This post reviews and makes available airplane noise data supplied by Massport. It offers background for the conversation about airplane noise in Belmont and Watertown.
A couple of things come out of the data. The data drive home, first-of-all, that the FAA’s 65 DNL threshold for noise compatibility with residential land use is simply a very high threshold. Areas experiencing noise above that DNL are areas that most people would experience as unmistakeably noisy, much noisier by any measure than Belmont or Watertown. The data also yield a practical insight: Flights departing from runway 33L are very concentrated over two narrow corridors in Belmont and Watertown, but spreading them out by as much as 1000 meters in either direction would not make a detectable difference in experienced noise levels.
MassPort’s recent Belmont Noise Monitoring Report concluded that the noise levels related to flight operations in Belmont are far under those recognized as incompatible with residential land use by the FAA. I’ve been interested to better understand the computations underlying MassPort’s conclusions, given that some residents do feel disturbed by the noise. MassPort was kind enough to furnish the detail data underlying the report.
The detail data came in two Excel files:
- A file containing actual second by second measurements. This is a big file — 2.3 million records for 27 days at 86,400 seconds per day. Too big to post for download, but I’m happy to share the disk with anyone interested.
- A file correlating noise events to flight operations at Logan. During the study period, 2071 Logan flights correlated to identifiable noise events at the monitoring site. You can download the flight operations file here.
The report and the underlying data do correlate well and appear to provide very useful information about the intensity of the airplane noise in an affected location.
- The report is based on a noise measurement device installed in a well chosen location. The device was installed in the back yard of a home in Belmont where the residents have been particularly disturbed by the airplane noise. The location is, in fact, close to the flight path for many planes. The radar/earth image above is copied from page 9 of the report. The image shows that the monitoring location lies at the southeastern edge of the path for runway 33L departures that branches over Belmont. The monitoring location is also 0.5 miles northwest of the edge of the path that branches over Watertown. The radar/earth image shows a dense area of flight tracks for each path branch which is roughly half a mile wide, with some tracks going well outside that dense area. (The image on page 9 shows a distance scale if you zoom in on it).
- The report covers a relevant period — during the 27 days of the report, the usage of runway 33L was relatively heavy — 24% of airport departures as compared to under 20% in each of the last 7 full years.
- The second-by-second detail does correlate as it should with the flight operations data. One can look at the second-by-second noise level increasing as a plane approaches and reaching a peak level that matches with LMAX column in the flight operations file.
- I was able to closely reproduce the computation of SEL or “Sound Exposure Level” in the flight operations file for a selected flight. The SEL is the noise level in decibels that would result if all the noise energy from the single flight — which might actually be audible for a minute or so — were concentrated into one second. Page 8 of a Virginia Tech training document shows how the SEL computation is done:.
- scale up from the decibel number for each second of the flyover to noise energy for that second (divide decibel level by 10 and then exponentiate 10 to that number);
- add that energy across all the seconds of the flyover (or closely approximate that by using only the seconds during which the noise level is within 10 decibels of the peak);
- scale the sum back to decibels (take the log base 10 of the sum and multiply it by 10).
- I was able to exactly reconstruct the computation of day night noise level from the SEL values. The day-night noise level is the average noise energy from flight operations (with a 10 decibel up-adjustment for noise between 10PM and 7AM). DNL can be derived from the SEL’s for each flyover as follows:
- scale the SEL for each fly over back to energy (divide by 10 and exponentiate 10 to that number);
- sum that energy across all fly overs and then divide by the number of seconds in the period (27 days * 24 hours * 3600 seconds ) for an average energy;
- scale that average energy back to decibels (take the log base 10 of the average and multiply by 10).
In SQL, that computation reads as follows: SELECT 10 * ln( sum( 1 / ( 27 *86400 ) * exp( ln( 10 ) * ( sel + if( hour( eventstarttime ) >21 OR hour( eventstarttime ) <7, 10, 0 ) ) /10 ) ) ) / ln( 10 ) FROM flightevents. Applying that query to the flight operations file (that you can download above and then import into your favorite database for querying) yields a total flight operations DNL of 44.5 decibels — exactly the flight operations DNL computed in the report. Selecting only 33L departures, I got a DNL of 44.1 decibels, again, exactly as in the report. I was also able to validate the all-operations daily DNL levels at page 8 of the report.
