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Mobility and Transport

Time Based Separation at Heathrow

Middlesex, United KingdomHeathrow Airport Limited, NATS, Lockheed Martin, EUROCONTROL

Aircraft arriving at airports are traditionally separated by fixed distances dependent upon the amount of spiralling turbulence, or wake vortex, they create as they fly. With fixed distance based separation, in strong headwinds, the ground speed drops so it takes longer to travel the same distance. This results in reduced landing rate and is a significant cause of arrival delays.

Prior to TBS deployment, Heathrow Airport experienced over 400,000 minutes of arrival delay each year, with 80% of this attributable to adverse weather conditions. Wind was accountable for 44% of all delay, making it the single highest cause of arrival delay and also resulted in large numbers of flight cancellations. As Europe's largest hub airport any delay can cause a chain reaction across the European network.

To counteract the effect of wind on the landing rate and provide resilience for airport operations, Time Based Separation (TBS) replaces distance separations with time separations.

The safety case for time based separation was based on 5 years of data collection and analysis by NATS and EUROCONTROL to determine wake vortex behaviour across all aircraft types and all wind conditions.

TBS uses live data downlinked from the aircraft to dynamically calculate the actual winds on final approach to determine the optimal safe wake vortex spacing between aircraft. Real-time separation indicators are provided to controllers to assist with managing final approach separations.

The deployment of TBS followed two years of 'agile' development building on the successful validation of the concept within a SESAR research programme and early studies from both EUROCONTROL and NATS.

Award Criteria

  • Contribution to increasing capacity of ATM systems
  • Contribution to reducing ATM costs
  • Early implementation
  • Potential to be replicated over the ATM network
  • Innovative aspects
  • Promoting partnerships
  • Contribution to change management
  • Promoting SES and SESAR beyond the Union's boundaries

Explanation

Contribution to increasing capacity of ATM systems:

Under normal conditions NATS air traffic controllers land around 42 aircraft an hour at Heathrow, the world's busiest dual runway operation, however that falls dramatically in a strong headwind when aircraft fly more slowly over the ground.

Having to maintain a fixed separation distance between arrivals cuts the landing rate and has a significant effect on airport capacity. The Time Based Separation system uses real-time wind data to calculate the optimum safe time between arriving aircraft, therefore allowing separation distances to be dynamically adjusted in order to maintain the landing rate.

For example on 30 March 2015, with a 35 knot headwind on final approach, NATS controllers landed on average of two more aircraft per hour and halved delays when compared to similar conditions. On 2 March before TBS was introduced, winds averaging 30 knots at 3000ft generated 9750 minutes of Air Traffic Flow Management (ATFM) delay.

Analysis undertaken during November 2015, where there were 15 days affected by strong headwinds, showed that over 25,000 minutes of delay was saved as a result of TBS. On 10 November, with a 40 knot headwind at 3000ft, no arrival regulations were required and the landing rate was 3-4 movements an hour higher than it would have been without TBS.

A snapshot of the benefits to capacity that TBS has brought can be seen below:

  • 83% of aircraft experienced smaller Arrival-Arrival separations (May-July 2015)
  • TBS has on average saved 78NM per day in Arrival-Arrival distance separations on Heathrow final approach
  • 178NM saved per day in strong wind conditions (>20kts)
  • Across all wind conditions an additional 1.2 movements per hour
  • In strong wind conditions an additional 2.9 movements per hour

Since TBS went live on 24 March 2015 there has been no increase in wake turbulence events and no increase in the number of go-arounds.

Contribution to reducing ATM costs:

Whilst TBS doesn't directly reduce the cost of ATM its introduction has delivered major benefits to Heathrow Airport, the airlines and the flying public at no additional cost. TBS is delivering a reduction in wind related ATFM delay of over 60%. This is achieved by an average increase in the landing rate of 1.2 arrivals per hour over distance based separations across all wind conditions, increasing to an average of 2.9 arrivals per hour in winds over 20kts. As a result of this, there has been a marked reduction in weather related flight cancellations.

