By ICCAN Analyst Stuart Dick
One of the impacts of the Coronavirus (Covid-19) lockdown in the UK was our reduced ability to travel which had a direct influence on the aviation industry. With many flights cancelled, airport activity was severely reduced. At ICCAN, we have been interested to see how aircraft noise around airports changed during the lockdown period and get a picture of how this affected communities.
During June and July ICCAN commissioned Ipsos MORI to conduct a survey among communities living around five UK airports. This gave a snapshot of people’s experiences and how they responded to the change.
In this article, we look at flight and noise data we have received from the Civil Aviation Authority (CAA) about London Heathrow Airport. This helps us to examine some of the changes in aircraft movements and noise measured on the ground during the lockdown.
London Heathrow Airport experienced a sharp decline of aircraft movements from week commencing 9 March 2020 until week commencing13 April 2020, after which they began to increase gradually (Figure 1). During the fall, total average daily aircraft movements dropped from 1148 to just 161. On 9 March, narrow body twin engine aircraft, such as the Airbus A320 or Boeing 737, accounted for 46% of all aircraft movements, but by 13 April this was only 19%. New generation wide-body twin-engine and wide-body twin-engine aircraft had increased their share of aircraft movements by 13 April, to 30% and 33% respectively, up 13% and 19% from 9 March. Noisier, wide-bodied four-engine aircraft, such as Boeing 747s, were declining rapidly and many have since been retired.
As the lockdown progressed, more wide-body twin-engine aircraft were returning to London Heathrow (Figure 1). It’s possible that some of these aircraft may have been cargo-only flights. Indeed, Heathrow’s cargo air transport movements (ATMs) increased from March 2020 which were consistently and considerably greater than the same months of 2019 (Figure 2).
In contrast to the increase in cargo ATMs, the monthly passenger ATMs (Figure 3) dropped to consistently low numbers from April 2020 to June 2020, before experiencing a very slight recovery in July and August 2020 as lockdown was eased.
So how do these changes in aircraft movements and ATMs impact aircraft noise around Heathrow airport?
There are many noise monitoring sites on the ground surrounding Heathrow airport2 and the data from these sites can be used to calculate long-term averages of noise including daytime noise expressed as dB LAeq, 16 hr. In our review of noise metrics, published in July3, we explain what different noise metrics are and how they might be used. While we recommended that average measures should continue to be used, we also encouraged the use of supplementary metrics to better reflect the way in which noise is experienced on the ground.
For this piece we have considered two noise monitoring sites, which show contrasting daytime patterns of noise data during 2020 and in 2019. Noise monitor 11 (NM11) is located less than one mile to the east of Heathrow airport in Hounslow. Noise monitor 509 (NM509) is located in Cobham, around 15 miles south of Heathrow airport.
Over 2019 and 2020, aircraft noise at the monitor in Cobham was lower than in Hounslow. Cobham is significantly further away from Heathrow than Hounslow, and aircraft operate at a higher altitude over the monitor there. Cobham also experiences fewer overflights than Hounslow. During the period covering early March to end of June 2019 (weeks 10 – 27), the average aircraft noise level at Hounslow (Figure 4) was 60 dB LAeq and the average aircraft noise level over the same months in 2020 was 54 dB LAeq. Despite an average 6 dB drop in noise, there were still some occasions where weekly average aircraft noise in 2020 roughly equalled noise in 2019, as in week 11 and 12 (early March, Figure 4).
At Cobham (Figure 5), the average aircraft noise level covering March to end of June 2019 was 46 dB LAeq, compared to 36 dB LAeq over the same months in 2020. The 2020 average aircraft noise was consistently lower than in 2019 with the lowest weekly average being 26 dB LAeq during early July (week 27) in 2020. By comparison, the lowest weekly average aircraft noise for the same period in 2019 was 44 dB LAeq during weeks 22 and 26 (late May and June respectively).
In any given area, as well as aircraft, there are other background noise sources, such as road traffic and natural sources. If aircraft noise is the dominant source of noise, then you can expect little difference between aircraft noise levels and total noise. This was the case for the Hounslow monitor during both 2019 and 2020 (Figure 4). In comparison, there is a much greater difference between aircraft noise and total noise at Cobham (Figure 5), and this difference increased during 2020, compared to 2019, suggesting that there could have been far fewer aircraft flying over Cobham during March to June 2020.
Looking at this data tells us a bit more about how the lockdown impacted on aviation noise for people living around an airport like Heathrow, and that average noise levels were lower in both Hounslow and Cobham compared with 2019.
A closer look shows quite a different picture in these locations, however. At Hounslow, aircraft noise seemed to be the dominant source of noise since it was closely aligned to total noise in both 2019 and 2020. While, at Cobham, there was a much greater difference between aircraft noise and total noise over both years but the difference was greater in 2020. This suggests that aircraft noise was not the dominant source of noise in Cobham during 2020 and other noise sources contributed more to total noise. Therefore, the contribution of aircraft noise to total noise was lower given the greater distance from Heathrow airport.
That said, these data cannot give a complete picture since the noise has been averaged. Whilst LAeq takes account of the noise from all aircraft overflights, single events such as overflights of noisier aircraft are not evident in LAeq measurements, nor is a fall in the number of ATMs. This is why ICCAN recommends that airports also adopt a supplementary metric which can take account of frequency, such as the Number Above (Nx), and help to tell a more accurate story about the noise that people experience on the ground. In this way, we can see how many noise events exceed a certain threshold and take account of noisier single events3.
- Aircraft movements: Any aircraft take-off or landing at an airport.1
- ATMs: Air Transport Movements. Take-off or landings and all scheduled movements including air taxi movements.1
- LAeq: The equivalent sound level of aircraft noise, averaged over a given time period (e.g. 16 hours, 07:00 – 23:00) using the A-weighted scale.3
- 2015. Notes and FAQs – UK airport data. 2015 © Civil Aviation Authority. https://www.caa.co.uk/Data-and-analysis/UK-aviationmarket/Airports/Datasets/UK-Airport-data/Notes-and-FAQs—UK-airport-data/ Accessed 30/11/2020.
- 2020. Noise monitor locations. https://webtrak.emsbk.com/lhr4. Accessed 15/12/2020
- 2020. A review of aviation noise metrics and measurement. © Crown copyright 2020 https://iccan.gov.uk/iccan-review-aviation-noise-metrics-measurements/. Accessed 16/12/2020