Fuel efficiency has always been part of aviation’s DNA. And every oil crisis has pushed the industry to look for new ways to reduce aircraft fuel burn. In the current environment, this also means taking a fresh look at operational levers such as Cost Index.
Developing technical solutions takes time. Changing operational policies and procedures can happen much faster. In the current environment, one principle stands out more clearly than ever: every drop of fuel counts.
Fuel vs. time-related costs: adjusting the Cost Index
So what Cost Index should be used when every drop counts?
As fuel costs rise while time-related costs remain unchanged, the Cost Index should decrease. Today, with fuel prices 2–4 times higher than last year, the Cost Index should decrease accordingly.
But this also raises a valid question: when fuel becomes the priority, is Cost Index still the right way to think about flight optimization? Wouldn’t it be better to fly in a way that minimizes fuel burn, regardless of time-related cost?
Yes, it would. And the best way to do that is to use Cost Index = 0.
With CI = 0, the flight planning system and optimization tools such as FlyGuide FPO optimize speed and cruise altitude for minimum fuel burn on a given route.
What changes when CI = 0?
Flight planning:
- Fuel required to fly to the alternate airport decreases (and if alternate fuel is not yet being planned with CI = 0, it is worth considering regardless of the current situation)
- Trip fuel decreases
- Depending on the airline’s fuel policy, other fuel components may also decrease
- The aircraft requires less block fuel on a route planned with CI = 0 than on one planned with CI > 0
- Lower planned fuel means lower aircraft weight, which in turn reduces actual fuel burn through the Cost of Weight effect.
Flight management:
- Speeds recommended by the FMS or in-flight tools such as FlyGuide FPO become fully optimized for minimum fuel burn
- Recommended cruise altitudes from the FMS or FlyGuide FPO also move toward those that minimize fuel burn
How much fuel can this save?
That depends on the current Cost Index, the level of OCC and pilot compliance, and the in-flight optimization tools in use.
For a typical low-cost carrier that used CI = 10 last year, we estimate that implementing CI = 0, together with the right toolset and good compliance, can reduce fuel burn by around 1%.
What are the side effects of implementing CI = 0?
On-Time Performance
Cost Index 0 increases flight time. On short-haul flights, typically by a few minutes. On long-haul flights, by around a dozen minutes.
The impact varies from flight to flight. In some cases it is negligible. In others, more noticeable. It depends on route length, wind component, and altitude constraints.
To mitigate the impact of CI = 0 on OTP, it is worth introducing a procedure that allows crews, during cruise, to increase CI above 0 once the predicted landing time becomes reliable, so the flight does not arrive too late.
This should be done thoughtfully, by checking what increasing Cost Index actually delivers in terms of time & fuel difference. If the time saving is marginal, CI = 0 may still be the best choice. If not, CI can be increased up to a predefined level respecting in-flight fuel managment criteria. In FlyGuide FPO pilots can verify the CI change impact on time and fuel burn and adjust accordingly.
Note: CI units differ across FMS types and configurations: CI = 1 kg/min = 1.323 hlb/h.
Higher time-related costs
If crew, maintenance, or leasing costs are time-dependent, they may increase. The scale of the impact depends mainly on how significant those costs are and what Cost Index was used previously.
Pilot comfort
Slightly lower speeds and higher cruise altitudes may reduce pilot comfort. That said, aircraft are designed to operate efficiently at such speeds and altitudes. Aircraft manufacturers already provide training materials that can support a transition to CI = 0.
To support this change, StorkJet has also prepared a dedicated Knowledge Base in the app for pilots.
What are the main barriers to achieving savings with CI = 0?
Compliance
For a new policy to deliver results, the whole company needs to be aligned. Everyone needs to follow it, and everyone needs to provide feedback when issues or limitations appear.
StorkJet provides tools to monitor the use of Cost Index, as well as the selected speeds and altitudes on operated flights. This makes it possible to fine-tune policies and achieve the best possible outcome wherever feasible.
Air Traffic Control
ATC instructions to maintain higher speeds vary by region and traffic density. This can negatively affect compliance, although it should affect all operators more or less equally.
If there is an opportunity to influence local ATC policy, it is worth opening a dialogue to align speed instructions with today’s fuel-saving reality. One example would be reducing mandated descent speeds by 20 knots for all traffic.
Conclusion
In the current fuel and aviation market environment, CI = 0 is one of the most immediate and practical operational levers airlines can use to reduce fuel burn. With the right procedures, tools, and operational alignment in place, it can deliver measurable results across the network.
This is the first article in a short series on practical fuel-saving opportunities in airline operations. The next articles will look at ground operations, including APU and CG, runway selection, and tankering.
These topics, along with other key aspects of fuel efficiency, will also be discussed during our Fuel Efficiency Forum in Cancun. Contact us if you would like to join.
