Flight Redemptions

What is CI in Aviation? (Cost Index)

Updated: February 20, 2024

The Importance of Cost Index in Aviation

In the world of aviation, there are numerous terms and concepts that pilots and aviation professionals must be familiar with. One such term is the Cost Index, also known as CI. Cost Index is a crucial factor in flight planning and operations, as it directly impacts the efficiency and profitability of an airline. In this article, we will explore the significance of Cost Index in aviation and its role in optimizing flight performance.

What is Cost Index?

Cost Index (CI) is a numerical value that represents the trade-off between two key factors in aviation: fuel cost and time. It is a method used by airlines to determine the most economical speed and altitude for a particular flight. The Cost Index is calculated by considering the fuel cost per hour of operation and the cost of time spent on the flight. By assigning a specific value to the Cost Index, airlines can optimize their flight operations by finding the balance between minimizing fuel consumption and reducing flight time.

When planning a flight, airlines need to consider various factors, such as fuel prices, aircraft performance, and passenger demand. The Cost Index helps airlines make decisions regarding the optimal speed and altitude for a flight, taking into account these factors. By adjusting the CI value, airlines can prioritize either fuel efficiency or time savings, depending on their operational goals.

The Relationship between Cost Index and Fuel Efficiency

One of the primary factors influencing the Cost Index is fuel efficiency. Airlines strive to minimize fuel consumption to reduce costs and improve environmental sustainability. The Cost Index provides a means to achieve this goal by enabling airlines to calculate the most fuel-efficient speed and altitude for a given flight.

By setting a lower Cost Index, airlines prioritize fuel efficiency over time savings. This means that the aircraft will fly at a slower speed, known as the long-range cruise speed, and a lower altitude. Slower speeds result in reduced fuel burn, as the engines operate at their most efficient levels. Additionally, flying at lower altitudes allows the aircraft to take advantage of more favorable atmospheric conditions, further reducing fuel consumption.

Conversely, a higher Cost Index value indicates a greater emphasis on time savings over fuel efficiency. Airlines may choose to increase the speed of the aircraft, known as the high-speed cruise speed, and select a higher altitude. Although this approach results in increased fuel consumption, it allows airlines to reduce flight time and potentially improve schedule adherence.

Impact of Cost Index on Flight Planning and Operations

The Cost Index plays a crucial role in flight planning and operations. It affects various aspects of a flight, including route selection, altitude optimization, and fuel management. By carefully considering the Cost Index, airlines can make informed decisions to optimize their flight performance.

One key area where the Cost Index influences flight planning is route selection. When planning a flight, pilots and dispatchers evaluate different routes based on factors such as winds aloft, air traffic congestion, and fuel prices. By considering the Cost Index, airlines can select the most efficient route that balances fuel consumption and flight time. This ensures that the flight operates at the optimal speed and altitude, maximizing overall efficiency.

Additionally, the Cost Index impacts altitude optimization during a flight. As aircraft climb to higher altitudes, the air becomes thinner, resulting in reduced drag and improved fuel efficiency. However, climbing to higher altitudes also requires more fuel initially to overcome the increased gravitational forces. By considering the Cost Index, airlines can determine the most appropriate altitude for a flight, taking into account the trade-off between initial fuel burn and long-term fuel savings.

Furthermore, the Cost Index affects fuel management during a flight. Airlines continuously monitor fuel consumption and adjust the aircraft's speed and altitude accordingly to optimize fuel efficiency. By utilizing the Cost Index, airlines can make real-time adjustments to the flight plan, ensuring that the aircraft operates at the most fuel-efficient levels throughout the journey.

It is important to note that while the Cost Index is a valuable tool for flight optimization, other factors such as weather conditions, air traffic control constraints, and aircraft performance limitations must also be considered. The Cost Index should be used in conjunction with these factors to make well-informed decisions that prioritize both fuel efficiency and operational requirements.


Cost Index is a critical concept in aviation that allows airlines to strike a balance between fuel efficiency and time savings. By assigning a specific value to the Cost Index, airlines can optimize flight performance, route selection, and fuel management. Whether prioritizing fuel conservation or schedule adherence, the Cost Index provides a valuable tool for airlines to make informed decisions that impact their operational efficiency and profitability.

Understanding the significance of Cost Index is essential for pilots, dispatchers, and aviation professionals involved in flight planning and operations. By effectively utilizing the Cost Index, airlines can achieve optimal flight performance, reduce costs, and contribute to a more sustainable aviation industry.

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