Culver City community meeting

The City of Culver City will be having its 2nd community meeting regarding LAX overflights. The meeting consists of a Community discussion and a panel about the FAA’s SoCal MetroPlex’s (NextGen) project and the flight path impacts over Culver City. I will join council members Jim Clarke and Meghan Sahli-Wells in the City Council Chambers on Thursday, August 27, 2015 – 6:00—8:00 PM.  Address is:Culvercityseal

  • City Council Chambers, City Hall
    9770 Culver Blvd. Culver City, CA 90232

Persons who are unable to attend the meeting, but wish to provide the City with written
comments may do so by any of the following means BEFORE 4:00 p.m. on August 27, 2015:

  1. By LETTER to the City Clerk, City of Culver City,
    9770 Culver Blvd., Culver City, CA 90232;
  2. By FAX to the City Clerk at 310-253-5830; or
  3. By E-MAIL to

The Agenda will be available for viewing on the City’s website on or after August 25, 2015 at, or at the City Clerk’s Office or the Julian Dixon Library, 4975 Overland Avenue.

Flyer attached:

15-08-27__Courtesy Notification – LAX Community Meeting Notice FINAL-maps


Meteorological effects change sound propagation.

Local and Seasonal Meteorological differences change sound propagation.

Sound propagation is affected by atmospheric conditions. The FAA’s Environmental Assessment(EA) assumes a homogeneous atmosphere with a single temperature, humidity level and pressure. This doesn’t correlate with real-world conditions.

inversion layers

Inversion layers will refract sound waves and distribute them in a cylindrical pattern

Southern California is subject to persistent meteorological effects, such as inversion layers and prevailing winds. Temperature and humidity are not a constant across all altitudes and not all climate zones follow standard atmospheric assumptions. Ignoring atmospheric variables when modeling noise across distances can result in errors of 5-20dB.

Sound is typically modeled as a sphere of sound energy- where noise propagates equally in all directions from its source. Noise attenuation and direction of propagation will differ depending upon meteorological conditions. Increasing temperatures, wind and overcast have a downward spreading effect which increases noise to the ground. Inversion layers can refract sound waves resulting in higher noise levels at the ground.

In the summer, from the ground, planes appear louder due to high pressure inversion and increasing temperatures. Persistent seasonal changes can cause a shift in noise impacts for months further separating modeled vs perceived noise.

Temperature and humidity vary according to height

An earlier comment [Average weather calculation does not represent Noise impacts from overflights] pointed out the inaccuracies in using a single average value for temperature and humidity across Southern California’s diverse climate. Temperature and humidity vary with altitude. A standard reference atmosphere differs in vertical temperature -3.5 °F/1000 ft, and this likely is used in the modeling software. According to San Diego weather balloon data and SCAQMD’s Sodar data,  Southern California’s lower troposphere doesn’t follow a uniform progression of temperature change.

The use of ground-based measurements of temperature and humidity will be inaccurate when modeling sound levels unless the changing vertical atmospheric variables are taken into account.

Inversion Layers

In the atmosphere, temperatures normally decrease with an increase in height. An inversion layer occurs when temperatures increase as altitude increases.  Portions of Southern California spend more time under an inversion layer than not.[5] Inversions not only capture smog in southern California, they also effect sound propagation. Primary inversion layers can occur at heights between 900 and 13,000ft.

High pressure inversion [4]

High pressure inversion [4]

Regional subsidence inversion

Regional subsidence inversion

Marine inversion layer

Marine inversion layer

When planes fly above an inversion layer the aircraft noise reaching the ground is spread out farther at a lower intensity, when the aircraft is below the inversion layer the overall sound will be greater and spread over a farther distance. Arriving and departing aircraft cross the inversion layers which happen at different altitudes, and different intensity, depending upon time of day, season, and geographic location.

Southern California and the Los Angeles Air Basin are prone to inversion layers when warm air overlays a ground level layer of cooler air. Our coastal areas undergo a Marine Atmospheric Boundary Layer(MABL) as cool westerly winds from the ocean flow under the warm air from the land. The MABL are early day events that can occur during any month, but are most common during the dry season that runs from May through October.

