2023-01 · NASA ASRS report 1968153
Flight Crew reported loss of Cabin Pressure Control in climb. The Cabin Altitude climbed above 12;500 ft. and the O2 masks were deployed. The Flight Crew requested priority handling and immediately descended. The Flight Crew preformed an air turn back and made an overweight landing at departure airport.
As we were climbing above FL150; we noticed the Cabin Altitude climbing at 700 ft./minute and at that moment the Cabin was passing through 9;500 ft. After requesting priority handling; we followed the CABIN ALTITUDE procedure and deployed the O2 to the Passengers. I believe I asked for a descent to the lowest safe altitude and were cleared to 12;000 ft. We were not far from ZZZZ so I knew we would not be held above 10;000 ft. for very long due to the mountains in the area. I asked the FB (First Officer B) to run a non-normal overweight landing assessment.As I was completing the overweight landing checklist; the checklist indicated we needed to do a flaps 25 landing. However; the landing assessment indicated we needed to do a flaps 20 landing. This is where the confusion for me and the FO started....Both of us firmly believed that all overweight landings were done at flaps 20 yet the checklist indicated flaps 25.... Our belief was supported by the landing assessment completed by the FB from the 'non-normal' section of the landing app as I had instructed him to do.Not having any resolution with the conflicting information; I decided to complete the approach using flaps 20 since it provided a better margin of safety if a go around would have been necessary with one or two engines operating. This airport has terrain in proximity and the runway in use has an 'Engine failure Procedure' missed approach. Considering all of this; I was satisfied to continue the approach and landing at flaps 20...We held over the airport for a couple turns to complete our checklists then commenced our approach to XXR. Once we cleared the runway; we stopped on the inner taxiway so the Fire Chief could give us his report. Our Company Mechanic was the liaison to communicate with the Fire Chief...He used turbo fans to cool the gear then offered to hose off the landing gear with water. I did not know if water was appropriate with the gear as hot as it was so I asked Local Maintenance and Maintenance in ZZZ through the Sat-phone if I should give the Fire Chief the go-ahead. They offered no guidance. So I agreed with the Chief and they commenced with watering the hot landing gear down.I asked the FB to refer to the Brake Cooling chart in the QRH to get a time for cooling which was about 85 minutes. While we sat there five tires flattened out.Coordination with our Maintenance; Operations and Dispatch in ZZZ all worked well to see to our needs. Air stairs were provided along with busses to transport everyone to the terminal. I held everyone on the plane until the gear temperatures were in a safe range... Some of the difficulties with this event included communications with the Controller I was talking to initially at the start of the event. Her English was fine but the quality of her radio was horrible. I remember asking her a half a dozen times to repeat her clearance because we couldn't understand her. Day 0. XA15 ZAfter I submitted this report; the review page had errors.. The nose number should be Aircraft X. I don't know the tail number offhand.. The aircraft type is 777-300.Day 0 0XA21 ZThe date of the event... in Zulu time was Day 0.With regard to the pressurization issue; Maintenance will make the determination as to why it happened. I flew this aircraft a week earlier. When I showed up to the aircraft to begin that sequence; the cockpit was filled with Mechanics trying to clear three status messages. I believe they were for both Outflow Valves and one for Cabin Altitude. Regarding the procedures for the overweight landing... Having time to review the events; the biggest distraction for my decision making was my preconceived notion that flaps 20 is the setting for an overweight landing. My First Officer (FO) had the same perspective. Now having reviewed the procedure; I see that the flaps 20 landing is tied to a single engine landing and not a two engine landing. During our annual training we go through this exercise and it is always tied to an engine failure. I think this is why my convection for insisting on using flaps 20 was so strong. Adding to that; I asked the FB for a non-normal landing assessment which is the; Flaps 20 landing (overweight; etc.) failure.... Located in the non-normal category in the landing app. This also supported my decision for a flaps 20 landing...It is obvious now that it was the wrong place to go for that information. Using the Normal landing assessment for this abnormal situation was the place to go. Reviewing all of this in the aftermath of this event; it is obvious that flaps 25 was the appropriate flap setting.Some of the abnormal procedures as they are written are difficult to understand. In the heat of the moment; there were a couple of decision questions that I couldn't understand. Now after a careful review; I have a better understanding of this procedure but in the heat of the moment it was very confusing. Suggestions:Complete understanding of the checklist procedures.
