Luton and District Association for the Control of Aircraft Noise
Aircraft Noise
Human Response to Noise
There is very wide range of response to noise. While one person sleeps soundly at night with aircraft 300 feet overhead producing noise at ground level which is 8 times as loud as that which is scientifically rated as likely to awaken, another can tell you the time at which the same aircraft passed over his house at 3,000 feet.
Measurement of sound levels
Sound is measured in decibels (dB) which follow a logarithmic scale because human perception fits such a representation – a sound which we rate as twice as loud as another is measured 10 decibels higher. In aircraft terms, a ‘plane which produces 80 dB on flyover will be perceived as twice as noisy as one which produces only 70 dB. A decibel is one tenth of a bel, named for Alexander Graham Bell, and is used in its place because it represents the smallest change we can detect under laboratory conditions; a difference of 3 dB between aircraft is generally regarded as the minimum we will be aware of.
Sound is usually measured on an “A-weighted” basis, dB(A), which means that the sound pressure waveform picked up by a microphone is put through a filter which weights it to mimic the variations in sensitivity of the human ear to the different frequencies within it. However, this ignores low frequency vibration which is annoying and can generate audible noise by, for example, rattling windows and doors.
The figure below shows the sound pressure waveform (blue) and meter readings (red) for an aircraft taking off at about 1 mile from the end of a runway.
Noise indicators
A large variety of indicators or metrics can be used to present noise measurements - see our pages explaining the most common and alternatives. However, most information about aircraft noise is generated by computer models which use measurements of aircraft noise collected when the various aircraft types are approved to fly.
Noise Limits
There are no accepted limits or targets for noise exposure beyond the boundary fences of airports. The Government’s Planning Policy Guidance (PPG24) specifies constraints for building where aircraft noise is likely to be a problem but these do not apply in reverse: “You can build your airport next to my house but I cannot build my house next to your airport”. PPG24 expresses various levels of constraint on development based on Leq day and night indicators and states that development should not be permitted where noise events regularly exceed 82 dB(A) LAmax at night.
The World Health Organisation (WHO) recommends that daytime Leq should not exceed 55 dB(A) to avoid significant annoyance. It also recommends that outside maximum noise (LAmax) from aircraft over-flights should not exceed 60 dB(A) if sleep disturbance is to be avoided in rooms with open windows. British Standard BS8233, which specifies noise insulation standards for buildings, specifies similar noise limits and, in particular, an upper target of 55 dB(A) L eq for outside areas.
