Date: 201908
Local time of day: 1801-2400
Location: ZZZZ.Airport, FO
Flight conditions: VMC
Aircraft: A319
Operator: Air Carrier
Operating under: Part 121
Flight plan: IFR
Mission: Passenger
Flight phase: Climb
ATC / advisory: Center ZZZZ
Aircraft component: Air Conditioning and Pressurization Pack
Component problem: Failed
Reporter organization: Air Carrier
Reporter function: Pilot Flying; First Officer
Reporter qualification: Flight Crew Multiengine; Flight Crew Instrument; Flight Crew Air Transport Pilot (ATP)
Human factors: Situational Awareness
Second reporter function: Relief Pilot; First Officer; Pilot Not Flying
Anomaly: Aircraft Equipment Problem Critical; Deviation / Discrepancy - Procedural MEL / CDL; Deviation / Discrepancy - Procedural Published Material / Policy
Detector: Person Flight Crew
When detected: In-flight
Result: Air Traffic Control Provided Assistance; Flight Crew Landed in Emergency Condition; Flight Crew Returned To Departure Airport; Flight Crew Overcame Equipment Problem; General Flight Cancelled / Delayed
Contributing factors: Aircraft
Primary problem: Aircraft

Narrative: I was the PF (Pilot Flying). Flight was dispatched from ZZZZ to ZZZ2 with Pack 2 on MEL. Normal take off; on climb I noticed cabin altitude at 13;000 ft.; I yelled out cabin altitude is high; emergency descent. We descended to 10;000 ft. no masks dropped. At 10;000 ft.; we assessed problem. Pack 1 now failed. I told Captain [to advise ATC] and divert to ZZZ1. Captain agreed and [sent] ACARS [message to] Dispatch. Dispatch said no; go to ZZZZ. Now we are overweight. We held for a while to burn off approximately 22;000 ft. Landed uneventfully. CFR (Crash Fire Rescue) called out as well as paramedics. Cabin was getting hot. Captain kept calling FA (Flight Attendants) to check up on them and passengers due to heat in back. We landed underweight. Also no ECAM warning was ever received as pack 1 failed. No warning; no bells; no horns; etc. My ears were normal on climb out. No popping until I caught the cabin climbing.


Second narrative: Pack 2 was on MEL. Boarding; Push; Taxi; Takeoff uneventful. At around 13;000 ft.; flight crew noticed high cabin altitude and climbing. [ATC was advised] and the aircraft was promptly put in a descent to 10;000 ft. Oxygen masks were briefly used. Investigation of systems showed pack 1 not working; but no failure warning was ever given to flight crew. APU was started to provide bleed air to Pack 1; without success. Overweight landing in ZZZ1 was considered but Dispatcher highly advised against using this airport and recommended return to ZZZZ. Further communication with Dispatch could not be completed due to non-ACARS reception. Brief relay/contact was established through Center and Aircraft Y. Flight descended further and flew holding pattern in full configuration to burn fuel in order to get below MLW (Maximum Landing Weight). Cabin and cockpit started to heat up quickly to around mid-90 [degrees] Fahrenheit. Fuel burn/holding pattern took about 1.5 hrs. At the end of the holding pattern; overweight landing in ZZZZ was considered again; due to passengers feeling sick (heat related) and concern about possible avionics failure due to high heat. Landing successful. Water was given to passengers and one passenger was briefly given medical attention.I still do not understand why the Pack / Bleed 1 failed without an ECAM. Overhead panel was checked multiple times for possible configuration error; but Pack 1 could not be put back online. Do not dispatch airplanes with a single bleed and/or APU inoperative to challenging locations (terrain; geopolitical; remoteness; etc.).


Synopsis: A319 flight crew and Dispatcher reported loss of cabin pressurization due to failure of only operating pack during single pack operations.