The need for live flying training for air forces

For western militaries who have reduced their combat air fleets since the mid-1990s, there is an imperative to maximise training for their 4th, 5th and, in future, 6th Generation fighters.  Sensor and weapons ranges have increased and, with the reduction in live flying in favour of synthetics, every flight hour is precious.

A war in Europe, increasing instability in the Middle East and a growing threat from China has focussed the need for realistic and collaborative training, and yet, the same basic airspace structures and Special Use Airspace (Box 1) has been in existence for decades. Air force thought leaders see that this construct is no longer fit for current, nor next generation air forces that require coordinated, collaborative multi-domain training; utilising Red Air, EW, tankers, crewed & uncrewed vehicles in a Live Virtual Constructive environment that could (and should) extend across FIR boundaries.  This is increasingly important as the F-35 user community grows across the European NATO countries and with the USAFE.

Box 1: Special use airspace

Why the scarcity of airspace is an issue

NATO States have now committed to deploying up to 750 F35s in Europe by 2033, including those of USAFE, mostly based at RAF Lakenheath. Deploying these aircraft to full capability requires extensive Force Generation exercises, which States are struggling to accommodate given the current limits of airspace reservations (RSAs / SUAs) set against the demands of F35 sensor and weapons ranges. Force Generation is the purpose of air forces, and visibility of effectively coordinated exercises acts as a strong deterrent to NATO’s adversaries.

Alongside the demands on airspace from the F35, and other 5^th generation fighters, there are growing demands on airspace through civil traffic growth and new aircraft types, as society embraces Uncrewed Air Systems (UAS), Advanced Air Mobility (AAM), High Altitude Long Endurance (HALE), and Space Launch and Recovery operations.

This growth in both civil and military demands for airspace must also be set against the commitment of European governments to Net Zero by 2050. The challenge is to grow traffic, maximise Force Generation and minimise emissions. Airspace has a key role to play in meeting this challenge as: (a) there is currently a lack of appropriate special use airspace to support live flying; and (b) geographically fixed volumes of special use airspace are not conducive to optimum civil flight routing.

The future deterrence of Europe depends on air forces increasing the amount of live flying

The concept of the ‘flexible use of airspace’ (FUA) has been implemented in Europe for 25 years. Flexibility means that military users book the airspace that they plan to use, use it, and if they no longer need it for the day of operations, they return it to civil use. In doing this the military have no sight of the routes that are most useful to airlines. They book the fixed geographical areas they want, and the airlines submit flight plans that fly around those areas.

Because civil flight trajectories are influenced by winds, each day has a new optimum trajectory, but there is no change in the routing because the special use airspace is fixed. So, on some days the special use airspace booked by the military is blocking significant traffic flows, on others it blocks minor flows.

Can we re-engineer the system to be more flexible?

To reduce the impact on civil flights and deliver more daily training we see the need to leapfrog the next incremental changes in special use airspace with a bold conceptual and technological step.

This means a new paradigm about how we design and manage airspace.

Counterintuitively, we believe we should make special use airspace larger, but more finely structured. With more space to plan exercises in, we can shape exercises to fit the mission, the traffic flows and therefore the climate; avoiding heavy civil traffic flows allows for larger airspace volumes at the same time as giving civil flights shorter paths, saving fuel costs and emissions (Box 2).

This is beyond the current flexible use of airspace, giving fluidity to the whole airspace, shaped by winds on a daily basis. This is ‘smarter airspace management’ and the implications for special use airspace are profound, so that it is:

1. enlarged, potentially by 50-100% – imagine joining areas across the North Sea;
2. activated according to impact on civil traffic flows, not fixed volumes – imagine minimising the impact on civil flights before they flight plan;
3. finely segmented, comprising elemental volumes that are 5-10NM in area by 5000ft in altitude – imaging shifting an exercise by 10NM to finesse a carbon reduction;
4. divided into training volumes based on daily mission needs not predefined segments – imagine planning the mission being allocated the airspace volume that is just right;
5. as tightly packed as mission volumes and safety buffers require – imagine accelerating training through more exercises in parallel.

In an industry that changes glacially, this may seem a big leap, but it is not rational to meet the challenges of this century with incremental solutions. And the solutions are not so much bold as living up to the expectations of what the civil-military concept of the ‘Flexible Use of Airspace’, introduced just twenty-five years ago, should mean.

These ideas align with other concepts, particularly the SESAR Dynamic Management of Airspace and Military Mission Trajectory concepts. This has even been referred to in SESAR as ‘floating’ military airspace¹.

