Greener skies

Measuring flight efficiency to reduce emissions

NATS has created a flight efficiency metric to aid ATC companies in reducing aviation emissions through using optimised flight paths – known as the ‘3D inefficiency score’ (3Di). There is no equivalent measurement for environmental performance anywhere in the world.

3Di has been developed in collaboration with airlines (including British Airways, Virgin, BMi, Aer Lingus, Ryanair, EasyJet, Flybe) and IATA and the UK Civil Aviation Authority (CAA). It took nearly three years of painstaking research and development, analysing radar tracks from every flight since January 2010 and further large samples of operations every year going back to 2006. This helped us establish an average efficiency rating for vertical and horizontal trajectories – how smooth a climb and descent, and how direct a route we can provide for each flight.

How does 3Di work?

The 3Di score is a flight efficiency measure that extends the European horizontal flight efficiency one to include vertical elements. It applies to domestic airspace, for the airborne portion of flight only.

In the horizontal plane, it compares the actual radar groundtrack against the (most direct) great circle track – between first and last radar point. Inefficiency in the horizontal plane is defined by the difference between these two distances.

It compares the actual vertical profile (from radar data) against a modelled ideal flight, defined as a continuous climb to the aircraft’s Requested Flight Level (for cruise), followed by a continuous descent approach. Inefficiency is the difference between the ‘actual’ and ‘ideal’ flight profile.

We then combine these factors to give an inefficiency score for each flight in our airspace.

By analysing historic performance, we have determined our ‘par’, or average performance. Based on this analysis, the CAA has set a ‘par’ for 2012, 2013 and 2014.

A world first

We first deployed 3Di on 1 January 2012, making us the world’s first air traffic management company to be incentivised on its environmental performance. It felt entirely appropriate that it should go live on the same day airlines entered the EU emissions trading scheme.

Initial analysis shows we could save around 600,000 tonnes of CO2 before 2015, saving our customers £120m in fuel costs.

In 2011, our team’s efforts were recognised by the award of the UK Operational Research Society’s President’s Medal for the best practical application of operational research in industry. The Society was particularly impressed with the way that NATS had managed to demonstrate the ATM contribution to a flight’s overall environmental performance by stripping out inefficiencies that were being caused by others.


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