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Digital Evolution of Separation Minima in En-route and TMA

It is anticipated that this work will support the development of a future SESAR solutions that will make it possible to move away from 'pre-determined' one-size-fits-all minima that are in use in current operations towards a more dynamic view of separation minima, whereby ATC separates aircraft to an assured minimum risk (dynamically determined for each pair of aircraft depending on the aircraft types, the geometry of the encounter and the atmospheric conditions) rather than a defined distance standard'.

The new separation scheme may include the consideration of reduced vertical separation minima, potentially including the possibility of using a minimum vertical separation of 500 ft. from the ground to unlimited, which may allow the use of intermediate flight levels, e.g. 275, 285, 295, 305…. This reduced vertical separation scheme is referred to as RVSM 2.0 and would dramatically increase airspace capacity both in en-route and the TMA. The new separation scheme may also consider the use of combined separation minima (i.e. XXX feet vertical and YY NM horizontal) in order to increase flexibility and make maximum use of airspace capacity.

In the current environment, the 1.000 ft. or 5NM separation minima prevent most wake encounters, but wake encounters are still possible between aircraft that are separated above the prescribed minima. The new separation scheme may also increase the separation minima above what is applied today (e.g. to 1.500 ft. instead of 1.000 ft.) in certain cases in order to reduce the instances of wake encounters between aircraft that are correctly separated above the minima, thereby increasing safety.

It is anticipated that the development and implementation of new separation minima for en-route will follow a similar step-wise approach to RECAT, in which at first the new minima would be dependent on static aircraft characteristics, and in the future it may be possible to define dynamic minima dependent on dynamic aircraft characteristics (weight, atmospheric conditions, etc.). It is expected that the new static minima would be dependent on the geometry of the encounter and the wind and other atmospheric characteristics (e.g. height of the tropopause).

This concept presents key human performance challenges and for this reason the human performance aspects related to the applicability of a new separation scheme will need to be considered. Like for RECAT-2, it is expected that ATCOs will need support tools in order to be able to apply a more complex separation scheme. It is expected that RECAT EU and RECAT-2 experience and lessons learned in human performance and development of Optimised Runway Delivery (ORD) tools will be useful.

Proposals shall consider altimetry requirements, potentially considering the use of GNSS based geometric altimetry in combination with barometric altimetry to support the reduction of vertical separation minima.

Although the key objective is the redefinition of the wake minima, there is also the need to start researching the potential for reduction of MRS, because where the newly defined minimum wake separation (MWS) is lower than the applicable minimum radar separation (MRS), the new reduced wake minima will only be applicable if MRS can be safely reduced. For this reason, the reduction of the radar separation minima scheme is also in the scope of this topic. This may need to consider minimum surveillance performance requirements, and vertical navigation performance requirements. The new MRS may also be geometry dependent (e.g. reduced separation when in-trail) or include combined separations (e.g. 500 ft. and 1 NM).

The consideration of separation minima between IFR RPAS or between IFR RPAS and manned aircraft is out of scope for this topic.

It is anticipated that the development and implementation of a new separation scheme will be a lengthy process. The solution may develop an interim concept to predict encounters where two aircraft that are separated above the current minima will cross with a geometry where preliminary research results indicate that there is an increased risk of a wake encounter. The research of such an interim concept may need to evaluate the emerging legal/liability aspects.

It is anticipated that the research may require live data collection, big data analysis and use of machine learning.

Keeping aircraft separated from each other is one of the core functions of ATM. In the SESAR concept, ground automation supports air traffic controllers in their task of providing separation management. Separation management starts by strategically limiting the density of potential separation conflicts (i.e. limiting traffic density and traffic complexity), but is ultimately ensured tactically by keeping aircraft separated at or above the pre-defined separation minima. The RECAT and Time Based Separation (TBS) activities in SESAR have made it possible to update the separation minima between successive aircraft on final approach, thereby increasing runway throughput and safety. Further refinement of separation minima between aircraft on final approach (Pair Wise Separation RECAT-2) and between departures is ongoing in SESAR 2020 Wave 1 solution PJ.02.01 with important results expected to become publicly available at the end of 2019. However, in en-route and TMA, the tactical separation minima are essentially the same as they were decades ago.

Previous research SESAR exploratory research (R-WAKE project) has developed an initial concept for updating the wake separation minima scheme applicable in en-route and TMA (except where RECAT applies), and a new operational improvement is in the process of being added to the European ATM Master Plan. The objective of this topic is to build on R-WAKE’s work to progress on the definition and initial validation of this concept.

The new separation scheme for en-route is expected to bring large benefits in terms of airspace capacity, in many cases literally allowing capacity to be doubled thanks to Reduced Vertical Separation Minima (RVSM) 2.0 which will make it possible to use of the intermediate flight levels (…,275, 285, 295, 305,…). Safety will also be increased, by reducing the instances of en-route wake encounters by prescribing new separation minima under certain atmospheric conditions and/or between certain specific aircraft pairs.