The annoyance caused by airplane noise can have adverse effects on those living near airports. Can anything be done when the plane lands to mitigate the noise? In this episode, we talk to Anders Johansson (Royal Institute of Technology, Sweden) about his research into how airplane configuration and weather may affect landing noise.
Associated paper: Anders Johansson and Karl Bolin "Analysis of landing noise from Airbus A321neo using long term noise measurements and flight recorder data." The Journal of the Acoustical Society of America 153, 3482 (2023); https://doi.org/10.1121/10.0019713
Read more from The Journal of the Acoustical Society of America (JASA).
Learn more about Acoustical Society of America Publications.
Music Credit: Min 2019 by minwbu from Pixabay. https://pixabay.com/?utm_source=link-attribution&utm_medium=referral&utm_campaign=music&utm_content=1022
The annoyance caused by airplane noise can have adverse effects on those living near airports. Can anything be done when the plane lands to mitigate the noise? In this episode, we talk to Anders Johansson (Royal Institute of Technology, Sweden) about his research into how airplane configuration and weather may affect landing noise.
Associated paper: Anders Johansson and Karl Bolin "Analysis of landing noise from Airbus A321neo using long term noise measurements and flight recorder data." The Journal of the Acoustical Society of America 153, 3482 (2023); https://doi.org/10.1121/10.0019713
Read more from The Journal of the Acoustical Society of America (JASA).
Learn more about Acoustical Society of America Publications.
Music Credit: Min 2019 by minwbu from Pixabay. https://pixabay.com/?utm_source=link-attribution&utm_medium=referral&utm_campaign=music&utm_content=1022
Kat Setzer 00:06
Welcome to Across Acoustics, the official podcast of the Acoustical Society of America's publications office. On this podcast, we will highlight research from our four publications. I'm your host, Kat Setzer, Editorial Associate for the ASA. Today we'll be talking to Anders Johansson of the Vehicle Engineering Department at the Royal Institute of Technology in Sweden, whose article, "Analysis of landing noise from Airbus A321neo using longterm noise measurements and flight recorder data" published in the June 2023 issue of JASA and was featured in the AIP Publishing Scilight, "Noisy airplanes no more." Thanks for taking the time to speak to me today, Anders, how are you?
Anders Johansson 00:47
Fine, fine. Thank you.
Kat Setzer 00:48
Good. So first, tell us a bit about your research background.
Anders Johansson 00:52
So I'm into noise. So the article that I wrote is part of my PhD, so I'm a PhD candidate, and prior to that, I was working with the noise from wind turbines. But then I was more concerned on how you perceive noise from wind turbines, so I was not dealing with physical levels, like in this article.
Kat Setzer 01:14
Yeah. So this study is concerned with aircraft noise, specifically in terms of when the aircraft is landing. Can you give us some background on aircraft noise?
Anders Johansson 01:21
So aircraft noise is part of the environmental noise, like road noise or train noise. And that type of noise affects you... I mean, it's a long-term effect. So that could have increased the prevalence of heart disease, sleep disturbance, and metabolic outcomes of some sort. So if you're exposed to high levels of this type of noise, your body will be stressed in some sense. And then if you live close to a highway or an airport, that's not good for you.
Kat Setzer 01:56
Okay. Yeah. So it makes sense. Like it's not causing hearing loss or anything like that, but it is just that general day to day...
Anders Johansson 02:03
Yep. Yeah, for sure. So I mean, I guess if you feel like, okay, this is a bit disturbing, like the kitchen fan in your kitchen or something like that. So it's not like it directly affects your hearing; it's not creating tinnitus. I mean, it could but then you need to be very close to the to the aircraft.
Kat Setzer 02:22
Right. That makes sense. So why is landing noise of particular interest to researchers?
Anders Johansson 02:28
So one maybe would think that the departure, because that is the point when the aircraft rev the engines to max, and that it's also maybe the most noisiest phase, but the climb rate, or the takeoff of the aircraft is very steep, so they leave the ground very quickly. And when you land the aircraft, the landing trajectory, it's much more elongated. So that will cover a larger area and expose more people to noise. So in that sense, it affects more people.
Kat Setzer 03:03
Okay, yeah. Got it. So what efforts have been made thus far to reduce landing noise planes?
Anders Johansson 03:09
Throughout the years, I mean, in the in the beginning with jet engines, they were very noisy. But then they rebuilt the engine, so they had a higher bypass ratio so that airplanes became quieter. And also, they worked on acoustic liners in the engines and improved the aerodynamics of the fuselage. But at the time, also the traffic, the number of airplanes in the air increased. So in some sense, if you look on the yearly average there, the noise is still constant in that regard. Yeah, so that's one that's one technical language with the source, they try to make the aircraft quieter. But then also there is, like I've been looking at in this article procedures, are the ways that you can fly quieter. And one way is to try to keep the distance between the ground and the airplane as long as possible. So when you land an airplane, you are coming from cruise altitude, and then there's this intermediate stage, so where you fly in a holding stack, at level flight, so say that you're at 2500 feet or something like that. That will affect a lot of people when you're flying around because noise from aircraft at that level will be heard on ground, and that causes annoyance that we were talking about before. So instead if you land from top and descent and just in a straight line, then you will minimize the noise on ground. So that's one way to do it. The noise that we are concerned in this article is for the last phase of the landing, which is called the final approach and that is. Basically a straight line extending out from the runway at a three degree angle. And all aircraft landing has intercept this line. So the trajectory is fixed, so you can't make any turns or avoid certain noise sensitive areas, for instance. So what I've been trying to explore, is there anything that you can do with aircraft? Can you change the throttle or the setting of the wings, or the deployment of the landing gear to minimize the noise from the aircraft? So is there a way to fly quieter?
