How is the cost index for a flight determined?

The cost index for a flight is determined primarily by the flight plan and is entered into the Flight Management Computer (FMC). The cost index represents the trade-off between time and fuel consumption for a flight, allowing airlines to optimize costs according to their operational priorities.

When creating a flight plan, various factors such as the aircraft type, operating costs, and specific airline policies are taken into account to establish an appropriate cost index. By inputting this value into the FMC, the aircraft's systems can make adjustments to optimize altitude and speed during the flight, balancing fuel efficiency against schedule adherence.

This process reflects operational strategies aimed at managing costs effectively, which may vary from one flight to another based on economic considerations and traffic conditions. Thus, the selection of the cost index is rooted in pre-flight planning rather than real-time instructions from air traffic control or solely influenced by the aircraft's operating company without going through the established flight planning procedures.