B777-200 flight crew reported that the ground crew did not fully close the main cargo door during loading. This caused a cabin pressurization failure; leading to an air turnback and precautionary landing.
Synopsis
B777-200 flight crew reported that the ground crew did not fully close the main cargo door during loading. This caused a cabin pressurization failure; leading to an air turnback and precautionary landing.
Narrative
Climb out passing 9500 ft.; got cabin altitude alert. Aircraft wouldn't pressurize. We leveled off; determined need to return to ZZZ. We requested vectors to dump area and dumped fuel to get to max landing weight. [We requested priority handling] and flew ILS XXL. Taxied back to park.Fatigue. Slept first six hours of 30-hour layover. Attempted to sleep 6 hours prior to alert; was unable to sleep. Release had listed a MEL for Main Cargo Loading." Upon pushback we got EICAS for "MAIN CARGO DOOR." My fatigue combined with expectation bias led me to direct the FO (First Officer) to override the message - override the checklist. The load crew did not fully close the Main Cargo Door. Maintenance reported "all doors closed and locked" prior to push. We started the left engine; taxied to XXL and started the right engine abeam the terminal. After the initial EICAS; we received no other alerts until the cabin altitude alert.I should have pulled the crew together and reviewed the messages. The load team should have properly closed the door. Maintenance should not have reported "doors closed and locked" when they were not. It seems odd that the takeoff configuration check doesn't incorporate doors; maybe it should. I should have been better aware of my degraded state due to fatigue."
Second reporter narrative
Upon climbout we had a cabin pressurization warning at 10;000 ft. The pressurization didn't go to manual until passing 8;000 ft. and we noticed our cabin pressure was the same as our outside altitude. We were able to level off at 12;000 ft. and eventually descend to 10;000 ft. to get rid of the cabin altitude warning. We elected to return to ZZZ since we weren't pressurizing. Our weight was 595;000 lb. With discussion with the crew; we decided to hold and dump fuel. ZZZZ gave us holding instructions and we dumped fuel for 4 minutes to get on max landing weight. We shot the ILS to XXL and the Captain made the landing. We requested priority handling for priority.Fatigue was not a factor in this event for me. I try to always set myself up to get 8 hours of sleep upon showtime. With a XA:00 van I woke up at XW:00 with 7-8 hours of uninterrupted sleep. We had a standard flight plan with a MEL of [the] Main Cargo Loading system. Everything up to pushback was standard and normal. Upon the pushback is where the confusion happened. The ground crew advised us doors were closed [and] they were ready for push. The Maintenance Guy told us all doors were closed and locked. Before pushback we had a Main Cargo Door message. The Captain elected to cancel the message relating to the MEL. With the MEL being Main Cargo Loading system and a caution message of Main Cargo Door; we had an expectation bias it was part of the MEL. After start-up and a takeoff configuration check; nothing seemed out of the ordinary. Pulling up to the gate the ground crew advised us the relief valve on Main Cargo Door was slightly open. We then refueled and proceeded to ZZZ.Expectation bias was the main cause of this event. A confusion of a MEL and what was displayed as a caution message made it seem that both things were related when in fact they weren't. My situational awareness should have been much higher with a better understanding of the MEL. With Maintenance telling us doors were closed and locked we assumed it was related to MEL. We should have slowed down and talked it over better with the crew.
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Source: NASA Aviation Safety Reporting System (public domain). Reports are voluntary submissions and are not verified by NASA.