No 11: Number of planes matter most to overflown communities

This is the first of a number of blogs I will write on what the aviation industry could do to assist communities impacted by noise.

 

The main lesson I learnt in over twenty years representing residents under the Heathrow flight paths is that what matters to communities above all else is the number of planes flying over them.

Airport communities are usually reluctant campaigners. They want to see less noise and fewer aircraft over their heads. Planes have become less noisy over the last 50 years. That is welcome. But numbers have increased significantly at most airports, particularly since the introduction of cheap flights. It is now the volume of planes which is the big problem.

Most communities have little interest in how many planes in total use an airport or even how many runways it has; their prime concern is the number of planes overhead. Each person has their own tolerance level but the tipping point invariably involves an increase in aircraft numbers

Of course, there are other factors involved: the noise of each aircraft; its height; how it is flown; the time of day (and, particularly, the time of night); as well as non-acoustical factors. And most airports could do a lot more in rewarding best practice in order to mitigate the impact of many of these things

But, if I am right, that the number of planes is the key factor, it should feature front and central in the when the industry is planning its future. Wherever possible, flight paths should be varied to provide respite.

6 July 2024

No 12: Good Operational Practices Cut Noise

Some airports adopt good operational practices. Many don’t.

There are a number of operational practices which can reduce the noise from planes.

Arrivals

Continuous Descent Approach (CDA)

Aircraft can descend in one of two ways: either in a step-by-step fashion or using CDA. CDA can cut noise by between 2.5 and 5 decibels.

At Heathrow nearly 90% of aircraft use CDA. At many airports across Europe it is hardly used at all.

The angle of descent

International rules require aircraft to land a 3 degree angle. Some airports, such as London City with smaller planes and tall buildings to avoid, are permitted to land more steeply. On their final approach to London City planes land at 5.5 degrees. Heathrow is one of the very few large airports to try a steeper angle. It trialled a 3.2 degree approach. It was operationally possible but only had a small impact on noise levels – up to 0.5 decibel reduction. What could make more of a difference is what is known as a ‘two-segment approach’. This involves planes using a steeper angle – perhaps even 5 degrees – further away from the airport before reverting to 3 or 3.2 degrees for the last few miles as the plane steadies to land on the runway. Until trials have been done it is not possible to be certain of the noise improvements but they could be significant.

Lowering the landing gear

For modern aircraft landing gear is the dominant noise source on approach. When landing gear has been lowered noise levels increase by between 3 and 5 decibels. So, the later landing gear is lowered, the less noise. In order to get a stabilized approach landing gear needs to go down at an altitude of 1000–2000ft, about 2–3 minutes before touchdown. It is difficult for an airport to enforce the point at which landing gear is lowered but it is possible to highlight airlines and aircraft which lower it sooner than necessary. ‘

Departures

Rate of ascent

Common sense would suggest that the faster you climb, in order to get as high as you can as soon as possible, would reduce noise levels. In essence, that’s correct but it is a little more complex. If a plane uses all its power to climb steeply on leaving the runway, that will benefit most communities directly under the flight path. But it has four downsides:  it will increase noise for people very close to the airport. It will increase air pollution levels in the vicinity of the airport. It will have a significant impact on the wear and tear of engines. It will spread the noise so that communities living either side of the flight path up to about 4,000ft will get more noise

In summary, the way planes are flown in and out of airports can make a big difference to noise levels. If some airports can adopt good practices, why can’t they all?

15 July 2024