B787 flight crew reported the loss of cabin pressurization control; resulting in dumping fuel and diverting to the nearest airport.
Synopsis
B787 flight crew reported the loss of cabin pressurization control; resulting in dumping fuel and diverting to the nearest airport.
Narrative
Climbing through about 28;000 feet; we experienced excessive cabin altitude. The cabin altitude indicated 9000 feet and was continuing to climb. I stopped climbing the aircraft; and the First Officer and I both donned oxygen masks. I then asked her to advise ATC of the problem and request a lower altitude; which she did. We were then cleared to FL200 with a subsequent clearance to 15;000. I then initiated a rapid descent towards that altitude. In the meantime; the cabin altitude had climbed to a maximum of 10;300; but as we descended it turned around and began descending back below 10;000 again. The passenger oxygen masks did not deploy. I asked the FO to run the Cabin Altitude checklist. Structural integrity was not in doubt as there was no vibration. We then requested an air return back to ZZZ and [advised ATC of] emergency and were given a clearance back towards ZZZ VOR then ZZZ. As we approached 15;000 the cabin altitude was now approximately 4500 and under control; but we requested to continue descent to 10;000 where the cabin altitude descended to about 3;500 feet. Once at this altitude; we were cleared to hold at present position about 80 miles southwest of ZZZ to dump fuel and advised ATC and recorded the aircraft position. It was also during this hold I finally had time to call dispatch and advise them of our situation. At the completion of the dump; recorded position again and later gave this to dispatch. It was also in this phase I coordinated with the flight attendants; gave them the TEST and advised the passengers of our situation. The dump time was about 23 minutes; at the completion of which; we requested a clearance towards ZZZ VOR and then flew the ILS approach to runway XY. The approach and landing were all normal.
Second reporter narrative
[Report narrative contained no additional information.]
Source: NASA Aviation Safety Reporting System (public domain). Reports are voluntary submissions and are not verified by NASA.