Date: 201907
Local time of day: 0001-0600
Location: ZZZ.Airport, US
Aircraft: EMB ERJ 170/175 ER/LR
Operator: Air Carrier
Operating under: Part 121
Flight plan: IFR
Mission: Passenger
Flight phase: Climb
Airspace: Class A ZZZ
ATC / advisory: Center ZZZ
Aircraft component: Pressurization System
Component problem: Malfunctioning
Reporter organization: Air Carrier
Reporter function: Pilot Flying; First Officer
Reporter qualification: Flight Crew Multiengine; Flight Crew Instrument; Flight Crew Air Transport Pilot (ATP)
Second reporter function: Flight Attendant In Charge; Flight Attendant (On Duty)
Anomaly: Aircraft Equipment Problem Less Severe; Inflight Event / Encounter Other / Unknown
Detector: Person Flight Crew
When detected: In-flight
Result: Flight Crew Landed in Emergency Condition; Flight Crew Diverted; Flight Crew Returned To Departure Airport
Contributing factors: Aircraft
Primary problem: Aircraft

Narrative: Leveled at FL320 during climb to cruising alt of FL340 en-route from ZZZ. We received a CABIN ALT HI EICAS while climbing through FL330. After cancelling the MASTER WARNING the CA (Captain) and I donned our oxygen masks and established communication. No abnormal sounds prior to alert. I called for the QRC and we initiated the emergency descent per the procedure. During the descent back through FL330 the CABIN ALT was approximately 8;800. CA and I confirmed it was descending; or at least under control; to determine it was more than likely a leak and not an explosive decompression. Prior to EICAS message; climb pressurization seemed normal; all indications in the green. CABIN ALT typically around 6;900 in the low FL300s. CA contacted Center and informed them we had a CABIN ALT HI alert; we needed an immediate descent to 10;000 and that we needed vectors back to ZZZ. We were given present heading and a descent to FL240. After finishing the QRC we moved to the QRH and began those procedures. I remained on the controls so that CA could better manage the EP (Emergency Procedure).Around this time we received an EMERG call from the cabin. The FA (Flight Attendant) informed us that the masks had dropped and asked what to do. CA informed we had received a CABIN ALT HI and were descending now to thicker air. CA advised to tell the passengers to put the masks on and breathe normally. CA confirmed on overhead panel that the PRESSURIZATION and PASS OXY switches were both in AUTO and they were. We were given subsequent descents to FL180 and then 10;000 with vectors for a turn back to ZZZ. During this time CA made an initial PA informing the passengers to breathe oxygen from the masks; that we were returning to ZZZ; and that the aircraft was under control. We also received a message from Dispatch asking about the situation. Dispatch then sent new Performance numbers for the return flight and [amendment] 1 to our release for return to ZZZ. They also asked if there were any injuries.At this point we had leveled at 10;000. The Cabin Alt was reading 0. For ease of communication the CA and I removed our masks and stowed them. Due to the low Cabin Alt and our 40 min plus flight back; CA decided to not to press the DUMP button in order to keep the PACKs running and the CABIN ALT low. I concurred with the decision. No structural damage was suspected. QRH actions were complete.[Minutes later;] CA called FA back and asked about injuries; the general state of the passengers; any noticeable structural issues; and to confirm that the LAVs were clear per the QRH. The FA confirmed the LAVs were clear; no injuries and that the passengers were mostly doing pretty well; but that one woman seemed very excited and was concerned about seeing her children. FA asked about whether the passengers should keep the masks on; as some of them seemed to be running out; and CA recommended to keep them on for now; but that he would advise. CA relayed the injury information to dispatch and told them no emerg medical assistance was required at the gate at this time. CA made a second PA to the passengers explaining that we believe we received the alert due to a faulty seal; told them again that the aircraft was under control; apologized for the excitement and said that we would be back at ZZZ in approx. 30 min. Third PA made telling passengers to remove masks as we were in thicker air and to prepare for a normal landing in approx. 20 min. Approach vectored us for the ILS at ZZZ. We had previously relayed our FOB (Fuel On Board) and SOB (Souls On Board) to ATC. After running the numbers; we confirmed that we would be below max landing weight and would not require an additional write up for that. We had 75 pax and were above MLW (Maximum Landing Weight) at takeoff. We informed ATC that we would not need to stop on the runway and should be able to land normally and taxi in under our own power. Previous ATC comms led us to believe they were coordinating for us to stop on the runway. CA made another PA to the passengers telling them to expect a normal landing and to remain seated and buckled in after landing. I contacted the FAs and told them to expect the same and that no brace calls were needed. After we were on a long base to final CA took controls in the left seat because it was an emergency aircraft. Normal landing. CFR (Crash Fire Rescue) was standing by but not needed. Taxi and parking normal.Before speaking to Dispatch; I initially left the flight deck and made a final PA to the pax; advising them to deplane normally and that [company] agents would be immediately available to address any questions or concerns they may have. The CA and I then personally ensured all of the passengers were deplaned safely and properly and that no injuries had occurred that we were not tracking. All 75 walked off plane and seemed in remarkably good spirits overall. CA spoke to dispatch; and the pilot on duty; to inform them of the situation.CA's writeup in the logbook: 'CABIN ALT HI EICAS AT FL330. ALL PAX MASKS DEPLOYED. NO AURAL INDICATION. CAB ALT APPROX 8;800 AT FL320 IN DESCENT. MASKS DEPLOYED AUTO.' As CA spoke with MX; I contacted [Maintenance Control] on the phone. I provided a narrative and was advised to provide relevant details to on-sight MX personnel. CA went down to the ramp to visually inspect the vent flap on the FWD EBAY with a mechanic. He mentioned it had a lot of play when were first spoke to them after landing. Vent flap had approximately 3/4 to 1 inch of play upward and the inside of the EBAY was just barely visible. Other aircraft have maybe a 1/4 inch of play. Note on the aircraft: upon receiving the plane from the previous captain he mentioned that it had a series of write-ups regarding the CABIN ALT climbing to 8;700 then back down to normal around FL220 accompanied by a thumping or hissing sound. Troubleshooting had previously led to a realignment of the FWD E-BAY vent flap door; a replacement of FWD E-BAY seal and the manual [shut off valve] for the LAV being adjusted. Aircraft had been released back to flight following episodes. The write-up out of ZZZ1; signed off [days earlier]; involves a similar incident to ours; but occurred at FL220. I believe the vent flap fluttering in the wind maybe the source of the noise and the leak. Prior to my initial preflight CA asked me to pay special attention to the areas affected by the troubleshooting. I saw nothing obviously abnormal; but it is worth noting that we never manually check the play in the vent flap per procedure.Actions and CRM by CA and FAs were commendable. Very calm and professional reaction to abnormal situation.


