Narrative:

Climbing to our cruise altitude of FL240 (single pack operations; MEL 21-51-01) flight crew received a left bleed duct warning message for approximately 20 seconds then the message extinguished and the left bleed duct caution message appeared. Captain; flying pilot; requested to reference the QRH. He notified ATC that we were resolving an abnormal situation and that we would like to level off at FL200 until our situation was resolved. ATC then granted the request. First officer; non flying pilot; ran the QRH and was able to correct the abnormal. Captain then set the pack temperature within 5 degrees of actual temperature (to protect the pack). After several minutes it appeared that all was fine; so I advised ATC that we would like to climb to our final altitude (FL240). As we began to climb to FL240 we again; received a left bleed duct warning message for approximately 20 seconds then the message extinguished and the left bleed duct caution message appeared. At this time the cabin altitude was climbing. Captain declared an emergency with ATC and requested an altitude of 10;000FT. ATC granted our request and cleared us down to 11;000FT. While descending; first officer attempted to correct the problem with use of the QRH but was unsuccessful. We then advised ATC that we would like to divert to ZZZ (5 minutes flying time ahead of us) and clearance was granted. Flight crew then completed QRH procedures; checklists and communicated situation to flight attendants. We then attempted to communicate with dispatch via commercial radio but were unsuccessful. We then asked ATC to relay our intentions to dispatch and they said they would. Flight landed in ZZZ without incident and taxied to the gate under its own power and deplaned normally. Upon post flight duties; captain and mechanic determined that incorrect MEL procedure was referenced; which led to incorrect pack being utilized. As it was written; the MEL seemed to refer to 21-51-01; but in fact referred to 21-52-01. Because of this; the pack that was inoperative was actually the pack utilized for the flight. During the descent; in order to attempt to retain some pressurization within the cabin; the non-MEL'd pack was selected; but it also failed and was unable to remain on-line. We descended rapidly enough that we were below 10;000' before the cabin reached 10;000'; and none of the passengers even realized that we had lost pressure; other than the fact that it became very hot. The high ambient temperatures compelled us to land quickly; as cabin temperatures quickly rose to 37+ degrees C. Contributing factors: the MEL was written in a manner that described an inoperative valve; and the incorrect MEL referenced that valve; and this crew followed that MEL procedure which included configuring the airplane packs; which we did; albeit incorrectly. Also contributing were the extremely high ambient temperatures and single pack operations. Corrective actions: standardized verbiage on MEL's; and mechanics use this verbiage when transcribing to the MEL book. Also; on dispatch release; if MEL would clearly state which pack was inoperative (left or right); instead of generic verbiage. MEL numbers were only 1 digit off; and crew didn't catch that; but instead saw written word that matched the writeup and utilized that procedure; leading to incorrect pack being utilized for flight.

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Original NASA ASRS Text

Title: A CRJ-900 crew misread an air conditioning MEL and disabled an operational pack. The flight departed using a faulty pack which ultimately faulted. The crew descended and diverted to an enroute airport for repairs where the error was discovered.

Narrative: Climbing to our cruise altitude of FL240 (Single Pack Operations; MEL 21-51-01) Flight Crew received a L BLEED DUCT warning message for approximately 20 seconds then the message extinguished and the L BLEED DUCT caution message appeared. Captain; flying pilot; requested to reference the QRH. He notified ATC that we were resolving an abnormal situation and that we would like to level off at FL200 until our situation was resolved. ATC then granted the request. First Officer; non flying pilot; ran the QRH and was able to correct the abnormal. Captain then set the pack temperature within 5 degrees of actual temperature (To Protect The Pack). After several minutes it appeared that all was fine; so I advised ATC that we would like to climb to our final altitude (FL240). As we began to climb to FL240 we again; received a L BLEED DUCT warning message for approximately 20 seconds then the message extinguished and the L BLEED DUCT caution message appeared. At this time the cabin altitude was climbing. Captain declared an emergency with ATC and requested an altitude of 10;000FT. ATC granted our request and cleared us down to 11;000FT. While descending; First Officer attempted to correct the problem with use of the QRH but was unsuccessful. We then advised ATC that we would like to divert to ZZZ (5 minutes flying time ahead of us) and clearance was granted. Flight crew then completed QRH procedures; checklists and communicated situation to Flight Attendants. We then attempted to communicate with Dispatch via commercial radio but were unsuccessful. We then asked ATC to relay our intentions to Dispatch and they said they would. Flight landed in ZZZ without incident and taxied to the gate under its own power and deplaned normally. Upon post flight duties; Captain and Mechanic determined that incorrect MEL procedure was referenced; which led to incorrect PACK being utilized. As it was written; the MEL seemed to refer to 21-51-01; but in fact referred to 21-52-01. Because of this; the PACK that was INOP was actually the PACK utilized for the flight. During the descent; in order to attempt to retain some pressurization within the cabin; the non-MEL'd PACK was selected; but it also failed and was unable to remain on-line. We descended rapidly enough that we were below 10;000' before the cabin reached 10;000'; and none of the passengers even realized that we had lost pressure; other than the fact that it became very hot. The high ambient temperatures compelled us to land quickly; as cabin temperatures quickly rose to 37+ degrees C. Contributing Factors: The MEL was written in a manner that described an INOP valve; and the incorrect MEL referenced that valve; and this crew followed that MEL procedure which included configuring the airplane PACKS; which we did; albeit incorrectly. Also contributing were the extremely high ambient temperatures and SINGLE PACK operations. Corrective actions: Standardized verbiage on MEL's; and Mechanics use this verbiage when transcribing to the MEL book. Also; on dispatch release; if MEL would clearly state which PACK was INOP (Left or Right); instead of generic verbiage. MEL numbers were only 1 digit off; and crew didn't catch that; but instead saw written word that matched the writeup and utilized that procedure; leading to incorrect PACK being utilized for flight.

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.