Narrative:

We had returned to gate in ZZZ with a right pack fault status message. I talked to maintenance control and dispatch during the process to get the discrepancy written-up; the MEL documented; get a new IFR dispatch release to us; and get more fuel. Dispatch was told of the exact nature of the MEL. I was told a new release with appropriate performance would be sent. We duly received the new release which stated in the remarks on the flight release; 'add MEL 21-51-4B/ aircraft restricted to fl 310 new performance'. We noted this and made sure all other items were checked as per the MEL. We even noted that as per the MEL; this was new performance based on this MEL. As all seemed in order; we departed. Well into the flight; dispatch called us and told us to amend the landing weight to reflect the one pack inoperative; which we did. As we had [already] taken off; amending the takeoff weight was of no value. Dispatch did not ask their computer for performance based on one pack inoperative; as far as I can determine. I did not pick up the lack of a remark on the maintenance release that one pack was inoperative; nor that the maximum landing weight (mldw) was not based on one pack inoperative. I thought the flight release remark about new performance meant that all performance issues had been taken care of in the new packet. I had no easy way to tell what specific defaults would be changed so did not know what to look for. One has to trust dispatch that the data sent is correct. Though I do know now! The MEL does not specifically tell you that performance has to take into account one pack inoperative. It just talks in more general terms that inoperative environmental [air conditioning] components need to be accounted for. It seemed counter intuitive that one pack inoperative would affect adversely landing and takeoff weights. I think that the MEL should be very specific and say not only how the release would be affected but what to check for in the release; such as; check release for 'remarks one pack inoperative bleeds.'

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Original NASA ASRS Text

Title: A CRJ-700 returns to the gate with a right Pack Fault Status message. Right Pack was deferred inoperative under MEL 21-51; a new Release was issued and aircraft departs. Dispatch later notifies Flight Crew their New Performance Release was not based on one Pack inoperative and Crew would have to amend their Takeoff and Landing Weights.

Narrative: We had returned to gate in ZZZ with a right Pack Fault Status message. I talked to Maintenance Control and Dispatch during the process to get the discrepancy Written-up; the MEL documented; get a new IFR Dispatch Release to us; and get more fuel. Dispatch was told of the exact nature of the MEL. I was told a new Release with appropriate Performance would be sent. We duly received the new Release which stated in the Remarks on the Flight Release; 'add MEL 21-51-4B/ Aircraft restricted to FL 310 New Performance'. We noted this and made sure all other items were checked as per the MEL. We even noted that as per the MEL; this was New Performance based on this MEL. As all seemed in order; we departed. Well into the flight; Dispatch called us and told us to amend the landing weight to reflect the one Pack inoperative; which we did. As we had [already] taken off; amending the Takeoff Weight was of no value. Dispatch did not ask their computer for Performance based on one Pack inoperative; as far as I can determine. I did not pick up the lack of a Remark on the Maintenance Release that one pack was inoperative; nor that the Maximum Landing Weight (MLDW) was not based on one Pack inoperative. I thought the Flight Release Remark about New Performance meant that all performance issues had been taken care of in the new packet. I had no easy way to tell what specific defaults would be changed so did not know what to look for. One has to trust Dispatch that the data sent is correct. Though I do know now! The MEL does not specifically tell you that Performance has to take into account one Pack inoperative. It just talks in more general terms that inoperative Environmental [air conditioning] components need to be accounted for. It seemed counter intuitive that one Pack inoperative would affect adversely Landing and Takeoff Weights. I think that the MEL should be very specific and say not only how the Release would be affected but what to check for in the Release; such as; check Release for 'Remarks ONE PACK INOPERATIVE BLEEDS.'

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.