The completion of the German D-KULT research project at the end of 2025 marks the first time that practical results on how to avoid climate-impacting contrails in aviation are available. Research shows that strategically optimising flight planning to reduce climate impact offers opportunities, but that further research is needed.
Project launch in 2022
The D-KULT project was funded by the German Federal Ministry for Economic Affairs and Energy (BMWE) and ran from June 2022 to August 2025 as part of the LuFo VI-2 aviation research programme. Among the partners were the German Aerospace Centre (DLR), DFS, the German Meteorological Service (DWD) and German airlines. The D-KULT project name derives from the German for 'demonstrator for climate and environmentally friendly air transport'. The aim of the project was to develop procedures to reduce the climate impact of air traffic. The main way of doing this was for aircraft to avoid flying through areas where ice-saturated air layers cause long-lasting, or persistent, contrails to form. These so-called potential persistent contrails, or PPC, contribute significantly to global warming.
Two research approaches
In one approach, the researchers analysed tactical avoidance. Tactical avoidance involves air traffic control guiding aircraft around the relevant areas. Real-time simulations have shown that this approach was not practicable, however. Purely tactical re-routings lead to a 20 to 60 percent loss in airspace capacity and an increased workload for air traffic controllers.
Strategic avoidance is considered to be much more promising. Strategic avoidance would see airlines expanding their flight planning systems to include climate optimisation functions. Airlines would thus be able to select suitable routes before the flight took off. In one test with 100 flights, PPC areas were avoided in a targeted manner. However, this test was very time-consuming to plan and carry out manually, as it was based on individual flights. It is therefore not yet possible to transfer this approach into regular operations.
Intensive discussions – further research required
Further research has to be carried out before procedures can be used in regular operations. Researchers from the German Aerospace Centre (DLR) are currently investigating the effects on fuel consumption and the carbon footprint. One thing is clear: A positive climate impact will only occur if the benefits of flying around the areas exceed the additional CO₂ emissions required to do so. Initial calculations show potential but raise new questions. In addition, the underlying weather and climate data proved to be less robust than expected. DFS has intensified the scientific dialogue with the DLR and DWD to develop new approaches. The DLR is coordinating the D-KULT project and is itself involved with five institutes.
Commenting on the project, Arndt Schoenemann, CEO of DFS, said: "D-KULT has laid important foundations, but research must continue, both nationally and internationally." The goal remains a coordinated approach by airlines, air navigation service providers and the European air traffic control network management to effectively avoid climate-relevant contrails."
Media contact:
Nanda Geelvink
Telephone: +49 (0)6103 707-4164
E-mail: presse@dfs.de
DFS Deutsche Flugsicherung GmbH (DFS), the German air navigation service provider, is a State-owned company under private law with 5,800 employees as at 31 December 2025. DFS ensures the safe and punctual flow of air traffic over Germany. Around 2,200 air traffic controllers guide more than three million flights through German airspace in peak years, up to 10,000 flights every day. The company operates control centres in Bremen, Karlsruhe, Langen and Munich as well as control towers at the 15 designated international airports in Germany. The subsidiary, DFS Aviation Services GmbH, markets and sells products and services related to air navigation services, and provides air traffic control at nine regional airports in Germany and at Edinburgh Airport in the United Kingdom. DFS is working on the integration of drones into air traffic and has set up a joint venture, Droniq GmbH, with Deutsche Telekom. Other subsidiaries include R. Eisenschmidt GmbH, which markets publications and products for general aviation, and Kaufbeuren ATM Training GmbH (KAT), which provides training for military air traffic services personnel. The joint venture FCS Flight Calibration Services GmbH offers flight inspection services.