All around the world civil aviation is a part of market economy with rare exceptions. No matter who operates aircraft, large air company or small regional air club, everybody tries to reduce operation costs and therefore save money. Reality of aviation business requires a huge amount of factors to be considered on a daily basis: economics, marketing management, crew scheduling, flight operations, engineering and maintenance management, technical condition of aircraft etc. And the most effective way to take all these factors into account is to use the Cost Index (CI).
CI is used to take into account the relationship between time- and fuel-related costs.
Used appropriately, the CI feature of the flight management computer (FMC) can help airlines significantly reduce operating costs.
Generally, the total cost of a specific trip is the sum of fixed and variable costs:
- CF = cost of fuel per kg
- CT = time-related cost per minute of flight
- Cc = fixed costs independent of time
- ∆F = trip fuel
- ∆T = trip time
Since we can't affect the fixed cost, we need to minimize the variable cost (fuel- and time-related).
As an example, time-related costs contain the sum of several components:
- Hourly maintenance cost. Excluding cyclic cost.
- Flight crew and cabin crew cost per flight hour. Usually it includes crew salaries, rest cost, crew availability etc.
- Marginal depreciation or leasing costs. The cost of ownership or aircraft rental for extra flying. In practice, these costs are commonly called marginal costs : they are incurred by an extra minute or an extra hour of flight.
CI is used to take into account the relationship between fuel-related costs and time-related costs.
With time-related costs, the faster the aircraft is flown, the more money is saved in time costs. This is because the faster the aircraft is flown, the more miles can be flown for time-related components. It also means that more miles can be flown between inspections when considering maintenance costs.
However, if the aircraft is flown at such a high speed, the fuel burn increases and total fuel cost for the trip increases.
Let's take a look on two extreme cases:
1. CI = 0
In this case time cost as low as zero and fuel cost is extremely sufficient (greatest influence of fuel cost in the operating bill). It is the minimum fuel mode for the best range (MRC).
2. CI = MAX
In this case fuel cost means nothing compared to the time cost. It is the MINIMUM TIME MODE for Maximum Speed (VMO/MMO)
CI and ECON speed
It is normal for the FMS to adjust the mach number (MN) by .01 when the head wind or tail wind components exceed a programmed threshold value: the airplane will slow down with a tail wind, speed up with a headwind (automatically) by .01 mach in an effort to minimize the fuel burn.
Looking at the figure above you can see from the total operating cost curve that the speed which gives the minimum total operating cost is the most economical speed to fly.
Increasing CI from zero to maximum will increase the ECON speed from the maximum range speed to maximum operating speed.
- the higher the flight level, the higher the ECON Mach,
- the higher the aircraft gross weight, the higher the ECON Mach.
Typical cost indexes
Let's get through some typical CI examples. It will help to make flight planning more precise and accurate.
(MRC = Maximum Range Cruise; LRC = Long Range Cruise)
|A32X||CI = 0||CI = 50-80||CI unknown|
|A330||CI = 0||CI = 30-60||CI unknown|
|A340||CI = 0||CI = 30-60||CI unknown|
|B737 CL||CI = 0||CI = 10-30||CI = 30|
|B737 NG||CI = 0||CI = 10-30||CI = 35|
|B744||CI = 0||CI = 25-80||CI = 230|
|B757||CI = 0||CI = 15-50||CI = 85|
|B767||CI = 0||CI = 15-50||CI = 70|
|B777||CI = 0||CI = 90-150||CI = 180|
|MD80||CI = 0||CI = 10-50||CI unknown|
|MD11||CI = 0||CI = 80-120||CI = 200|
|A32X||CI = 10-20|
|B763||CI = 60|
|Short/Medium haul (Delayed flight)||CI = 10 (CI = 99-250)|
|Long haul (Delayed flight)||CI = 50 (CI = 100-500)|
|American Airlines (flight duration < 4 hours)|
|A32X||CI = 27|
|B737||CI = 35|
|B757||CI = 80|
|B772||CI = 85|
|A32X||CI = 30|
|A330 & A340||CI = 70 - 90|
|A380||CI = 60|
|B744 & B748||CI = 70|
|Normal ops||CI = 8|
|Delayed flight||CI = 50|
- Airbus Flight Operations Support & Line Assistance - Getting to grips with the cost index (issue II - May 1998)
- Michael A. Burris - Cost Index Estimation by Boeing (August 2015)
- CAE Oxford ATPL book - Flight Performance and Planning
- 531824 - Creation
- 200696 - Update
DATE OF SUBMISSION
- 17:46, 16 November 2019
- This documentation is copyrighted as part of the intellectual property of the International Virtual Aviation Organisation.
- The content of this documentation is intended for aviation simulation only and must not be used for real aviation operations.