Most fuel efficiency best practices focus on optimizing the aircraft and the flight execution. But what happens on the ground can also have a significant impact on fuel consumption and CO2 emissions. In particular, the accuracy of the Zero Fuel Weight estimation plays a key role in that matter. It turns out that its impact goes beyond fuel efficiency.
This article covers all you need to know about Zero Fuel Weight Error and the multiple benefits of reducing it.
What is Zero Fuel Weight Error?
A key input for flight planning is the planned Zero Fuel Weight. It serves as the basis for most flight plan calculations from which fuel quantities required for the flight are determined. With that in mind, we can easily imagine that the difference between the planned and actual Zero Fuel Weight, called the Zero Fuel Weight Error, heavily impacts the flight.
Effect of Zero Fuel Weight overestimations on flight economics
When the Zero Fuel Weight is overestimated, flight plan fuels are higher than needed, and a part of the loaded fuel is not necessary to operate the flight. This causes overconsumption compared to a flight planned with an accurate Zero Fuel Weigh because extra weight is carried. This effect is accentuated for long-haul flights, where the cost of weight is higher due to the duration of the flight. You can read this article on the cost of weight for further details.
Zero Fuel Weight estimation errors also influence the flight path selection by the flight planning system. This is even more true for airlines using advanced algorithms capable of finding optimal 4-dimensional flight profiles. Different lateral and vertical paths can be found based on Zero Fuel Weight. Consequently, the flight is operated on a non-optimal lateral and vertical path, increasing the overconsumption.
Zero Fuel Weight overestimation can yet have another downside for flights meeting the Take-Off Weight limit of the aircraft. Indeed, the weight overestimation directly causes a loss in payload, and hence a loss in revenue for the flight. This effect is especially sensitive for cargo flights where Take-Off Weight limit is more often met. If you want to learn more about the benefit of fuel efficiency solutions for cargo airlines, you can read this article.
Effect of Zero Fuel Weight underestimations on safety and flight economics
When the Zero Fuel Weight is underestimated and not compensated for before departure, flight plan fuels are lower than needed. Such flights can then face safety issues, and “Safety First” will always be the mother of all decisions in an airline. Hopefully, before departure, pilots would typically add extra fuel to compensate for the Zero Fuel Weight underestimation and regenerate safety margins. But repetitive Zero Fuel Weight underestimations are harming pilots’ confidence in the flight plan, and pilot extra fuel tends to increase in such cases. Hence, even when safety issues are avoided, Zero Fuel Weight underestimations still have downsides as they result in overconsumption.
Also, Zero Fuel Weight underestimations causes an overconsumption due to a non-optimal lateral and vertical path, for the same reasons as for Zero Fuel Weight overestimations.
Significant savings are yielded by reducing Zero Fuel Weight Error. In its Fuel Book, IATA states that for a fleet of 130 aircraft with typical mixed operations, savings for cutting half of the Zero Fuel Weight Error represent around 2,600,000 kg of fuel and 8,200 t of CO2 per year.
How to reduce Zero Fuel Weight Error?
Estimating the Zero Fuel Weight accurately is difficult because a range of perturbations exists: no-show and go-show passengers, wrong estimations of the baggage mass in passenger flights, and payload estimation difficulties in cargo flights. However, there are some best practices to reduce Zero Fuel Weight Error.
The most basic rule to keep in mind is that “if you cannot measure it, you cannot improve it,” as stated by Lord Kelvin. Airlines need to set up data feeds and calculation methods for the Zero Fuel Weight Error. Best-in-class fuel efficiency solutions like SkyBreathe® Fuel Efficiency are very valuable here. Indeed, they automatically compute the Zero Fuel Weight Error on each flight and feature global results easy to interpret with charts and figures. Airlines can then find patterns of where their estimations are inaccurate and identify ways to improve them.
Advanced airlines also tend to bring closer all the functions related to load estimation and operational control. This contributes to raising awareness of all stakeholders on the need for accurate load estimations and improving collectively based on the figures compiled from the airline’s operations.
So far, we have seen how it is possible to reduce Zero Fuel Weight Error through back-office analysis. Still, it is also possible to set procedures so that the pilot can compensate for part of the effects just before departure. The key is to provide the proper guidelines to the pilot to take the right action on the go. The best way to do so is to include predefined fuel corrections in the flight plan for various variations above and below the planned Zero Fuel Weight. Other options can be considered, but, in all cases, it is paramount that pilots are fully included in the fuel efficiency program of the airline. To learn more on this topic, check out this article on how to set up an efficient fuel team. For that, dedicated tools like MyFuelCoach™, allowing pilots to engage in fuel efficiency, are valuable.
In this article, we have learned what Zero Fuel Weight Error is, where it can come from and how it can impact flight safety, fuel efficiency, and even revenue in some cases. We have seen that reducing Zero Fuel Weight Error yielded significant savings potential of several million kg of fuel and CO2 per year for a fleet of 130 aircraft with typical mixed operations. A set of best practices to reduce Zero Fuel Weight Error has been reviewed, ranging from analysis for back-office teams, to instantly actionable guidelines for pilots, to tools to spread a fuel efficiency culture.
You are now ready to improve the operations of your airline by reducing Zero Fuel Weight Error!
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