Thank you for your letter dated 23rd November. I am grateful that you continue to engage in a constructive dialogue with us on these important issues. With regard to the recent conversation you had with a pilot, I would make the following comments in response:
Aircraft altitudes on departure
Heathrow’s departure routes and procedures regarding climb gradients were designed in the 1960s. As modern aircraft fleets have replaced older technology, we have seen a steady increase in aircraft altitudes. Indeed, the recent analysis undertaken by independent analysts PA Consulting shows that over the last five years, there has been an upward trend in the altitude of departures over Wokingham. [It would be good if they would publish this data, in comprehensible form, for all to see. AW note]. This is what we would expect with modern aircraft fleets. However, further improvements beyond this will be limited in the short term because of the airspace constraints that NATS work within.
Heathrow’s airspace is one of the most congested in the world due to: the proximity of four other major airports (Gatwick, Stansted, City and Luton); the location of the four holding stacks; and the interaction between arriving and departing traffic. Taken together, these mean that until changes are made to the whole of London’s airspace through the Government’s modernisation programme, it will not be possible to increase further the height of aircraft.
As part of any future changes to climb gradients, the noise impacts of steeper climb gradients will have to be considered. There will always be trade-offs. While getting aircraft at greater altitudes more quickly may benefit some, it will also result in increased noise for others. [ie. it is even noisier for those living near the airport, who are already subjected to the worst noise. A benefit? AW note].
Aircraft altitudes on arrival
The majority of aircraft coming into land at Heathrow already perform what is known as a Continuous Descent Approach or CDA. This is a procedure aircraft perform after leaving the holding stacks, from approx. 6,000 feet and before they lock onto the final approach (the last 10 miles or so when aircraft line up in a straight line into the airport). It involves aircraft maintaining a steady angle of approach when landing at the airport, as opposed to stepped approaches which involve prolonged periods of level flight. [And then engine thrust too. AW note].
Continuous Descent Approaches reduce noise because they require less engine thrust and keep the aircraft higher for longer. Some 87% of arriving aircraft currently use CDA at Heathrow.
In order to achieve the objective of keeping aircraft higher before they reach the final approach, there are a number of ways this might be possible in future. The first is to introduce a steeper final approach angle, which would mean aircraft approach the airport at a higher altitude. Currently the approach angle of the final approach (known as the Instrument Landing System) is set at 3 degrees. This means that depending on the point that aircraft join it, they will be at a set height from touchdown. We are currently trialing a slightly steeper approach with a view to increasing it further in the future. [This omits to say the steeper angle is only 3.2 degrees, which makes virtually no difference, and is largely for PR purposes. AW note].
We are also investigating the feasibility of what are called ‘segmented approaches’. A two-segmented approach adopts an intermediate approach phase flown at a steeper angle, before transitioning back to a standard 3 degree approach. This would potentially provide noise benefits further out during the approach phase, without affecting the final approach phase.
Aside from the procedural change that NATS made in 2014 to the Compton route, which has meant more flights over areas in the Wokingham area, there have not been amendments to procedures that change the way aircraft are directed.
For areas closer to Heathrow, improvements [meaning technical advances. AW note] in aircraft navigational technology has meant there is a trend for aircraft to be more concentrated with the established departure routes. [By improvements, he means that GPS-type technology enables planes to navigate more accurately – it has not meant any improvement to those living under the newly concentrated routes. AW note].
In areas further away from the airport, including areas in your constituency, the independent analysis shows that there is still a degree of natural dispersal once aircraft are over 4,000 feet (the point that they can leave the departure route). Nevertheless, it confirms that there has been an overall increase in aircraft numbers passing over the area which will account for the increased over flight some people experience. [No explanation is given of why there are now greater numbers. Heathrow is, in theory, almost “full”. AW note].
Our view is that in planning future airspace changes, the industry should explore how new precision technology could be used to create alternating departure routes that would provide period of predictable respite from noise for residents. [Is there evidence that this is what people over flown actually want? Has research been done? AW note]. Currently aviation policy [DfT policy. AW note] favours concentration over dispersal, although we understand that, as part of a consultation on airspace policy next year, it will seek views as to whether this is still the right approach. It will be important that you and others make your views known during this process.
Regarding better planning of arrivals, NATS has just adopted a new operational procedure – known as ‘XMAN’ – that cuts the amount of time that aircraft circle in holding stacks. This is done by slowing down traffic in their en-route phase when delays are anticipated on arrival.
Traditionally NATS has only been able to influence an arriving aircraft’s approach to Heathrow once it enters UK airspace – sometimes only 80 miles from the airport. This limits the opportunity to manage the flow of traffic and can result in additional time spent in the holding stacks. [Bearing mind the location of Wokingham, this seems to be irrelevant to Mr Redwood’s constituents’ problem. link AW note].
Under the XMAN system, if delays in the Heathrow holding stacks begin to build, air traffic controllers in the Netherlands, France, Scotland and Ireland are asked to slow down aircraft up to 350 miles away from London to help minimize delays on arrival. Absorbing delay in the en-route phase, when aircraft are higher and more efficient, saves fuel and CO2 while minimising noise for the communities living beneath the stacks.
I would be happy to meet to discuss these issues in more detail.
Chief Executive Officer.