Pair Wise Separations (PWS) / RECAT-2

In revising the European Wake Turbulence Categorisation and Separation Minima, RECAT-2 has developed a static separation matrix of distance and time for both arrivals and departures.


Capacity limitations, caused by today’s overly conservative wake separations at constrained airports, increase arrival traffic flow congestion and generate delays.

Following on from the improvements obtained from the introduction of European Re-Categorisation (RECAT-EU), further enhancement is possible either by defining pair wise separations or by the local optimisation of wake categories.


Separations may be used either when integrated into the Separation Delivery Tool (as used for Time-Based Separation, TBS) or for category groupings based on the local fleet mix/capacity needs, with the ability to adapt to fleet mix changes over time.

By taking into account the characteristics of the lead and following aircraft (such as landing weights and speed profiles), the wake generated by the lead aircraft and the resistance of the following one can be assessed when delivering the applicable separation minima, while maintaining safety levels.


  • Further enhancements of RECAT-EU deliver safe and more efficient spacing, either for pair wise or for category groupings based on the local traffic mix.
  • Pairwise separations increase runway throughput by 5 to 10% which makes for 30% to 120% of additional benefit, compared to the RECAT-EU scheme.
  • The optimised six category scheme increases runway throughput by 5 to 15%, compared to RECAT-EU.
  • This makes for additional movements and avoids extra arrival traffic flow congestion.
  • Capacity-constrained airports over the next 20 years will benefit from Pair Wise Separations.
  • Reduced wake separations address arrival capacity limitations, which in turn decrease airborne delays.
  • Separation minima reduction also helps ATCOs manage traffic more efficiently, largely compensating for the use of six categories.
  • The Optimised Separation Delivery Tool facilitates separation between aircraft and reduces ATCO workload.


The introduction of full pairwise separation (with HMI) is expected to be a logical next step following the introduction of TBS with the ATCO support tool.

The optimisation of six categories can benefit airports without A380 operations, with a high number of bizjet movements or for any traffic mix for which the RECAT-EU scheme does not bring sufficient gains.

Dynamic Pair Wise Separations (D-PWS) / RECAT-3

Developed as part of the European Wake Turbulence Categorisation and Separation Minima, RECAT-3 allows for the dynamic adjustment of aircraft spacing, using wake turbulence measurement, real-time weather conditions and data from air and ground systems.


Capacity limitations, increased arrival traffic flow congestion and delays are some factors affecting busy airports. Further improvements made in the European Re-Categorisation (RECAT-EU and RECAT-2) of wake turbulence address these operational constraints.          


The application of Dynamic Pair-Wise Separations (D-PWS) for arrivals on final approach and for departures takes into account the operating conditions that affect the wake encounter risk and the characteristics of both the lead aircraft and the one following it (i.e. weights and speed profile).

Aircraft spacing is determined according to the real-time ground-based measurement of wake decay. Once the separation has been defined by a ground or airborne system, the flight crew can adjust their spacing to optimise runway throughput safely.

Further solutions may also consider runway occupancy time constraints and they may be extended to flight phases other than approach and take-off.

Dynamic Separation can either use the Optimised Separation Delivery tool (as developed for TBS, WDS or PWS-RECAT-2) or it can delegate spacing management to the flight deck.


RECAT-3 is expected to help achieve maximum runway throughput and to substantially increase capacity.

  • Thanks to wake detection through airborne or ground systems, the risk of wake turbulence encounters is reduced to almost zero.
  • Since flight crews have access to wake turbulence detection systems, they have heightened awareness of surrounding wake turbulence events: a fact which also enhances safety.
  • Real-time aircraft and weather data-sharing allows tactical self-adjustments in spacing and evasion manoeuvres to be made to avoid wake vortex encounters.
  • D-PWS improves the accuracy of runway occupancy time prediction, due to collected and real data exploited by a predictive ground-based system.

Development and Deployment

Initial D-PWS is being developed for SESAR 1 (2015/2016) and further developments will be made in SESAR 2020 Wave 2 (2018/2020).

Deployment will be from 2022 onwards for ground-based solutions and beyond for airborne systems if interoperability with the ground has to be ensured.

Vincent Treve

Runway Throughput & Wake Project Manager
+32 (0)2 729 5197

Frédéric Rooseleer

Safety Assessment Specialist
+32 2 729 4662