The accuracy of the report does, of course, depend on the accuracy of the association between flight operations and measured noise events. That association is done entirely by MassPort using radar data and we have no ability to verify that association. On the other hand, we have no reason to doubt it, as the data do hang together well.
Noise intensity by hour
One question that comes up in conversation about the noise issue is the intensity of noise during certain hours. The data supplied by MassPort allows us to compute DNL by individual hour. The table below shows the DNL by hour for the noisiest 30 individual hours during the period.
What this table shows is that even in the busiest hours of the 27 days in question, the DNL did not exceed the 65 decibel level deemed to merit remedy by the FAA. And note that the very highest DNL’s are all in night hours so that, in the DNL computation they are boosted 10 decibels. The highest single-hour unboosted DNL was March 20 at 5PM with a DNL of 54.9, 10 decibels lower than the 65 level. 10 decibels of DNL is a very different hourly noise level — equating to either a 10 decibel (very noticeable) increase for each noise event in the hour or a 10 fold increase in traffic. For more hourly detail in spreadsheet form, click here.
- To reach the annual 65 DNL threshold, Belmont would have to have traffic equal to its worst single day-time hour during every single night hour (from 10PM to 7AM) and would also have to have a 10-fold increase in traffic over that worst single day-time hour during every single day-time hour 365 days per year.
- To reach the annual 65 DNL threshold, Belmont would have to have 100 times as many flights as it does — Belmont’s DNL is under 45. To achieve a 20 decibel increase, Belmont would have to have 100 times as much sound energy.
- To reach the annual 65 DNL threshold with Belmont’s current traffic level, it would have to be 10 times closer to the airport than it is, in other words it would have to be under a mile away from the end of the runway. Only certain parts of East Boston and Winthrop are that close. Of course, in those locations, people hear all the planes Belmont hears at a noise level 20 decibels higher (because the planes are under 1/10 as high), but they additionally hear a lot of other air traffic. They also can hear airport ground operations.
The comparisons for Watertown, if measured, would be very similar to the comparisons for Belmont.
Flights by aircraft type (33L Departures)
The flight operations file contains 2071 records, consistent with the report. It identifies 1534 of them as 33L departures, also consistent with the report. The data confirm that 33L departures are almost all of the noise problem — the DNL for events other than 33L departures is only 34.0, well below the ambient DNL. Only 25 of the non-33L events had a peak one second noise level (“LMAX”) greater than 65. Focusing on the 33L departures, 10 aircraft types account for 1229 (80%) of the departures and have comparable LMAX averages:
MD88s account for only 17 flight events, but 12 of the top 20 most noisy events based on LMAX (13 of the top 20 based on SEL).
Flights by POCA Altitude (33L Departures)
The average altitude at Point of Closest Approach for flight events in the file is 1861.4 meters or 6107.0 feet for 33L departures. This is a little different than the report which states an average altitude of 6269 feet. I can’t explain this by backing out the elevation of the monitoring station — it was under 15 meters (50 feet) above sea level. Note: The Point of Closest Approach Distance (POCADistance) is consistently within 1 meter of the squareroot of the sum of the squares of the POCAAltitude and POCARange (if POCAAltitude is adjusted down by 20 meters, a few meters more than the true elevation of the monitoring station). This is the correct mathematical relationship for distance to have to altitude and range.
|Altitude (meter range)||Count||Average LMAX|
83% of the flights (1275 of 1534) fall within the 1400 to 2200 meter altitude range.
Flights by POCA Range (33L Departures)
Looking at the table below, it emerges that there are two Point of Closest Approach ranges with high traffic, one with roughly 200 flights ranging 300-500 meters from the monitoring site and a second with roughly 700 flights ranging 1100 to 1400 meters from the site. Based on the graphic reproduced above, it appears that the first peak may correspond to the Belmont path and the second peak to the Watertown path. There is a smaller third peak around 1800 meters which appears to correspond to the Arlington path.
