**6.6 Continuous descent operations: CDO**

Continuous descent arrival (CDA) is an aircraft operating technique designed to reduce aircraft noise, fuel consumption, and emissions. In this method, an incoming aircraft sinks with minimal engine performance and largely avoids horizontal flight phases. Ideally, this happens at idle. Without the use of CDA, an airplane goes down step-by-step. When performing CDA, the aircraft lingers high up in the air for extended periods of time, operating at a low engine thrust. This causes a reduction

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*Energy Efficiency Management: State of the Art and Improvement Potential Analysis…*

in fuel consumption, emissions, and noise during the descent profile. The most optimum CDA starts at the top of the descent and ends as soon as the plane starts the last approach and follows the glide path to the runway [54] (compare **Figure 7)**.

To sum up, energy efficiency management should always be used and aspired to because of the overwhelming economic and ecologic benefits in the transport sector. One of the most important advantages is, above all, the potential for saving fuel, since low fuel consumption leads to cost savings and consequently to reduced CO2 emissions. The application of energy-efficient technologies and methods therefore not only has economic aspects but is also good for the environment. This chapter shows that there are already several propulsion technologies and developments in the areas of rail freight and airfreight, but they are not yet completely revolution-

Rail freight currently has mainly internal combustion engines and electric motors in use. In particular, the invention of electrically powered railroads has been a significant advance in improving energy efficiency. By using modern drive technologies and methods in rail freight transport, many potential savings can be achieved. In the field of electric locomotives, regenerative braking can be used, for example, with rechargeable energy storage systems (RESS). This allows the current generated during dynamic braking to be stored and reused, and it offers a potential of 10–20% of energy consumption to save. Other powertrain technologies such as the dual power hybrid locomotive as well as diesel multiple units (DMUs) and electric multiple units (EMUs) are particularly effective and efficient. The dual power hybrid locomotive convinces with the advantage that the diesel engine can be converted to a purely electric drive with just a single push of a button. Although EMUs prove to be a high financial burden, they are considered to be very environmentally friendly and energy-efficient. The most fuel-efficient and advanced engine in this regard is the highly clean diesel-electric locomotive with repower kits. Compared to other locomotives, this model has the advantage of not requiring urea additives to reduce NOx emissions. Since the purchase of a completely new diesel-electric locomotive is extremely expensive, repower kits are a cost-effective option that can also reduce fuel consumption and emissions. This can save up to 25% on fuel and about 50% on lubricating oil. To optimize energy efficiency, the use of energy management and control technologies should be promoted. It has been proven that the distributed power controller is 5% more efficient than the traditional push-pull configuration. In conjunction with electronically controlled pneumatic brakes, it is possible to achieve fuel savings of almost 30%. Rail freight transport should focus on natural gas locomotives in terms of renewable energy. With this technology hardly more diesel fuel is needed. Only 5% of the diesel fuel is needed to reach full power, with the remaining 95% being replaced by natural gas. Natural gas

locomotives can save over 1 million liters of diesel per locomotive per year.

Airfreight is extremely attractive as a transport method. The aircraft as a means of transport brings many benefits. The reliability, safety, and speed ensure steady growth in this sector. It should be noted, however, that fuel consumption, as measured by effective numbers, is highest. Due to the specific CO2 emissions, airfreight drives global warming. All the more important are the technologies and opportunities that contribute to improving energy efficiency. The potential here is in different areas. Propulsion technologies, aerodynamics, composites, as well as flight behavior itself can have a huge impact on the energy efficiency of freighters. The solar energy systems announced by the EU for the production of "solar kerosene" act primarily as an optimal way to supply clean fuel to aircraft, but in this process, CO2 is also

*DOI: http://dx.doi.org/10.5772/intechopen.86552*

ized and provide room for further improvements.

**7. Conclusion**

in fuel consumption, emissions, and noise during the descent profile. The most optimum CDA starts at the top of the descent and ends as soon as the plane starts the last approach and follows the glide path to the runway [54] (compare **Figure 7)**.