Early implementation ("First mover"):

TBS was introduced into full operational service at Heathrow Airport on 24 March 2015 in response to customer feedback, nine years ahead of the legal requirement for TBS to be operational at Europe's busiest airports and two years ahead of NATS initial plans.

The deployment of TBS follows two years of 'agile' development building on the successful validation of the concept within a SESAR research programme and early studies from both EUROCONTROL and NATS.

Early and consistent engagement with the regulator, as well as the airport and airlines was crucial to achieving this timescale.

Video materials & crew briefings engaged customers and airspace users and resulted in strong support for the implementation of TBS.

TBS is a world first, that offers significant benefit to Airline customers and the busiest dual runway airport in the world, delivering an assured, resilient operation. It sets an industry benchmark that is already delivering benefits to customers in the UK and in turn having a positive impact on the wider European network.

Potential to be replicated over the ATM network:

The modular design of the system ensures that it is easily adapted to accommodate a variety of runway configurations and ATC operating methods not only in weather situations but also in optimising runway capacity through helping controllers deliver consistent spacing on final approach.

TBS is mandated to be in operation at Europe's busiest airports by 2024. Many of the lessons learned from the development work carried out on TBS and the work to take it from concept to implementation will be valuable across Europe in the coming years.

Innovative aspects:

A key feature of TBS is that it uses downlinked real time live wind data from the aircraft to dynamically calculate the headwind effect on final approach and determine the optimal safe wake vortex spacing between aircraft. Separation indicators are provided to controllers to assist with managing final approach separations.

In addition to conducting real time simulations to develop algorithms, assess controller workload and validate benefits, NATS and EUROCONTROL studied the arrival paths of over 150,000 aircraft at London Heathrow, using state of the art LIDAR equipment to accurately measure the behaviour of aircraft wake vortices. This helped to inform the safety case for the introduction of TBS.

Another innovative aspect of the TBS implementation was the close collaboration between the ANSP, airport and airlines. There was strong engagement from all parties throughout the process to help ensure timely and successful implementation, through for example crew briefings supported by NATS and promotion of the concept by the airspace users.

Promoting partnerships:

To develop and deploy TBS successfully, significant work was required to understand wake vortex behaviour in headwinds, develop operational procedures and validate air traffic controller support tools. Working in partnership NATS and EUROCONTROL studied the arrival paths of over 150,000 aircraft at London Heathrow, using state of the art equipment to accurately measure the behaviour of aircraft wake vortices. The results proved that the stronger the headwind component, the quicker the wake vortices dissipate, allowing the distance between aircraft to be reduced on final approach, and providing the underlying evidence for safety assurance.

The wake vortex database developed by EUROCONTROL and NATS has not only been used for TBS, but is also the basis for further improving and optimising the ATC rules and practices. These rules need to assure that wake vortex separations are efficient in terms of runway capacity but are also demonstrably safe. In order to realise the benefits of more efficient and tailored vortex separations it is essential to provide tools that support the controller task. The collaboration of EUROCONTROL, NATS, Lockheed Martin and Heathrow Airport Limited has resulted in the successful delivery of such a capability.

Early engagement with customers and airspace users enabled the implementation of TBS to be tailored to the requirements of the airport and its users.

Contribution to change management:

The deployment of TBS followed an 'agile' development process, building on the successful validation of the concept within a SESAR research programme and early studies from both EUROCONTROL and NATS. Originally planned for deployment in 2017/2018, this 'agile' approach allowed the TBS project to be accelerated cutting the delivery time from 4 years to 2 years.

The development and implementation of TBS at Heathrow demonstrated the benefit of close collaboration between all parties – ANSP, airport and airlines – in order to successfully accelerate the introduction of a SESAR concept, ensuring it was in operation and delivering benefits to airspace users at the earliest possible opportunity. This proactive approach demonstrates what is possible when all stakeholders are engaged in the process from an early stage and all help each other to manage the change that a significant deployment of this kind requires.

Promoting SES and SESAR beyond the Union's boundaries:

The implementation of TBS at Heathrow has generated significant interest from around the world including USA and Middle East, promoting the benefits of a SESAR concept as well as demonstrating that SESAR is already being deployed within Europe.

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