The numbers in the left column of the chart below each represent the low end of a 100 meter range for horizontal range at closest approach (POCA).
|Horizontal Range (meter range)||Count||Average LMAX|
Worth noting: the altitude differences among locations in Watertown and Belmont are too small to make a difference: The top of Oakley Country club is at 65 meters and the Belmont Hill Club is at 87 meters as compared to the average POCA altitude which is 1800 to 1900 meters. Note also: The particularly noisy few flights in the 0-200m range happen to include noisy MD88’s and are noisy for that reason, not because of their being directly overhead.
Flights by destination by POCA range (33L Departures)
The following table allocates flights by destination to the ranges identified above and the allocation does appear to make sense geographically, with Watertown(?) getting most of the eastern seaboard destinations, Belmont(?) getting more of the southwestern destinations and Arlington(?) getting the most westerly destinations.
|New York LaGuardia||115||102||1||0|
|New York JFK||84||69||1||2|
|West Palm Beach||25||16||0||0|
|La Desirade (Caribbean)||11||5||0||1|
Note that the 32 destinations shown above account for 1335 flights, 87% of the 1534 33L departures in the study. The selected ranges account for a total of 83% of the flights to those destinations, with the Watertown track alone accounting for 58%. The following is the query generating this table: SELECT arrivalairport, count( eventid ) , sum( if( pocarange >1100 AND pocarange <1400, 1, 0 ) ) AS watertown, sum( if( pocarange <600, 1, 0 ) ) AS belmont, sum( if( pocarange >1700 AND pocarange <2000, 1, 0 ) ) AS arlington FROM `flightevents` WHERE departurerunway = ’33l’ GROUP BY arrivalairport ORDER BY count( eventid ) DESC.
Selecting the top 10 destinations on the Watertown track, all easternboard destinations, and recomputing the range table for only the 774 flights to those destinations, it is striking that 400 of the 774 fall within the 1200-1300 meter POCA range and 639 fall within the 1100-1400 meter range — in other words, the flights are following a very consistent path as intended under the RNAV system. SQL for this query is: SELECT floor( POCArange /100 ) , count( eventid ) , avg( lmax ) FROM flightevents WHERE departurerunway = ’33L’ AND (arrivalairport = ‘LGA’ OR arrivalairport = ‘DCA’ OR arrivalairport = ‘PHL’ OR arrivalairport = ‘JFK’ OR arrivalairport = ‘EWR’ OR arrivalairport = ‘BWI’ OR arrivalairport = ‘CLT’ OR arrivalairport = ‘RDU’ OR arrivalairport = ‘MCO’ OR arrivalairport = ‘RSW’ ) GROUP BY floor( POCArange /100 )
One has to wonder why such a detailed analysis wasn’t done on the number of complaints in Belmont and Watertown to determine if in fact this ‘issue’ affects many of the citizens.
A review of the MassPort published numbers indicates that for the first six months of 2014, there were no more than 22 unique monthly callers from Belmont (June had only 8), and for Watertown, a max of 15 for the first part of year.
Considering that Belmont has a population of about 24,000 and Watertown 33,000 – the numbers of complainers are below trivial. Especially when the numbers are further analyzed to show that Belmont complainers submit more than twice the average number of complaints compared to the average of all the communities listed (ranging from 25 to 40 communities).
In other words, a highly vocal, miniscule minority has engaged in ‘issue exaggeration’.
One would expect that elected representatives would be aware of this characteristic, and be more selective of the real issues that deserve their attention and resources.
As a note – I live right underneath the departure path – and the term ‘noise’ is subjective – the Belmont landscaper’s leaf blowers and chainsaws produce far more ‘noise’ in any given month than the overflights.
