Narrative:

Captain performed the internal safety checklist; while first officer performed the external walk around. Captain went over the trip can and sent out an arcars message requesting of the release.once the release came out; captain briefed flight attendants about the flight and informed the flight attendants about the following write up;-northeast 25-xx-X : emergency equipment compartment for gallery 2-MEL 21-xx-xx-X : pack flow control valve-MEL 21-xx-xx-X : air conditioning packscaptain informed the flight attendants about the inoperative pack 1 system and that would mean the pilots in the cockpit will have to adjust the air conditioning for the cabin and that if [flight attendants] need adjustments in the cabin; they should feel free to call the cockpit for the necessary adjustments.first officer completed the external walk around and did not notice anything unusual during the walk around. Captain and first officer went over the mels; and discussed setting reference ecs on takeoff data to off in the mcdu and leaving the APU on during takeoff as MEL 21-xx-xx-X calls for. There was also an EICAS message; if I remember correctly; the EICAS message was 'ram air fault'; which has to do with MEL 21-xx-xx which is a sub-part of MEL 21-xx-xx-X.first officer then briefed the flight as he was the pilot flying and captain was the pilot monitoring.captain handed the paperwork to the gate agent and the doors were closed for an on time departure. Both pilots completed the before start checklist to the line and below the line. First officer made a courtesy call to ground for push back; aircraft X was cleared to push back at pilots discretion for runway 17L and to call for taxi.ramp crew gave the pilots the go-ahead to start the engines. First officer started engine 1. It was a normal engine start; the tow bar and headset was then disconnected. Captain made a PA announcement and the after start checklist was completed. After start starting engine 2; a 'blue' EICAS message; if I remember correctly 'pack 2 fail' came on; then extinguished after captain pushed out and then pushed in the pack 2 button. Both pilots completed the taxi out checklist.once cleared for takeoff; both pilots completed the before takeoff checklist; and lined up and wait. Captain then transferred the flight controls to first officer . It was a normal takeoff. During the climb out; captain (pilot monitoring) noticed that the APU was off. Crew discussed the APU should be turned back up as required by MEL 21-xx-xx-X for takeoff. Captain turned the APU back on. After completing the after takeoff check list; pilot monitoring turned off the APU. As we continued the climb; an EICAS caution message 'bleed 2 overpress' appears. Pilot flying said; 'cancel and identify'. Pilot monitoring said 'bleed 2 overpress' and then referred to the QRH as called for by the pilot flying. After pushing out then in bleed 2 button; the EICAS message did not extinguish. Captain then viewed the ecs status page and noticed that both pack 1 and 2 had very low psi. While performing the 'bleed 2 overpress QRH'; the psi on pack 2 increases after cycling the bleed 2 button; but then drops down to a low psi. An ACARS message was sent to dispatch about the EICAS message; dispatch responded that we should perform the QRH procedure. At that point; captain then turned on the APU; but the APU did not come online; an EICAS message 'APU fail' appeared; captain then turned the switch to off and tried for the second time to turn on the APU but then got and 'APU fail' message; soon after that; 'cabin altitude hi' EICAS message appears. At this point; aircraft X was leveling at FL310.both pilot donned the oxygen mask and established communication as the epc calls for. Pilot flying said he has a loud squelching noise in the oxygen mask headset. Pilot monitoring could hear the pilot flying loud and clear.pilot monitoring requested 10;000 ft. From ATC. ATC said he could not clearly hear the request. Pilot monitoring repeated the request. ATC said he still could not clearly hear the request. At this point; pilot monitoring was talking via the oxygen mask; this distorted the pilot monitoring voice. Another pilot from another airplane then repeated aircraft X's request. The other pilot from another airplane said; 'they said they request 10;000 ft. Due to cabin hi altitude'. At this time; ATC cleared aircraft X to FL240.as we continued the descent; ATC could not clear aircraft X below FL240 due to traffic. Captain [advised ATC] and asked for 10;000 ft. ATC then gave aircraft X a heading and altitude of 10;000ft. As we continued the descent; pilot monitoring continued the epc and referenced the QRH for the cabin altitude hi. The pilots then talked to the flight attendants; who informed the pilots that all the oxygen mask but one (seat 4A) had deployed and used at the back. The 'dump button' was never pushed in and even though a PA announcement was made; the announcement did not include 'remove oxygen mask' as stated in the QRH. Both pilots decided to return back to ZZZ; captain then requested vectors to ZZZ; ATC advised aircraft X that ZZZ1 is closer than ZZZ. Captain then asked for the current weather at ZZZ1. The weather at ZZZ1 was reporting broken at 500 ft. And low visibility. The weather in ZZZ was a lot better than the weather in ZZZ1. ATC gave aircraft X vectors to ZZZ. Captain also informed dispatch that [priority handling was requested] due to cabin altitude hi and aircraft X is returning back to ZZZ. Dispatch then suggested diverting to ZZZ1 instead of ZZZ; after considering the current situation; which at this time; the cabin altitude had stabilized; flight crew decided to divert to ZZZ1. Pilot monitoring then requested vectors to ZZZ1 and made a PA announcement about diverting to ZZZ1 due to having a maintenance crew out in ZZZ1 and also if necessary; a better chance to switch aircrafts. Approach checklist to the line and below the line was then performed; but the EICAS message 'bleed 2 overpress' still remained.control rower vectored flight aircraft X to ZZZ1 for the ILS approach xxr. After landing; aircraft X was escorted to [gate] by the emergency truck. At [gate]; aircraft X deplaned and egress was given.we switched airplanes and proceeded to ZZZ2.

