FMS Cost Index?

So in terms of FMC programming, I wanted to check my understanding of the Cost Index. I am assuming it’s something that changes the flight profile (speeds, rate of climb etc) to try to save money in a virtual flight. So you can sort of trade off time vs money (in terms of fuel use, crew use as well I’d guess).

Is that right?

I’ve been using a wiki I found for typical values, so I guess it varies per carrier plus length of route (short/long haul):

Probably more than most of us care to know about the subject in this Airbus doc, but in summary, given a bunch of variables, the speed which results in the highest profit on a particular flight.

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Sorry I can’t help ya’ out on this one. None of our FMSs (Universal UNS-1K) have a Cost Index. I think that is more a thing for airline FMCs (Airbus, Boeing, Embraer). We do have an efficiency page that shows lbs. per nautical mile that you CAN use to get the more economical fuel flows…

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You made me have to go look. This is it (for our plane)…showing ground/air nm per pound of fuel…things you are interested in when changing FLs to lower fuel flow or take advantage of or get out wind. You can obviously also alter these numbers by changing power to find best fuel economy (max range)… All this is obviously totally unrelated to your question…LOL


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The cost index will be a company provided value for the route being flown. Basically as you said above, it will change managed speeds to a set value that some boffin would have calculated to provide best cost efficiency of running the plane.

It can change depending on what the company wants. Ours usually stays around a set value but does fluctuate. I have had high enough cost index’s that you need to be careful transitioning from cruise to descent as managed profile puts you close to the barbers pole and needs a bit of forethought.

But its a figure you shouldn’t concern yourself with. Its calculated and accounted for in the flight plan that is done for you.

For the a320 size, we typically run CI approx. 9-15 (short to medium haul). Have had as high as 50,


Note that Cost Index also has an impact on maintenance, saves a few cycles on the engine(Not on Life Limits Parts though) when certain parts get less wear by running de-rated(fake de-rated really). Actual de-ration is done by changing a plug on the FADEC/ECU.

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Here’s a good article about Boeings cost index. The theory still applies.

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Airliners fly more efficiently if they cruise with a fluid mach that is allowed to float a bit as conditions change. Our companies prefer us to make speed changes through CI values when practical. The airlines are allowed to place weights on what costs are more impactful than others under their unique circumstances. At my airline on the 737-800 at a moderate weight a CI of 10 will give climb and cruise values of roughly 275/.76/.76; 30 will give 280/.77/.77; 50 will give 300/.79/.79 and 100 will give 330/.80/.805. There are times where controlling authorities don’t appreciate a “floaty” mach (say, overwater tracks) and then we just set a fixed value and ignore cost index.

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Thanks for the replies gents - exactly what I wanted.