Measuring noise

Understanding how aircraft noise can be measured

Aircraft noise

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.

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.

Comparison of Noise Levels
Typical Sound Approximate noise level (dBA)
Pneumatic drill, 7m away 95
Heavy diesel lorry at 40km/h, 7m away 85
Medium Aircraft Descending at 1000ft 70
Busy general office 60
Quiet office 50
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.

How noise is 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.
  • View Lmax data on a range of aircraft

Illustrative videos

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. 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.

Small Aircraft
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  
Small Aircraft
Height in Feet Transiting
15000-16000 Embraer E170 at 15,000ft 42.5 dBA
Medium Aircraft
Height Descending Climbing
1000-2000 Airbus A321 at 1,400ft 69.6dBA  
  Boeing B737-400 at 1,400ft 70.7 dBA  
  Airbus A320 at 1,400ft 64.9 dBA  
  Airbus A319 at 1,400ft 67.7 dBA  
  Airbus A319 at 1,400ft (with train noise included in clip for comparison)  
2000-3000   Boeing B737-800 at 2,800ft 70.9 dBA
3000-4000 Boeing B734 at 3,300ft 62.1 dBA Boeing B737-800 at 3,700ft 70.8 dBA
  Airbus A319 at 3,500ft 64.1 dBA Airbus A319 at 3,800ft 70.2 dBA
  Airbus A320 at 3,700ft 64.7 dBA   
  Airbus A321 at 3,700ft 58.1 dBA  
  Airbus A319 at 3,800ft 60.3 dBA  
4000-5000 Airbus A320 at 4,100ft 59.2 dBA Airbus A319 at 4,500ft 69.7 dBA
    Airbus A319 at 4,800ft 67.9 dBA
6000-7000 Airbus A321 at 6,000ft 60.2 dBA  
Medium Aircraft
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
Large Aircraft
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

Changing flightpaths can mean a change in noise impacts.  The airspace change process requires wide consultation if those changes are below 7,000ft.  All airspace changes undertaken by NATS are summarised here.  The airspace change process is described in the CAA’s publication CAP1616.


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