Inversion Layers

San Diego low level inversion layer- Based on DTINV 1960-2007 [4]

Thermal inversion layers and their effects are not included in the noise modeling but it would increase the accuracy.

SCAQMD Sodar Wind Profiler at LAX demonstrates the daily wind direction changes during the day at differing altitudes.[8]

SCAQMD Sodar Wind Profiler at LAX[8] demonstrates the daily wind direction changes during the day at differing altitudes.

The Santa Ana winds are a regional subsidence inversion where warm air from the high deserts slide on top of cool marine air. Most significant is the summertime specific High Pressure Inversion: A high pressure system from the Western Pacific Hadley global circulation cell will sink warm, dry air on top of the marine layer, trapping it in an inversion.[4]

Inversions vary seasonally, but are a dominant feature in California air basins.[5] “June Gloom” is a common name for the annual inversion layers affecting the Los Angels Basin in late spring.

Wind effect on sound

Wind effect on sound – (a) High-wind, neutral conditions. (c) Low-wind, clear daytime conditions. (f) Low-wind, clear nighttime conditions. TL is transmission loss. [2]

Prevailing Winds

Southern California has prevailing directional winds of varying speeds. Wind refracts sound downward, distributes sound a farther distance downwind, and shortens distribution upwind.  Wind can vary sound between 10-20 dB.[2]

Modeling sound propagation requires factoring vector wind-speed, downwind conditions, and atmospheric stability to arrive at results that can have high-confidence values for accuracy.



The following graphs demonstrate the consistency of wind-speed and direction in six of the nine Southern California climate zones.[3] The EA fails to incorporate the effects of the prevailing wind on overall sound levels.

Wind direction and speed - Long Beach

Long Beach Prevailing Wind Directions; Summer:WSW, Winter: E

Wind direction and speed - LAX

LAX Prevailing Wind Directions; Summer:WSW, Winter: E

Wind direction and speed - San Diego

San Diego Prevailing Wind Directions; Summer:WNW, Winter: NE

Wind direction and speed - Riverside

Riverside Prevailing Wind Directions; Summer:SE, Winter: E

Wind direction and speed - Barstow

Barstow Prevailing Wind Directions; Summer:W, Winter: WNW

Wind direction and speed - Palm Desert

Palm Desert Prevailing Wind Directions; Summer:N, Winter: SE

Ground reflections

Ground level reflections can increase the amount of sound that is transmitted to the listener. In Southern California the sound wave’s interaction with the ground will be impacted by the semi-arid climate and urban sprawl. The relatively flat ground, lack of grass and other sound absorbing vegetative ground cover will result in greater reflections.[6] The suburban sprawl and predominately low lying buildings will add additional reflections to the direct source.

The model uses direct source of sound and doesn’t include any indirect reflections unless they were incidentally recorded with the aircraft’s noise profile.

Yearly DNL/CNEL aggregate vs seasonal aggregates

DNL/CNEL is a measures aggregate of noise events over the day. A yearly aggregate is an average of daily aggregates. Depending on the climate area within the study seasons can dramatically change the effect the atmosphere has on sound propagation. In order to represent noise over the year the DNL/CNEL values need to take into account our seasonal and regional atmospheric effects.
Noise perceived on the ground from the same aircraft flown during winter and summer will have a different spread and dB readings. Summertime aircraft will be perceived as louder. For this reason a single yearly DNL value will not properly reflect the seasonal range in noise differences.

DNL metrics should account for seasonal differences. DNL for specific locations should be expressed as a range, or use the worst case values as default.

Acoustic Modeling Constraints

The FAA’s Integrated Noise Model’s (INM) use of SAE AIR-1845 parameters and noise-power-distance (NPD) data enable the simulation of aircraft in a variety of thrust and 3D operational conditions. INM’s accuracy is dependent upon a matrix of empirical profiling of each aircraft configuration and use of formulas to extrapolate values.

