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Question: What is "cost index" when used for aircraft flight planning purposes?

(Posted by: spearing on 2007-02-13 09:40:33)

To our aircraft pilots: What is "cost index " when used for flight planning purposes? Can you provide an example?

Posted by: AHK on 2007-02-14, 00:37:44

Cost Indexing is the practice of evaluating the effect of one cost factor in the hopes of minimizing the sum of those factors. Many jet aircraft are equipped with various performance computers for the purpose of determining the best speed at which to travel (ie the economy speed) in order to minimize the total operating cost of the flight. To do this the FMC needs information about time-related costs and fuel cost. Fuel costs are based on the price and amount of fuel needed to complete the flight (legally, with reserves etc). Rather than enter all of these individual factors into the onoard FMC, most airlines use a ratio of the two costs to determine the economy speed for a given flight on a given day. This ratio is called the Cost Index, and it determines the economy speed for a flight by minimizing the total cost of operation. Cost Index = Cost of Time / Cost of Fuel

Posted by: pampapilot99 on 2007-02-13, 18:48:40

Cost Index (CI) is the relationship or ratio between time and the cost of fuel. It is based on a balance. At a higher Mach Number, the fuel cost will be greater, but it will be balanced out by the fact that the time factor is lower, and vice-versa. Flight Management Systems are able to come up with the Mach number and altitude to balance the time cost with the fuel cost, therefore establishing a CI. Each aircraft type and each airline will have unique values for this index.

Posted by: mig31_firefox on 2007-02-13, 20:07:52

I second the answer above. Couldn't have put it better myself and I am an FMS development engineer.