Does anyone have an idea of what is it? From what I gathered from the web, it seems that this is the margin of error between the actual, real fuel consumption of the aircraft and the fuel consumption recorded in the aircraft systems (FMC?). I read that the system only estimates the fuel consumption via the fuel flow, which has some degree of inaccuracy.

Airbus and Boeing seemed to have different terms for this, PERF Factor, Fuel factor. The seem to be close in definition but I'm not really sure.

  • $\begingroup$ Are you looking for accuracy of metering (difference between metered fuel flow vs actual fuel flow) or accuracy of consumption prediction (difference between actual consumption and fuel planning)? $\endgroup$ – mins May 20 '17 at 9:27
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    $\begingroup$ You should give more context. Where can you find this expression ("fuel biases")? $\endgroup$ – Manu H May 20 '17 at 12:01
  • $\begingroup$ Sorry for giving scarce details. It's supposed to be part of IATA's guidance on Fuel Efficiency / Conservation practices. I've only heard about it, but not have actually read the material, and was just asking around what it is. Net research yielded a comparison between the calculated consumption by the aircraft's computer vs the flight plan, so I asked if that was it. But I think it affects the resulting fuel load duriing flight planning, the same way as degradation from the airframe and engine does. $\endgroup$ – Skull Leader May 20 '17 at 14:58

Fuel bias is as you described it. As the engine ages, it burns more fuel than a brand new one.

The fuel flow (and drag) corrections are entered into the FMS. This would allow the FMS calculated quantity not to disagree with the tanks totalizer. The figures are based off previous flights and engine tests.

Maintenance personnel can refine the database by entering correction factors for drag and fuel flow. (737 manual)


There are also "biases" to consider, depending on the make and model of aircraft. For example with Gulfstream aircraft, our flight planning experts typically add a 16% bias for flights of less than three hours. However, biases depend on the age of the aircraft, how the operator flies it, planned flight level, and speed.

So, it’s best practice for operators to compare actual fuel burns with flight plan burns to confirm accuracy. (Source)

Boeing does not call it bias when I checked the 787/737 manuals, but 'bias' is likely a flight planning software term.

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(Source) From a flight planner for a flight sim.

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(Source) Random real flight plan. Note: company software differs.

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Boeing 787 FMS interface where the drag and fuel flow corrections are entered.

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    $\begingroup$ This coefficient seems to help predicting more accurately the quantity of fuel in the tanks at any time (crossing waypoints, at touchdown). But the OP seems to look for the accuracy of metering leading to a difference between actual consumption and metered consumption (which may also affect future prediction, but that doesn't seem to be the main point). $\endgroup$ – mins May 20 '17 at 9:25
  • $\begingroup$ Thanks for trying to make do of what scant details I have. Sorry for the confusion, I really am just really wondering if what I read would be the definition for the term. Really thanks ! So it seems that besides drag coefficient(I presume this is a composite number that considers both airframe and engine degradation), there might be some factor entered just to align the fuel flow with the flight planning software fuel predictions. $\endgroup$ – Skull Leader May 20 '17 at 15:01
  • $\begingroup$ @SkullLeader - as shown above, the drag and fuel flow (FF) corrections are already separate entries. I hope that helps. $\endgroup$ – ymb1 May 20 '17 at 15:55

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