Narrative:

This aircraft had a new revision of the ACARS software used to create manifests and calculate weight and balance. The old system would auto-populate the current fuel on board and add that to the zero fuel weight to get the proper gross takeoff weight. The new system will still show the current fuel on board; but [instead] does the same calculation using the release fuel and subtracts the taxi out fuel.we were over fueled by just over 1;200 pounds and did not notice this discrepancy when sending for the takeoff speeds and engine performance numbers. When the manifest was presented and the numbers entered; we had calculated takeoff data for a weight of 78;801; the actual takeoff weight was closer to 80;000 pounds. We were still within all of our restrictions but the flex data de-rated the takeoff thrust for the lighter weight and the cg was likely off. This resulted in an anemic takeoff and a feeling of being out of trim on rotation. Once reaching cruise we looked at the takeoff manifest and tried to calculate where the numbers came from and realized that the new system does not use current fuel on board; but [instead] uses the release numbers and allows the pilots to manually input a takeoff fuel number. This was not specified in the documentation put out to pilots; except in a single voice-over on a video. Certainly inadequate warning of such a significant change.the cause of this event is a change in the way our computer calculates our takeoff numbers from the way it previously did with little to no warning to the pilots of this major change in the operation of an integral calculation to the safety of our daily operation.suggestions: immediately provide an emailed alert bulletin to the pilots pointing out this change; and revise the new software to use the fuel on board for takeoff calculations and not the release fuel. Often pilots will add fuel; fueler will do it without a pilot request; or a crew will take an aircraft that was fueled for a different flight and re-tasked with more fuel than is on the release. There is no reason for the takeoff manifest to use a hypothetical number when it has access to the actual number. You may want to provide pilots with the ability to change that number if we need to for longer/shorter than expected taxi or many other reasons; but the default should be fuel on board -taxi out; not release fuel - taxi out.

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Original NASA ASRS Text

Title: EMB-175 flight crew reported degraded performance on takeoff after having the incorrect fuel on board loaded in the FMS; which they attributed to an FMS software revision.

Narrative: This aircraft had a new revision of the ACARS software used to create manifests and calculate weight and balance. The old system would auto-populate the current fuel on board and add that to the zero fuel weight to get the proper gross takeoff weight. The new system will still show the current fuel on board; but [instead] does the same calculation using the release fuel and subtracts the taxi out fuel.We were over fueled by just over 1;200 LBS and did not notice this discrepancy when sending for the takeoff speeds and engine performance numbers. When the manifest was presented and the numbers entered; we had calculated takeoff data for a weight of 78;801; the actual takeoff weight was closer to 80;000 LBS. We were still within all of our restrictions but the flex data de-rated the takeoff thrust for the lighter weight and the CG was likely off. This resulted in an anemic takeoff and a feeling of being out of trim on rotation. Once reaching cruise we looked at the takeoff manifest and tried to calculate where the numbers came from and realized that the new system does not use current Fuel On Board; but [instead] uses the release numbers and allows the pilots to manually input a takeoff fuel number. This was not specified in the documentation put out to pilots; except in a single voice-over on a video. Certainly inadequate warning of such a significant change.The cause of this event is a change in the way our computer calculates our takeoff numbers from the way it previously did with little to no warning to the pilots of this major change in the operation of an integral calculation to the safety of our daily operation.Suggestions: Immediately provide an emailed alert bulletin to the pilots pointing out this change; and revise the new software to use the fuel on board for takeoff calculations and not the release fuel. Often pilots will add fuel; fueler will do it without a pilot request; or a crew will take an aircraft that was fueled for a different flight and re-tasked with more fuel than is on the release. There is NO reason for the takeoff manifest to use a hypothetical number when it has access to the actual number. You may want to provide pilots with the ability to change that number if we need to for longer/shorter than expected taxi or many other reasons; but the default should be Fuel On Board -Taxi Out; not Release Fuel - Taxi Out.

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.