B757 Flight Crew reports being dispatched with one engine bleed valve inoperative. At FL340 the left engine bleed valve closes automatically and an emergency is declared. Attempts to reset or use APU air are unsuccessful initially and flight descends to 10000 feet and diverts.
Synopsis
B757 Flight Crew reports being dispatched with one engine bleed valve inoperative. At FL340 the left engine bleed valve closes automatically and an emergency is declared. Attempts to reset or use APU air are unsuccessful initially and flight descends to 10000 feet and diverts.
Narrative
While in operations during pre-flight; we received a call from Dispatch informing us that there was an MEL that deactivated the right engine bleed valve. Told that we were limited to FL350 or below; and could not be dispatched into known icing. After arriving at the aircraft; we realized that we would have only one pack available for use at a time. At one point in the flight; at FL340; we briefly skimmed the tops of some clouds. The temp was -40. As a precaution I turned on the engine anti-ice. We were past the cloud tops in about 10 seconds. The anti-ice was not turned off after we were past the clouds. Much later at FL340; we noticed pressure changes in our ears. Checked the pressurization panel and noticed that the left engine bleed light was on. The First Officer noticed the anti-ice on and turned it off. He recycled the left bleed switch; it did not reset. APU running; we tried to pressurize with it. We were above FL200 and it had some effect and appeared to slow the cabin climb. During all of this we got clearance to FL240 and were descending. I declared an emergency and got clearance to 10;000 ft. The First Officer tried switching packs initially; no help. Tried resetting bleed again; no help. As we got lower First Officer again switched packs and again reset left bleed and then gained control of pressure. We leveled at 10;000 feet. The cabin got no higher than 9500 feet; no problem with the passengers all very calm. The masks did not deploy. I briefed the Flight Attendants; did not require a cabin prep. I talked to the passengers and assured them that it was only a pressure problem and that the aircraft was running normal. With control of pressure; Dispatch decided to send us to ZZZ for ease of passenger connections. We continued at 10;000 and landed with no further problems.
Second reporter narrative
We were dispatched with the right engine bleed valve inoperative. At altitude the left engine bleed valve closed and left packed tripped. Our ears popped; we noticed the left engine bleed and pack trip off lights; and I asked for the APU. It was already on so even though we were at 340 I reconfigured to the APU air while the Captain got lower and started down. Initially the left pack came back on then tripped again. I switched too the right pack; same thing. The cabin altitude climb slowed when the APU was feeding the pack. At FL240 I noticed the engine anti-ice on and turned them off. No effect. Eventually as we got low enough; FL180; the pack worked fine on APU air. When we reached 12k I switched back to the left eng bleed; which worked until landing at our divert airport.
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Source: NASA Aviation Safety Reporting System (public domain). Reports are voluntary submissions and are not verified by NASA.