Narrative:

At approximately 20;000 feet during our climb we got a master caution cabin altitude above 10;000 feet. We started a descent immediately (requested and received clearance from ATC - no emergency declared) and as soon as we started down we noticed that pack #1 was off - we reset it and it came back on immediately; and the cabin started to descend - we leveled off at approximately 15;000 feet with a cabin altitude of about 9800 feet and descending. We then slowly climbed back to our cruise altitude of 24;000 feet. We continued with no further problems. Pack #2 was on MEL as well as the ram air valve. At some point during the climb the #1 pack tripped off. What I find interesting to safety is the lack of any real notification that the pack #1 had tripped off and there was now no pack operating. There was no master/caution or chime - the only notification we got was a change in the already present blue EICAS message which I think was something like 'pack 2 valve closed' to 'pack 1-2 valve closed.' the '1-' was the only change and neither of us noticed it - it should have flashed; and maybe it did for a few seconds - I don't know because neither of us noticed it. We were both awake and alert; climbing out and talking like it was any other flight - we just did not see the change in the EICAS message nor did we notice any difference in the noise level in the cockpit. On the ground a pack coming on or off is obvious; but not climbing out with all the air noise in the cockpit. The system software should be modified so that a pack tripping off when it is the only pack operating should at least get a master caution and single chime if nothing else. The current notification was not enough for us to notice; and I believe that very few flight crews would have noticed that - only if they just happened to be looking at it when it happened would they notice the flashing blue EICAS message; and I think it only flashes for 4 or 5 seconds; otherwise the simple addition of '1-' to the message is all but unnoticeable.

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Original NASA ASRS Text

Title: EMB145 Captain experiences a cabin altitude warning at FL200 after being dispatched with one pack inoperative. During descent and trouble shooting it is discovered that the second pack had tripped of at some time during the climb. After resetting the tripped pack the crew climbs to FL240 and continues to destination.

Narrative: At approximately 20;000 feet during our climb we got a master caution Cabin Altitude above 10;000 feet. We started a descent immediately (requested and received clearance from ATC - no emergency declared) and as soon as we started down we noticed that pack #1 was off - we reset it and it came back on immediately; and the cabin started to descend - we leveled off at approximately 15;000 feet with a cabin altitude of about 9800 feet and descending. We then slowly climbed back to our cruise altitude of 24;000 feet. We continued with no further problems. Pack #2 was on MEL as well as the Ram Air Valve. At some point during the climb the #1 pack tripped off. What I find interesting to safety is the lack of any real notification that the pack #1 had tripped off and there was now no pack operating. There was no Master/Caution or Chime - the only notification we got was a change in the already present blue EICAS message which I think was something like 'PACK 2 Valve closed' to 'PACK 1-2 Valve closed.' The '1-' was the only change and neither of us noticed it - it should have flashed; and maybe it did for a few seconds - I don't know because neither of us noticed it. We were both awake and alert; climbing out and talking like it was any other flight - we just did not see the change in the EICAS message nor did we notice any difference in the noise level in the cockpit. On the ground a pack coming on or off is obvious; but not climbing out with all the air noise in the cockpit. The system software should be modified so that a pack tripping off when it is the only pack operating should at least get a master caution and single chime if nothing else. The current notification was not enough for us to notice; and I believe that very few flight crews would have noticed that - only if they just happened to be looking at it when it happened would they notice the flashing blue EICAS message; and I think it only flashes for 4 or 5 seconds; otherwise the simple addition of '1-' to the message is all but unnoticeable.

Data retrieved from NASA's ASRS site as of April 2012 and automatically converted to unabbreviated mixed upper/lowercase text. This report is for informational purposes with no guarantee of accuracy. See NASA's ASRS site for official report.