In January 2025 we completed a project funded by the UK Airspace Modernisation Strategy (AMS) Fund. The fund is managed by the UK CAA to support the aviation industry in modernising UK airspace, and has the environment as its overarching principle.
Our project was based on the premise that by deeply enhancing the ability to understand how flights and airspace interact, we can identify opportunities for systemic environmental improvements supported by airlines, air navigation service providers (ANSPs) and regulators.
The project was focused on saving airline fuels and emissions through digital technology
Civil use of special use airspace
We developed advanced analytics to explore the interaction between civil flights and special use airspace.
The project identified benefits of tens of thousands of tonnes of fuel and emissions savings through simple actions that could be taken by airlines with the encouragement and shaping of regulators and ANSPs.
Air distance wind-based analytics
We created a way to measure flight efficiency in the way that airlines do, taking advantage of winds.
We made an extraordinary finding that Free Route Airspace is only Direct Route. This work highlights that millions of tonnes of fuel and emissions were overpromised but can now be delivered as a consequence of this AMS project (and a solution we are starting to develop).
Analytics for charges modulation
We developed a method of designing airspace charges for environmental benefits.
This was a global first in validating enroute charges modulation. This has the potential to save up to 3% of flight time on certain key routes and is timely to support regulatory policy development for both the UK and Europe (Single European Sky 2+ regulations).
Advanced airspace design tools
We created advanced tools to design and optimise airspace in a highly-modular way.
This was a global first in demonstrating highly-modular airspace designs,whichhave the potential for special use airspace to be optimised for both military exercise productivity and civil airline emissions.
Details on these benefits and next steps
Civil use of special use airspace
What we did
An analysis of a sample of special use airspace showed that up to 20% of civil flights went around the airspace when they could have routed through it. The analysis compared flights against the airspace use plan. We call these flights ‘missed opportunities’ and the extra cost to airlines was estimated to be nearly £2M in fuel, £0.5M in other operating costs and an additional 6,000 tonnes of CO2 emissions per year (£20M and 60,000tCO2 over 10 years).
Next steps
Better flight planning by airlines and supportive tactical action by ANSPs is needed. Regular independent monitoring of airspace performance is key to identifying and delivering benefits.
Figure 1: Many flights route around SUA when they could have gone through it
Air distance wind-based analytics
What we did
The air traffic management (ATM) industry measures flight efficiency as the ratio of ground track distance to great circle distance. We developed the ‘air distance’ metric to reflect what matters to airlines – flight time, not distance; as the engines burn more fuel according to the time they operate, not the distance travelled.
By analysing Free Route Airspace with the air distance metric, we discovered that 90% of flights were within 1% of the great circle distance, but 60% of these flights had air distances greater than the ground distance (and vice versa). This led us to the breakthrough understanding that airspace designated as Free Route Airspace is not operating as such; it is direct route only and means that the benefits of free routing are not being delivered.
Figure 2: Flights through the Scottish FIR are 90% direct route, not ‘free route’
While this discovery is a bit of a disappointment for fans of Free Route Airspace, it can be turned into a positive to get FRA back on track and deliver the promised benefits of millions of Euros and millions of tonnes of CO2.
Further details on the discovery are here, but the summary diagnosis is as follows:
- Free Route Airspace removed most internal waypoints and airway segments, but these were not replaced with user-defined waypoints from flight planning systems. Why? It has proven highly challenging to flight plan service providers (CFSPs).
- Flight planning is now a complicated challenge with updating the Route Availability Document (RAD) restrictions. These seem to have effectively replaced the fixed route structure.
- The ATM industry measures flight efficiency as a proxy; it compares ground track to great circle. A direct route is pretty much on the great circle so looks very efficient but only so in still winds. Our Air Distance indicator reveals this issue.
Hence, the ATM system is inadvertently constraining traffic flows to be less efficient while we have a measurement method that makes inefficient routes look efficient.
