Aircraft noise evolution at local airports

Now that the chapter has assessed the current noise-level exposure of Milan Bergamo Airport and the measures implemented to reduce it, it turns to investigating the evolution of aircraft noise across the years, in relation to the important increase in air traffic. Table 15.7 shows the population and the area exposed to L_fcn > 65JB(.fl) every five years, starting at 2007. In the first five-year term (2007—2012), Milan Bergamo Airport registers a compound annual growth rate (CAGR) of 6.11 per cent in terms of aircraft movements, without increasing the people exposed to aircraft noise, while affecting a slightly larger area (CAGR equal to 1.73 per cent). In the second five-year term (2012-2017), aircraft movement CAGR is 2.23 per cent, leading to an increased CAGR on the population and the area exposed to L_Jcn > 65dB(A) of 1.18 and 1.56 per cent, respectively.

Overall, local airports register a lower CAGR for BGY in terms of aircraft movements, with a decrease of air traffic during the first five-year term. This is combined with an initial decrease of the number of people and kilometres of area affected (CAGR equal to -2.30 per cent and -2.64 per cent, respectively) in the first five-years term. There is a strong difference between BGY and other local airports. Milan Bergamo Airport tends to affect areas that are less dense in terms of population. The ten-year CAGR on population density of BGY is equal to -1.22 per cent, while other local airports register a positive CAGR of 1.99 per cent. This difference, which may partially reflect the

Table 15.7 Variation in the exposure to aircraft noise (L_den > 65JB(t1)) of local airports over several years

Table 15.8 Deviation analysis on the number of people exposed to > 65i//j(.4j

different approaches in mitigation strategies among airports, emerges clearly when conducting a deviation analysis (Table 15.8). The ten-year increase in population exposed at Milan Bergamo Airport is equal to 12.5 per cent. This value is mainly due to the increase in the area exposed to aircraft noise (24.0 per cent), but it is mitigated by the fact that the overall new area affected has a lower population density (-11.5 per cent). This is in contrast to other local airports, whose variation on the population exposed to L_rfen > 65dB(ff) over ten years depends only on an increase in population density of the area exposed. Interestingly, this is also true when looking at five-year periods. From 2007 to 2012, the population exposed to aircraft noise does not present any variation at Milan Bergamo Airport, while an increase in the area exposed to L_fei > 65dB(%l) indicates a change in the characteristics of the area exposed, in terms of population density. In the same period, at other local airports, the population exposed to aircraft noise decreases by -2.30 per cent, mainly thanks to a decrease in the area exposed (-2.64 per cent).

Another interesting insight comes from comparing the magnitudes of the increase in aircraft movements and population density. As shown in Figure 15.5, BGY’s ten-year increase in aircraft movements is 5.42 (2.49) times the ten-year increase in population (area) exposed to aircraft noise. This is not always true for other local airports, which in the same period register an increase of population exposed to aircraft noise which is 3.23 times the increase in aircraft movements. By considering each local airport separately, Figure 15.6 shows their place with respect to the ten-year CAGR of aircraft movements and an exposure ratio (computed as the ratio between the 10-years CAGR of population exposed to L_dcll > 65dB(ff) and the ten-year CAGR of aircraft movements). Among all local airports, BGY has the highest increase in the number of aircraft movements from 2007 to 2017. The majority of airports, which do not present variations in population density affected by aircraft noise, register a CAGR of aircraft movements that does not exceed 1 per cent. In three cases out of six (BFS, NCL, VLC), aircraft movement ten years CAGR presents negative

Figure 15.5 Growth of aircraft movements, population and area exposed to L_dtn > 65dB(X) of local airports

Figure 15.6 Efficiency of local airports in terms of noise exposure reduction over ten years

Noise assessment of local airports 297 values. An increase in aircraft movements higher than 3 per cent is registered for Alicante (ALC) and Lisbon (LIS) airports, which however present an increase in population exposed to aircraft noise which is much larger, showing a ratio of 2.40 and 3.12, respectively.

The achievement of such results also depends on the noise-mitigation and-reduction measures implemented by BGY across the years. On the one hand, the collaboration with Ryanair, the main carrier operating at Milan Bergamo Airport, has led to a relatively new fleet operating at the airport, with a lower impact in terms of noise with respect to other airports. On the other hand, BGY has been shifting its product mix in favour of passenger traffic. To contain the noise impact, the airport has been gradually reducing the cargo traffic, which is usually characterised by employing older and louder aircraft and by operating during the more-noise-sensitive periods of nights. In addition, the usage of preferential routes and the implementation of descendent profiles has played a significant role. Evidence shows that BGY has faced an increase in the areas exposed to aircraft noise, but these areas are characterised by lower population densities. This is not due to a depopulation effect of the area nearer the airport. The main reason lies in the use of alternative preferential routes to spread the noise burden over larger but less densely populated areas. In this regard, over the years, different tests have been performed in collaboration with airlines and approved by national authorities (e.g. ENAC and ENAV) to measure the noise impact of alternative paths.