew in with respect to troubleshooting the pressure indication control panel; and that they could evaluate the system on the ground in ZZZ1 but there was not anything that could be reset or diagnosed in flight from their standpoint. At this time we were climbing through about 15;000 ft. and the panel was reading the same as it had previously; there was a slight cabin pressurization rate with no Cabin Press warning. The Captain and First Officer held a discussion between themselves if they were feeling any symptoms of hypoxia and both pilots were free of such physiological effects. The Captain relayed to Maintenance Control that there seemed to be something wrong and it was the Captain's concern that the pressure vessel could exceed limitations of maximum pressurization differential and for safety of flight wanted to descend back down to 15;000 ft. At this time we were climbing through approximately 16;000 ft. Maintenance Control asked the Captain if the call could be forwarded to Dispatch to make sure there was enough fuel on board to safely operate the flight to ZZZ1 at a lower altitude than planned. The Captain agreed and the call was forwarded.While waiting for the call to be picked up by Operations the Captain once again did a self check and felt no physical effects of hypoxia. The Captain asked the First Officer if he was feeling hypoxic; which the First Officer stated he was not. The Captain then asked the First Officer to call the flight attendants to see if they; or the passengers were feeling off at all; which might indicate high or low pressurization problems. According to the First Officer the reports from the back were that all was seemingly normal. The flight attendants also reported that they did not hear any whooshing or whistling sounds that might indicate a leak in the pressure vessel. We had just leveled off at 20;000 ft. with no master cautions or master warnings. The pressure indication control panel read the same here as it had at the other points indicated in the climb.When Operations picked up their line they quickly ran performance numbers and we agreed that in the interest of safety we would descend to 15;000 ft. While still on the phone with Operations the Captain asked the First Officer to request a descent with ATC. This request was immediately granted; if it was not; it was this Captain's intent to [request priority handling] and inform ATC of our descent to 15;000 ft. Before we reached 15;000 ft. on our descent the Captain started feeling light headed and experienced tingling in his fingers and increased popping in his ears. When asked; the First Officer reported similar altitude effects. It was our assumption that since we were descending the symptoms would not develop too severely as we were descending into more dense air. We then called the flight attendants back and they reported similar hypoxic effects and also frequent ear popping. At about 16;000 ft.; we decided to continue our descent down to 10;000 ft. which we had no problem obtaining clearance for with ATC. At this point the Captain determined we were about 130 miles South of ZZZ1; which was our filed destination. We were also almost directly over ZZZ2. The Captain did another self assessment and felt that it was probably best to not continue to ZZZ1; but wanted to check with the rest of the crew to see how they were feeling about a diversion. The First Officer also reported that he felt like the more conservative approach was to divert to ZZZ2. The Captain specifically remembers feeling that it was irresponsible to continue the flight as planned with an undiagnosed pressurization problem; but with multiple crew members reporting symptoms of hypoxia. This Captain also thought about the fidelity of the operation and did not want to be too aggressive in a manner that would bring unneeded scrutiny on our company if the decision was made to continue and people arrived in ZZZ1 feeling sick. The Captain decided then that in the interest of safety; as the most conservative decision; the flight would divert to ZZZ2. He then called Dispatch back and informed the Dispatcher that we would be diverting to ZZZ2. The Captain asked the First Officer to request vectors from ATC back to ZZZ2 and to inform them that we would be diverting. The Captain then called the flight attendants to inform them about our upcoming change of plans and to make sure everyone in the back was feeling okay. The flight attendants reported feeling relieved that we were diverting and that nobody in the back was reporting feeling sick. This was good news and the Captain determined that emergency services would not be necessary upon landing. Descending through 10;000 ft. both the Captain and First Officer began feeling light headed and were experiencing mild cognitive decline. The pilots then took turns briefly donning oxygen masks in an attempt to raise our blood oxygen levels and stave off hypoxic effects which was helpful. The Captain made an announcement to the passengers informing them that due to a mechanical difficulty we would be making a brief stop in ZZZ2 for safety.The Captain and First Officer then came together to ensure that we were on the same page and to catch each other up. We briefed our approach and ran the descent and approach checklists. The First Officer then landed the aircraft at ZZZ2; once clearing the runway we received a parking spot from Operations; proceeded to the terminal and terminated our flight. [Report] also filed. This was a challenging situation to identify and manage because of the nature of the failure that we experienced. In talking with maintenance personnel in ZZZ2; the nature of the failure that we experienced; a faulty cabin pressure controller; not only provides information to the gauges we use to monitor the pressurization status of the aircraft; a component inside of it also triggers the master warning for a high cabin pressure altitude if the airplane loses pressurization. When we thought we were using independent systems to verify the pressurization status of the aircraft; we were in fact relying on the same system that waspresenting multiple failures throughout many aircraft fail safes.


Synopsis: Q400 flight crew reported aircraft failed to pressurize due to a failed cabin pressure controller and crew began to feel hypoxic effects; requiring a decent to a diversion and a precautionary landing.