Date: 202001
Local time of day: 0601-1200
Flight conditions: VMC
Light: Daylight
Aircraft: EMB ERJ 170/175 ER/LR
Operator: Air Carrier
Operating under: Part 121
Flight plan: IFR
Flight phase: Climb
Aircraft component: Pressurization System
Component problem: Malfunctioning
Reporter organization: Air Carrier
Reporter function: First Officer; Pilot Flying
Reporter qualification: Flight Crew Multiengine; Flight Crew Air Transport Pilot (ATP); Flight Crew Instrument
Human factors: Human-Machine Interface; Communication Breakdown; Troubleshooting; Workload
Anomaly: Aircraft Equipment Problem Critical; Deviation / Discrepancy - Procedural Published Material / Policy
Detector: Automation Aircraft Other Automation
When detected: In-flight
Result: Air Traffic Control Provided Assistance; Flight Crew Landed in Emergency Condition; Flight Crew FLC complied w / Automation / Advisory; Flight Crew Diverted; Flight Crew Requested ATC Assistance / Clarification
Contributing factors: Aircraft
Primary problem: Aircraft

Narrative: I was the assigned First Officer for Flight XXXX from ZZZ to ZZZ1. The other crew assigned to the flight were [the] Captain and Flight Attendants. The Captain was a 'green' Captain with less than 100 hours in this aircraft type as PIC. I was the Pilot Flying and the Captain was the Pilot Monitoring.The aircraft assigned for this flight had 3 MEL items.Emer Equip CompartmentsPack Flow Cntrl VlvsAir Conditioning PacksThe crew and I arrived at the gate a few minutes prior to our show time. After getting the release from Ops I performed the external walk-around and did not find any irregularities. Upon returning to the cockpit I conducted my internal safety checks and Post Power Up Configuration flow. I then obtained both the current ATIS as well as our clearance and filled out the takeoff/landing distance card.Approximately 15 minutes prior to our scheduled departure I gave the takeoff brief after the Captain had finished programming the MCDU. During this brief the Captain and I discussed the items on the MEL list. Bleed Air #1 was already placarded as 'Inop'; the Captain set ECS to 'Off' for takeoff per the release and MEL notes; and we agreed we would leave the APU 'On' until after takeoff as this was a recommendation in the MEL notes with the Bleed 1 'inop'. After this briefing we completed the Before Start checklist.We pushed back from the gate. After ground equipment had been removed we conducted the Flight Control check and After Start checklist. During the taxi to the runway the Captain instructed me to start Engine 2. After confirming a good start and starting my timer; I inadvertently shut down the APU as a matter of habit; forgetting that we had briefed to leave it on. I then conducted the Taxi checklist and shortly afterward the Before Takeoff checklist when we were directed by Tower to taxi into position and hold on the runway. After getting into position on Runway XXL the Captain passed the flight controls to me.The takeoff was normal. At approximately 2;000 feet the Captain noted that the APU had been turned off. He attempted to start it but the start failed and an EICAS message 'APU Fail' was presented. As the Flying Pilot I then directed the Captain to 'run the QRH for APU fail'. However; the message went away because the Captain had turned the APU switch to 'OFF' and subsequently said the QRH procedure wasn't necessary because the EICAS message had cleared. I did not question this.At approximately FL300 the EICAS presented a yellow caution 'BLEED 2 OVERPRESS' message with a single chime. I called 'cancel and identify' and the Captain called out the message as presented. I then directed him to run the QRH for this item. At this point the aircraft was leveling off at our assigned altitude of FL310. The Captain was approximately a third of the way into the 'BLEED 2 OVERPRESS' QRH procedure when the EICAS presented a red 'CABIN HIGH ALT' warning with a triple chime. After canceling and identifying the warning we immediately donned our O2 masks and attempted to establish crew communication. I could not hear myself speaking and believed I had a problem with the microphone in my mask; but I could hear the Captain. He also said he could hear me. I then instructed the Captain to perform the EPC for 'CABIN HIGH ALT' as I began a controlled descent. The Captain then called ATC to declare our emergency and request a lower altitude.ATC replied to the Captain they could not understand what he said and asked him to repeat his request; which he did. ATC replied they still could not understand his request. At this point another aircraft told ATC of our issue and request. ATC then cleared us to descend to FL240 and I set this in the altimeter; selected green FLCH; selected manual speed set at 250; then put out our speed brakes at full. I did not turn off the auto-throttles. The aircraft was descending at approximately 3;500 to 4;000 ft./min.I was having a great deal of trouble seeing outof the O2 mask. The plastic face plate itself was clouded and difficult to see clearly out of; especially when sunlight was hitting it directly. This was not due to my breathing. The plastic of the face plate itself was clouded and unclear. I had to hold my right hand up to block the sun to prevent excessive glare and further reduce my ability to see clearly. The problems I was having with the O2 mask were excessively distracting to me during the course of our [expedited] descent to 10;000 ft. I had to lean in close to the PFD/MFD in order to see them clearly.Very quickly approaching FL240 the Captain again called ATC asking for 10;000 ft. ATC replied they were unable due to conflicting traffic. The Captain again [requested priority handling] and ATC cleared us to descend to 10;000 ft. on a vectored heading. I set the altimeter to 10;000 