Time Based Separation

Strong winds, yet no delays: a study into the options provided by TBS. 

Strong winds can cause severe delays at Schiphol. Or even cause flights to be cancelled. A potential solution has now been found for this: Time Based Separation (TBS). It is already a huge success at London Heathrow. So Schiphol, what are we waiting for?

Keep your distance

Schiphol currently uses Distance Based Separation (DBS). Here, air traffic controllers maintain a minimum distance between landing aircraft. On behalf of Stichting KDC, To70 is investigating the options for TBS at Schiphol. Project leader Arjen de Leege explains: “The disadvantages of DBS are obvious when there is a headwind. The ground speed of landing aircraft decreases in the event of a strong headwind. As the minimum distance of three nautical miles (NM) between aircraft remains the same, it takes longer to cover this distance. And ultimately this causes a decrease in landing capacity.” 

Calm before the storm

TBS is less dependent on wind speed. Air traffic controllers still calculate distances, just as with DBS. But in this case the distance is based on time. “Pilots notice this, for example, because if there is a strong headwind they can fly much closer to the aircraft in front of them,” Leege continues. “TBS also takes into account wake turbulence caused by wing tip vortices. These vortices can be hazardous to other aircraft. The time in which the vortex remains active depends on the weather conditions.” DBS applies a standard distance based on the most unfavourable weather conditions. In the case of strong winds, however, the vortex is only active for a short time, allowing distances to be reduced.  

TBS in future

To70 has used simulations to determine the landing capacity at Schiphol. Leege is enthusiastic about the outcome of the study. “In the event of a strong headwind, the capacity using TBS is one to two aircraft more per hour. During a storm, that can rise to as many as five aircraft per hour!” TBS therefore also offers Schiphol opportunities for reducing the number of delays and cancellations. The capacity is then less dependent on the wind. “But a great deal of work still needs to be done before we can implement this. TBS requires new systems and procedures. LVNL will certainly take the results of this study into account when it makes its decision.”

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