Refraction of sound by vertical gradients of temperature and wind, inversion layers, separation of climates by horizontal segregation, scattering of sound by atmospheric turbulence and ground reflections are not readily within the abilities of the modeling software.[7] Sound calculations depend upon direct line-of-sight and ignore indirect contributors to noise.

An objective of acoustic modeling is to accurately simulate the propagation of aircraft noise to ground and return results that would approximate those found in a ground study. Comparing no action against a proposed action, when there are differences in flight altitudes, will be prone to error. Accurate modeling is also particularly important when attempting to determine which geographic areas fit within the noise criteria of DNL 45 dB, 60 dB and 65+ dB.

To correctly model noise at the ground, atmospheric conditions such as thermal gradients, prevailing winds and vertical segmentation of the atmosphere should model the characteristics of the study area.

Averaging a daily aggregate, like DNL, over a year results in discarding important information about the range of noise that occurs. DNL should be reported for each day.

If the EA is to effectively communicate with the public about the expected noise impacts of the proposed action, and be used to support changes to the airspace, it needs to more accurately represent how noise will be distributed.



[1] Atmospheric Factors in the Propagation of Sound, Doug Sheadel, Air and Waste management Association (2008)
[2] Sound Propagation in the Atmospheric boundary layer, D. Keith Wilson, Acoustics Today, (Spring 2015)
[3] California Climate Zones and Bioclimatic Design, The Pacific Energy Center’s Guide(2006)
[4] Illustrations are after those in Richard P. Turco’s book, Earth Under Siege, and Cal State University Northridge online resources for Geography 103
[5] Impact of Climate Change on the Frequency and Intensity of Low-Level Temperature Inversions in California,  Sam Iacobellis et al, California Air Resources Board (2010)
[6] Noise Reduction by Vegetation and Ground, D. Aylor, Journal of the Acoustical Society of America, (1972)
[7] Review of Integrated Noise Model (INM) Equations and Processes, David W. Forsyth, NASA (2003), NASAICR-2003-21241 4
[8] South Coast Air Quality Management District operates 4 SODAR wind profiler sites in the Metroplex.

Supplemental noise metrics can help public understand changes

The use of noise Metrics other than DNL can better tell Communities how airspace changes will affect them.

Design of airspace is also a design of noise on the ground and communities needs to be involved in these decisions. People living under a flight path may experience a deleterious effect on their health, negative impacts on quality of life, and reduced property values due to air traffic. Communities have a need to understand new noise impacts, and have recourse if the proposed impacts don’t match what actually occurs.

Airspace changes were made as part of the SoCal NextGen project and community leaders were not invited to take part in the decisions. An exact understanding of the change in noise impacts when communicated to the public will reduce negative reporting, increase community acceptance and thereby increase the effectiveness of the SoCal NextGen project.

The Environmental Assessment needs to include Supplemental noise Metrics and Analysis to make the proposed changes more understandable to the public.

1.) Day-night average sound level (DNL) represents an average of noise over a 24-hour period. The DNL noise metric offers a heuristic correlation between community noise exposure and percentage of people annoyed. Although widely used and adopted by the FAA, the DNL metric is inadequate to predict public response to all noise impacts. DNL accounts for less than a fifth of the variance in the association between aircraft noise exposure and the prevalence of High Annoyance in communities.[7]

DNL annoyance

Annoyance Caused by Aircraft Noise in Residential Communities Near Major Airports

DNL is most effective correlating higher noise levels + 65 dB and the percentages of people highly annoyed (%HA).  The large amount of scatter among the data drawn from surveys point to real uncertainty between the relationship of %HA and DNL. At the lower DNL’s, starting at <55 dB, the correlation to annoyance is less pronounced.  Correlation coefficients for annoyance of individuals are low, on the order of 0.5 or less.- As noise decreases DNL becomes less effective as a predictor of annoyance.[8][13]

FAA Order 1050 allows supplementing the DNL “to describe aircraft noise impacts for specific noise-sensitive locations or situations and to assist in the public’s understanding of the noise impact.”[9]

The ACRP released a FAA sponsored handbook for airports on dealing with a variety of community issues including noise. [10] On Page 114 under “Noise Metrics and Community Response” the report states:

“Cumulative aircraft noise contours often are challenged by airport neighbors as not representing what can be heard and measured every time an aircraft flies over their home. Long duration measurements and computer technology may show the contour patterns are correct for the community, but they fail to capture the discrete nature of the single events that people actually find and complain about.”

