Aircraft noise

A single aircraft interrupting our conversation or waking us from our sleep is annoying, but we can live with it. As the number of flights increases, these disturbances become too regular and our enjoyment of outdoor life – and even indoor life – is reduced by the stress of the repeated intrusions. People can become sensitised to aircraft noise once it passes a certain level, at which point they tend to notice all the flights. This causes stress, and increased stress is a well documented cause of hypertension and associated health  problems. The Department for Transport uses a software tool called WebTAG to put a monetary cost on the health impacts of repeated noise disturbance,

Aircraft noise wakes people at night, disrupts concentration and conversation during the day, destroys the peacefulness of a rural environment, and can spoil outside social events. The increasing noise from Luton Airport affects many rural towns and villages, especially in Hertfordshire, as well as Areas of Outstanding Natural Beauty. People feel powerless – particularly if, when they complaint to the Airport, they are told “the plane is flying on its permitted track and within normal limits”. So what can be done about it?

First of all, it’s worth being aware of where the planes to and from Luton Airport will be expected to fly, and what affects the choice of routes. Wind direction has the biggest effect: aircraft always take off and land into the wind, so with a broadly east/west runway the aircraft will take off towards South Luton and the M1 during prevailing westerly winds, and arrive over Stevenage, St Paul’s Walden and Breachwood Green to land. Conversely on an “easterly” day (about 30% of the time), they fly in the opposite direction, taking off over Breachwood Green towards Stevenage, and arriving over Kensworth, Caddington and South Luton. Because of airspace owned by the London Gliding Club at Dunstable Downs, westerly departures – which occur 70% of the time – bank left having crossed the M1, and affect Pepperstock, Slip End, Markyate, Flamstead, Gaddesden, south Redbourn, south Harpenden and north St Albans.

Aircraft are noisiest when throttled up to full power for takeoff and initial climb, with flaps out and wheels still down. They gradually become quieter as they gain altitude, the flaps and wheels are retracted to “clean up” the airframe, and the throttle is reduced. On landing, the engines are throttled back but the rumble of air passing over the untidy airframe – with flaps out and wheels down – contributes significantly to the noise generated. Also the “glide slope” of a landing aircraft is shallower than the climb angle, and the speed is reduced, so it is lower over the ground for longer during landing.

Different people have different sensitivity to noise levels, the pitch of noise and the time it lasts. It has proved difficult over the years for researchers to come up with one single measure for the annoyance produced by aircraft noise but a value which correlates fairly well with the reported annoyance is the average “noise footprint” taken over a day (16 hours) or night (8 hours). Other measures include the peak loudness of flights passing a given point, and the number of flights exceeding a given loudness during a day.

People don’t hear noise in average values, and the factors such as the peak loudness of a given flight, how long the aircraft takes to pass, the time of day or night when the noise occurs, the background noise level, the pitch of the noise and even how large and intrusive the aircraft looks all contribute to what annoys people. The World Health Organisation has shown clear links between stress caused by noise (especially at night) and health effects such as strokes, high blood pressure and heart problems. Its recommendations for maximum noise levels are currently not followed by the UK Government.

When it comes to measuring and reporting noise, various factors such as the weather (air pressure, temperature, wind direction and speed), type and size of aircraft, type of engines, takeoff weight (how full the aircraft is and how much fuel it carries) and how fast it climbs, all play a part in determining how loud it will sound to someone on the ground. A given aircraft flown in the same way by a given airline can appear to sound twice as loud on some days compared to others. And depending on whether you are directly beneath the flight path or off to one side, the noise level also varies.

So when aircraft noise is measured, it’s important to be clear about what is being measured, how the measurement was taken, and whether there is enough data to provide a representative average which is statistically reliable. Much of the work LADACAN does when attending the consultative committees at Luton Airport is to check and hold the airport operator to account over the reliability and accuracy of its noise reports. We also press for reductions in the maximum noise thresholds above which aircraft are fined, and insist that the airport operator respects its planning conditions. This kind of monitoring and lobbying is vital in trying to ensure the “social contract” set up when planning permission is granted, is respected. Luton Airport has a disgraceful record of disrespect for such conditions, having knowingly allowed the capacity to grow faster than the airlines could introduce quieter aircraft – purely to satisfy commercial pressures.

For those interested in more detail, a well-researched 2017 Parliamentary briefing on aviation noise can be downloaded here:

Fundamentally, the national policy on aviation noise and oversight of the aviation industry as a whole, and the relationship between local councils and regional airports, is shaped by government. On the next page we summarise some of the issues with government policy on aviation noise.