The History of Time-Based Separation (TBS): Celebrating 10 Years Since TBS Landed at Heathrow

NATS, Leidos and Heathrow Airport are celebrating the tenth anniversary of Time-Based mostly Separation (TBS) – utilizing time intervals to handle plane separation on method as an alternative of mounted distances – delivered as a world first when their groundbreaking Clever Strategy arrival spacing instrument went stay in 2015. Have a look again on the early years of TBS and its improvement and implementation on the world’s busiest two-runway airport and the massive advantages this instrument has introduced, together with saving nearly 3 years of airborne holding time all through the ten years.

Having been concerned in getting TBS into Heathrow, I used to be fortunate sufficient to expertise the advantages first-hand simply three days after it went stay. I used to be flying again to Heathrow, arriving at peak time within the early night. Whilst you might see on the flight standing boards at our departure airport that the remainder of Europe was fighting delays as a result of robust winds, we arrived at Heathrow 5 minutes early on stand – at a peak hour throughout robust winds! Proof that TBS did what we had hoped it will.

When flight delays happen, notably within the morning, it creates a domino impact all through the day leading to rotational delay and cancellations. In 2003, Heathrow, British Airways and NATS appeared intimately on the causal elements behind the airborne holding and delays. We recognized a number of causes and areas which we might doubtlessly enhance: This included headwind associated delays, capability constraints, airborne holding, and extra.

These elements have been essential in resulting in the event of Time-Based mostly Separation (TBS). Nobody had accomplished this earlier than – the security case wanted to be confirmed, and the instruments and procedures wanted to be developed from scratch.

Bettering Security Efficiency

NATS began actively making ready the bottom for Time-Based mostly Separation in 2007 when LIDAR knowledge assortment started at Heathrow, assisted by an on-loan Eurocontrol WindTracer LIDAR – extremely correct distant sensing know-how. 5 years and 150,000+ flights later, in each wind situation possible near the bottom and additional up the method, evaluation proved that it will be secure to cut back the arrival distance gaps proportionally because the headwind part will increase, considerably recovering delay time.

While TBS was being developed, NATS labored intently with the UK CAA as the primary regulator on the earth to allow time-based separations. This security case has now been adopted by ICAO, who printed TBS separations in Procedures for Air Navigation Companies Air Visitors Administration (PANS-ATM) November 2024.

Collaboration & Improvement

Creating and implementing TBS required an enormous collaborative effort; new instruments and procedures have been wanted to allow TBS to work, and endorsement and experience from throughout the trade was essential to success. With funding and help from SESAR, the airways, and Heathrow Airport, NATS and Leidos began the construct of the ultimate product in 2014 and it went stay in simply over a yr later.

Help and preparation from airways and Heathrow Airport noticed a easy introduction of TBS. We labored with the airways to enhance their pace compliance on ultimate method, giving ATC the arrogance to vector plane nearer collectively. We additionally labored intently with Heathrow and a number of the principal airways to make sure that crews have been prepared for the introduction of TBS having beforehand been accustomed to plain mounted distance-based separation. Airways even helped by showing in explanatory movies to assist temporary everybody earlier than the system went stay. Unusually, the primary two days of TBS operation noticed gentle winds resulting in a disappointing begin for TBS. Then, with robust winds on day 3, the advantages have been clear for all to see.

On 24 March 2015, Heathrow turned the primary airport on the earth to make use of TBS when it went stay within the London Terminal Management Ops Room, the place it has been operating ever since.

Controller Response and the Go-Dwell Expertise

So, how did ATC reply to TBS? TBS was developed by controllers, for controllers; the event was accomplished in collaboration with this core group. Because of their involvement, TBS’ touchdown at Heathrow was easy and managed. The core group helped to simplify the instruments and procedures to make it straightforward to be taught and use.

It took only some days to see the results of TBS; after abnormally gentle winds within the first couple of days following deployment, the headwinds elevated, reaching over 30 knots at 3,000ft. The system got here into its personal, instantly recovering the capability that may have been misplaced.

Importantly, TBS was very nicely accepted by Air Visitors Controllers. Just a few days into stay operation, we requested if we might flip the system off to make a small change to the software program adaptation, however the controllers requested us to go away it operating and do the difference in a single day – a testomony to the wonderful work by the TBS Core Group that designed the instrument and procedures.

The airways and the airport might immediately see a profit; inside the first yr of TBS operation, Heathrow noticed a 62% discount in headwind delays.

Outcomes & the Future

In yr one, TBS allowed Heathrow to land a median of two.9 extra plane per hour on robust wind days enormously decreasing delays and airborne holding. Crucially, this was all achieved with none enhance in reported wake vortex encounters or go-arounds.

This was just the start of the story for TBS. We realised that we had a really efficient new product with a robust use case and ongoing developmental potential. The TBS instrument (now often called Clever Strategy) was then used to implement RECAT EU separations and add Optimised Runway Supply and Runway Occupancy Time separations in 2018. This enhanced the advantages of the system additional. It was this normal that went stay in Toronto Pearson in 2022 and Amsterdam Schiphol in 2023.

In March 2024 an settlement was signed permitting incorporation of Clever Strategy into Indra’s ATM techniques, a number of the most generally used techniques in management centres world wide. And, in December 2024, Heathrow turned the primary airport on the earth to utilise Pairwise ultimate method separation, utilizing wake vortex separation individually tailor-made for every pair of plane, providing much more advantages to Heathrow’s airways, passengers and to the environmental financial savings.

Since its implementation, the advantages of TBS have been excellent. Over the ten years since TBS went stay, it has minimize airborne holding by a complete of 1,500,000 minutes, equating to nearly 3 years of holding time saved. This has saved over 100,000 tonnes of gasoline – value roughly USD 70 million primarily based on March 2025 jet gasoline costs – and helped contribute to extra sustainable aviation by saving over 300,000 tonnes of CO₂.

TBS is a key characteristic of arrival spacing instrument Intelligent Approach, which continues so as to add new options permitting busy airports to get essentially the most out of their runways and provide important environmental financial savings and operational resilience to any airport that adopts it.

Thanks to everybody at Heathrow Airport, NATS, Leidos, Suppose, Eurocontrol, SESAR, all concerned airways, our prospects and the numerous different organisations who made TBS occur initially and who proceed to help the product.