Airspace efficiency

We have developed a pioneering metric, known as 3Di, 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

Reducing the aviation industry’s carbon footprint is one of the biggest challenges we face. Following the publication of the European Destination 2050 Roadmap, which sets to achieve net zero carbon emissions in the aviation sector by 2050, NATS is making available free-of-charge the formula of its industry-leading environmental performance metric to the wider industry to deliver efficiency gains.

If you are interested in having a conversation about 3Di, we would really like to hear from you. Simply complete our get in touch form and one of the team will be in contact.

During Quarter 4, traffic remained steady compared to previous months.  The end of October saw the usual change from summer to winter schedules, and November was relatively quiet before the traffic picked up quite strongly again through December.  In October the average number of daily flights was 4,500 and this dropped to 4,200 in December.

Weather conditions remained stable for most of the quarter with no prolonged periods of disruptive weather, such as strong winds or thunderstorm activity, which can have a negative impact on 3Di scores.  There was one weekend in December where low visibility across much of the UK coincided with peak traffic levels and resulted in higher-than-expected 3Di scores.

3Di scores for October, November and December were 22.5, 21.1 and 22.7 respectively. The end of year 3Di figure for 2021 was 21.5, representing a reduction of 2.4 points compared to the end of 2020 (23.9). This result was 6.0 points below the CAA regulatory target of 27.5.

During relatively low traffic levels, the 3Di performance has been very positive.  As traffic continues to build back to pre-pandemic levels, NATS continues to look at new opportunities to improve environmental performance.  These include airspace and procedure changes and also direct dialogue with our Airline and Airport customers.

Note:  During RP3 the CAA has agreed that certain flights can be excluded from the reported 3Di score.  The CAA expected NATS to remove an average of 0.6 from the reported score for the year.  NATS interpretation was different, and we removed all the excluded flights from the final reported score.  Due to the relatively high number of training and positioning flights in 2021, the impact of the exclusions was greater.  In 2021 if those excluded flights had been added back in, the final score would have been 23.3, still well below the regulatory target.