NATS gets planes to fly slightly slower in order to cut time waiting in Heathrow stacks
Heathrow holding times on the decline thanks to new technology
Efforts to reduce the amount of time aircraft spend in holding stacks before landing at Heathrow Airport are paying off, according to new statistics from air traffic control company, NATS.
Since 2014 NATS and Heathrow have been working together to find ways of cutting the amount of time aircraft spend in the stacks, with the latest figures now showing an average reduction of around a minute, equating to a saving of more than 3,000 hours that aircraft spend in the hold each year.
Average holding times were about 8.5 minutes at the beginning of 2014, with that figure now just over 7.5 minutes and falling as low as 6.5 minutes in August this year.
Juliet Kennedy, NATS Operations Director, said: “A minute out of average holding times might not sound a huge amount, but when you consider about 10,000 flights use the holds each month it adds up to a serious reduction in delay, carbon emissions, fuel burn and noise.”
NATS estimates that the fall in airborne holding has saved over 35,000 tonnes of CO2, the equivalent to more than 11,000 tonnes of fuel, worth £4m at current jet fuel prices.
Most passengers who have flown into Heathrow will have experienced their flight circling in one of the four holding stacks around London. The airport needs a ready supply of inbound traffic in order to ensure it makes the best use of its two runways. However, holding is inefficient in terms of fuel burn and emissions.
The reduction in holding has been achieved through the use of two new air traffic management tools. Introduced in April 2014, XMAN – or cross-border arrivals management – involves NATS coordinating with its counterparts in France, the Netherlands and Ireland to slow inbound aircraft down from 350 miles away, when delays over London begin to build.
As a result aircraft don’t land any later, but do spend less time circling in the holds.
A new way of separating arriving aircraft has also made a major contribution. Since March 2015 NATS has separated arriving aircraft into Heathrow by time instead of set distances in an effort to cut delays due to headwinds. Time Based Separation has cut headwind delays by over 50% and by helping to maintain the landing rate has also cut the time aircraft spend holding.
Jon Proudlove, Heathrow’s Airside Director, said: “Fewer delays and reduced emissions are the result of investment in innovative technology and collaborative working between Heathrow, NATS and airlines. This is a significant step forward in what will be a series of innovations supporting the predictable delivery to plan. A predictable operation is essential in delivering a great passenger experience and reducing environmental impact.”
Both changes are part of a wider initiative to modernise the UK’s airspace and air traffic management technologies. Air traffic is forecast to grow by 40% by 2030 and changes to the way UK airspace is structured and used will enable reductions in noise and emissions while improving capacity.
20 May 2016
For those that don’t know, holding stacks are the airport’s ‘waiting rooms’ for arriving aircraft. Whenever aircraft cannot proceed to land immediately, flights enter at the top of the stack – usually at around 11 or 12 thousand feet before gradually spiralling down to 7,000ft.
The NATS air traffic controllers in London Terminal Control at Swanwick and at airport towers around the country, then direct the aircraft onto the final approach path for the airport. The separation between arriving aircraft pairs is largely dependent on their size. A heavy A380, which whips up a lot of air turbulence in its wake, followed by the lighter B737 requires 7 miles separation, whereas the gap between two A380s is just 4 miles.
Choosing the optimum combination of arrivals is the key to making the most of the available runway capacity and at Heathrow, which is scheduled to 98% capacity, having a constant stream of arrivals allows optimum sequencing to take place and is absolutely vital to the smooth running of the operation.
It will be many years before aircraft can arrive at an airport ‘just in time’ so in the meantime we need to have a slight oversupply of aircraft to ensure that runway capacity is not wasted with unnecessary gaps. As such holding stacks are incredibly useful, but they are also noisy, inflexible and mean aircraft burn more fuel at lower levels and emit more CO2.
With the advent of more sophisticated satellite based navigation systems it’s now possible for aircraft to follow routes with an incredible level of accuracy. That means we’re able to be smarter about airport arrivals using a concept called Linear Holding.
There are two different types of linear hold, the trombone and the point merge. Both work by keeping all the arriving aircraft at the same level, but separated in the horizontal plane by satellite navigation tracks. At exactly the right moment – to the second – the aircraft is vectored off the linear hold and onto final approach. The big difference is that these linear holds can be much higher than a traditional stack, potentially up to 20,000 feet, and are therefore quieter for people living underneath and more fuel efficient for the airlines.
The traditional stack holds would remain for use in exceptional circumstances but they would be moved further out and raised up.
We’ve actually introduced one linear in the UK already; with the implementation of a point merge hold for arrivals into London City Airport. Instead of flying over land, arrivals now join the point merge arc out over the North Sea before being peeled off in the optimum order for a continuous decent approach into the airport.
The introduction of linear holds is just one example of the benefits of modernising the structure of UK airspace, much of which was designed in the 1950s and 60s. Air traffic is forecast to increase by 40% by 2030 and we need to act now if we’re going to keep pace with rising demand, while at the same time working to take advantage of the technologies that can help us minimise the impact of noise on the ground.