This glossary is written for virtual airline and flight simulation use within Virtual Air Canada Airline. It is not intended as a real-world aviation reference.
CI
Cost Index
Cost Index (CI) is a value entered into the Flight Management System that represents the ratio of the cost of time to the cost of fuel. Mathematically, it is expressed as CI = (time cost in /kg or $/lb). A CI of zero directs the FMS to compute the most fuel-efficient speed - the Maximum Range Cruise (MRC) speed - while a high CI directs the FMS to fly faster, accepting higher fuel burn in exchange for reduced flight time. Airlines derive their cost index values from actual operating economics: aircraft ownership costs, crew pay, maintenance rates tied to flight hours, and the current fuel price all feed into the calculation.
The FMS uses the CI to compute the Optimum Cost Speed (ECON speed) - a speed profile that balances fuel and time costs across all phases of flight, including climb and descent. A higher CI results in a higher climb speed (reaching cruise altitude faster), a higher cruise Mach number, and a higher descent speed. Cost indices are typically issued by the airline’s operations control center or dispatch department and are included in the OFP. A single airline may use different cost indices on different routes or at different times of day depending on schedule pressure, fuel price, and payload.