Box 2: Because airspace is fixed, it is rarely efficient

Smarter airspace will accelerate sustainable aviation

Around the world, governments are placing increased pressure on all sectors of the economy to decrease carbon emissions in line with the IPPC’s 1.5 degree global warming target, also referred to as Net Zero 2050. These demands also include Defence. In the UK, the MoD accounts for approximately half of government carbon emissions and 40% of this is the responsibility of the Royal Air Force; most caused by burning aviation fuel.

The RAF is working on new fuels to meet its Net Zero obligations, but there are other levers that it can pull. Through the smarter airspace concept, we can use airspace in a way that minimises interactions with civil traffic flows, reducing civil aviation emissions at the same time as increasing military mission effectiveness.

What tools are needed?

The tools for smarter airspace management are being developed by Airspace Unlimited, and their development has been supported by the UK’s Airspace Modernisation Strategy Fund. From our interactions with the RAF over the last two years we have been encouraged around these bold concepts.

During 2024 we developed airspace design tools to rapidly assess multiple hypotheses for design and management of the airspace, with realistic traffic flows with winds and route charges factored-in. Being able to design airspace changes and concurrently measure the impacts on traffic means we can drastically speed up airspace change and re-envisage how multiple users can use the skies above us in the most effective and efficient ways.

We are delivering these tools as a tiered capability to transform airspace, to support States in: analysing the airspace to understand how it may be improved; designing the airspace to be more flexible, using ‘Variable Profile Area’ 5-10Nm design rules; and ultimately managing the airspace on a rolling 24-7 basis.

Our medium-term goal is to reduce the impact of special use airspace on civil flights and save 1% of civil flight time, which could amount to 2Mt CO2 saved a year across European NATO States. In the shorter term we are focusing on highly-modular ‘Variable Profile Areas’. By disaggregating airspace into elemental volumes, say 10Nm x 10Nm x 5000ft, we can pack more exercises into existing airspace design. This means we can achieve more exercises on a daily basis and accelerate training and force generation programmes, all while reducing the interaction with civil traffic flows.

The future is in sight

Air Forces, including the Royal Air Force, are seeking to optimise, to get the best out of what they have; however, they are constrained in their training while attempting to increase combat effectiveness. It simply doesn’t make sense to conduct live training in airspace that is not fit for purpose – we should strive for the win-win-win scenario that airspace optimisation can bring.

This work is also addressed at the growing demands on airspace driven by multiple new users types: Uncrewed Air Systems (UAS), Advanced Air Mobility (AAM), High Altitude Long Endurance (HALE), and Space Launch and Recovery operations.

1. SESAR Solution 04.07.07 Operational Services and Environment Description. ↩︎

What is Free Route Airspace?

Free Route Airspace (FRA) is an airspace within which airspace users may freely plan their routes between an entry point and an exit point. It was introduced in Europe to give airlines better flight routing opportunities than could be achieved with the fixed route structure. Free Route Airspace was also mandated under the EU ‘pilot common projects’ regulation: EU 716 (2014).

SESAR Solution #33 further describes ‘free routing’ as “the ability of an Airspace User to plan/re-plan route according to the User defined segments (i.e. segments of great circle connecting any combination of two user defined or published waypoints)”.

Implementing FRA has not been a simple matter, requiring traffic simulations to ensure that the airspace did not introduce multiple conflict points from unpredictable entry and exit points into the free route airspace.

The potential benefits of FRA were believed to be considerable, with various benefits estimated at 1.3%¹  of up to ~2%²  of flight distance at the network level. Implementation did not require new technology, just changes to airspace and operations, creating a strong business case for it.

So, what’s wrong?

We were intrigued that most flights through FRA seemed to be direct from entry to exit point, with little other variation. In comparison, our AirOpt simulation tool in ‘freely routing’ mode shows a variety of routes, based on a high density of nodes (waypoints). For example, when optimising flights around highly modular special use airspace (SUA) designs or simulating the effect of enroute charge modulations (reference SES 2+). We can also clearly see the effect of charges on airline routing, so why not winds? (See the NE corner of the Scottish FIR in the figure below for flights that take a 30° turn as they skirt the higher FIR charges.)

By analysing ADS-B flight tracks we confirmed them to be mostly direct through FRA, meaning that they follow the shortest distance between two points on the earth, known as a great circle.

An issue for most simulations and cost benefit analyses over the last ~25 years is that it is assumed that the wind has no effect on routing, or that winds average out. It is also difficult to include the winds without sophisticated computer models and high power processing. In other words, the ATM system appears to be designed and measured in still winds but operated in a wind-variable world. This is why we developed the ‘Air Distance’ metric, in various forms, presented later in this article.

