Why lowering aircraft acceleration altitude improves fuel efficiency?

In commercial aviation's highly competitive world, optimizing fuel efficiency is a crucial financial and environmental strategy for airlines. Did you know that operators continuously looking to optimize their fuel efficiency procedures to reduce aircraft fuel consumption and CO2 emissions? Among these, are innovative fuel-saving practices, such as Reduced Acceleration Altitude (RAAL). This eco-flying technique applied during the climb phase of a flight, can help airlines boost their fuel programs, providing that noise abatement procedures allow it.

In this piece, we'll give you all the details on RAAL, why you should use it, and how to overcome challenges to implement it.  

What is Reduced Acceleration Altitude?

Reduced Acceleration Altitude involves starting the acceleration of the airplane sooner, at a lower altitude than normal operations. Usually, planes ascend to a specific altitude before they start to speed up to a faster, more efficient flying speed. When the acceleration starts at this lower height, the plane can switch to the efficient flight mode more quickly and reduce drag. This means it faces less resistance from the air, making it more efficient.

Go the extra mile >>> Everything you need to know about RAAL. 

This method is to be used in combination with Noise Abatement Departure Procedures (NADP), which are protocols used by aircraft during takeoff to minimize noise pollution, namely NADP1 and NADP2. The choice between these noise abatement departure procedures is specific to each airport.

  • NADP1Noise Abatement Departure Procedure 1

    NADP1 focuses on noise reduction near airports, involving a steep climb and later acceleration. Many large airports, especially in Europe, prevent accelerating before 3,000 feet to mitigate the impact of aircraft noise on nearby communities. 

    Figure 1. NADP 1 by Captain Pat Boone 
    Source:  https://b737mrg.net/mrg_download/B737MRG_noise.pdf 

  • NADP2Noise Abatement Departure Procedure 2

    NADP2 allows for earlier acceleration, reaching optimal performance sooner than with NADP1 (acceleration under 3,000 feet). RAAL fuel efficient procedure matches with NADP2.

    Figure 1. NADP 1 by Captain Pat Boone 

Boeing claims that the fuel saved by flying an NADP2 procedure vs an NADP1 procedure is 67 kg on a Boeing 737-800 with winglets and 197 kg on a Boeing 777-200ER.

Why apply a Reduced Acceleration Altitude?

Implementing RAAL offers several benefits:

  • Fuel Efficiency: Reducing acceleration altitude can boost fuel efficiency based on the ability to clean the aircraft earlier in the flight. This cleaning involves retracting the aircraft's flaps and slats sooner than usual, which in turn reduces drag. By minimizing resistance from the air at an earlier phase, airplanes can achieve greater fuel efficiency, making for a smoother and more economical journey.

    In 2023, the SkyBreathe® airline community saved more than 88 000 tons of fuel by applying the Reduced Acceleration Altitude best practice. That represents more than 278 000 tons of CO2 emissions prevented from going into the atmosphere. 

  • Reduced Emissions: With improved fuel efficiency comes a reduction in carbon emissions. 
    By embracing eco-flying techniques such as RAAL, the industry shows its commitment to innovate and progress to achieve net zero CO2 emissions by 2050. This serves as a model for other sectors to follow suit in reducing their carbon footprint and environmental impact. 

Related content >>> Fly Net-Zero 2050: how airlines use data to improve fuel efficiency?

The challenges of Reduced Acceleration Altitude

While the benefits are clear,  integrating the RAAL eco-flying technique into standard aviation procedures requires overcoming various challenges, from technological adaptations to operational considerations: 

Coordination with Air Traffic Management:

Working together with Air Traffic Control (ATC) is crucial, as this practice may affect traffic flow and separation. Lowering the acceleration altitude can potentially affect the sequencing of aircraft in the airspace and may require adjustments in air traffic flow management. It's essential to ensure that reduced acceleration procedures are integrated seamlessly into existing air traffic management systems to maintain safe and efficient operations.