ft.; selected green heading; then set the heading bug to the assigned heading.ATC then asked us how many souls were on board; what our fuel state was; and what our intentions were. The Captain gave them this information and requested to be cleared direct back to ZZZ; stating that he understood the weather to be better there than at ZZZ1. ATC then cleared us direct to ZZZ and I began reprogramming the FMS to return to ZZZ. I had trouble doing this both because I could not see clearly and did not get the FMS programmed quickly. I recall at one point ATC asked us why we had not turned direct to ZZZ. I told the Captain I was having trouble and he helped me set ZZZ as our destination. I then set direct ZZZ; selected LNAV; and we turned direct for ZZZ off of the vector we had been given.As I was doing that the Captain was using ACARS to communicate with the company. Shortly thereafter he told me that the company wanted us to divert to ZZZ1 rather than ZZZ and that we were going to divert to ZZZ1 instead of ZZZ. He had obtained the current weather there from ATC; noting that arrivals were landing west on XXL and XXR. The Captain then got an ATC clearance to fly direct to ZZZ1 and I changed our destination to ZZZ1in the FMS. Upon reaching 10;000 ft. we took our O2 masks off. I put on my headset but just after doing so I immediately heard a horrible feedback in the form of a high pitch feedback whine such as what happens when an open microphone is too close to a speaker. Like trying to see through the O2 mask; this was highly distracting and nerve-wracking to me. I had to hold the microphone of my headset in my closed left fist in order to prevent the feedback. The Captain then reminded me to close the doors to the O2 mask compartment and then press the test button there to disable the O2 microphone; which I did. This resolved the feedback issue.The Captain then made a cabin PA and I asked him if all emergency QRH checklists had been completed. He told me yes they were completed. He then got the landing speeds for the ILS XXR from ACARS while I reviewed the ILS XXR approach and set the localizer frequency in the standby Nav 1 & 2 with autotune enabled. I then briefed the approach for the ILS XXR and called for the approach checklist which we completed. ATC gave us a vector to the downwind for the ILS XXR and descended us to 5;000 ft. A short time later we were turned onto the downwind and cleared to 3;000 ft. We were turned onto base after passing the fix ZZZZZ on the ILS XXR approach; then turned to intercept the localizer and cleared for the ILS XXR approach. From this point onward we flew the standard company precision approach profile (ILS) and landed without further incident.The taxi-in was normal. We exited XXR at [Taxiway] XX and were told to contact ground. After contacting ground we completed the taxi-in checklist and were progressively taxied around the west side of the field to gate XXXX. Once there and parked we ran the shutdown checklist. The passengers were deplaned into the gate area. We were given a replacement aircraft approximately an hour and a half later; re-boarded our passengers; and flew to ZZZ without further incident. One of our flight attendants elected not to continue. It is also my understanding that the O2 mask for seat 4A did not deploy and there was a passenger in that seat.In looking through the QRH after this event and reviewing this event with the Captain; I determined we did not complete the QRH procedures properly. In the case of the red 'HIGH CABIN ALT' warning the pressurization 'DUMP' button was not pressed upon reaching 10;000 ft. as called for at the end of that QRH procedure. Also; in the case of the yellow 'BLEED 2 OVERPRESS' caution message; if the steps listed in the first part of the procedure fail to clear the EICAS message; the end of that procedure calls for 1) idling the affected engine's thrust lever and 2) performing a 'ONE ENGINE INOPERATIVE APPROACH AND LANDING'; which is not what we did. During this event I believed we had completed these checklists.1. I suggest moving the 'APU.....AS RQRD' item from the 'After Start' checklist to the 'Before Takeoff' checklist. It is standard line practice to taxi out to the runway on engine #1 (E1) before starting engine #2 (E2) when the Captain judges we are just a few minutes away from taking off. Moreover; 9 out of every 10 captains I have flown with leave the APU on to start E2 rather than perform a cross-bleed start. Because of the combination of these two factors; having the 'APU....AS REQUIRED' on the 'After Start' checklist rather than the 'Before Takeoff' checklist appears to defeat the purpose of having this on the checklist in this particular case. If this item was on the 'Before Takeoff' checklist I believe this would have caught my error in turning the APU off after starting E2 on the taxi out to the runway.2. I cannot overstate how distracting it was for me to be unable to see clearly out of the O2 mask. From the moment I put it on it was a distraction that bled time and attention away from effectively dealing with the [situation]. With everything that had happened and was happening at the time; I did not think to inspect it after arriving at the gate in ZZZ; so I cannot say with certainty if the face plate was simply dirty or the plastic itself was the cause. What I know for certain is I never had an issue with them in the sims before; but those are used on an almost daily basis and are cleaned regularly. Also; the sim is usually dark and so real sunlight (i.e. glare) is never experienced while using the O2 mask in training. I am unsure of how this issue can be addressed effectively on the line in a practical way.




Synopsis: E175 First Officer reported difficulty seeing through the oxygen mask following a loss of pressurization.