2.) Aircraft noise is also a concern to the larger population that is outside the DNL 65 noise contours. The SoCal Environmental Assessment addresses DNL 60 and DNL 45 contours- but still needs to discuss the noise effects that aren’t being represented. Concern about aircraft noise impacts can occur below DNL 45 dB when  aircraft noise significantly exceeds ambient noise levels. According to an ACRP survey, 75% of noise complaints come from people living outside the DNL 65 Noise contour. Annoyance levels can occur almost anywhere along a flight path.[11]

3.) DNL 65 dB was established in 1980, and reaffirmed in 1992 as a criteria to represent community noise impacts. Since the early 90’s there have been changes in aircraft technology, operations, public expectations, and scientific knowledge. More than 95% of all current social surveys of reaction to noise were conducted overseas. The foundations that the DNL 65 dB criterion were established upon should be brought up to date. 

The goals of improving public understanding and improving the predictability of noise impacts may need separate metrics.[12] Individuals hear aircraft on a per plane basis. The number and intensity of the individual noise events that make up DNL are critically important to public understanding of the effects of noise around airports. [13]

4.) Based on the results of surveys it has been observed that noise exposure can explain less than 50% of the observed variance in annoyance, indicating that non-acoustical factors play a major role. [13] Outreach to communities can help reduce this gap. The questions important for the public are:

An Example of Daytime Average Sound Level (DL, LAeq,15h) Color Noise Contours (Source: Noise Study for the St. Petersburg-Clearwater International Airport Phase I, Wyle Laboratories, Inc. Wyle Report WR 05-15, December 2005)

An Example of Daytime Average Sound Level (DL, LAeq,15h) Color Noise Contours
(Source: Noise Study for the St. Petersburg-Clearwater International Airport Phase I, Wyle Laboratories, Inc. Wyle Report WR 05-15, December 2005) [12]

  1. How many times airplanes fly over,
  2. Where are the exact flight tracks and how is it different,
  3. How loud is each event,
  4. What time of day,  (day, night, evening or periods of heavy operations)
  5. What type of airplanes,

Or they need more information on how flights may interfere with activities such as:

  1. Sleep,
  2. Conversations,
  3. Watching television and,
  4. Enjoying the outdoors.


The use of the best available technology and known noise assessment techniques will help the FAA engage with communities in an open dialog, and inform all affected residents and communities about what they can expect to experience. The FAA should:

  1. Involve communities in the design phase of the airspace redesign,
  2. Report on total noise effects,
  3. Consider impacts outside the DNL 65-45 Noise Contours that may cause annoyance- specifically ambient sound level differences,
  4. Reevaluate the relevance of DNL and the DNL 65 criteria,
  5. When reporting on noise impacts address the public’s primary questions.
  6. Make available supplemental analysis tools such DNL Color Shading, flight-frequency diagrams, multiple-metric tables and contour maps [12],
  7. Employ supplemental noise metrics that show number and intensity such as Lmax, SEL, N70, N60, N50, N45.

Example table Number-of-events Above (NA) for NAS North Island and OLF Imperial Beach outside DNL 65 dB area

Example table Number-of-events Above (NA) for NAS North Island and OLF Imperial Beach outside DNL 65 dB area [12]


[7]  The Schultz Curve 25 Years Later, Fidell, 2003; Fidell and Silvati, 2004
[8] Annoyance from Transportation Noise: Relationships with Exposure Metrics DNL and DENL and Their Confidence Intervals, Miedema & Oudshoorn, April 2001.
[9]  Source FAA Order 1050.1E, Appendix A, Paragraphs 14.4c, 14.5a, 14.5e; and Federal Interagency Committee on Noise, Federal Agency Review of Selected Airport Noise Issues, August 1992.
[10]  ACRP: Aircraft Noise: A Toolkit for Managing Community Expectations, 2007