Second narrative: I was working as A-FA (A Flight Attendant) in my galley fixing a drink for a passenger when I heard an unusual sound in the cabin. I look around since I have my back turned and saw that the oxygen masks had deployed. I threw away my service items and put away my carts just as B-FA made an announcement in the PA to don the oxygen masks. I pulled a mask for myself and sat on my jumpseat as B-FA and I both attempted to contact the flight deck. There was no answer the first time. I look at the cabin and the passenger in 3A is looking at me very concerned. I signaled a thumbs-up to ask if she is okay and she shook her head to say no. I went over to her; put a new mask on myself and tried to get her to breathe slowly as she was breathing short; rapid breaths. She slowly calmed down as she held my hand. The flight deck called and B-FA and I answered; we were updated with the situation. I went back to check 3A and get my MRT (Manual Release Tool) when I saw that B-FA was already in the cabin checking on everyone. B-FA made several announcements to don the oxygen masks correctly (over nose and mouth) and to bring it to our attention if someone needed help. As I was walking through the cabin 14D and 22D also made it known that they are EMT and a nurse practitioner; respectively. The flight deck called multiple times to coordinate and spoke on the speaker shortly to tell the passengers that the plane is under control and we are heading back to ZZZ. At a certain point; the flight deck also made an announcement that it is no longer necessary to don the oxygen masks but to keep it on if passengers choose to or feel lightheaded. B-FA also made multiple announcements for passengers to let us know if they need medical attention upon landing. I asked passenger 3A as well if she prefers to be met with EMTs but she declined and assured me she is okay before we landed. We had a normal landing in ZZZ.


Synopsis: EMB-175 flight crew reported cabin depressurization during climb.