The UK has launched the first state-backed trial of contrail avoidance across an entire oceanic airspace region. The scheme, known as Operation Blue Skies, will examine whether relatively minor changes to aircraft trajectories can reduce aviation’s non-CO₂ climate impact at operational scale.
The £5m, 30-month programme will be conducted in Shanwick Oceanic airspace, covering the eastern half of the North Atlantic corridor. Atmospheric modelling suggests the region is responsible for around 5% of global contrail warming, with a significant proportion concentrated between November and February.
Contrails form when water vapour in aircraft exhaust freezes around particles in cold, humid conditions at altitude. Although many disappear rapidly, persistent contrails can spread into cirrus cloud that traps outgoing heat. While estimates vary over their precise climate effect, Google, which is taking part in the project, said warming contrails account for roughly one-third of aviation’s overall climate impact.
Operation Blue Skies will use artificial intelligence to forecast areas where strongly warming contrails are likely to develop. Rather than substantially rerouting aircraft, selected flights could be instructed to make relatively minor altitude changes to pass above or below these contrail-sensitive atmospheric layers. NATS will coordinate the manoeuvres using existing ATC procedures, with safety assessments and controller training forming part of the programme.
Two test periods of around four months each will be carried out during the 2026/27 and 2027/28 winters. During each of these periods, trials are expected to take place on around 20-40 days, primarily during periods of lower traffic. Around 10,000 flights pass through Shanwick during the relevant trial hours each year. However, only a small percentage of flights that are expected to encounter contrail-forming conditions will have their flight plans altered.
The project brings together Google UK, NATS, the Met Office, Contrails.org, Imperial College London and the University of Cambridge. Google is developing the AI forecasting models and will use machine learning and satellite imagery to help determine whether interventions prevented contrails. The Met Office is creating a new UK contrail forecasting capability, while Imperial and Cambridge will independently assess operational effects and the resulting climate benefit.
The Department for Transport is contributing £2.65m through the Aerospace Technology Institute Programme, while Google is providing around £1.4m of AI expertise, engineering and computing resources in kind. If successful, the project could provide a blueprint for incorporating contrail avoidance into routine air traffic management without requiring modifications to existing aircraft or engines.
