B737 flight crew reported cabin depressurization while at cruising altitude. Flight crew diverted and landed uneventfully.
Synopsis
B737 flight crew reported cabin depressurization while at cruising altitude. Flight crew diverted and landed uneventfully.
Narrative
While at cruise at FL370; we started deviating around a weather system and I suddenly felt my ears pop. The First Officer had a similar issue and we both looked up at the cabin pressure and noticed the differential pressure was starting to rise from where it had been stable around 7600. The cabin altitude remained stable around 5000-6000. The First Officer; who was the pilot flying; was given the radios and I proceeded to run the non-normal auto-fail or unscheduled pressure change checklist. The differential pressure continued to rise the whole time. There was also never any abnormal indication aside from this. It was at this time the First Officer (FO) and I decided to request a descent as the situation was not getting better. In coordination with ATC; we started a descent down to FL310. I continued to run the checklist and switched the controller to MAN. This did nothing and the cabin pressure remained stable. The differential pressure continued to rise pegged on the 9 red line. We decided to continue the descent. Around FL250 the cabin altitude started to decrease; but the differential pressure continued to stay on the red line. It is at this time I decided to [request priority handling] and seek an alternate airport. There were a couple of options; ZZZ1 or ZZZ. We chose ZZZ as it was the closest airport. I messaged Dispatch and we continued our descent to 10000; then 8000. The cabin altitude went all the way to zero and went negative until I opened the outflow valve at pattern altitude to depressurize the aircraft. The landing at ZZZ was uneventful. I wrote up the issue; debriefed the Dispatcher; chief pilot; and Maintenance.
Second reporter narrative
Cruising at FL370 on the way to ZZZ2; we started to deviate around a pop up storm and I suddenly felt a very abnormal ear popping. The Captain felt the same thing and as we looked up at the cabin pressurization panel; we noticed the differential pressure (the big needle); starting to rise from its original position of around 7500-7600 a decent rate but yet the cabin altitude stayed at 5-6000. I was the pilot flying; and so the Captain gave me the radios as well so he could start going through the appropriate checklists. The non-normal auto-fail or unscheduled pressure change checklists. As that was going on; we both noticed the differential pressure rising the whole time. Unfortunately; there was never any type of abnormal indication aside from this. It was at that time; the Captain and I asked for a descent down to FL310 to see if that would help the problem as it wasn't getting any better. The Captain continued to run the checklists and switched the controller to MAN Mode. But this did nothing at all and the cabin pressure remained stable; yet the differential pressure continued to rise and stayed on the 9 red line. We decided to continue our descent down and around FL250; the cabin altitude started to decrease but again; the differential pressure stayed on the redline. It was at that moment the Captain [requested priority handling] and I suggested to start down to 10;000 while he decided on an alternate airport. We chose ZZZ as it was the closest airport for us to get down and figure things out. Captain started messaging Dispatch to let them know of the situation and we were going to ZZZ. We continued down to 10;000 then 8;000 and the cabin altitude then went all the way to 0 and then kept going to the left to make it go into the negative range until Captain opened the outflow valve at pattern altitude. The landing at ZZZ was an uneventful one as we had mitigated the rest of the risks.
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Source: NASA Aviation Safety Reporting System (public domain). Reports are voluntary submissions and are not verified by NASA.