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Original NASA ASRS Text

Title: Air carrier Captain reported that a loss of pressurization during climb resulted in a diversion.

Narrative: Captain performed the internal safety checklist; while First Officer performed the external walk around. Captain went over the trip can and sent out an ARCARS message requesting of the release.Once the release came out; Captain briefed Flight Attendants about the flight and informed the Flight Attendants about the following write up;-NE 25-XX-X : Emergency Equipment Compartment for gallery 2-MEL 21-XX-XX-X : Pack Flow Control Valve-MEL 21-XX-XX-X : Air Conditioning PacksCaptain informed the Flight Attendants about the inoperative pack 1 system and that would mean the pilots in the cockpit will have to adjust the air conditioning for the cabin and that if [flight attendants] need adjustments in the cabin; they should feel free to call the cockpit for the necessary adjustments.First Officer completed the external walk around and did not notice anything unusual during the walk around. Captain and First Officer went over the MELs; and discussed setting REF ECS on takeoff DATA to OFF in the MCDU and leaving the APU on during takeoff as MEL 21-XX-XX-X calls for. There was also an EICAS message; if I remember correctly; the EICAS message was 'RAM AIR FAULT'; which has to do with MEL 21-XX-XX which is a sub-part of MEL 21-XX-XX-X.First Officer then briefed the flight as he was the pilot flying and Captain was the pilot monitoring.Captain handed the paperwork to the gate agent and the doors were closed for an on time departure. Both pilots completed the before start checklist to the line and below the line. First Officer made a courtesy call to ground for push back; Aircraft X was cleared to push back at pilots discretion for Runway 17L and to call for taxi.Ramp crew gave the pilots the go-ahead to start the engines. First Officer started engine 1. It was a normal engine start; the tow bar and headset was then disconnected. Captain made a PA announcement and the after start checklist was completed. After start starting engine 2; a 'blue' EICAS message; if I remember correctly 'Pack 2 fail' came on; then extinguished after Captain pushed out and then pushed in the pack 2 button. Both pilots completed the taxi out checklist.Once cleared for takeoff; both pilots completed the before takeoff checklist; and lined up and wait. Captain then transferred the flight controls to First Officer . It was a normal takeoff. During the climb out; Captain (pilot monitoring) noticed that the APU was off. Crew discussed the APU should be turned back up as required by MEL 21-XX-XX-X for takeoff. Captain turned the APU back on. After completing the after takeoff check list; pilot monitoring turned off the APU. As we continued the climb; an EICAS caution message 'Bleed 2 overpress' appears. Pilot flying said; 'cancel and identify'. Pilot monitoring said 'bleed 2 overpress' and then referred to the QRH as called for by the pilot flying. After pushing out then in bleed 2 button; the EICAS message did not extinguish. Captain then viewed the ECS status page and noticed that both pack 1 and 2 had very low PSI. While performing the 'Bleed 2 Overpress QRH'; the PSI on pack 2 increases after cycling the bleed 2 button; but then drops