Next steps
Bold and fast action can be taken by ANSPs supported by regulators to address the current short comings. The good news is that the solution will be a fraction of the cost and effort already expended in developing direct routing. Airspace Unlimited are working on a prototype solution that can fit into current processes.
Analytics for charges modulation
What we did
Charges modulation is an air traffic services concept to address the impact of high user charges (enroute unit rates) on airline flight routing. As airlines tend to fly the lowest cost routes, high charge differences between neighbouring States’ leads to longer flights and more emissions.
The UK is surrounded by low-cost charge areas (Ireland and Norway), which distorts flight routes and adds costs and emissions to some flights. We identified two areas where a charges modulation could benefit UK flights and simulated a ‘charges zone’ in which a charges modulation (lower charge) could be applied.
An example is in Figure 3, which shows a narrow charges zone with reduced unit rate, to encourage flights from Manchester to Tenerife to route through the UK airspace rather than redirecting through Irish airspace. This simulation showed a 3% reduction in flight time, showing the potential for lower flight costs and emissions.
Next steps
We presented the results at the iCNS conference in April 2025 and are continuing to update our aviation industry colleagues. While the concept of charges modulation has been around for over 15 years, the AMS funded work is the first to show how it could be employed in detail.
Figure 3: Charges modulation applied to a narrow charges zone can lead to shorter routes and less CO2
AirOpt-Design, an advanced airspace design capability
What we did
A key requirement for airspace design is to be able to show how flights will route in the new design. However, most, if not all, current airspace design tools are set up to make incremental changes to the existing airspace. This means that these tools reflect either fixed or direct route airspace but not ‘free route’. This is the same with flight planning systems.
Our aim was to develop an advanced airspace design tool that is superior to existing tools and flight planning systems to support highly-modular airspace designs. This included assessing airspace designs according to other special use airspace (current and future), user charges and winds so that we could future-proof designs according to different scenarios. AirOpt-Design is also fast to execute in spite of the high number of variables this entails.
The AirOpt simulation is based on finding the lowest cost path through a ‘graph’, which is used to simulate airline routing in the same way that wind-optimal flight planning is performed. Graphs comprise sets of points or ‘nodes’, which are connected by edges. In our AirOpt simulations we apply a high-density graph, meaning that the nodes are 0.125° in latitude and longitude apart or about 7.5NM. Nodes are connected by edges separated at up to the fourth nearest neighbour, which gives a variety of routing angle options.
We refer to our routing capability as ‘freely routing’ and it represents how flights would ideally route if not subject to route or capacity management constraints (Figure 4). The idea is to support designers in finding the best routes and waypoints to improve the underlying airspace – beyond incremental design.
Figure 4: Freely routing offers superior insight and opportunities for airspace design than existing airspace design tools
Next steps
We have been road-testing AirOpt-Design in a variety of projects, including for EUROCONTROL and a European Air Force. We are developing further functions of AirOpt-Design as a ‘pre-design’ function, supporting rapid development of future airspace designs with multiple scenarios. Once an optimum design concept is reached simulations can focus on waypoint positioning before applying other tools, such as NEST, to optimise flow management.
Conclusions
The AMS-funded project for a digital transformation of airspace management has been ground breaking:
- new civil-military analytics have shown the potential for combined stakeholder action to save millions of tonnes of fuel and emissions;
- an extraordinary finding that Free Route Airspace is only Direct Route, identifying millions of tonnes of fuel and emissions savings to begained;
- the first project to validate designs for enroute charges modulation, which has the potential to save up to 3% of flight time on certain key routes; and
- advanced airspace design tools that pave the way for highly-modular airspace designs, with the potential for significant military exercise productivity, and airline emissions reductions.
Next steps
- We need to scale the outputs of this project to deliver the identified benefits.
- States need to be able to independently monitor the performance of their airspace with wind based analytics that better reflect how airlines actually fly.
- We are developing an approach to turn direct route airspace back into free route airspace.
- In the medium term, the static approaches in this project can be made dynamic, reflecting the fact that aviation is a wind-driven activity, albeit currently measured and managed as if in still air.