At NATS we are very aware of the impact that aircraft noise has on those who live under flight paths. That’s why we work with airports, airlines and communities to help shape and inform options to better manage the effect of noise and minimise the impacts wherever possible.
What is Aircraft Noise?
Noise is defined as unwanted sound that may result in disturbance and annoyance. Aircraft noise is caused by airflow around the aircraft fuselage and wings as well as noise from the engines, with different aircraft producing different noise levels and different noise frequencies and tones. Aircraft are individually less noisy than in previous generations with a reduction of noise by more than 90% since jet aircraft entered service in the 1960s. However as traffic continues to grow as demand for air travel increases, this improvement is often counteracted by the number of aircraft overflying an area.
The way that people experience noise from all types of sources can significantly differ. But noise is not always just about decibels; the pitch, vibration, variation in intensity and the length of exposure time can have impacts too. The level of annoyance also varies owing to factors such as the length of time a person lives in an area affected by aircraft noise, personal sensitivity, the impact of outside influences and the activity the individual is engaged in at the time e.g. sleeping, working, watching TV.
Approximate noise level (dBA)
Pneumatic drill, 7m away
|Heavy diesel lorry at 40km/h, 7m away||85|
|Medium Aircraft Descending at 1000ft||70|
|Busy general office||60|
|Quiet bedroom, library||35|
|Threshold of audible sound||0|
The noise level of aircraft can vary immensely depending on a number of factors;
- How high aircraft are above the ground.
- Whether aircraft are directly overhead or how far they are laterally displaced from the receiver (in any direction).
- Whether aircraft are arriving or departing which can affect the amount of engine thrust they are using (and therefore the noise level) and the amount of air resistance around the fuselage, wings and undercarriage.
- The weather which can increase or decrease the experience of noise depending on conditions. Weather can also affect where aircraft are in the sky since aircraft take-off and land into the wind, affecting which runways are used.
Why are we interested?
Noise not only has the potential to cause disturbance and annoyance to those overflown. In areas of very high noise exposure there is evidence of links relating aircraft noise to health impacts, such as sleep disturbance, cardiovascular impacts, and potential impacts on memory and learning in children.
Owing to the relatively small airspace available for a large number of UK flights, noise disturbances can sometimes be unavoidable. However, at NATS we are doing our part where we impact airspace noise. We aim to reduce this impact by working with communities, airlines and airports to understand the issues and find the best solution for the highest number of people.
This is why tackling noise forms an important part of our Responsible Business Report.
How is NATS making a difference?
Under our licence from the Civil Aviation Authority we are required to ensure that the UK airspace system operates safely and efficiently. With this is mind we conduct a rolling programme of airspace redesign, ensuring the system can cope effectively with growing air traffic. Our aim is to balance impacts of a range of factors, such as efficiency and safety, as well as noise to ensure that the positives outweigh negative impacts.
As part of this process we can investigate the ways in which latest navigation technology can be used to mitigate noise and other environmental impacts. However, airspace redesign inevitably involves change – you can’t always mitigate noise in one area without impacting another.
We therefore consult with both airspace users and communities who might be affected by the proposed changes. Consultation is about attaining or confirming views and understanding “what good looks like” from the perspective of communities and other stakeholders.
Consultees have a crucial role, feeding such information into the design process to allow us to make design decisions that best meet the collective need across all stakeholders. Decisions based on the outcome of a consultation are closely scrutinised by our regulator, the Civil Aviation Authority. NATS takes a proactive approach to community engagement and noise mitigation. Some of our work includes:
- Working collaboratively with airports, airlines and community groups to deploy ground breaking action to tackle noise disturbance to communities near London’s main airports through our noise respite trials
- Pioneering work with a UK-based innovator to jointly develop self-powered noise sensing units that can be used in vast quantities to collect noise information in a way not done before. The data we gather from this will inform future designs, by promoting quantitative evidence alongside the concerns of residents to ensure that we can deliver the best possible solutions.
- NATS led launch of the Sustainable Aviation Continuous Descent Operations (CDO) campaign. CDOs keep aircraft higher for longer offering noise reductions of between 1 and 5 decibels per aircraft on approach (as well as reducing CO2 emissions).
- Investigation of precision navigation that allows aircraft to fly routes with increased accuracy, potentially reducing the number of people exposed to aircraft noise by directing aircraft over less noise sensitive areas where possible.
How is Noise measured?
