2024-03 · NASA ASRS report 2099795
B747 flight crew reported a cabin pressure problem while climbing through 31;000 feet. Crew descended to keep cabin altitude in normal range and continued to destination at the lower altitude.
Climbing through approximately FL310 for FL320; the ECS data block populated showing Cab Alt of ~>7000 in amber and climbing rapidly.. The cabin rate of climb was ~1200FPM and increasing with outflow valves showing fully closed.As PF I selected ALT HOLD and advised the FO to request an immediate descend due to pressurization problem. If any delay I asked him to [declare priority handling] and state were initiating a descend to 10K (no terrain as were over the ocean).I began an expeditious descend; ZZZZ Control acknowledged our [priority handling] call and gave us a heading approximately 20deg left of our track.While descending the cabin altitude was still climbing (the highest it ever reached was 9800 feet) but the rate kept decreasing. Around FL270 the cabin rate reached zero FPM and past 26500 the cabin altitude began to descend. I asked the FO to request a change of our altitude from 10000 to FL 200 (approved) and I switched to V/S and shallowed out our descend.After leveling off at FL 200 we opened the CABIN ALT AUTO Emergency Checklist. Cabin altitude kept decreasing and it appeared the pressurization controller was now functioning properly. I mentioned to my crew that because of our descend the pressurization auto controller seemed to be working at the lower altitude. I explained our choices were to run the electronic checklist and then control the pressurization manually - since the pressurization was now working - to stay at the lower altitude and override the opened up Emergency Checklist. Wed be descending very soon anyways and since our fuel was still looking good I was now leaning toward overriding the checklist and resuming normal ops. They concurred.With control of the cabin pressurization regained we canceled the [priority handling] with ATC; rejoined the airway and flew a normal arrival; approach and landing into ZZZZ without further issue.I sent a note to our dispatcher explaining the situation and advised of our new destination fuel estimate. (~31K)
On departure from ZZZZ1 and climbing through approximately FL310 for FL320; the crew saw that a data block for the ECS display had appeared on the display indicating an ECS abnormality. The cabin altitude displayed was climbing through 9500 feet at around 1000 fpm. The captain; PF; selected altitude hold and commanded a level off. We requested immediate descent from ZZZZ control due to a cabin pressurization problem. The controller queried whether we were an emergency aircraft; we [declared priority handling] and began a descent to FL220. The cabin pressurization remained under 10000 at FL220 and the flight proceeded to destination at FL220 with a normal descent and landing. The crew cancelled the [priority handling] once it was determined that the cabin altitude was under control and holding below 10000 and that we had adequate fuel to proceed to the destination safely.
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Source: NASA Aviation Safety Reporting System (public domain). Reports are voluntary submissions and are not verified by NASA.
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