The fundamental rationale of the cost index concept is to achieve minimum trip cost by means of a trade-off between operating costs per hour and incremental fuel burn. In essence, the cost index is used to take into account the relationship between fuel-and time-related costs. The idea behind this document is to revisit the cost index concept with a view towards balancing both fuel and time related costs.
In addition to navigation functions, the Flight Management Computer (FMC) carries out real-time performance optimization aimed at providing best economics, not necessarily in terms of fuel consumption, but rather in terms of direct operating costs. The purpose of this brochure is to clarify the cost index as a tool aimed at achieving this flexibility with regard to aircraft performance.
Moreover, some misconceptions need to be cleared up with regard to its utilization and more in-house analysis is required for its determination, always bearing in mind that the primary and essential goal of the cost index is trip cost or mission optimization and not speed control.