Airspace efficiency

Measuring environmental performance


Our pioneering metric

We have developed a pioneering metric, known as 3Di (three-dimension inefficiency), to measure the environmental efficiency of UK airspace. The 3Di metric provides a score which helps us monitor the efficiency of UK airspace by comparing the actual flight path of an aircraft to the ‘preferred profile’ (or the most efficient possible flight path).

Every year, every commercial flight in UK airspace is given a 3Di score. At the end of each year, these scores are combined to give an annual score which can be compared to targets set by the Civil Aviation Authority, our regulator, in consultation with our customers.

How is the score calculated?

The 3Di score runs on a scale from 0 inefficiency to 100+ inefficiency and calculated based on both horizontal and vertical efficiency.

The horizontal efficiency compares the actual radar ground track against the most direct track possible over ground, essentially calculating the additional miles flown.

The vertical efficiency measures the amount of level flight that occurs below the airlines’ preferred cruising level; the more time spent at a lower cruising altitude, the more penalising for a flight’s 3Di score.

An example 3Di scale

How can NATS influence the 3Di score?

The biggest improvements to our 3Di score can be delivered by changes to the design and operation of airspace, and by improving access to shared airspace. But the way our air traffic controllers direct aircraft day-to-day also has an impact. Some of the ways our controllers can positively impact 3Di include: 

  • More continuous climb and descent operations
  • More direct routes across UK airspace  
  • Reduced airborne holding time at destination airports  
  • Working with neighbouring air traffic control providers and military airspace users to deliver more direct routes
  • Achieving or exceeding the customers preferred cruise level 

The challenge for our controllers is being able to direct air traffic in a way which has a positive impact on 3Di and simultaneously dealing with a high volume of flights in our network, limited runway capacity which leads to aircraft holding, and occasionally bad weather.

We also recognise that the 3Di score is also influenced by variables and factors outside of our control, including the actions of our airline customers, airports, neighbouring air traffic organisations, the military and other airspace users.

As an indicator of the UK’s overall airspace efficiency the score is not a pure reflection of NATS efficiency. But, the 3Di measure ensures that we not only focus on what we control, but how we can improve the resilience of our operations to influences such as the weather and to work collaboratively across the industry to deliver efficiency gains.

Our controllers strive to positively impact the 3Di score

3Di score for Q2 2020

Our regulator, the Civil Aviation Authority, has set a challenging target for our airspace efficiency in 2020, with a target 3Di value of 27.8.  With air traffic movements in UK airspace dramatically reduced as a result of the impact of covid-19 the 3Di scores for April to June were a good deal lower, in the range 15-17.5 points.  This is because during periods of low traffic levels, air traffic controllers have the opportunity to provide more optimum routings, smoother climbs and descents, reducing fuel burn, CO2 emissions and our 3Di scores.

The NATS 3Di score at the end of the second quarter of 2020 was 25.6 making our performance 2.2 points ahead of our regulatory target.

We recognise that as an industry we absolutely have to ‘build back better’. The Government is clear on environmental priorities and that the aviation industry has to start doing things differently.  We are working to understand how we can build the airspace efficiency improvements we’re seeing now safely into the air traffic system as traffic returns. We continue to identify and target improvement in 3Di hotspots across the network.

We are improving the accessibility of 3Di performance reporting data for our air traffic control employees to enable them to manage airspace more efficiently, day-to-day. In addition to this we are regularly briefing our operational staff on the best ways to safely improve the flight profiles of the aircraft they control and in doing so, realise emissions reductions.

These initiatives are on top of our ongoing focus on airspace and procedural changes to reduce CO2 emissions


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