Narrative:

The captain initially called maintenance control and advised them of an issue with computing a flaps 1 takeoff. The call was transferred to me; and I launched the flight planning tool to input the data so I could see for myself what the situation was. With the current load of 60 passengers; 50 carry on bags; and 2 heavies; the flight planning tool data came back and indicated the aircraft was approximately 2;000 over max takeoff weight. The first flight release did not show a weight restriction with the planned load. The captain and I speculate that the reason for the weight restriction was due to a rapid temperature rise along with a rapid decrease in station pressure. The flight was planned to avoid adverse weather over the midwest and the aircraft was restricted to FL310 due to an inoperable air conditioning pack. The captain went back to the gate to unload payload in order to meet takeoff requirements under the new conditions. During this time I was in constant communication with the captain to determine what payload we could take. Operations indicated that they did not want to remove people; and to remove bags. I determined under the current conditions we could take 54 people and 0 bags. A short while later the captain told me that operations told him there would only be 24 passengers and 20 bags on the flight. With 24 people and 20 bags there was no further takeoff weight issue. I am unaware of the specifics regarding the inability to compute a flaps 1 takeoff with ACARS performance data during the beginning of this situation; or what indications the crew received that initially showed the requirement to burn 400 pounds of fuel before departure. Bottom line is there was a gross difference between the calculated performance during the planning stages; and the actual performance capability at the time of takeoff. Previously flights have been computed that were planned with alternates and no 'alternate burn' found on the fuel summary; flights will occasionally 'drop out' or reset; and there are other instances when other categories of fuel; such as taxi fuel show zero. I suggest each dispatcher and flight crew look over every aspect of every release with intense scrutiny prior to departure due to the intermittent reliability of our planning software.

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Original NASA ASRS Text

Title: A Dispatcher reported that an air carrier crew could not calculate Flaps 1 takeoff data with the current passenger; baggage; and out side air temperature at ABQ. After returning to gate the load planning software was found to have some errors enabling previous flights to depart with various load inaccuracies.

Narrative: The Captain initially called Maintenance Control and advised them of an issue with computing a Flaps 1 takeoff. The call was transferred to me; and I launched the Flight Planning tool to input the data so I could see for myself what the situation was. With the current load of 60 passengers; 50 carry on bags; and 2 heavies; the flight planning tool data came back and indicated the aircraft was approximately 2;000 over max takeoff weight. The first flight release did not show a weight restriction with the planned load. The Captain and I speculate that the reason for the weight restriction was due to a rapid temperature rise along with a rapid decrease in station pressure. The flight was planned to avoid adverse weather over the Midwest and the aircraft was restricted to FL310 due to an inoperable air conditioning pack. The Captain went back to the gate to unload payload in order to meet takeoff requirements under the new conditions. During this time I was in constant communication with the Captain to determine what payload we could take. Operations indicated that they did not want to remove people; and to remove bags. I determined under the current conditions we could take 54 people and 0 bags. A short while later the Captain told me that operations told him there would only be 24 passengers and 20 bags on the flight. With 24 people and 20 bags there was no further takeoff weight issue. I am unaware of the specifics regarding the inability to compute a Flaps 1 takeoff with ACARS performance data during the beginning of this situation; or what indications the crew received that initially showed the requirement to burn 400 LBS of fuel before departure. Bottom line is there was a gross difference between the calculated performance during the planning stages; and the actual performance capability at the time of takeoff. Previously flights have been computed that were planned with alternates and no 'alternate burn' found on the fuel summary; flights will occasionally 'drop out' or reset; and there are other instances when other categories of fuel; such as taxi fuel show zero. I suggest each dispatcher and flight crew look over every aspect of every release with intense scrutiny prior to departure due to the intermittent reliability of our planning software.

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.