UK air navigation service NATS has applied its intelligent arrival separation system to a mixed-mode single runway for the first time, with implementation at London Gatwick.
The system uses dynamic time-based – rather than distance-based – approach spacing in order to maintain sufficient arrival rates in strong headwind conditions.
Headwinds reduce the groundspeed of inbound aircraft flying at a set airspeed. This means a longer interval between two arrivals spaced a fixed distance apart.
“Having to maintain set separation distances in those conditions reduces the landing rate and can have a significant knock-on effect to the airport operation,” says NATS.
NATS has gained experience in time-based separation following implementation at London Heathrow in March 2015.
It has modified its ‘Intelligent Approach’ dynamic separation tool in order to adapt it to Gatwick’s single runway.
NATS has designated the concept ‘advanced mixed-mode’, adding that it will use Eurocontrol’s recategorised wake-turbulence separation minima for arrivals and departures.
It says the introduction of time-based separation to a mixed-mode runway is founded on an “extensive data-collection campaign” of wake-vortex behaviour at Gatwick, over several years.
“A system of using real-time aircraft data to derive wind information has been proven using operational data,” states NATS in an aeronautical notification of the Gatwick plan issued in February.
“When in stronger headwind conditions, a moderate reduction in separation distances from lead and follower aircraft may be observed in comparison to [Eurocontrol wake minima].”
The notification stresses the importance of accurately adhering to assigned speeds, adding that pilots are requested to comply with speed adjustments “as promptly as is feasible”.
NATS says its modified tool, developed in co-operation with Leidos Innovations UK, takes into account the strength of live wind and the time required for departing aircraft to take off between the arrivals.
“Spacing provided between aircraft will be designed to achieve maximum runway utilisation within the parameters of safe separation minima – including wake-turbulence separation – and runway occupancy,” says the notification.
“It is important to the validity of the separation provided, and to the achievement of optimum runway capacity, that runway occupancy time is kept to a minimum consistent with the prevailing conditions.”
London Gatwick chief operating officer Mark Johnston says the scheme will provide “more reliable landing times” and “minimise delays”.
NATS expects the time-based separation will improve the runway efficiency and reduce the holding time for aircraft, estimating that the measure will cut annual carbon emissions by 11,000-19,000t.