Kat Setzer 05:37
Okay. Got it. That makes sense. So I guess when you're taking off, or flying up high, which flying up high, it doesn't really matter. Because you're far way, right?
Anders Johansson 05:46
Yeah, yeah.
Kat Setzer 05:47
But this is just kind of like that period, when you know that you have to be close to the ground.
Anders Johansson 05:51
Yeah.
Kat Setzer 05:52
Okay. So what was the goal of this study? Because we've been seeing that, during this phase, more or less the airplanes, they fly in the same way, I've been able to see that the noise varies, like, 5 to 10 dB from the mean within this area. So what's happening here? Why is some aircraft noisier and why are some others quieter? And can you use this? Is this affected by the aircraft? Is it due to the speed or something else, or the engines, or is it the wind? So that was the, what we were trying to understand. Okay, so how did you take measurements of the landing noise?
Anders Johansson 06:31
So we just basically, we had a great big scheme from the beginning, they were gonna put out a lot of microphones that would cover all this area. So they were just ordinary microphones that we put out on the approach route.
Kat Setzer 06:48
Okay, that makes sense. Very straightforward. So in your article, you mentioned that you also take into consideration the aircraft configuration as well as meteorological considerations, like wind. Can you explain what you were looking for, and how you dealt with these factors?
Anders Johansson 07:02
So, how we dealt with them... So those were, all the aircraft parameters are recorded by the, what's called the "black box" in that plane, and it's called the flight recorder data, FR data. So we log that data and also we log the meteorological conditions, so what was the temperature and so on, and wind conditions. And we did this for one year. So we had a great variation in different conditions. So then we took the sound level measurements as the, what you can call the dependent variable, then we took all the flight data and meteorological data is the independent variables. And with that we run a regression model that maps the relationship between the sound on the ground and these variables.
Kat Setzer 07:55
So how did these parameters end up correlating with landing noise?
Anders Johansson 07:59
So, in the end, we saw that it was the speed and the configuration of the aircraft that was determinant of the noise on ground. So about 70% of the noise variation were explained by these two variables. So it ended up we couldn't see any big effects from the wind or weather conditions, as I guess the source receiver distance is too short for the sound propagation to be altered by these parameters.
Kat Setzer 08:31
What is suppression, and how was that important to your analysis?
Anders Johansson 08:34
Yeah, so, when I had run my regression model, I saw some peculiarities in the output. And suppression in regression analysis is that if you add one variable... I can give an example here. So say that you you're going to take a math test, and then you could say that the study time is a predictive variable for test and that you can make linear relationship between these two, but then maybe you can add a third variable like nerviosity for taking a test and that nerviosity can account for some variants in the study time variable. So that you, what do you say, that enhances or it really removes some unrelated variants from these predictor variables. So, we had this in the measurement because we measured the distance between the aircraft and also the speed of the aircraft and they covary, so when these two were in the in the regression model at the same time, they enhanced each other. So if you compare it to the zero-order correlation... I mean, what you expect is that this zero... the correlation will help you put in more variables that will decrease. But when you have suppression, it increases instead.
Kat Setzer 10:07
What would you say are the main takeaways from the study?
Anders Johansson 10:10
I mean, the main takeaway is that the high dependence on aircraft speed and the configuration of the aircrafts, that those two parameters are vital for if you want to model or determine the sound on the ground.
Kat Setzer 10:26
Were you able to come to any conclusions about how to mitigate landing noise and if so why?
Anders Johansson 10:31
So maybe not from this study or the results in this study, but I'm continuing with more data. So the one thing that we found out was that if the pilot could extend the landing gear, or deploy the landing gear, as late as possible, that would reduce the noise. So depending on the position along the flight path, the aircraft can be louder or quieter. So it could be like this. So if it's loud in the, in the beginning, it may be quieter, later on, and vice versa. So there's this trade off. But from the data that we looked at now, we can see that the most optimal trajectory follows if you extend the landing gear as late as possible, because the landing gear are also the components that generate the most noise.
Kat Setzer 11:20
Yeah, that's really interesting. Well, thank you again for taking the time to speak with me today, Anders. Hopefully the insights you gain from this research will be able to help the reduce noise affecting the communities around airports. And I wish you the best of luck on your future endeavors, including finishing your doctorate, and hopefully we read more about your research in JASA.
Anders Johansson 11:39
Thank you. Thank you very much.
Kat Setzer 11:42
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