London Heathrow Airport air traffic controllers have begun using an enhanced time-based separation (TBS) system to reduce wake separation between landing airliners.

The new system, part of what UK air navigation service provider National Air Traffic Services (NATS) calls its optimized runway delivery tool, is expected to increase capacity at the airport by at least one arrival and one departure per hour, increasing the airport’s operational resilience and improving punctuality.

The system went active March 16.

Heathrow has been making use of TBS since 2015, primarily on windy days to help maintain the flow rate of landings at the two-runway airport. Research using Lidar sensors found that strong headwinds dissipated the effect of wake vortices, allowing landing separation distances to be reduced. The system’s introduction has already saved thousands of minutes of delays each year.

The improved version of the system, known as eTBS, is making use of the latest European Wake Vortex Reclassification (RECAT-EU) categories. Developed by Eurocontrol, RECAT-EU has redefined the minimum distances required for wake vortices to be dissipated. Aircraft have been allocated into six different weight categories, with the Airbus A380 redefined as a “super heavy,” while the Boeing 747 becomes an “upper heavy.”

Narrowbody types, such as the Airbus A320 and Boeing 737, become “upper medium” types. The RECAT-EU work has reduced the separation distances needed for some types, but increased them for other types depending on how they react to wake turbulence.

The eTBS tool gives the air traffic controllers separation markers to the runway threshold based on the RECAT-EU definitions. The tool also provides controllers with runway occupancy indications for pairs of arriving aircraft when that is more limiting than wake separation.

Tony Osborne,