Optimising aviation

Improved air traffic management techniques like to avoid flying holding patterns, “green landings” and the use of relatively low speed airplanes for domestic aviation can reduce the emission of greenhouse gases substantially. Depending on their penetration up to 3% CO2 emission reduction can be achieved for green landings and 10-60% CO2 emission reduction for low speed airplanes. Moreover, these techniques will lower the NOx and soot emissions, thereby improving the air quality around the airport.

In 2002, aviation accounted for 3 trillion revenue passenger-kilometers (RPKs), or approximately 10% of world RPKs traveled on all transportation modes and 40% of the value of world freight shipments. Among all modes of transport, demand for air travel has grown fastest (Lee et al.).  It is estimated that emission reductions of 70% per passenger kilometer in aviation are possible over the next 50 years, provided that technological and operational developments are fully pursued (PBL & ECN, 2009) including a switch towards low-carbon fuels. Airplane manufactures are targeting a 50% reduction in aircraft fuel consumption by 2020. The manufacturers are looking at airframe improvements (e.g. light weight materials and aerodynamic improvements) to provide about 25% of the reduction, while between 10% and 15% efficiency improvement should come from engine manufacturers. The remainder, about 10 % (European Commission, 2009), needs to come from air traffic control for example
  • by ensuring that the shortest route (direct routing) can be followed in between the origin and the destination,
  • by ensuring that aircrafts are not flying holding patterns around the airport before they land for too long and
  • by reducing the vertical separation minimum (RVSM -Reduced Vertical Separation Minimum). The vertical separation minimum is the vertical separation required between airplanes (IPCC, 2007)
  • by deploying airplanes with a lower average velocity, and hence a lower fuel consumption, like airplanes using turbo propellers for domestic aviation.
In this article only low speed airplanes, and improved landing procedures, as an example of air traffic control will be discussed.
The SESAR European Air Traffic Management Master Plan (Single European Sky ATM Research, 2009) lists many available techniques and suggestions to improve Air Traffic Management. This list of techniques includes pre- and post flight time management optimization, enhanced ground terminal design and on board flight dynamic optimization techniques.

Low speeds of airplanes can drastically reduce the fuel consumption.  Employing the slower turboprop propelled airplanes can reduce the aviation fuel consumption in domestic flights (Smirti, M. et al, 2009) by about 30% compared to airplanes with small jet engines (Babikian et al).

Improved landing procedures can lower the fuel consumption. At present, aircrafts usually descend in stages with the engines at full speed. In many cases, they must circle the airport in order to time the approach. The so called green approach, where advanced computer technology makes it possible to save 100 kg fuel on each landing, has been tested by Scandinavian Airlines (SAS). SAS performed its first green approach on a flight from Luleå to Stockholm and has implemented about 600 green approaches. The advantages of green approaches are reductions in emissions, fuel costs and noise level. With the new navigation system, the approach begins about 45 minutes before the aircraft lands, which results in the aircraft almost gliding down with very low engine revolutions.

Today, air traffic controllers use tactical speed, route, altitude and vector instructions, based on a first come-first serve principal (Oprins et al, 2009). Simulations show, that in highly automated future air traffic management systems aircrafts may be able to land within ± 30 seconds of each other, in contrast to 120 seconds in the current system. These automated air traffic management systems can minimize the time that aircrafts have to circle around the airport before they land.

Feasibility of technology and operational necessities : 

Slower speed turboprop airplanes are an alternative to jet airplanes for regional flights. The reduction in fuel consumption that can be achieved by deploying turboprop airplanes comes at the expense of longer flight times and thus higher personnel costs. Without any further support, the economic feasibility of deploying turboprop airplanes therefore depends on the ratio of the fuel prices and the cost of personnel.

Improved air traffic control and landing systems are principally possible at every airport. They require investments in software used in the airplane and in air traffic control and training of the pilots and air traffic control personnel.

Status of the technology and its future market potential 
The use of low speed airplanes implies using existing technologies in a more efficient manner. Improvements in air traffic management are ongoing; technologies and software are being developed to improve the possibility to manage airplane routes most effectively.

Contribution of the technology to protection of the environment 
Nitrogen oxides (NOx), carbon monoxide (CO) and hydrocarbons (HC) are produced in the aircraft engine within the combustor and vary in quantity according to the combustor conditions. Nitrogen oxides are produced in the high temperature regions of the combustor primarily through the oxidation of atmospheric nitrogen. Thus, the NOx produced by an aircraft engine is sensitive to the pressure, temperature, flow rate, and geometry of the combustor. The emissions vary with the power settings of the engine, being highest at high thrust conditions (Baughcum et al, 1998). The NOx emissions of an airplane with turbo propellers is about equal to the NOx emission of a small passenger jet (90 passengers) expressed in grams of NOx per kilogram of jet fuel. However, depending on the flight conditions the regional jets can be 10% to 60% less fuel efficient than turboprops. Thus planes powered by turbo propellers can produce 10% - 60% less NOx, than their jet powered counterparts.

