Narrative:

We had been sitting at ZZZ for quite a while waiting out an ATC delay. When we started boarding; I noticed that our left pack had turned off with no associated caution messages. I selected the left pack switch to off and then back on and the pack turned back on. Shortly thereafter though; we heard a whirling sound and the pack temperature rose taking the pack offline with a little puff of smoke from our vents and a 'hot' smell. Meanwhile we were issued a further delay of 2 1/2 hours so we deplaned and I contacted maintenance and dispatch to get the pack deferred and issue a new release. While we were in the process of the deferral; ATC called and said that we could go when we were ready so we boarded up again; got some additional fuel for the lower cruising altitude and then departed. Prior to the departure; the first officer (first officer) and I reviewed the MEL TR associated to the deferral and the special procedure for transferring bleeds from the APU to the engine. In the TR there is a requirement to reduce the thrust to 60% N1 prior to transferring bleeds so we made the decision to delay the bleed swap until we were clear of the terrain in the area. The only requirement of the TR is that it must be completed prior to 15;000 feet. Around 5-6;000 we transferred the bleeds per the TR with no issues. As we were passing through around 20;000 feet I went on to the PA to turn off the seat belt sign. As I was talking; I noticed that the airflow from my vent was gone. I looked at the environmental control system (ecs) page and noticed that the right pack was off; but there were no caution messages as to why the pack went offline. We began a rapid descent and [advised] ATC. We were issued a clearance to 10;000. I transferred controls to the first officer and made a PA announcement to the passengers. When I came back; I made the mistake of going to the QRH to try to figure out what was going on with the pack instead of referring to the qrc for emergency descent. After we reached 10;000 we turned around back to ZZZ and started the APU. Since there were no caution messages associated with the pack going offline; I made the decision to try the pack using the APU bleed air. It turned on and worked normally so we decided that since we had pressurization and air conditioning that we would hold for a while to burn off some fuel because we were significantly over max landing weight. After arriving at the gate and during the debrief we identified that we should have run the qrc which would have included dropping the passenger O2 masks. The root cause was not adhering to the new SOP of using the qrc first. The confusion of the pack going off with no apparent reason distracted my attention to the pack issue instead of the descent.for me; I'm going to make it an important part of my future IOE trips to get into the qrc with students and run through some scenarios to become more familiar with the items on the list as well as trying to incorporate it into my daily thought process.

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Original NASA ASRS Text

Title: The flight crew of a Bombardier CRJ-200 reported when in climb with one pack deferred; when the other pack failed; they went to the QRH to troubleshoot and neglected to proceed per the QRC for emergency descent.

Narrative: We had been sitting at ZZZ for quite a while waiting out an ATC delay. When we started boarding; I noticed that our left pack had turned off with no associated caution messages. I selected the L PACK switch to off and then back on and the pack turned back on. Shortly thereafter though; we heard a whirling sound and the pack temperature rose taking the pack offline with a little puff of smoke from our vents and a 'hot' smell. Meanwhile we were issued a further delay of 2 1/2 hours so we deplaned and I contacted maintenance and dispatch to get the pack deferred and issue a new release. While we were in the process of the deferral; ATC called and said that we could go when we were ready so we boarded up again; got some additional fuel for the lower cruising altitude and then departed. Prior to the departure; the First Officer (FO) and I reviewed the MEL TR associated to the deferral and the special procedure for transferring bleeds from the APU to the engine. In the TR there is a requirement to reduce the thrust to 60% N1 prior to transferring bleeds so we made the decision to delay the bleed swap until we were clear of the terrain in the area. The only requirement of the TR is that it must be completed prior to 15;000 feet. Around 5-6;000 we transferred the bleeds per the TR with no issues. As we were passing through around 20;000 feet I went on to the PA to turn off the seat belt sign. As I was talking; I noticed that the airflow from my vent was gone. I looked at the Environmental Control System (ECS) page and noticed that the R PACK was off; but there were no caution messages as to why the pack went offline. We began a rapid descent and [advised] ATC. We were issued a clearance to 10;000. I transferred controls to the FO and made a PA announcement to the passengers. When I came back; I made the mistake of going to the QRH to try to figure out what was going on with the pack instead of referring to the QRC for emergency descent. After we reached 10;000 we turned around back to ZZZ and started the APU. Since there were no caution messages associated with the pack going offline; I made the decision to try the pack using the APU bleed air. It turned on and worked normally so we decided that since we had pressurization and air conditioning that we would hold for a while to burn off some fuel because we were significantly over max landing weight. After arriving at the gate and during the debrief we identified that we should have run the QRC which would have included dropping the passenger O2 masks. The root cause was not adhering to the new SOP of using the QRC first. The confusion of the pack going off with no apparent reason distracted my attention to the pack issue instead of the descent.For me; I'm going to make it an important part of my future IOE trips to get into the QRC with students and run through some scenarios to become more familiar with the items on the list as well as trying to incorporate it into my daily thought process.

Data retrieved from NASA's ASRS site 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.