Aircraft noise and its effects 4
4.1 Introduction to aircraft noise
Broadly speaking, aircraft noise can be categorised into two different sources: ‘air noise’ and ‘ground noise’.
4.1.1 Aircraft ‘air noise’
Air noise from aircraft is created by aircraft arriving or departing from airports. It is generally caused by air passing over the aircraft’s airframe (fuselage, wings and underframe) and noise from the engines. When air passes over the airframe it causes friction and turbulence which results in noise. Engine noise is created by the sound of the engine’s moving parts and by the sound of air being expelled from the engines at high speeds. The degree of noise generated varies according to aircraft type and size and the way in which the aircraft is flown.
Aircraft manufactured today are generally much quieter than they have been in the past and ICAO set increasingly stringent certification standards for aircraft noise emissions. As a result, the aircraft fleet operating to and from Glasgow Airport is becoming progressively quieter over time. For example, the new A320neo which has started operating at Glasgow Airport has been shown to be 2 to 6 dB quieter10 than the original A320.
Whilst we have no direct control over the aircraft fleet that airlines who fly to and from Glasgow Airport choose to operate, we can influence the adoption of quieter aircraft technology through our differential landing charges and wider industry groups such as Sustainable Aviation, an alliance of UK airlines, airports, aerospace manufacturers and air navigation service providers. In this Noise Action Plan we have also committed to undertake a review of our differential landing charges and other methods of incentivisation to determine if it would be viable to introduce additional measures at Glasgow Airport.
DRAFT
4.1.2 Aircraft ‘ground noise’
Ground noise is any noise produced by aircraft whilst on the ground and is often related to the following activities:
Aircraft travelling (taxiing) between the runway and stands (where they park), including queuing
Aircraft at their stands with their auxiliary power units (APU) or ground power units (GPU) running
Engine testing (ground running)
Ground noise impacts tend to be limited to those areas closest to the airfield where they can be more prominent relative to air noise.
Engines need to be tested for safety reasons, and engine running forms part of the maintenance programme for aircraft. We understand that this noise can cause disturbance to residents closest to the airfield and therefore we adopt strict measures to restrict the location, duration and time of day that engine ground running can occur. We do not allow engine ground running above ground idle during the night, unless required due to exceptional circumstances.
We have introduced new actions in this Noise Action Plan to minimise noise from taxiing aircraft and the noise from aircraft APU/GPUs. In addition, we have introduced a new action to undertake noise monitoring of engine ground running to better understand its potential impact on our closest neighbours. We will use the information for this monitoring to review our ground running policies and investigate potential further control measures.
4.2 Measuring aircraft noise
Measuring sound and describing its impacts or effects is an inherently complex process. Noise is defined as unwanted sound and some individuals find noise more disruptive than others. Any attempt to define and measure sound, particularly as a single number, therefore has limitations, and cannot fully capture the spectrum of personal experiences of noise. However, seeking to quantify sound is essential to managing the noise challenge.
There is not a single metric that meets all needs for assessing, quantifying or communicating noise effects and there is a need to use a number of different metrics. For example, some metrics are better correlated with health effects, whilst other metrics can be more useful for communicating and understanding impacts, or for use in performance management monitoring. The key metrics used in the Noise Action Plan are summarised below, but we use a great deal more metrics in quantifying noise at Glasgow Airport, for example in relation to our Airspace Change Proposal (ACP) (see Section 2.6).
4.2.1 The LAeq,T (equivalent continuous sound level) metric
There are a range of metrics which are used to describe sound and inform UK Government policy relating to aircraft noise. The most common international measure of environmental noise is the LAeq, meaning ‘equivalent continuous sound level’. This is a measurement of the total sound energy over a period of time. It is easiest to think of this as an average, but important to note that all the sound energy in the time period is captured by this metric.
In the UK, daytime aircraft noise is typically measured by calculating the equivalent continuous sound level in decibels (dB) over 16 hours (07:00 to 23:00) to give a single daily figure (LAeq,8h). Nighttime aircraft noise is most typically measured over an eight-hour night period (23:00 to 07:00). The average noise exposure is commonly calculated for the 92-day summer period from 16 June to 15 September. The summer day period is used because people are more likely to have their windows open or be outdoors, and because aviation activity is generally at its busiest during the summer periods. For Noise Action Plans, the Environmental Noise (Scotland) 2006 regulations (as amended) require LAeq to be calculated over a full calendar year, rather than the 92-day summer period.
Separate assessment for day and night recognises that daytime and night-time noise can lead to quite different effects (principally daytime annoyance and night-time sleep disturbance) and thus it is better to define and measure daytime and night-time noise separately.
4.2.2 The Lden (day evening night equivalent sound level) metric
The day evening night equivalent sound level (Lden) noise metric is a 24 hour noise metric that applies a 5 dB(A) penalty to noise during the evening (19:00 to 23:00) and a 10 dB(A) penalty to noise during the night (23:00 to 07:00), reflecting relatively higher sensitivity to noise during these periods. Lden is frequently used to quantify aircraft noise in Europe as it was adopted as a common environmental noise indicator for the European Union in the Environmental Noise Directive (2002/49/EC) for road, rail and industrial sources, as well as aircraft noise. It is also a requirement in Scotland to use this metric for strategic noise maps under the Environmental Noise (Scotland) 2006 regulations (as amended). It is typically calculated over a full calendar year.