[11] ACRP: Compilation of Noise Programs in Areas Outside DNL 65, Transportation Research Board, 2009
[12] Technical Support For Day/Night Average Sound Level (DNL) Replacement Metric Research. FAA Report Number: DOT/FAA/AEE/2011-02 2011
[13] Improving Aviation Noise. Planning, Analysis and Public Communication with. Supplemental Metrics. Guide to Using Supplemental Metrics. DOD Noise Working Group, December 2009

Average weather calculation does not represent Noise impacts from overflights

Single factored Environmental variables do not adequately represent climate across the diverse SoCal area. Temperature and humidity change how sound propagates. Noise effects borne by differing meteorological characteristics are not modeled correctly resulting in average noise values being incorrect up to .6dB near airports.

The Southern California Study Area is over a large and diverse geographic location and has multiple distinct climates, micro-climates and ecosystems. The FAA’s Environmental Assessment collected meteorological data from 41 years but averaged it to a single set of environmental variables- thus ignoring significant climate gradients :

Variable Annual Average
Temperature (F) 62.4
Barometric Pressure (in-Hg) 29.98
Relative Humidity (%) 71.5

1.) Using Average values will not adequately represent the sound impacts. Differences in temperature and humidity effect the attenuation of sound through the air. As humidity rises, the absorption of sound energy decreases which means noise will be higher in coastal areas than the drier inland- when considering humidity. Higher temperatures, such as those encountered inland, will reduce absorption and also mean higher noise across the frequency range.[1]

Effects of Humidity and Temperature on  sound propogation

(left) Frequency dependence of attenuation as a function of relative humidity at 20°C.
(right) Attenuation as a function of temperature for various percentages of relative humidity. [2]

2.) Temperature and humidity vary over day and night conditions, as well as during the day. In Southern California temperatures can vary over 20 degrees and Humidity 30% when comparing day to night measurements.  Average Daily Values should not be used as the distribution of aircraft flights across the day is highly weighted to daylight hours. Daily temperatures include the colder nighttime hours when less aircraft fly. Humidity and temperature should be modeled with either daytime/nightime, or time-of-day weightings of aircraft flights for each airport.

The Southern California Climate:
The offshore currents help create subtropical and Mediterranean climates along the coast. Moving inland the climate becomes more continental, with humidity decreasing as areas turn more temperate, semi-arid and hot arid similar to the Sahara Desert. The temperature gradient between the cool coast and warm inland is about 7 °F in winter and 25 °F in the summer.
East LA and parts of San Gabriel Valley averages the warmest winter high temps (72 F) in all the western US while Santa Monica averages the warmest winter lows (52 F) in all the western US. During the summer the temperature gradient between the Santa Monica Airport (75° F) and Burbank Airport (95 °F) is over one degree per mile. The temperature gradient is most extreme between Santa Barbara and Death Valley, with temperatures differing by up to 35 °F in the summer– Death Valley recorded the highest temperature in the world at 134 °F. San Bernardino airport, 70 miles inland, is rated as temperate -the winters reach 40 °F and the summers 109 °F, whereas San Diego Airport is in a semi-arid warm steppe climate.

socal climate zone map

Southern California Climate Zones – California Energy Commission

The California Energy Commission has separated the Southern California study area into 9 distinct climate zones.[3] Yearly temperatures across zones can vary 70 degrees and humidity up to 90%.

The study’s single static environmental variables poorly model the real environmental variables of airports and communities in Southern California. Overall noise of aircraft will vary depending upon local humidity and temperature.
See additional information in comment Meteorological effects change sound propagation

3.) Operationally, an increase in temperature will decrease an aircraft’s rate of climb. This will result in a need for additional thrust or an extended period at lower altitudes- both conditions will increase noise.

4.) Below is a table of airports and the correction needed. For each Airport city I’ve included the Average Relative Humidity (%)*, Average high temp (F)*, Calculation of the Sound Attenuation (dB/m)[4], and some of the resultant errors and correction values from using the single static environmental variables.

