Date: 201910
Local time of day: 1201-1800
Location: ZZZ.TRACON, US
Light: Daylight
Aircraft: EMB ERJ 170/175 ER/LR
Operator: Air Carrier
Operating under: Part 121
Flight plan: IFR
Mission: Passenger
Flight phase: Climb
Airspace: Class B ZZZ
ATC / advisory: TRACON ZZZ
Aircraft component: Oxygen System/Crew
Component problem: Failed; Malfunctioning
Reporter organization: Air Carrier
Reporter function: Captain; Pilot Not Flying
Reporter qualification: Flight Crew Air Transport Pilot (ATP); Flight Crew Multiengine; Flight Crew Instrument
Human factors: Distraction; Other / Unknown
Anomaly: Aircraft Equipment Problem Critical
Detector: Person Flight Crew
When detected: In-flight
Result: Flight Crew Landed in Emergency Condition; Flight Crew Returned To Departure Airport; Flight Crew Requested ATC Assistance / Clarification
Contributing factors: Aircraft
Primary problem: Aircraft

Narrative: This is the second flight of the day. We (my crew) had a plane swap in ZZZ; and boarded the plane. We began pre-flight duties. I quickly noticed three MELs deferments [for] ELT; Potable Water system; and Air Cond Pack. Working through them; I noticed there was a placard associated with the Potable Water system that was missing and wanted to ask about the ram air doors associated with the Air Pack MEL. I called Maintenance Control and was informed to add placard for the Potable Water system and then confirmed the ram air doors (associated with the Air Cond Pack deferment) were deactivated. With the exception of the cabin being slightly warm; the rest of the preflight went without incident and we complied with the Air Cond Pack MEL. I made an announcement to the passengers that the cabin should cool once we are airborne. My First Officer was designated as Pilot Flying; and we departed ZZZ via Runway XXL. We climbed out via the ZZZ5 with a bunch of vectors; but without issue. We were given a climb to 23;000 feet and normal speed. Climbing through 19;000 [feet]; First Officer and I noticed the cockpit was unnaturally warm. I checked the ECS page and noticed that not only was Pack 1 not operating (as expected); but also Pack 2 wasn't operating. Very shortly after that realization; we received an EICAS message and associated warnings with a Cabin Alt High. I advised First Officer to stop our climb and put on his oxygen mask. I grab my mask and realized the straps that inflate and wrap around the head; would not fully inflate. I pulled it over my head and realized my communication with my First Officer was intermittent (either because of the mic or oxygen flow). First Officer called for the QRC Cabin Alt High. I grabbed it and began running the check list. First Officer began a decent to 10;000 feet. I received a call from the cabin crew Flight Attendant. I momentarily answered and advised 'We are doing an [urgent] descent; standby.' As we worked through the check list; First Officer noticed my issue with the oxygen mask and took the radios and coordinated with ATC down to 10;000 [feet]. We [advised ATC] and [ask them] to standby. Leveling at 10;000 [feet]; I removed my mask and finished up the check list in the QRC and QRH. The check list drove us to press the cabin dump button and depressurize the cabin. We were advised by ATC that ZZZ1 was close and available. First Officer and I discussed shortly and I advised First Officer and ATC we would return to ZZZ below 10;000 [feet] for a normal Landing. I spoke with both flight attendants and advised them that we were depressurized and that we would be making a normal Landing in ZZZ with no need to brace. They said they understood. Sent a quick message to Dispatch about [advising ATC]. I advised First Officer to take the radios and continue flying. I checked the fuel and landing weight and asked First Officer if he was ok with flying the landing into ZZZ. He said he was; and based on our past flights; I was too. We requested and was able to decent to 8;000 feet from 10;000 [feet] to keep from getting any additional cabin alt high (9;700 feet.) messages. We received direct to ZZZ at 8;000 feet as requested. We briefed and set-up for Runway XXC into ZZZ and ran the decent check list. I spoke with the flight attendants (they said it was very warm) and I made an announcement to the passengers. ATC asked if we had the [situation] under control; I said we do. ATC started to assign us a STAR; but then allowed us to maintain our direct clearance to ZZZ. We were given a descent and dogleg to intercept the localizer to [Runway] XXC. We landed without issue. Exited the runway at P5 (I believe). I said we would taxi in as normal and First Officer spoke with crash/rescue and advised (after speaking with flight attendants) that we didn't expect any injuries onboard. They advised that they would follow our aircraft into the ramp; which they did. We blocked into gate.




Synopsis: EMB-175 Captain reported that during a loss of pressurization and descent; the Captain was unable to don O2 mask because the head strap would not inflate.