Air carrier flight crew reported a cabin altitude alarm during cruise. Crew referenced QRH and diverted for an uneventful landing.
Synopsis
Air carrier flight crew reported a cabin altitude alarm during cruise. Crew referenced QRH and diverted for an uneventful landing.
Narrative
On Day 11 while operating our second flight of the day; we experienced a 'cabin altitude' alarm after leveling off at our cruise altitude of FL370. The captain and I immediately performed our recall items and noticed that the cabin altitude had reached approximately 11;000ft. Since I was the 'pilot flying' I maintained control of the aircraft and handled the communications with ATC while the captain ran then QRH procedure and appropriate checklists. I requested priority handling with ATC and requested a descent to 10;000ft. No damage to the aircraft was suspected prior to descending.Upon leveling off at 10;000ft I requested direct ZZZ1 while the captain communicated with the passengers; flight attendants; and dispatcher. I started to gather weather information for nearby airports for possible divert option's. Dispatch indicated that ZZZ was a good alternate for the passengers and maintenance so we elected to divert to ZZZ in the interest of safety.Remainder of flight was uneventful into ZZZ. Additional services on the ground were declined since we had no injuries or aircraft damage. Once at the gate; maintenance had noticed the aircraft had experienced a similar cabin altitude event on Day 0.Cause: Performing our recall items and running the appropriate checklists ensured we were mitigating risk the best we could. Division of duties and focusing on each of our tasks all us to continue safely operating the aircraft. Captain and I also debriefed the event once at the gate to reflect on how we handled each of our tasks.
Second reporter narrative
On Day 0 I was operating Aircraft X to ZZZ1. Shortly after leveling off at FL370; we received the Cabin Altitude warning and horn. The cabin altitude was about 11;000'. We performed the memory items and appropriate checklists. I ran the checklists and coordinated with the flight attendants; company; and passengers while my first officer flew the airplane and descended to 10;000'. The Cabin Altitude checklist redirected me to the descent checklist. This procedure required me to manually deploy the oxygen masks. I believe that the masks had already automatically deployed but I cannot confirm. We also completed the deferred items and the non-routine landing checklist.At 10;000'; we attempted to continue to ZZZ1. I attempted to contact the dispatcher through Crew Connect but he couldn't hear me very well. I considered Dispatch Direct but sent a few ACARS messages instead. I asked him for preferable alternates. He suggested ZZZ. I saw that it was nearby and liked the services available so I responded with 'diverting to ZZZ.' I updated the cabin crew and the passengers as necessary to explain that we would be landing in ZZZ in favor of safety. I declined emergency vehicles after verifying passenger health and aircraft structural integrity. We landed in ZZZ and taxied to the gate without further events. I debriefed the event with my FO to discuss what we could have done differently or improved upon. I spoke briefly with the mechanics to relay what had happened. They said that a similar event happened about 10 days prior. Cause: Possible aircraft defect. High altitude.
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Source: NASA Aviation Safety Reporting System (public domain). Reports are voluntary submissions and are not verified by NASA.