What is “cost index” when used for aircraft flight planning purposes?
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.