(*Average High Temp is used as I couldn’t readily find average time-of-day, or daytime/nighttime, temperature for all cities. Likewise the average time-of-day, or daytime/nightime, Relative Humidity was similarly not readily available. The resulting calculations will represent a conservative value and could be lower. I recommend the FAA gather this data to increase the accuracy of noise modeling.)

Airport CityHumidity (%)Avg high temp (F) Sound Absorption coefficient (dB/m [4]) EA Error (%)EA Error @ 45dB (dB)EA Error @ 65dB(dB)
Culver City75.4474.86°0.061980.2690.120.18
Long Beach81.5673.92°0.059440.5240.240.34
Palm Springs81.2979.44°0.055540.910.410.59
San Diego80.8974.11°0.059650.5030.230.33
Santa Ana80.1075.65°0.059020.5650.250.37
Santa Barbara83.5773.91°0.058460.6210.280.40
Santa Monica76.7375.00°0.06120.3440.150.22
Van Nuys79.7277.57°0.057830.6850.310.45
EA Variables71.5062.4°0.06468000

The Sound Absorption coefficient can be multiplied directly on the aggregate DNL values, or the underlying data.


Using a single temperature and humidity value for all of Southern California introduces inaccuracy in the noise modeling. So Cal has a diverse climate with distinct atmospheric conditions which are not adequately being represented.

There is an error of +.6 dB @ DNL 65 dB and +.4 dB near Palm Springs. Airports in Ontario, Santa Ana, Santa Barbara and Van Nuys all have .4 dB error at DNL 65.

In the released 4(f) noise data there are (91) noise points from the 2015 proposed action that would now qualify for the DNL 45 dB criteria and (4) that would move into DNL 65 dB when adjusted for the appropriate Sound Absorption Coefficient.

The FAA needs to accurately report noise impacts by:

  1. Using the correct temperature and humidity, or the appropriately calculated Sound Absorption Coefficient, for each environmentally distinct area,
  2. Weighting Sound Absorption Coefficient to match time-of-day aircraft noise with time-of-day temperature and humidity, or at the very least a daytime/nighttime difference.

Using the the census block or grid point noise data may bring other locations in the study area into the DNL 65 dB, DNL 60 dB, or DNL 45 dB noise criteria thresholds. Further study in this area may be warranted.


[1] Absorption of Sound in Air versus Humidity and Temperature, Cyril Harris (1966), Journal of the Acoustical Society of America, 40, p. 148.
[2] Graphic from Handbook For Acoustic Ecology, Barry Truax editor (1999)
[3] California Building Climate Zone Map, California Energy Commission
[4] ISO 9613-2:1996 Attenuation of Sound During Propagation Outdoors, Part 1: General Method of Calculation.

Aircraft Noise mapping from Cultural data

The FAA has released a portion of the noise impact results used in the Environmental Assessment. The data is on cultural resources identified by the Department of Transportation as potentially having noise sensitivity. It’s mostly parks, wildlife refuges, open spaces and historic sites – it’s called 4(f) data. The FAA also used modeled census block and grid-based noise impacts but they haven’t released it in data format. I’ve captured the 4(f) data from the EA and mapped it in an interactive format to help people better visualize the noise impacts.

There are 2 types of information: Overall Noise from aircraft, and the Change in Noise from the old flight paths to new. The noise is expressed in DNL dB units which (roughly) is an average of all noise over time.

a.) Here is a map of the overall db DNL levels using the proposed action. The dB represents just the noise from airplanes and doesn’t take into account any other ambient noises:

b.) Here is the map of the change in dB DNL (comparing the proposed action to they way it is now):

A dB DNL is difficult to subjectivify as we hear noise on a per plane basis – DNL is an aggregate.

The FAA didn’t release all the noise data. To evaluate the noise impacts, as well as the study methodology in regards to noise, they need to release the additional data. I requested it and they expressed to me that they weren’t sure if they should release as a Freedom of Information Act request, or as part of the EA.

