B-757 pilot crew reported a pressurization failure and diversion to a suitable alternate.
Synopsis
B-757 pilot crew reported a pressurization failure and diversion to a suitable alternate.
Narrative
Operating as Flight ABCD from ZZZ to ZZZ1. The aircraft used was a B757-200 ; which was the same jet that we operated/flew to ZZZ on the same morning. ZZZ is not normally a layover station in the company system. The reason for the layover was the MX (Maintenance) status of the aircraft. During the layover; line maintenance worked through the cause of the AOG status and ultimately replaced a Cabin Pressure Controller.Throughout the layover; both I and the FO reviewed the ongoing notes/work and discussed the progress of MX as well as our concerns that there might be a deeper issue with the aircraft that a non-Hub station would rectify; with the ultimate independent decision that we would accept the aircraft with the previously known MELs (see A/C MX sheet). Although we are not test pilots; we decided to trust the system. If the aircraft has been signed off as airworthy in accordance with all applicable regulations. We discussed that we would monitor the application systems and their performance.For this leg; I was PM. We used Runway XX during VMC conditions. We made a right turn directly to ZZZ [VOR] with an initial climb to 10;000'. We had several frequency changes and altitude clearances to FL230; with a final clearance to our planned cruise altitude of FL340. While climbing from FL230 to FL340; very cognizant of cabin altitude performance. While monitoring system performance after leveling off; the climb rate of the cabin did not stabilize. The indications on the pressurization were increasing cabin altitude; rate of cabin climb of approximately 500/min; and a decreasing cabin differential PSI. We talked that we only had a few minutes before we would be in the same situation as the previous flight and get the CABIN ALT HI Warning(s). Approximately 3 minutes after level off; we did received the CABIN ALT HI warning(s). We donned O2 masks; requested priority handling with ATC; and requested a direct descent to 10;000'. ATC acknowledged our request but could only clear us to 14;000'. Since I was already PM I elected to continue in this role. The FO accomplished a moderately steep descent; being cognizant that there was no reason to make the situation worse by over-stressing the aircraft. During descent; I accomplished the relevant QRH for the CABIN ALT HI. We leveled off at 14;000' for a very short time with a further clearance to 10;000' at which point the CABIN ALT light extinguished. We removed our O2 masks to aid in communication. I continued in the PM role to communicate with ATC and Dispatch. I informed our dispatcher (the same as our previous flight) that we had the same event. He said he understood and asked us where we wanted to go and offered ZZZ2 and ZZZ1. While the FO and I quickly discussed our options; distance to each destination; fuel burn; MX opportunities; etc.; and our attention too focused on the presented destination(s) information; we let the aircraft speed decay to an unacceptable state. We relied on automation to control speed; which the Autothrottle system did not. The FO did a fantastic job with recognition and quickly stabilized the energy state of the aircraft. Once we reviewed the pertinent destination information; we elected that ZZZ2 was not the best option for MX reasons; and my unfamiliarity with ZZZ2 and our Fuel over destination for both ZZZ1 and ZZZ3. We were slightly closer to ZZZ3 than ZZZ1; and we determined that our fuel state would also be higher with ZZZ3 as a destination. We informed ATC that we would like to head directly to ZZZ3. At some point after turning around; we discussed that it would probably be best that I accomplish the landing; considering the problem(s) we have had. The approach (ILS XYL) and landing (RWY XYL) were normal and uneventful. After clearing the runway; we canceled the priority handling. CFR (Crash Fire Rescue) was waiting for us; we taxied to the gate under our own power. CFR followed us for a short distance. Cause: Equipment malfunction/ not operating correctly. The aircraft seems to have some gremlins. Suggestions: Extended MX; investigation
Second reporter narrative
We departed ZZZ off Runway XX. We had flown the plane in from ZZZ1 the previous morning and encountered a loss of cabin pressure with the CABIN ALTITUDE warning. QRH followed and flight continued on to ZZZ at 10;000 ft. Please see previous report for details of flight. The plane had a history of repeated R PACK TEMP EICAS messages. The right pack was still deferred on the release. Maintenance worked on the plane and ultimately removed and replaced the CABIN PRESSURE CONTROL #2 and we accepted the aircraft with the same 2 MELs as the previous flight. The also did a pressure check which passed. We discussed likelihood of occurring again; but felt this might solve the previous flights pressure issue.Nothing to note in our climb to 340 as we monitored cabin pressure alt and cabin rate; especially attentive when we got close to cruise. It seemed normal. Once we hit cruise altitude the cabin rate was still positive (400 to 500 ft per minute). Cabin altitude was at 8;000. Cabin rate was decreasing but didn't return to zero or negative; it remained positive. We discussed that we have only a few minutes before we are going to receive the CABIN ALT warning and CA acknowledged and agreed. Before we could communicate to ATC; we encountered the warning. We donned O2 masks; requested priority handling; and began a decent to a cleared altitude to 14;000 on a heading. We executed the QRH; making an expedited descent. With O2 masks on; no jumpers; and with the previous nights' experience we were expedient but not urgent in our descent as we didn't feel the need to overspeed the aircraft. CABIN ALT was not controllable. Same indications as previous flight CABIN AUTO INOP EICAS came on. At some point we were cleared to 10000 FT. We elected not do the QRH until we got to 10;000 feet for the CABIN AUTO INOP. Once at 10;000 feet we informed Dispatch. The CABIN ALT light was extinguished. The CABIN AUTO INOP EICAS was also extinguished so we did not run QRH. We removed our O2 masks as CABIN ALT decreased to 2000 ft upon reaching 10;000. At this point we were between ZZZ3 and ZZZ1 enroute to ZZZ4. Dispatch asked if what we wanted to do; they asked if needed new numbers for ZZZ2 and ZZZ1. We looked at FOD (Fuel Over Destination) at traveling at 10000 to ZZZ1 and ZZZ3; 10.5 vs 8.0 respectively. ZZZ3 was more conservative as we were closer. Dispatch gave us new numbers for ZZZ3. We elected to turn around to ZZZ3. As we were coordinating; I was PF. We were straight and level at 10000 ft. I noticed I had not selected the local altimeter setting coming through FL180. I selected the local altimeter and altitude showed 10;250. I decided to FLCH (Flight Level Change) to back to 10000 at 250. New numbers came at the printer and I retrieved them off the printer and gave them to the CA. At this time; we noticed our airspeed had dissipated to 175 knots and at this point I added power and recovered back to 250kts at 10000 feet. It was bizarre because ALT CAP and A/T were engaged and speed was set 250. Situation was stabilized at 10000 feet; 250 kts. At this point; we had decided to turn towards ZZZ3. Ultimately our decision was based on better FOD knowing we are traveling at 10000 feet. We briefed for a FLAP 30 ILS to RWY XYL. We swapped the controls. We decided that since we were still a priority A/C the more conservative route would be for the CA to execute the landing. We executed an uneventful landing to XYL. We exited the RWY. Emergency support followed us though no assistance was required. Cause: Plane could not keep adequate pressurization at cruise with only one pack.Suggestions: Nothing to prevent the pressurization issue. In hindsight we could've done a deliberate step climb to see if it would hold adequate pressure at each intermediate level. But that falls into a maintenance check and doesn't set a good precedent.
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Source: NASA Aviation Safety Reporting System (public domain). Reports are voluntary submissions and are not verified by NASA.