Our hypothesis was that free route airspace has become direct route and that, if so, there is an opportunity for increasing flight efficiency by getting free routing ‘back on course’. To explore the issue we have studied ADS-B tracks from Plane Finder through the Scottish FIR. The figure below shows tracks from 25 January 2025. It is striking that the majority of the tracks closely follow the great circle from entry to exit point of the FRA. A track is highlighted (coloured dots) that diverges from the great circle slightly, shown by the blue line. This may show some wind based routing but it is hard to tell from this data.

Figure 1: Example routing through Free Route Airspace (Scottish FIR)

We concluded that we had some evidence of direct routing being the norm and decided to consult experts within the industry, including with flight planning experts. We also compared horizontal flight efficiency (HFE) measurements using ‘ground distance’ and ‘air distance’. This led us to see that there are three parts to this story: computerised flight planning systems, route ‘availability’, and flight efficiency measurement.

Computerised flight planning systems

Computerised flight planning systems came into being in the 1990s. Computers made wind-based routing a reality, advised pilots on how much fuel to carry, navigate ATC and regulatory rules and generally save substantial amounts of fuel per flight. Free route airspace was to play to the strengths of these systems. However, the thing that makes flight routing algorithms work was also being taken away – the waypoints and the routes between them. We try to explain how this works in Box 1, but note that the flight routing algorithms only work when they have nodes (waypoints) and edges (airways) to route along. Taking away the nodes (waypoints) is not like going off road in a 4×4, it’s like seeing a hole in the road ahead and having to go back to the start to take a different route.

Box 1: How routing works for flight planning

Route availability

Route availability refers to routes that are published as being subject to traffic flow rules defined within the ‘Route Availability Document’ (RAD). Originally updated every 28 days, RAD updates are now almost daily. The RAD was introduced in 2006 and has played an important role in standardising and protecting routes from overload. It has grown to control free route airspace and fine tune flow management. Indeed, early experience with FRA led to the realisation that RAD restrictions could be used to manage the flow of traffic into and out of FRA at specific points.

Flight planning companies have two concerns though. The first is that the effect of RAD restrictions in FRA is to imitate the previous fixed route structure. This gives rise to the second concern, that growing complexity and almost daily changes to the RAD make it difficult to integrate changes into their databases. This can lead to errors when their customers’ flight plans are submitted through the IFPS, which cause flight plans to be rejected. Airlines will then fall back on ‘company preferred routes’, which are static and suboptimal for the day of operation.

Flight efficiency measurement

By measuring flight efficiency, ANSPs will know that they are delivering the optimal conditions for airline flight planning. This is currently measured with distance-based horizontal flight efficiency (HFE).

Air distance metric

While the great circle is the shortest distance, it is not always the shortest time through the airspace, i.e. when there is a head wind. What is confusing about directs is that they look the most efficient on the map but often they aren’t. If they were, then there would be no need for wind considerations in flight planning. To understand wind-based routing we created the ‘air distance’ metric, which accounts for the wind vectors along the flight track.

To better scope the issue, we have calculated the actual horizontal flight efficiency (HFE) known as ‘KEA’. This indicator compares the ground tracks (GD) with the great circle distance (GC) as flight inefficiency = GD/GC -1. From a sample of 526 flights from the 25 Jan data, the flight inefficiency varies as shown in the histogram below, where 89% of the flights were within 1% of the great circle distance. This is impressive track keeping born of the age of PBN.

We can use air distance (AD) in the same way, calculating flight inefficiency as AD/GC-1. The following histogram results, showing a wide distribution where ~40% of the flights had an air distance less than the great circle due to tail winds and the remainder ~60% had air distances greater than the great circle due to head winds.

Knowing the air distance would normally give us insight into the flight plan, e.g. why was one route taken over another? But when most flights are taking a direct, does this mean a direct was always the best route? We think this unlikely, and more likely that the multiple complicated factors involved in flight planning now constrain free routing to direct only.

It is likely that distance-based KEA is not an accurate measure of flight efficiency for calculating the benefits of free routing. Aircraft use fuel in accordance with how long the engines run for, not the distance over the ground. When HFE/KFE was introduced, it was a good high level indicator, but it was never intended for operational problem solving.

Conclusion

Free Route Airspace hasn’t been implemented as we expected, but rather as ‘direct’ route. This has arisen from three main factors:

• The difficulty for computer flight planning systems to model and determine user-defined waypoints and segments for a given day of wind conditions, alongside the myriad other roles of these advanced automation systems.
  
• The ever growing complexity from constraining traffic flows through the RAD.
  
• The measurement of flight efficiency according to the ground track, not the flight time.

Measuring the route system with distance no longer makes sense while striving to increase real flight efficiency for net zero targets. Worse than this, it makes direct routing look better than wind-based routing.