I hear people complaining many times when talking in the street and a plane coming over. I do not believe that people run in and then try to find the website to send in a complaint so that the actual numbers, IMO are most likely very low. I do agree that this would be a lower priority over many other issues. That said, I was woken on a night in May at 12:08am from a plane! I am not a super light sleeper and this has not happened before. I thought it was going to land on my house! I did file a complaint and got a letter stating that the noise was below levels..blah blah. Of course…so I do believe there are other even more important issues…and that the landscapers..though not many around my house..are most likely a larger issue with noise, that the plane noise does impact the quality of life while outside dining,sitting and sleeping with windows open(something we did not have to contend with years ago:).
Thanks, J. You are very right that many are undisturbed by the noise. kcoin is also right that not everyone knows where to complain.
Different people care about different things. Without losing sight of larger concerns, I do try to also attend to the concerns that may affect smaller numbers of people.
The plane noise at night is disturbing. It has woken me up on several occasions. As some of my neighbors have said, at times it sounds like a plane is going to land on our houses. The plane noise doesn’t bother me during the day – it’s just one more piece of the ambient background noise (road work, yard work, kids, etc.). Multiple flights at night, when there is very little other noise, is disturbing and seems to be increasing. I suspect lots of people are disturbed by the noise, but aren’t aware of where they can file a complaint or don’t believe it will make a difference.
Will – I don’t mind periodic airplane noise, but it seems that over the past 36 hours the flight path has changed, and there are planes constantly flying over Belmont. What is going on? thanks, Heidi
Heidi, there has been an unusual run of northwest wind. Northwest wind is unusual at this time of year. When there is a northwest wind they use the runway 30L for departures and that is what is causing the relatively high noise over the last few days in Belmont and Watertown. Usual prevailing wind should return soon.
There has been an increase of flights over Watertown over the last two days that is significant and very disruptive. Anecdotally, these seem to be taking place late at night (post 11 PM) and early in the morning (pre 7 AM).
I am always dubious of those who monitor themselves in order to determine if they’ve done something they were not supposed to do. These aircraft sound like they are flying lower than they should be.
I have to say that noise has noticeably increased in the last several months. It may be more so that the frequency has increase adding to the irritation factor.
We continue to become more irritated by this as time goes by and the number of overhead flights appear to be increasing.
And by the way isn’t there some statical correlation to how many people think/feel the same way but don’t take the time to raise their voice? I’m fairly certain that the number of complaints filed with Massport is not the specific number of people who are upset by this. And towns tend to have ordinances for when leaf blowing can take place- that isn’t so for aircraft flying overhead.
FYI, all the planes have every incentive to get as high as they possibly can as soon as they can to minimize fuel consumption. That is the goal of all the airlines.
These are very interesting data and provide a useful objective measure of the impact of the flight routes on our community.
With regard to J’s comment on the number of complaints that have been logged, it is important to note that it is highly likely that these represent only a tiny fraction of the actual number of people who have been disturbed by this noise. As with other socially based sampling methods, it is expected that, for various reasons, only a small portion of the population will in fact be motivated to respond. One needs to add to this the number of difficulties in this case of learning about the existence of this complaint reporting website or phone number in the first place, the unreliability of the web is that we have observed, as well as the obvious factors affecting human motivation and obtaining access to the reporting mechanisms.
Naturally, those who are aware of the reporting mechanisms are the ones who have used them most frequently. And the fact that those people have recorded so many incidents very likely shows the high level of impact on the much larger part of the community that has not submitted reports.
The FAA reports provide fascinating data. They clearly show that overflights in our area are frequent and that noise levels are in fact significant. Furthermore, many of the densest overflight periods are during times when people are most negatively affected. That is, during early morning and in the evening hours when people are at home, enjoying their yards for living rooms or attempting to sleep.
This brings up one major and notable flaw in the assessment that the FAA analysis provides. The equivalent sustained period of high decibel exposure (DNL) is a useful measure in so,e cases and one that makes special sense in industrial settings where long-term exposure to high decibel levels can have lasting effects on the human ear and other parts of the organism. It is a very indirect measurement, however, of the degree to which the citizens of the areas in question are actually affected by this flight pattern. We are not complaining about impairment of our auditory sense.