The human ear can handle an enormous range of sound levels. To measure this the decibel scale (dB) is used, which encapsulates the energy of sound with reference to the threshold of hearing using a logarithmic scale. This relates sound intensity to the smallest audible sound of 0dB, so a sound 10 times more powerful is 10dB, whilst a sound 100 times more powerful than the threshold of hearing is 20dB.
Noise measurement also needs to take account of the varying response of the human ear to different frequencies of sound with most sensitivity occurring at the 2-4 kHz range. Therefore the decibel unit used to express human response to loudness or annoyance includes a weighting that varies with both intensity and frequency. The most common measure of this is the A-weighted sound level known as dBA.
Knowing the scale of noise is only one element of capturing its impact, it is also important to consider how we measure the impact of an individual event. There are a number of decibel metrics by which aircraft noise is often described:
- Lmax which is a measure of the loudest part of a flight.
- Leq16h which describes the cumulative noise exposure from aircraft noise events over a 16 hour period. This measure is used to create noise contours connecting areas with the same noise exposure from 0700 to 2300 (the UK official description of daytime – a sixteen hour period). Research globally has found that annoyance due to aircraft noise is correlated with this cumulative metric.
- SEL is the sound exposure level of an aircraft event, measured in dBA of a one second burst of steady noise that contains the same total A-weighted sound energy as the whole event. SEL is often used to characterise the likelihood of sleep disturbance relating to aircraft noise as research has found that single event metrics are a better predictor of sleep disturbance than long term average noise metrics such as Leq16h
- DNL is a variant of Leq which includes a 10dB weighting for noise events at night and a 5dB weighting for events during evening periods, reflecting the potential for increased sensitivity to noisy events during those time periods.
The reality of aircraft flying overhead can be difficult to describe. Typically aircraft noise is given in the context of certain types of aircraft flying at certain levels. However, this can be difficult to understand in practice. To help with this the table below provides links to video clips of aircraft of different types at different heights. The aim of these clips is to be illustrative rather than scientific, as the noise experienced from an overflight will depend on a range of factors including how directly overhead the flight is, the weather, background noise and local environment. Noise Videos – already on the current site. The absolute level of noise from these clips will depend on your volume setting; most clips do however have some background noise such as birdsong, wind in trees and road/rail noise which should allow you to set the noise from the aircraft in a recognisable context.
|Height in Feet||Descending||Climbing|
|1000-2000||DHC Dash-8 at 1,400ft 66.8 dBA|
|4000-5000||Embraer E170 at 4,000ft 53.8 dBA|
|Height in Feet||Transiting|
|15000-16000||Embraer E170 at 15,000ft 42.5 dBA|
|Height in Feet||Transiting|
|9000-10000||Airbus A332 at 9,000ft 50.7 dBA|
|Airbus A319 at 9,000ft 45.8 dBA|
|10000-11000||Airbus A321 at 10,000ft 42 dBA|
|11000-12000||Airbus A319 at 11,000ft 49.2 dBA|
|13000-14000||Airbus A319 at 13,000ft 59.0 dBA|
|15000-16000||Airbus A319 at 15,000ft 45.2 dBA|
|Above 20,000||Boeing B752 at 25,000ft 40.2 dBA|
|Airbus A321 at 33,000ft and Boeing B737-300 at 35,000ft on same clip 35.7 dBA|
|Boeing B737-800 at 27,000ft 37.5 dBA|
|Height in Feet||Transiting|
|7000-8000||Boeing B772 at 7,000ft 52.8 dBA|
|8000-9000||Boeing B777-200 at 8,000ft 48.1 dBA|
|Boeing B767-300 at 8,500ft 59.9 dBA|
|10000-11000||Airbus A310 at 10,000ft 59.6 dBA|
|Boeing B744 at 10,000ft 53.5 dBA|
|11000-12000||Boeing B772 at 11,000ft 51.5 dBA|
|15000-16000||Boeing B747-400 at 15,000ft 43 dBA|
|Boeing B777-200 at 15,000ft 36.8 dBA|
|Above 20,000||Boeing B777-W at 30,000ft 42.6 dBA|
- Explore noise measurements in more depth with CAA publication CAP725, Appendix B, Section 4.
Read our blog for updates on progress with our NATS noise reduction initiatives.
If you have any further enquiries about NATS and noise mitigation please contact us here: http://www.nats.aero/contact/
Representative aircraft Lmax data Find out about representative Lmax data, together with information on how the data have been generated.
Noise respite trials Ground breaking and innovative action by the industry to tackle noise disturbance to communities near London’s main airports.