The initial phase of time-based separation (TBS) made its debut at London Heathrow airport last week. Rather than using traditional mileage-based spacing, the new system employs live wind data from airborne aircraft to dynamically calculate optimal safe time-based spacing between arrivals. At Heathrow, the normal arrival rate is 40 per hour, a number that can easily slip closer to an inefficient 30 per hour when high-wind conditions are present. Strong headwinds, present approximately 65 days each year, are considered the single largest cause of arrival delays at Heathrow.

NATS, working with Lockheed Martin, studied more than 150,000 flights before implementation to measure the behavior of aircraft wake vortices in strong headwinds. Those results showed vortices dissipate more quickly in windy conditions, proving aircraft can be safely separated on final approach using a time-based method.