This was a night takeoff out of ZZZZ and I was the FB (First Officer B) on this flight. Going into this flight we were advised that we needed to do an inflight check on the PACKs. The Captain talked to Dispatch to verify what we needed to do to accomplish the checks. The Captain mentioned that we needed to wait to chime the Flight Attendants (FAs) at 15;000 ft. due to mountainous terrain before they were let up to begin service. After the chime was made the First Officer (FO) noticed the Cabin Altitude was not scheduling appropriately; I think it was approximately around 9;200 ft. We all confirmed this was the case; we were still climbing along with the Cabin Altitude. When we hit 10;000 ft. on the Cabin Altitude we received the CABIN ALTITUDE Warning. The Alert was acknowledged; at that point I stated that we needed to get our oxygen mask on; which we all did. The Captain assigned the FO flying duties (the FO was already the pilot flying) and the Captain pulled out the QRC and started the CABIN ALTITUDE checklist from the card. We were still in the climb and needed to level off. The Captain asked if we all agreed if we were in an urgent situation and we did. The Captain [requested priority handling] and let ATC know that we needed to return to ZZZZ and level off and descend back down. We ultimately leveled off at FL210 but took some time to get back down below 9;000 ft. During this time the Captain had pushed the PASS OXYGEN switch since the Cabin Pressurization continued to climb (I think it topped out at approximately 12;600 ft.). During this time the Captain had me call the #1 FA and advise them that we lost our Cabin Pressurization and will be coming back to ZZZZ and doing a Precautionary Landing and to expect the fire trucks to be around. We would call them back with more information once we had time. We worked with ATC to get us to a minimum safe altitude and set up for a hold so we can run through the checklist. The captain asked me to run the landing distance for our weight which was approximately 638;000 pounds and an overweight landing. I proceeded to use the normal landing distance portion of the app and gave the weights the landing distance for the different brake configurations 3 through auto max; with a 5 - wet/good braking action and flaps 25 and a Pressure Altitude of 3;000 ft. After giving this information the Captain advised we needed to use Flaps 20 and I believe I said that is not an option and I was then directed to use the non-normal portion of the landing app. I pulled the information for FLAPS 20 Landing (overweight) and provided the landing distance with the before mentioned parameters. Going through the overweight landing checklist we all agreed that it would be a VREF 30 + additives (wind and gusts; 5 knots minimum) is above 170 kts. At that point VREF 25 was selected but still planned to use FLAPS 20 for landing. When doing the landing checklist; I mentioned that we will not be able to complete the checklist (unless we were to override; which I did not say) if we had VREF 25 and flaps set at 20. Since the plan was to land Flaps 20 it was then set to VREF 20. The FO made a nice landing using FLAPS 20 and auto max brakes and rolled out; while passing controls to the Captain around 60 kts; all the way to Taxiway X; which was 10;685 ft. down the runway.We started our taxi back to the gate and noticed our brake temps were hot. At this point the Captain stopped the aircraft; we talked to Ground and let them know we could not move; and the parking brake was not set. The Captain had us reference the QRH for the Recommended Brake Cooling Schedule and it appeared it would take approximately 85 minutes to cool. During this time the Fire Chief was already present; and they had checked our brakes; which were indeed hot. At this point the Fire Chief determined that they needed to cool the brakes with water and the team started to cool all the brakes with water. Eventually they were able to hook up a tow to ouraircraft and chock the wheels; so the captain and FO were no longer having to hold the brakes manually. Ultimately five of the tires' plugs opened to release the pressure in the tires. Since we were not able to taxi the Captain worked with Dispatch; since it was a little bit of a challenge due to the language differences; to get stairs; a lift for the wheelchairs; and busses so the Passengers can get off the aircraft and back to the terminal.Two more things to add about the Flight Attendants; they did a really good job of waiting for us to provide them with information vice calling us while we were in flight. Also; the Captain did a nice job trying to slow everything down; assign task; and keep all players in the loop.Cause: The loss of cabin altitude.Deciding to use flaps 20 and the use of the non-normal landing app and using flaps 20 overweight landing; vice just using the normal landing app and selecting flaps 25 or 30 if that is what is called for.Would help to have and overweight landing on the non-normal side of the landing app. Overweight landing is a non-normal and does place us in an emergency situation. It could give you the same answer as the normal side of the landing app; but maybe not cause any confusion. I now remember in training they had us pull up the non-normal side and note that there was not an overweight option on the landing app.Suggestions: If the cabin altitude were to hold and schedule correctly that would help. Maybe add overweight landing to the non-normal side of the landing app too.
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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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