HINCHE waypoint

I’ve previously asked for the FAA to release the waypoints but we still haven’t seen them. I need to rely upon the images of the google maps. (I did send a comment requesting the google map data as  short cut to get all the points but a brief conversation with FAA rep cast doubt about that data integrity. ) The google maps potentially have errors. The CLIFY drama could possibly have been a translation error. A few days ago I found an error with HINCHY- a waypoint on the easterly LAX approach. Here is my email and response:


Hi Stephen,
Here are the coordinates for HNCHE waypoint.  
HNCHE :  N34 00' 39.49 W118 30' 58.88


-----Original Message-----
From: Stephen Murray 
Sent: Tuesday, July 21, 2015 1:54 PM
Subject: Coordinates of HNCHE waypoint?

In the SoCal Metroplex Project Draft EA Los Angeles International Airport Area Proposed Arrival Procedures - East Flow the waypoint HNCHE ( on BIGBR) is described at  34° 0'39.49"N 118°19'42.80"W but this location puts it a few miles east of the point on the image. Can you correct the location and release the list of waypoint coordinates?

CNEL should be used instead of DNL in CA

CNEL is the California metric used to measure noise annoyances.

The FAA is using the wrong noise metric to describe aircraft noise in the Draft Environmental Assessment (EA). California’s differing cultural and environmental noise threshold expectations are reflected in the State’s mandate to use the Community Noise Equivalent Level (CNEL) metric for assessing airport noise exposure.[5] The FAA is using Day-Night Average Sound Level (DNL).  Both metrics add a 10dB penalty to aircraft operations between 10pm and 7am. The CNEL adds an extra 5dB penalty during the 7-10pm evening hours.

The FAA accepts the CNEL as a metric to measure the exposure of individuals to noise resulting from the operation of an airport.[6]  Using DNL instead of CNEL in the EA results will result in findings being out of synch with the general public’s expectations and is contrary to California Law.

[5]  CA Department of Transportation, State Aeronautics Act (Public Utilities Code Section 21669), California Code of Regulations (Title 21, Division 2.5, Chapter 6, Section 5000 et seq.).
[6]  Source FAA Order 1050.1E Appendix A, Paragraph 14.1.a., FAA Airports Desk Reference 17.1(c)

EA fails on Federally identified Noise Sensitive areas

The EA’s Noise Criteria fails when considering Section 4(f) properties and resources. Special consideration, such as cumulative impacts, needs to be given to noise changes in sensitive areas.

An Environmental Impact Statement (EIS) may be warranted to discuss noise impacts on sensitive sites.

The EA’s Noise Criteria doesn’t apply to Sensitive Areas.

FAA Order 1050.1E asks that special consideration be given to evaluating aircraft noise impacts on noise sensitive areas within national parks, national wildlife refuges and historic sites, including traditional cultural properties.  The FAA’s Draft Environmental Assessment (EA) identifies 3875 sensitive sites within the SoCal Metroplex that have increases between 1.5 – 5 dB DNL. The EA uses DOT Section 4(f) sites and lands which may qualify for this special consideration.[5]

Order 1050.1E continues: “..the DNL 65 dB threshold does not adequately address the effects of noise on visitors to areas within a national park or national wildlife refuge..” and further states that FAA Part 150 guidelines are also insufficient with these sites.

The order calls for a special consideration of these areas where “noise is very low and a quiet setting is a generally recognized purpose and attribute.” An alternate noise level or metric that would adequately address the noise effects needs to be used.[6] For example the St George EIS used Leq, Number of operations above 35dB and Time above Ambient as supplemental metrics.[7]

Cumulative effects of increases in noise must be evaluated.

Included in a special consideration should be evaluation of what impact the incremental increase in noise has on the total cumulative noise impacts of all airplane traffic [8]. Since some of these sites already have extremely low natural ambient noise levels of 25 dB [9] a “significant” threshold may have been reached.

Natural Ambient Noise

The EA Study area overlaid on National Park Service modeling of Natural Ambient Noise.  Ambient noise approaches 20dB (before human impacts)

The baseline of what measurement is a “quiet setting” must be defined. The existing DNL 60-65 dB and DNL 45 to 60 dB exposure level brackets don’t represent “quiet” and are orders of magnitude above ambient levels. A potentially suitable baseline the FAA should use as “quiet”, and the basis of measurements, is to use the per site existing ambient noise level.

