Pairwise Separation
A real game changer
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Improving punctuality at a capacity-constrained airport is no small feat. At Heathrow, where operations run at near maximum capacity, even minor delays ripple across not just the rest of the operating day, but the entire air traffic network. It’s that which makes Heathrow’s 2025 punctuality performance all the more impressive.
In 2025 Heathrow became Europe’s most punctual major hub
Through a combination of collaboration, innovation and the introduction of new air traffic management techniques, in 2025 Heathrow became Europe’s most punctual major hub. At the centre of that transformation was the introduction of Pairwise separation on arrivals, delivered in partnership with NATS, as a world first.
We spoke to Dale Reeson, Director of Operations, Airside, Airfield and Airspace at Heathrow, about what made the difference.
The moment that changed everything
“Punctuality is never an easy thing to improve,” Dale begins. “That’s why we’re so proud of what we achieved in 2025.” For an airport like Heathrow, where over 400 companies and organisations operate every day, improving performance isn’t something that can be solved in isolation or by one team alone.
It requires a coordinated effort across the entire airport ecosystem - from airlines to ground handlers and air traffic control. “The reason we achieved what we did was down to a huge cross-functional effort across all our partners,” he explains. “Airlines, ground handlers and, of course, NATS all played a critical role.”
The reason we achieved what we did was down to a huge cross-functional effort across all our partners.
While collaboration was a key foundation, there was one operational change that stood out: “One of the biggest pieces of work was the introduction of Pairwise separation on arrivals,” says Dale.
Pairwise separation is the latest enhancement to Intelligent Approach, the world’s only operationally proven time based separation tool as developed by NATS with technology partner, Leidos. It dynamically optimises the spacing between arriving aircraft, helping controllers to improve runway throughput while maintaining safety. At an airport like Heathrow, where capacity is tightly constrained, even marginal gains can have a significant impact.
Traditionally, wake separation has been based on six broad aircraft wake categories. Pairwise has replaced this with a granular, data-driven model based on the specific aerodynamic characteristics of each aircraft type - creating approximately 10,000 possible leader-follower combinations.
These more granular pair-specific calculations mean some aircraft combinations can safely operate with reduced spacing. This increases runway throughput without compromising safety, unlocking additional tactical capacity.
“I’ve said before that Pairwise has been a real game changer for our performance and I stand by that.”
An 80% improvement in performance
The results speak for themselves. “If you look at our arrivals performance in 2025, it was around 80% better than the previous year,” Dale says. “And one of the biggest contributors to that was the introduction of Pairwise.”
Beyond headline figures, the change has delivered something even more valuable to the operation: predictability. “It’s given us a much better level of operational stability and, at certain times of the day, it’s actually added an additional arrival per hour.” At Heathrow, that’s no small achievement. “For somewhere as capacity constrained as Heathrow, that’s absolutely priceless.”
It’s given us a much better level of operational stability and, at certain times of the day, it’s actually added an additional arrival per hour.” At Heathrow, that’s no small achievement. “For somewhere as capacity constrained as Heathrow, that’s absolutely priceless.
For passengers, punctuality is often measured in departure times. But as Dale explains, it all starts with arrivals.
Pairwise helping to create an environment of predicable performance, especially for the first flights of the day, is what’s made such a huge difference. “First rotation sets the tone for the entire day. What Pairwise has done is give us a much more stable platform at the start of the day, helping us get those early arrivals in as efficiently as possible.”
Pairwise has provided a stable platform to help organise early arrivals
“It means baggage gets where it needs to be, turnaround is smoother, and aircraft can get back out on time.” At Heathrow, there is very little room to recover from disruption once delays begin to build. “We have very limited resilience during the operational day. So having that tight, consistent arrivals performance from the start is absolutely vital.”
A partnership delivering results
The success of Pairwise separation is rooted in a long-standing partnership. “Our strategic partnership with NATS has been vitally important since it began in 2015,” Dale explains. “Aligning around safety, operational performance and investment in technology has been transformational.”
That alignment has enabled both organisations to deliver meaningful, lasting improvements, not simply one-off gains. Pairwise itself is the latest enhancement to Intelligent Approach, which introduced time-based separation as another world first back in 2015. “It’s that ability to work in lockstep that continues to deliver benefits like Pairwise.”
The impact of these changes hasn’t gone unnoticed across the industry. “Airport leaders often ask me whether they should consider Intelligent Approach,” Dale says. “And I’ve already said yes.”
The results at Heathrow, including becoming Europe’s most punctual major hub, provide a compelling case. “If you look at the transformation it’s delivered, it speaks for itself. I’d encourage anyone considering it to start that conversation with NATS.”
While the results in 2025 were significant, Dale is clear that this is just the beginning. “It’s no secret we have big ambitions,” he says, pointing to future plans including expansion and continued growth in demand. Meeting those ambitions will require continued innovation and collaboration. Ultimately, the transformation in performance comes down to people united around a common goal. “This has been a real team effort,” Dale reflects. “I’m particularly proud of all our Heathrow partners - the airlines, the ground handlers and NATS.”
It’s no secret Heathrow has big ambitions, including expansion and continued growth in demand. Meeting those ambitions will require continued innovation and collaboration. Ultimately, the transformation in performance comes down to people united around a common goal.
And at the heart of it all is a shared goal: delivering safe, efficient and reliable operations for passengers and airlines alike. “Good punctuality is the foundation of everything we do,” he says. “And what we’ve shown is what’s possible when the whole system works together.”