Because a majority of aircraft emissions are injected into the upper troposphere and lower stratosphere (typically 9– 13km in altitude), the resulting impacts on the global environment are unique among industrial activities. Aircraft emissions have an impact on atmospheric processes beyond the positive radiative forcing effects of CO2. The mixture of exhaust species discharged from aircraft perturbs radiative forcing two to three times more than if the exhaust was CO2 alone. Even though most aircrafts fly in so-called 'flight corridors', the effects of their emissions on atmospheric composition and chemistry go far beyond these regions and may even directly affect climate. The CO2 emitted by aircraft contributes 2-3% to the total anthropogenic CO2 emissions. However, the techniques discussed here reduce the emissions of greenhouse gases only at a lower altitude.

The use of turboprop planes reduced CO2 emissions equivalent to the efficiency gains over regional jet aircraft
It has been estimated that green landing approaches can reduce the fuel consumption of the airplanes by about 3% (Stockholm Arlanda Airport, 2006). Clearly green approaches contribute more to reduction in fuel consumption per passenger-kilometer for short domestic flights than for long-distance intercontinental flights.

Financial requirements and costs 
Slow-speed turboprop airlines: Analysis shows that the determination of minimum cost aircraft operations over distances of 1000 miles or less is highly sensitive to fuel prices and passenger costs (Smirti, M. et al, 2009). The results of the study show that the popularity of regional jets is due to their relatively low passenger costs when compared with the turboprop. Passengers value the faster flying time, the ability to fly on a jet aircraft, and also the potential for higher frequency service. The balance between operating and passenger costs is what makes the regional jet a lower cost aircraft for many stage lengths up to a fuel price of about $3.50/gallon. The market penetration analysis also indicates that at fuel prices just under $4.00/gallon, 90% of passengers can be served on a turboprop for a lower total cost per passenger compared with a regional jet. As fuel prices seen in 2008 were above $4.00/gallon, it is expected that where available turboprops replace regional jets over all distances up to 1000 miles if fuel prices return to their 2008 highs. As anticipated, the turboprop is very cost competitive over short distances because of the lower fixed and higher variable costs with distance.

The costs of the green landing technology are determined by the costs of the computer software in the airplane and at air traffic control and in training of the pilots and air traffic control personnel. No explicit cost estimates have been found.

Babikian, R., Lukachko, S. and Waitz, I.A., The Historical Fuel Efficiency Characteristics of Regional Aircraft from
Technological, Operational, and Cost Perspectives, available at http://web.mit.edu/aeroastro/people/waitz/publications/Babikian.pdf
Baughcum, S. L. et al, 1998. Year 2015 Aircraft Emission Scenario for Scheduled Air Traffic, NASA/CR-1998-207638, available athttp://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/19980055200_1998120133.pdf
European Commission, 2009. Council Decision of 30 March 2009 endorsing the European Air Traffic Management Master Plan of the Single European Sky ATM Research (SESAR) project
IPCC, 2007. Transport and its infrastructure. In Climate Change 2007: Mitigation. Contribution of Working Group III to the Fourth Assessment Report of the Intergovernmental Panel on Climate Change [B. Metz, O.R. Davidson, P.R. Bosch, R. Dave, L.A. Meyer (eds)], Cambridge University Press, Cambridge, United Kingdom and New York, NY, USA. available athttp://www.ipcc.ch/publications_and_data/ar4/wg3/en/ch5s5-3-3.html
Lee, J. J., S.P. Lukachko, and I.A. Waitz, Aircraft and Energy Use, in Encyclopedia of Energy, Volume 1.
Oprins, E., Zwaaf, D., Eriksson, F., van de Merwe, K. and Roeavailable, R., 2009. Impact of future time-based operations on situation awareness of air traffic controllers. Eighth USA/Europe Air Traffic Management Research and Development Seminar (ATM2009), available at http://www.atmseminar.org/8th-seminar-united-states-june-2009/papers/paper_016
PBL  & ECN, 2009. CO2 emission reduction in transport Confronting medium-term and long-term options for achieving climate targets in the Netherlands, PBL and ECN, ECN-B--09-015, available at http://www.mnp.nl/bibliotheek/rapporten/500076009.pdf
Single European Sky ATM Research, 2009. The European Air Traffic Management Master Plan, available at http://prisme-oas.atmmasterplan.eu/atmmasterplan/faces/index.jspx
Smirti, M. et al, 2009. The potential of turboprops to reduce aviation fuel consumption, University of California Transportation Center, UCTC Research Paper No. 883, available at http://www.escholarship.org/uc/item/5131891j

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