Sustained exposure to high decibel levels is not in fact an accurate description of the problem. It is the frequent and concentrated nature of the intermittent disturbances that the overflights cause that results in significant degradation of quality of life for many of us. This morning, for example, I measured over 20 flights per hour whose noise levels were sufficient to interrupt outdoor conversation during the hours of 6 AM to 8 AM. That is an average interval of a little more than two minutes and on multiple occasions the interval between overflights was only a little more than one minute.
The FAA measurements actually do not reflect this issue adequately. It might be difficult to do so with the same level of mathematical objectivity that their report does provide. (Though perhaps some actual visits to the affected neighborhoods to attempt to hold comfortable conversations during the overflights would provide useful metrics.) But it is quality of life and not DNL that we in the community are concerned with and the FAA’s report fails to capture this.
However, it is exactly the role of government to safeguard quality of life, so I would expect the FAA, MassPort and our elected officials to take actions to identify and resolve this problem. We should not be put off by the superficial objectivity and completeness of this interesting report.
I also agree that leaf blower noise is sometimes louder and is often more disturbing than aircraft overflights. I would like to see ordinances in place to reduce or eliminate this problem as well. But this fact does not reduce the significance of the disturbance caused by the new Logan Airport flight patterns.
Thank you, Peter it is a process. There has been a huge effort to minimize overall noise in the greater Boston area. It is ongoing and remains a central focus of state and federal officials.
Thank you for providing an update and on the airplane noise impact on Watertown and Belmont.
While I haven’t had a chance to dive into the report/data, I will share what are the salient issues for me and I suspect many others in this narrow band/corridor over Watertown/Belmont.
1) Notice: It would seem that the placement or location of a “superhighway” next to a residential neighborhood would require sufficient notice for the Town/ community to gather information and provide input into the process.
Essentially the FAA/Massport has effectively located an air “superhighway” over our neighborhood without notice or meaningful opportunity to participate in the process.
2) I do not know what the readings are for the flights over our house—and it maybe that they all fall below the threshold (65DNL). But the issue is the incessant nature of the noise when the planes are using 33L. To have planes fly over for several hours (2-3) at 1-2 minutes apart creates significant impact to quality of life. This is compounded when those time periods are early in the morning or late at night. The effect of the RNAV system –which I recognize may have some other benefits–is that a tighter swath of residents/neighborhoods feel much greater impact.
I appreciate you keeping us informed but would like to figure out how to best mobilize our federal/state officials and Towns to have meaningful input to mitigate the impact this has had on our communities.
I completely get it as I am on the Belmont branch of the new flight path.
There is, as a result of environmental settlement, a very structured and elaborate study process to control Logan noise. The mechanism for community participation is an entity called the Community Advisory Committee. There is, in fact, a full website devoted to it: http://www.bostonoverflight.com. Belmont and Watertown now do have members on the CAC.
We’re giving a lot of time to it in all the channels that exist. See my account of information from the FAA and the CAC.
Feel free to call directly on my cell at 617-771-8274 if you’d like to talk it through further.
Thank you for this excellent report. I live in Dedham and began searching for a solution to the same problem directly over my home. Your website will be a sample of what we as a community can do if organized.
Let me know if I can be helpful in any additional way.
Thank you for the data. It is fairly easy to follow the traffic on the live (10 minute delayed) portal:
I don’t see the afternoon and evening Europe bound traffic listed or discussed. This is a consistent pattern of large jet departures that go on also after 10PM. They go the usual route, up the Mystic river, turn over Tufts and North Cambridge, Fresh Pond, Watertown, and then continue with a giant loop over Newton and go out at sea eastwards exiting the main land over Hingham. An entire metropolitan area affected by noise and pollution, let alone waste of fuel, while the planes could go straight out eastwards over the ocean.
Also, I do have a decibel reader and it often hits 80DB when the planes go over my house at 130 Putnam st in Watertown.
I would like a monitor installed in my back yard permanently. I’ll be happy to share the data.
80 is a high reading. I’ll be in touch with you off line to discuss how to verify that.
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