Flight Crew reported the failure of the operational Cabin Pressure Controller during climb. With a failed CPC and the other CPC on MEL; the flight crew returned to departure airport.
Synopsis
Flight Crew reported the failure of the operational Cabin Pressure Controller during climb. With a failed CPC and the other CPC on MEL; the flight crew returned to departure airport.
Narrative
On the date and time noted; I was assigned to fly from ZZZ to ZZZZ. Upon arrival to the aircraft; I noticed that the primary Auto Pressurization Controller was MELed; and the aircraft was in ALT mode. After reviewing the MEL; noting that one operational AUTO mode was required for Dispatch; and performing the pre-flight check of the manual operation; in accordance to the MEL; we departed ZZZ without incident. During the climb; passing through approximately FL 280; the Master Caution light began to flash; with 'AIR' displayed. Also flashing was AUTO on the pressurization panel. Upon reaching the assigned altitude of FL 310; the numeric digits on the pressurization panel turned to dashes; and the AUTO light illuminated steady. The First Officer (FO) immediately put the pressurization into manual mode. Initially the pressurization was steady as we completed the QRH Checklist accordingly; but a few minutes later; the FO had a hard time controlling the pressurization. After consulting Dispatch; we decided to descend; and return to ZZZ. ATC cleared us to a point on the ZZZZZ Arrival into the ZZZ area; at 12;000 ft.; all the while; the FO was struggling to control the pressurization manually. We revisited the QRH for 'Uncontrollable Pressurization;' then completed the Diversion Checklist. I advised the Flight Attendants (FAs) that we were returning to ZZZ; as well as the Passengers. At 12;000 ft.; the pressurization was still difficult to control; so after a brief discussion between the FO and I; I made the decision to [request priority handling]; and was cleared to 10;000 ft.; then to 8;000 ft. We advised ATC that we would require a full-length runway rollout; on Runway X; the longer runway; due to the fact that we would be performing an overweight landing. We were eventually vectored to a visual approach for Runway X. I landed the aircraft without incident; and taxied to the gate.
Second reporter narrative
Experienced an AUTO FAIL with the Cabin Pressurization as we were continuing to climb to our cruise altitude of 39;000 ft. The aircraft was dispatched on flight to ZZZZ with MEL XX-XX-XX; operating cabin pressurization in ALT mode. Passing through approximately 29;000 ft.; we saw the AUTO FAIL flicker on the Pressurization Panel then a minute or so later; a Master Caution with the AUTO FAIL remaining illuminated. Ran appropriate checklist (AUTO FAIL 2.4); placed pressurization in manual and used outflow valve to control cabin pressure. Contacted Dispatch and decided best course of action was to return to ZZZ. Initially coordinated with ATC to return to ZZZ and descend to 12;000 ft. (route limit for them at time). Completed Diversion Checklist as we turned around and descended. Was able to control cabin pressurization; but as we reached 12;000 ft.; cabin pressure became more difficult to control so we descended to 10;000 ft. and [requested priority handling]. Coordinated with ATC for return to Runway X at ZZZ; due to heavy weight landing. Vectors; approach; and landing were uneventful and we returned to gate. Was little surprised to see an aircraft dispatched on international flight with this MEL.
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Source: NASA Aviation Safety Reporting System (public domain). Reports are voluntary submissions and are not verified by NASA.