Airport air traffic controllers do incredible work to keep flights moving in and out of some of the world’s busiest airspace. But with increasing pressure on that airspace — and on controllers — new systems are providing more information to help with optimised decision-making. One is Intelligent Approach, an arrivals spacing tool developed by UK air navigation service provider NATS and global technology supplier Leidos, that provides new live information to controllers, helping them to use runway capacity better.
At present, Leidos UK’s programme manager Danny O’Hare tells us, “most airports around the world still use fixed distance-based separation on final approach, with separation standards based on the International Civil Aviation Organisation (ICAO), RECAT EU wake vortex separation or ICAO rules for dependent separation for parallel runways.”
“Separation between successive arrivals is set up by controllers using their skill and judgement which is not a simple task. Additionally, changing wind conditions and aircraft speed mean that it is hard to truly optimise the separation between aircraft pairs,” he explains. “Runway occupancy also differs between aircraft types and by runway due to the position of exit taxiways, terminals and differences in aircraft performance. Weather conditions, such as strong winds and low visibility, which have their own separation minima, can make the task of separating aircrafts even more challenging.”
It remains a very human process, he notes, highlighting that “air traffic controllers do a great job managing this, but there is inevitably lost runway capacity as some additional margin between arrival pairs is applied to avoid minimum spacing and separation being infringed.”
To supplement this expertise, the Intelligent Approach system adds a dynamic indicator that progresses along the path of final approach on controllers’ displays. In essence, the controller’s aim is to have the aircraft aligned with the indicator in order to achieve optimised spacing and separation.
“The indicator is based on the position of the aircraft in front,” O’Hare says, “so it’s not like a fixed ladder that the controller needs to put the aircraft onto. In addition, the software has capture logic that allows the controller to change the arrival sequence if they need to, and the tool will automatically adapt to their actions. It is this element, together with an intuitive display, that makes it easy for controllers to adapt to.”
Intelligent Approach combines a number of critical, continually changing factors as part of providing this information to air traffic controllers, and takes into account:
- distance-based separation (DBS), using either the ICAO wake turbulence category or newer RECAT wake vortex separation standards
- time-based separation (TBS), including a headwind component
- runway occupancy
- dependent runway indicators where there are closely spaced parallel runways
Two further technologies are under development.
The first is pairwise separation, which O’Hare categorises as “separation individually tailored between each pair of arrivals. Before having this capability, this wake vortex separation grouped aircraft into categories so inevitably the category into which an aircraft is allocated has to allow for the most limiting aircraft performance. Pairwise individually tailors separation in increments of 0.1 miles allowing the runway capacity to be fully optimised. This is expected to deliver an additional two movements per hour over and above that already delivered by DBS/TBS. Pairwise is expected to go live next year.”
Pairwise separation moves beyond the six ICAO or RECAT wake vortex classifications, which currently result in a six-by-six grid of possible aircraft pairs: a Upper Medium Boeing 737-800 following an Upper Heavy A350-900, for example. Pairwise presents this as an individually calculated separation to the controller, beyond what would be feasible for a controller to calculate independently.
The second technology is optimised mixed mode, where an airport can combine arrival and departure sequence data for a mixed mode runway where both arrivals and departures are conducted from the same runway. Here, Intelligent Approach optimises arrival gaps to match departure runway occupancy, and Leidos estimates an additional two movements per hour per runway gain when it is deployed in 2024–25.
Already in use at London Heathrow and Toronto Pearson as Enhanced Intelligent Approach, the system is due to go live at Amsterdam Schiphol in 2023.
“When Intelligent Approach went live at London Heathrow an immediate benefit was seen. In instances where the landing rate in strong headwinds was measurably higher, Intelligent Approach helped reduce delays and airborne holding,” O’Hare explains. “Measuring the time interval between arrivals for a number of months, pre- and post-implementation, demonstrated a tactical capacity gain equivalent to over 1,410 seconds or 23.5 minutes of arrivals per day. As Heathrow is capped at 480,000 movements per year this translated into an overall punctuality improvement of 1.5-2.5 percent, a 50-60 percent reduction in delays due to headwinds and reduced airborne holding equating to an annual saving of over 31,000 tons of CO2.”
While this data all dates back to the pre-pandemic statistics, the prospects for optimisation are nonetheless impressive.
Implementation timescales are relatively short, with the company citing less than one and a half years for a new airport and air traffic control environment. Critically, no new ground infrastructure or airborne equipment is required: this is a software solution to a problem that requires little hardware integration.
The technology stack for the system includes five years’ worth of LIDAR wake vortex data collection from NATS, which was supported by European coordination body Eurocontrol. This dataset enabled the system to allow aircraft to approach more closely spaced as headwind increases and, at the same time, vortices dissipate faster. Also included is a detailed real-time model of wind data, including by processing data from aircraft Mode S transponders.
“Implementing this type of system does require the Air Navigation Service Provider, the airport and its operators to work together to make the most of the benefits available,” O’Hare tells us. “For example, as you start to put aircraft closer together on final approach, it is all the more important that aircraft follow their ATC instructed speeds closely. This was very successful at Heathrow, where speed compliance data is shared with the airlines to improve compliance, and allows controllers the confidence that aircraft will effectively do as they are instructed — or let ATC know early if they cannot do so for operational reasons.”
Author: John Walton
Published: 18th October 2022
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