Planning Summer 2025: the weather takes centre stage

The Network Manager’s (NM) planning for summer 2025 peak season traffic, as in 2024, focuses on four main actions: prioritising the first rotation; disciplined flight plan execution; delivering agreed capacities and taking a realistic approach to scheduling, including turnround times. But this year there is an addition to the list of priorities – weather.

Air traffic flow management (ATFM) weather-related delays in 2024 were responsible for 47% of all network delays between June and August 2024 and the single most important factor in the poor on-time performance of Europe’s ATM system (See How did Europe’s ATM system perform in summer 2024?). Europe’s climate is changing (See Europe’s changing climate – what we should expect), with thunderstorm activity increasing around 26% year on year and lightning strikes increasing 30%. During the summer months, when airline traffic is at its peak with airports and airspace at their most congested, these severe weather incidents are at their most disruptive, causing ripples of delay and uncertainty throughout the network.

So this year NM has developed a more structured approach to dealing with this growing challenge to the smooth running of Europe’s air traffic management network.

“What normally happens is the conductive weather appears and everyone acts for themselves; air navigation service providers (ANSPs) regulate the sector’s forecast to be impacted, and aircraft operators all start flying different routes to try to find a way around the delays,” said Steven Moore, Head of ATM Network Operations at EUROCONTROL. “That then leads to capacity problems in adjacent sectors and ANSPs struggling to deliver capacity to meet the increase in demand as needed.”

In 2025 NM is adopting a new disruptive weather mitigation strategy. Early in the year NM launched a campaign of getting all relevant stakeholders – airlines, airports, air navigation service providers – to agree to take proactive measures to schedule flights based on the weather forecasts ahead of the departing traffic. This will allow NM to plan more proactively to manage demand and capacity balancing so it can ultimately move traffic in a safer and more predictable way, reducing some of the delays associated with weather regulations and improving the stability of the overall network.

To succeed, it will require a high level of collaborative decision-making because NM does not have the power to do this without the agreement of all stakeholders.

“The airlines are really engaged,” said Steven Moore. “They are ready and willing to take some small deviations for the network to avoid areas of significantly bad weather in a more structured way.”

But for ANSPs, the challenges of engagement are more complex because the process and procedures for moving traffic to avoid forecast severe weather events in a pre-tactical way was still being fully defined in early spring. NM is not relying on having a 100% perfect process and buy-in from all stakeholders at the start; it is planning to use whatever accurate information is available in a more effective way in an iterative approach which will grow and improve in the years ahead.

To support NM’s disruptive weather mitigation strategy, the Network Manager Board approved the recruitment of six meteorological experts, including a coordinator and five specialists working across different shifts.

“This will not mean the weather delay problem will suddenly disappear,” said Steven Moore. “ANSPs who have brought met experts into their operations have taken time to get the full benefits, but we're positive it's a critical step in the right direction. It's also correct that NM should have an overview of the weather for the network and be able to talk knowledgably to all the embedded ANSP forecasters to get a common view of what the weather is, and what it's going to do. Very often we find there's slight differences between ANSP and Member State forecasters, depending on what the rules are, and we have to try and find a common way of approaching what the weather situation is going to be.”

One of the challenges is that stakeholders measure weather in different ways and have different forecast models. For example, one ANSP in the core traffic area of Europe has two models from its met services provider – so often must manage two very different views of what the weather will do. This means the ANSP will plan for the more disruptive forecast to ensure safety, while being under constant pressure to reduce the regulations. Other ANSPs take the forecast of the national service provider as the de facto forecast and apply regulations accordingly, even if other information may suggest the forecast might not be entirely accurate.

“I think this focus on the weather will clearly will make a huge difference this summer but the real gain in delay reduction will be progressive in years to come when met experts in the network operations centre become much more acclimatised and accustomed to what happens in the network when convective weather threatens and then materialises, or not, and this is where we really need the accuracy of the forecasts,” said Steven Moore, noting that “it is equally important for the network stakeholders to align and be able to plan on the forecast of the weather starting, as it is for the stakeholders to also plan for the weather event ending, e.g. increasing capacity based on the forecasts as quickly as it is reduced based on forecasts, rather than simply waiting to see the weather end.”

Apart from the weather, NM is making progress in other capacity-enhancing initiatives for the peak travel season.

“What we can really control this summer is making sure that we deliver on agreed capacities as a network rather than letting everyone down at the last minute by not providing the agreed capacity; in addition, the disciplined flight plan execution in the vertical phase of flight is also a real focus for this summer,” said Steven Moore, “where gains of up to 10% of capacity could be found if every flight flew at its last filed flight levels,” he added.

Around 40% of the continent’s 68 en-route ATM centres are now expected to open more sectors for Summer 2025 than in Summer 2024. However, 20% of the remaining centres will offer fewer sector openings than in 2024. Overall, for the network, with the anticipated increase in demand averaging 5.2% over the year, but peaking at levels much higher in already capacity-constrained areas during the summer months, we can expect to see delays in both of the core axes of flights to the SE and the SW. Here we can expect, in the days where other elements of disruption such as strikes, severe weather and system failures occur, a very high daily average of delay which will have a significant impact in the performance of the network overall. This will inevitably create a snowball effect and the network will have serious difficulties in managing the levels of traffic, with consequent severe levels of delay.

“If everyone plays their part and delivers on the things that we can control, namely providing the agreed capacities, delivering on realistic schedules, flying at the filed levels, prioritising the first rotation, and critically cooperate, collaborate and actively support the new process for managing adverse weather, we will have the best possible outcome. The last one is important – we cannot control the weather, but we can control how we respond to it, maintaining safety but also pushing for a greater Network approach – #thinkNetwork.”