down to a low PSI. An ACARS message was sent to Dispatch about the EICAS message; Dispatch responded that we should perform the QRH procedure. At that point; captain then turned on the APU; but the APU did not come online; an EICAS message 'APU fail' appeared; Captain then turned the switch to off and tried for the second time to turn on the APU but then got and 'APU fail' message; soon after that; 'CABIN ALTITUDE HI' EICAS message appears. At this point; Aircraft X was leveling at FL310.Both pilot donned the oxygen mask and established communication as the EPC calls for. Pilot flying said he has a loud squelching noise in the oxygen mask headset. Pilot monitoring could hear the pilot flying loud and clear.Pilot monitoring requested 10;000 ft. from ATC. ATC said he could not clearly hear the request. Pilot monitoring repeated the request. ATC said he still could not clearly hear the request. At this point; pilot monitoring was talking via the oxygen mask; this distorted the pilot monitoring voice. Another pilot from another airplane then repeated Aircraft X's request. The other pilot from another airplane said; 'they said they request 10;000 ft. due to cabin hi altitude'. At this time; ATC cleared Aircraft X to FL240.As we continued the descent; ATC could not clear Aircraft X below FL240 due to traffic. Captain [advised ATC] and asked for 10;000 ft. ATC then gave Aircraft X a heading and altitude of 10;000ft. As we continued the descent; pilot monitoring continued the EPC and referenced the QRH for the Cabin Altitude Hi. The pilots then talked to the flight attendants; who informed the pilots that all the oxygen mask but one (seat 4A) had deployed and used at the back. The 'dump button' was never pushed in and even though a PA announcement was made; the announcement did not include 'remove oxygen mask' as stated in the QRH. Both pilots decided to return back to ZZZ; Captain then requested vectors to ZZZ; ATC advised Aircraft X that ZZZ1 is closer than ZZZ. Captain then asked for the current weather at ZZZ1. The weather at ZZZ1 was reporting broken at 500 ft. and low visibility. The weather in ZZZ was a lot better than the weather in ZZZ1. ATC gave Aircraft X vectors to ZZZ. Captain also informed Dispatch that [priority handling was requested] due to Cabin Altitude Hi and Aircraft X is returning back to ZZZ. Dispatch then suggested diverting to ZZZ1 instead of ZZZ; after considering the current situation; which at this time; the cabin altitude had stabilized; Flight crew decided to divert to ZZZ1. Pilot monitoring then requested vectors to ZZZ1 and made a PA announcement about diverting to ZZZ1 due to having a maintenance crew out in ZZZ1 and also if necessary; a better chance to switch aircrafts. Approach checklist to the line and below the line was then performed; but the EICAS message 'Bleed 2 overpress' still remained.Control Rower vectored flight Aircraft X to ZZZ1 for the ILS approach XXR. After landing; Aircraft X was escorted to [gate] by the emergency truck. At [gate]; Aircraft X deplaned and egress was given.We switched airplanes and proceeded to ZZZ2.

Data retrieved from NASA's ASRS site and automatically converted to unabbreviated mixed upper/lowercase text. This report is for informational purposes with no guarantee of accuracy. See NASA's ASRS site for official report.