Airspace efficiency

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.

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

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.

• Find out more about the ways we'll be able to manage our environmental performance in the future

Air traffic movements (ATMs) in the UK were on the increase through July, August and September with an average of around 3150 flights per day over the quarter. This was positive news for the industry but still very much reduced compared to 2019 levels due to the impact of Covid-19.

NATS controllers have continued to deliver more efficient flight profiles for our customers and as a result the 3Di scores remained lower than we would expect for busy traffic scenarios. In particular, the amount of airborne holding was very low and for some airports there was no holding at all.

The 3Di scores for July to September were in the range 19.2 to 21.9. Despite the growth in traffic compared to the previous quarter, the Year to Date 3Di score at the end of Q3 fell to 24.0. This score is 3.8 points better than the CAA regulatory target of 27.8.