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Reducing the impact of non-CO₂ climate impact: EUROCONTROL MUAC and DLR partnering on contrail prevention

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Airplane with contrails

With two-thirds of aviation’s climate change impact believed to come from aircraft non-CO2 emissions, contrail avoidance has a key role to play.

Here, EUROCONTROL’s Maastricht Upper Area Control (MUAC) is conducting ground-breaking live contrail prevention trials with DLR, the German Aerospace Center (DLR), in a bid to reduce aviation’s non-CO₂ climate impacts. This contrail prevention trial is the first of its kind in the world, and will investigate the operational feasibility of contrail prevention by ATC and measure its impact.

The trial is assessing how to avoid warming persistent contrails with eco-efficient flight trajectories in live operations. MUAC is examining relatively minor operational measures such as small flight level changes, for example diverting aircraft 2,000 feet up or down from their normal flight path, to reduce persistent contrail formation and contrail cirrus. This requires creating a contrail prevention system, implementing operational procedures for contrail prevention, and the validation of the methodology with satellite image analysis by the project partner DLR.

The DLR has been working for decades on climate change and has contributed significantly to the current state of science.

The findings of these trials will help to fight climate change in a very practical way, Prof. Sausen underlines:

“While there have been many theoretical studies on how air traffic management could reduce the climate impact of aviation, the current joint MUAC-DLR experiment is the first one that tests the concept out on actual flights. This demonstration will show which practical difficulties have to be overcome if we are to implement ATM procedures to reduce the climate impact of aviation, and whether today's meteorological tools are good enough at forecasting areas where persistent contrails tend to form, and which should be thus avoided.”

Professor Dr. Robert Sausen Head of Department, Institute of Atmospheric Physics, DLR

But why exactly are contrails so harmful to the environment?

Condensation trails – so-called contrails – are formed by water, soot and cool air. When water vapour is ejected from the exhaust nozzle of an aircraft engine into sufficiently cold air, it condenses and freezes around soot and other particles in the air, creating tiny ice crystals. In certain atmospheric conditions, these ice crystals create layers of cirrus clouds, causing a ‘blanket’ effect which keeps warmer air trapped in the lower atmosphere. At night, this has a warming effect on the atmosphere. By avoiding ice-supersaturated regions (ISSRs) in the atmosphere, aircraft can reduce the likelihood of forming these persistent contrails.

MUAC estimates that only a very small proportion of flights will be affected by contrail prevention clearances. Optimised air traffic management will keep deviations from the requested flight level to a minimum and strive for environmentally optimised flight profiles. There will be no horizontal re-routeing as part of the trial, and flights in their climb or descent phase within MUAC airspace will in general not be affected.

“The objective of the trial is to ensure that environmental benefits are maximised, whilst minimising the impact on aircraft operators in terms of fuel burn. Ensuring a positive environmental balance between reducing greenhouse radiation effects whilst potentially increasing CO2 and other environmental pollutants is a key goal of the MUAC contrail prevention trial: an environmentally optimal flight profile.”

John Santurbano, Director of MUAC, EUROCONTROL

The next project milestone will be the presentation of the results of the statistical evaluation of the experiment. This will, Prof. Sausen explains “answer the question whether we have been successful in avoiding areas where persistent contrails can form. The results of the present experiment will allow us to better plan a demonstration for a wider region, i.e. beyond the MUAC area.”

What else can be done to reduce the impact of non-CO₂ emissions?

Improvements in air traffic management that result in a reduction of fuel burn will also reduce non-CO₂ emissions. This, Prof. Sausen underlines, could be complemented by advances in fuel technology: “in the short term, a smaller fraction of aromatics in aviation fuels will help; this could be achieved by bio fuels or power to liquid. In about two decades the use of hydrogen could help, with respect to the NOx related effects and probably also with respect to the radiative impact of contrails.” Bio fuels or so –called sustainable aviation fuels (SAF) are set to play a significant role to reduce the impact of non-CO2 emissions as they do not require modifications to flight trajectories or airport infrastructure. They have the potential to improve air quality and reduce contrail cirrus impact on climate. For Prof. Sausen, SAF are essential – but more drastic measures also need to be considered: “Incentives that foster the reduction of all aviation climate impacts are vital, such as by including non-CO₂ effects in the EU Emissions Trading System, and by extending such a system to aviation globally in such a way that avoids distorting the aviation market.”

The trial will run until 31 December 2021. For more information on the MUAC-DLR contrail prevention, watch the video clip.

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