Compliance with noise abatement regulations:

Understanding and adhering to local noise abatement procedures is essential and can vary across different regions and airports. Pilots and airlines must be aware of specific noise abatement procedures at each airport and comply with them to minimize the impact of aircraft noise on surrounding communities.

Diversity in aircraft performance:

Not all aircraft types may experience the same level of benefit from RAAL. Factors such as aircraft size, engine type, and weight can influence the effectiveness of reduced acceleration procedures. Some aircraft may require longer distances to reach optimal climb performance, while others may benefit more from reduced acceleration altitudes. Airlines need to consider the performance characteristics of their fleet and assess the feasibility and effectiveness of reduced acceleration altitude procedures on a case-by-case basis.

Related content >>> What you need to know about Reduced Acceleration Altitude

Addressing these challenges requires collaboration and cooperation among stakeholders to work towards implementing the RAAL procedure more effectively. Airlines can leverage advanced fuel efficiency tools and technologies to integrate reduced acceleration altitude procedures into their flight management systems. This strategy can maximize environmental benefits while enhancing operational and cost effectiveness.

How to implement RAAL in your fuel program 

For airlines considering the adoption of RAAL, there are two key points to consider carefully. By addressing these points thoughtfully, fuel teams can make informed decisions regarding the implementation of RAAL and contribute to their airline's sustainability goals.

1. Implementing Reduced Acceleration Altitude in flight operations

Pilots need thorough training to implement this strategy effectively, including recognizing the optimal scenarios for utilizing Reduced Acceleration Altitude. Training, coupled with the usage of analytical tools, can fortify the Flight Operations team's capabilities to monitor, measure, and implement this practice with utmost effectiveness. 

Take the example of SkyBreathe® 360° eco-flying solution. By harnessing aircraft data, the solution provides precise metrics for the fuel team to assess the impact of RAAL in terms of fuel savings, emissions reduction, and return on investment (ROI). Accessing advanced analytics allows airline teams to make well-informed and efficient decisions about their operational strategies.

Related content >>>  [CASE STUDY] Fuel efficiency at Philippine Airlines

sucess story Philippine Airlines

Figure 3. RAAL best practice implemented by Philippine Airlines to save fuel.
Source: [CASE STUDY] Fuel efficiency at Philippine Airlines

2. Enhancing pilot engagement 

Ensuring pilot commitment is essential since they are responsible for applying this fuel efficiency technique during the flight. Here are a few tips to help you engage your pilots:

  • Giving pilots access to relevant data can help you address any doubts about RAAL's safety and effectiveness, and encourage adoption.
  • Having clear company SOPs for RAAL assures pilots that your airline has thoroughly evaluated the procedure and offers official guidance for its application, instilling confidence in pilots.
  • Introducing RAAL in pilot training can foster a fuel-saving mindset, ensuring proficiency and practical application.

Go the extra mile >>> 5 tips for engaging pilots applying Reduced Acceleration Altitude

Here’s an example of how a pilot engagement app can boost RAAL best practice fuel savings results:

reduce acceleration altitude at ukraine international airlines since the introduction of MyFuelCoach

Have you considered providing pilots with access to their performance data?
By highlighting the impact of their actions and providing them with personalized feedback, you can help them develop their eco-flying skills and boost their motivation to apply fuel preservation procedures. Mobile apps such as SkyBreathe® MyFuelCoach are very effective in engaging pilots and improving their adherence to the airline’s fuel efficiency program.

To sum up 

Reduced Acceleration Altitude is an effective operational strategy for airlines seeking to reduce fuel consumption and emissions. The industry can make notable strides toward sustainable aviation thanks to this eco-flying practice by combining operational strategies, cutting-edge technology, and active pilot involvement.


Discover more fuel-saving practices to apply during a flight >> Read the full article!

22 eco-flying best practices for flight ops


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