Narrative:

The event began with the ACARS takeoff manifest. I noticed right away that the new ACARS - rev M had been implemented as referenced by our fuel on board (fob) and efb training slides. I entered the data the same as I had previous to this revision; expecting the system to automatically use fob minus taxi-out; to calculate our to (takeoff) fuel; as it had prior to the revision. Rev M defaults to using release fuel minus taxi-out to calculate to fuel. This subtle change resulted; on this particular flight; in us entering takeoff performance numbers for a takeoff weight approximately 500 pounds under our actual weight; due to the fact that we had been fueled approximately 500 pounds over release fuel. We failed to catch the change in the software; now requiring us to manually input the additional fuel weight and departed with the degraded takeoff performance data. We did not realize the error until halfway through the next leg of our trip; later in the day; after departing once again with inaccurate takeoff performance numbers. This time the error was greater and caught our attention during cruise fuel cross referencing.the cause of this event was the new revision implementation and our complacency in the previous software automatically using fob to calculate to fuel. The ACARS rev M training videos only briefly describe this change and do not highlight the potential threat to takeoff performance any time fob is greater than release fuel.I believe this situation and potential threat warrants either a change in the software to default back to using fob to calculate to fuel automatically; or a bulletin alerting crews to the potential danger of not manually inputting to fuel and departing with degraded takeoff performance numbers.

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Original NASA ASRS Text

Title: EMB-175 First Officer reported a takeoff with incorrect performance numbers attributed in part to a new ACARS software revision.

Narrative: The event began with the ACARS takeoff manifest. I noticed right away that the new ACARS - REV M had been implemented as referenced by our Fuel On Board (FOB) and EFB training slides. I entered the data the same as I had previous to this revision; expecting the system to automatically use FOB minus taxi-out; to calculate our TO (Takeoff) fuel; as it had prior to the revision. REV M defaults to using release fuel minus taxi-out to calculate TO fuel. This subtle change resulted; on this particular flight; in us entering takeoff performance numbers for a takeoff weight approximately 500 LBS under our actual weight; due to the fact that we had been fueled approximately 500 LBS over release fuel. We failed to catch the change in the software; now requiring us to manually input the additional fuel weight and departed with the degraded takeoff performance data. We did not realize the error until halfway through the next leg of our trip; later in the day; after departing once again with inaccurate takeoff performance numbers. This time the error was greater and caught our attention during cruise fuel cross referencing.The cause of this event was the new revision implementation and our complacency in the previous software automatically using FOB to calculate TO fuel. The ACARS REV M training videos only briefly describe this change and do not highlight the potential threat to takeoff performance any time FOB is greater than release fuel.I believe this situation and potential threat warrants either a change in the software to default back to using FOB to calculate TO fuel automatically; or a bulletin alerting crews to the potential danger of not manually inputting TO fuel and departing with degraded takeoff performance numbers.

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.