Google-led consortium launches airspace trial to test contrail-busting flight path changes

The UK Government and Google have launched a 30-month trial to investigate whether small changes to aircraft flight paths can reduce aviation's climate impact by avoiding the formation of persistent contrails.

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Operation Blue Skies will test the approach across the Shanwick Oceanic Control Area, the eastern half of the North Atlantic airspace managed by the UK's air navigation service provider NATS. The area is a major corridor for flights between Europe and North America and has been identified as a region where conditions conducive to contrail formation occur.

The programme will use artificial intelligence and weather forecasting to identify areas where aircraft are more likely to produce persistent contrails. Air traffic controllers will then instruct a proportion of flights to make small altitude adjustments to avoid those areas.

The operational trials will take place during selected periods in the winters of 2026/27 and 2027/28. On around 20 to 40 test days each winter, hundreds of aircraft are expected to make adjustments of up to 2,000 feet. Around 10,000 flights are expected to pass through the trial airspace during the testing periods.

The £5m programme is being supported by the UK Government through the Aerospace Technology Institute Programme, with the Department for Transport contributing £2.65m. Google is participating on a pro bono basis, providing AI research expertise, engineering resources and computing infrastructure.

The consortium also includes NATS, the Met Office, the University of Cambridge, Imperial College London and Contrails.org.

Contrails form when water vapour from aircraft exhaust encounters sufficiently cold and humid conditions at altitude. The water freezes into ice crystals, which can develop into persistent cloud-like formations.

While some contrails disappear quickly, persistent contrail cirrus can have a warming effect by trapping outgoing heat in the atmosphere. The UK Government identifies contrails as one of several significant non-CO2 effects of aviation, alongside nitrogen oxides, aerosols and water vapour.

The scale of their contribution to aviation's overall climate impact remains an area of scientific research, with estimates varying according to the methodology used. The Aerospace Technology Institute says warming contrails can account for up to half of aviation's total warming impact, although the trial's partners cite lower estimates.

Operation Blue Skies is intended to establish how effectively the effect can be reduced in real-world airspace rather than relying solely on modelling or individual flight demonstrations.

Google will provide forecasts identifying likely contrail-forming regions, while the Met Office is developing a contrail impact forecasting capability and will support the scientific assessment of the results. NATS will provide the air traffic management framework for the operational trial.

Keir Mather, the UK minister responsible for aviation, said the government was working with Google and UK researchers and innovators “to find practical ways to make flying cleaner”.

The trial follows earlier work involving individual airlines. Google and American Airlines have previously tested AI-based contrail forecasting to identify flights where changes in altitude could avoid conditions conducive to persistent contrails. Operation Blue Skies will move the research to an airspace-wide setting, where multiple aircraft can potentially be managed simultaneously.

The trial comes as the UK Government is pursuing a broader programme of airspace modernisation. In June 2025, the Department for Transport announced plans for a new UK Airspace Design Service, operated by NATS, intended to redesign parts of the UK's airspace and create more direct and efficient routes. The government said modernisation could reduce delays, fuel use and emissions while creating additional capacity for aviation growth.

The results will also contribute to the wider assessment of aviation's non-CO2 climate effects, an area in which the UK Government has said further evidence is needed to improve measurement and develop effective mitigation policies.