Narrative:

While proceeding to ZZZ and deviating around thunderstorms near the zzzzz intersection; we received significant reroute instructions from ATC. The new clearance was to proceed direct to the VOR; direct ZZZZZ1 intersection; then via the arrival. The mcdu recalculated the fuel at touchdown to be 2;400 lbs. As this was a few hundred pounds above reserve; and ATC indicated no delays into ZZZ; we elected to continue while closely monitoring the fuel situation. After crossing the VOR; we realized that our calculations on fuel remaining at the destination were not matching the amount being generated by the mcdu. While crossing ZZZZZ1 we checked with ATC again to verify no delays into ZZZ and declared a 'minimum fuel' state; but also started planning for a potential diversion into ZZZ1 (as it was the nearest suitable airport) should the fuel state continue to deteriorate per our calculations.shortly after crossing ZZZZZ1 we determined that there was no possible way to safely descend via the arrival due to having to fly past ZZZ for an approach to runway xx. We requested a diversion to ZZZ1; and asked ATC for a direct route to that airport. While proceeding direct to ZZZ1; ATC began vectoring us to the south for traffic. We determined that additional vectors were no longer possible due to our calculated fuel remaining on touchdown state. We requested priority handling to the airport with approximately 2;600 lbs. Of fuel on board.we completed a primarily thrust idle descent to ZZZ1 by the most direct routing possible; and continued actively monitoring the fuel burn vs. Amount remaining. We conducted a visual approach to a landing on runway xxc at ZZZ1. When we touched down; there was approximately 2;300 lbs of fuel on board the aircraft; and the mcdu fuel data was showing that we should expect to landing in ZZZ1 with 2;700+ pounds of fuel. This calculation was off by far more than figure of merit (fom). Upon exiting the runway; we taxied to a location on the airport as directed by ZZZ1 ground; and contacted dispatch for further instructions and coordination.[the cause was a] significant reroute while joining the original arrival into ZZZ; causing an approximately 1;500 lbs change to the arrival fuel. [The] mcdu fuel at destination calculations (which we factored into our initial continue vs. Divert assessment) were definitely inaccurate. This inaccuracy did not become clearly apparent until nearly the point in which we were preparing to descend via the new arrival. I have never seen the mcdu fuel data provide such an inaccurate number. I do understand the mcdu data is advisory; and it part of a larger fuel monitoring plan that should be utilized by the flight crew (hence the reason we were using the flight program printout and our own calculations to verify the data). Usually when landing; I am within 100 or so lbs. Of the mcdu projected landing fuel. The system generally appears to be quite accurate. The first officer (first officer) also indicated that he had never seen a situation like what we were seeing from the computer develop.I am personally going to increase my 'fuel at landing' (or contingency fuel) limitation to something closer to 2;800-3;000 lbs for this particular aircraft should future rerouting ever put me into a similar situation.it wouldn't hurt to provide a bit of additional ground and or simulator training regarding the fuel information provided by the mcdu. Although I feel that we appropriately used the information provided by the computer; and caught this issue by running our own calculations; it would be nice to have a better understanding of how the system generates these numbers.a simulator training scenario putting pilots into a minimum fuel / emergency fuel state would be very helpful. I would have like to see this situation in a training environment before encountering it in the aircraft.

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Original NASA ASRS Text

Title: EMB-175 flight crew reported that the MCDU (Multipurpose Control Display Unit) provided inaccurate fuel calculation which was far more than FOM (Figure of Merit); causing landing with less than minimum fuel.

Narrative: While proceeding to ZZZ and deviating around thunderstorms near the ZZZZZ Intersection; we received significant reroute instructions from ATC. The new clearance was to proceed direct to the VOR; direct ZZZZZ1 Intersection; then via the arrival. The MCDU recalculated the fuel at touchdown to be 2;400 lbs. As this was a few hundred pounds above reserve; and ATC indicated no delays into ZZZ; we elected to continue while closely monitoring the fuel situation. After crossing the VOR; we realized that our calculations on fuel remaining at the destination were not matching the amount being generated by the MCDU. While crossing ZZZZZ1 we checked with ATC again to verify no delays into ZZZ and declared a 'minimum fuel' state; but also started planning for a potential diversion into ZZZ1 (as it was the nearest suitable airport) should the fuel state continue to deteriorate per our calculations.Shortly after crossing ZZZZZ1 we determined that there was no possible way to safely descend via the arrival due to having to fly past ZZZ for an approach to Runway XX. We requested a diversion to ZZZ1; and asked ATC for a direct route to that airport. While proceeding direct to ZZZ1; ATC began vectoring us to the south for traffic. We determined that additional vectors were no longer possible due to our calculated fuel remaining on touchdown state. We requested priority handling to the airport with approximately 2;600 lbs. of fuel on board.We completed a primarily thrust idle descent to ZZZ1 by the most direct routing possible; and continued actively monitoring the fuel burn vs. amount remaining. We conducted a visual approach to a landing on Runway XXC at ZZZ1. When we touched down; there was approximately 2;300 lbs of fuel on board the aircraft; and the MCDU fuel data was showing that we should expect to landing in ZZZ1 with 2;700+ pounds of fuel. This calculation was off by far more than Figure of Merit (FOM). Upon exiting the runway; we taxied to a location on the airport as directed by ZZZ1 Ground; and contacted Dispatch for further instructions and coordination.[The cause was a] significant reroute while joining the original arrival into ZZZ; causing an approximately 1;500 lbs change to the arrival fuel. [The] MCDU fuel at destination calculations (which we factored into our initial continue vs. divert assessment) were definitely inaccurate. This inaccuracy did not become clearly apparent until nearly the point in which we were preparing to descend via the new arrival. I have never seen the MCDU Fuel Data provide such an inaccurate number. I do understand the MCDU data is advisory; and it part of a larger fuel monitoring plan that should be utilized by the flight crew (hence the reason we were using the Flight Program printout and our own calculations to verify the data). Usually when landing; I am within 100 or so lbs. of the MCDU projected landing fuel. The system generally appears to be quite accurate. The First Officer (FO) also indicated that he had never seen a situation like what we were seeing from the computer develop.I am personally going to increase my 'fuel at landing' (or contingency fuel) limitation to something closer to 2;800-3;000 lbs for this particular aircraft should future rerouting ever put me into a similar situation.It wouldn't hurt to provide a bit of additional ground and or simulator training regarding the Fuel Information provided by the MCDU. Although I feel that we appropriately used the information provided by the computer; and caught this issue by running our own calculations; it would be nice to have a better understanding of how the system generates these numbers.A simulator training scenario putting pilots into a minimum fuel / emergency fuel state would be very helpful. I would have like to see this situation in a training environment before encountering it in the aircraft.

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.