In summary, the current situation is that the ATM system is inadvertently constraining traffic flows to be less efficient while we have a measurement method that makes inefficient routes look efficient.

Our conclusion is that we need to revisit how we design FRA and consider how we help the flight planning process produce better outcomes for airlines. This could even mean adding waypoints and segments back in, but does not mean we have to go back to the fixed route system.

1. Gaxiola C. FRA CBA study. PhD Thesis. 2019 ↩︎
2. https://www.eurocontrol.int/concept/free-route-airspace ↩︎

Who has heard the old saying ‘Do more with less’? While this strategy is not sustainable, increasingly reality is rooted in the idea of doing more with what you have.

Optimisation, efficiency gains and operational enhancements are words that mean do more without additional resources. This should be the aim of every individual or organisation.

Waste should neither be encouraged or accepted. Unfortunately, there is waste in any system with multiple stakeholders and external influences. The air traffic management (ATM) system is no exception to this reality, our mission should be to identify where there are gaps in the overall performance and move to close these holes.

Many of the efficiency gaps within the ATM system are rooted in legacy airspace structures and operating procedures. Aircraft capability has far outrun the suitability of airspace structures particularly in the area of military training and airspace requirements.

Airspace Unlimited acknowledges that there will never be 100% efficiency, but there are real gains to be had by managing the assets we have more effectively. These structural gains come at a hugely discounted rate compared to the cost of developing new engines and fuels to fire them, and most importantly, are available now.

See what our Chair, Justin Reuter has to say in the latest Air and Space Power Association Bulletin:

https://airspacepower.com/wp-content/uploads/2024/02/Air-Space-Power-Association-Bulletin-Spring-2024-26-Feb-2024.pdf

We would like to thank the Air and Space Power Association for publishing this article. To read more visit www.airspacepower.com

Airspace Unlimited has been nominated for the Innovation of the Year Award through the #ScottishKnowledgeExchangeAwards.
Working alongside Dr. Sandy Brownlee of #StirlingUniversity, we have improved the overall performance of our system.
Focused on improving the #environmental footprint of the #aviationindustry, this video helps describe our collaboration with the University.

This statement was made by arguably the greatest ice hockey player of all time, Wayne Gretzky.

Gretzky holds most of the scoring records in the National Hockey League including the most goals (894) and most assists (1962).

The premise is clear, if you are not taking every opportunity to shoot, or waiting for the perfect shot you may never score.

What has this piece trivia have to do with improving the environmental credentials of the aviation industry?

The aviation business is extremely complex and the issues facing us in the push to de-carbonize are varied and in no way simple.

The industry carries a heavy regulatory burden along with one of the most stringent safety cultures in the world.  This framework often makes change seem to move at a glacial pace.

Work on Sustainable fuels, Hydrogen or Electric power plants and redesigned airframes is moving in a positive direction, but as a solution to the climate change discussion, these developments often resemble the ‘perfect shot’.

However, there are a number of small but significant gains that can be made by taking the shots available now.

These include improving airspace efficiency, developing operational improvements through available tools, or something as simple as encouraging better fuel management within the airlines and amongst individual pilots.

Airspace Unlimited has spent more than 3 years developing an Airspace Optimisation Tool (AIROPT) utilizing a unique algorithm to analyze airline Flight Plan Data, Military Airspace Reservation requirements along with accurate wind aloft forecasts to produce a dynamic airspace plan that can lead to a 1% reduction in overall carbon emissions.  These savings are directly measureable and lead to real savings in basic fuel burn.  

This functionality is another example of the ‘perfect shot,’ however there are additional capabilities that offer genuine opportunities to create small improvements through a number of different applications.  These capabilities create measurable gains that are available in a short time frame, and provide real environmental wins.

Aviation is the ultimate team sport.

There are no isolated actions.  Any operational action within the eco-system creates a ripple effect felt far beyond the immediate horizon.

Within this prism, expecting any one player/stakeholder to shoulder the responsibility of addressing the climate change challenge on behalf of the rest of us is untenable as much as it is unreasonable.

Our AIROPT tool embodies the very essence of the co-operative approach required to provide credible evidence of our environmental credentials to industry critics.

At Airspace Unlimited, an innovator in airspace usage, we believe that change is possible now in a range of different areas. This is why we are developing solutions to improve strategic airspace design, minimise environmental impacts through variation of ANSP charging schemes, and help to ensure maximum efficiency in activation times and geographic positioning of military airspace reservations. 

Gretzky would not have achieved anything without working with, and having the support of his teammates.   Waiting for someone else to step up and take the shot is not a strategy, it is a cop out. Our mantra is “…many shavings make a pile,” so let’s not put off until tomorrow, the small improvements we can make today.