The purpose of an EA is to decide whether an EIS is required. The Draft EA has four issues which must be addressed:

  1. Cumulative impacts of the incremental increases of noise from the proposed action must be considered and evaluated against a threshold.
  2. Changes in aircraft noise effects from DNL 65 dB from the proposed and no action alternatives need to be listed in a summary report which extends from DNL 65 dB to the lowest natural ambient noise level.
  3. The EA’s Noise Criteria needs to specify threshold values belowDNL 45 dB that describe how muchadditional noise isto be allowed. Suggested potential values are:
    1. 10 dB above natural ambient noise levels
    2. DNL 1.5 dB which follows the 65dB + (due to it being a sensitive area) or
    3. DNL 3 dB which follows the the 1990 EIS EECP determination about noise levels below DNL 65 dB.
    4. DNL 5 dB after the DNL 45-60 dB criteria.
  4. DNL has poor correlation to annoyance at lower levels (potentially as low as 0.5). A supplemental metric should be used to represent and communicate the effects of noise to the public. [6]

According to the results of the Section 4(f) properties and resources noise study, the Environmental Assessment has potentially significant indirect impacts in the form of noise where mitigation or a more detailed study may be required. There are: 3875 sites that have noise effect increases from DNL 1.5 dB up to DNL 5.0 dB. Use of added Metrics may help in the analysis and demonstration of the impacts.

Noise sensitive sites that receive an increase of 1.5 dB of noise or greater. [ Interactive map]

The below table is a selection of sites where the increase in aircraft noise level from the (OAPM’s) proposed changes exceeds DNL 5 dB. Attached as an appendix is a table of added sites where noise levels have exceeded DNL 1.5 dB.

Sensitive locations with Greater than 5dB DNL Increase in Noise
Protected Site NameArea (Acres)No Action in DNL dBProposed Action in DNL dBIncrease in DNL dB
Oakmont Park14.562733.26.2
Warrack Park31.9931.137.26.1
Avenue A Park0.2923296
Flag Hill Veterans Memorial Park7.822.828.86
Lillian Eaton Park0.4223.3295.7
John Tooker Civic Park4.4723.429.15.7
Oak Glen Creek Detention Basin18.2822.3285.7
Inman Family Trust19.429.635.25.6
Pablo Apis Park2.2925.530.95.4
Gates Canyon Park6.9435.240.65.4
Vail Ranch Park16.4325.731.25.4
Caroline Park18.3428.533.95.4
Paloma Del Sol4.4826.7325.3
Temecula Creek Trail Park4.5826.131.45.3
Hope Nature Preserve359.3831.236.55.3
Wildwood Canyon853.7923.428.75.3
Paseo Gallante Park1.6225.8315.2
Butterfield Stage Park2.5326.932.25.2
Upper Las Virgenes Open Space Preserve115.737.642.95.2
Steckel Park199.627.232.25.1
Emerson Wildlife Preserve-24.429.55.1
John Magee Park1.1226.931.85
Kent Hintergardt Park11.7126.231.25
Bryant St Detention Basin51.9322.427.55
5 Winds Ranch Open Space Preserve333.221.826.85
Ven-Tu Park-31.436.45

Table-B-ATAC_SoCal_Metroplex_Noise_Technical_Report-Above 1.5db

National Parks and Preserves, which have policies on soundscape management and controlling noise, are not included in the list of Section (4f) sites but should likewise be eligible for special consideration.

[5] Appendix A of the SoCal Metroplex Noise Technical Report, Section 4(f) of the Department of Transportation Act of 1966.
[6] Source FAA Order 1050.1E, Appendix A, Paragraphs 14.3, 14.4b.
[7] St. George Airport Environmental Impact Statement, FAA.
[8] Title 40 C.F.R. § 1508.7- Cumulative Impact., Grand Canyon Trust v. FAA (2002)
[9] Ambient noise levels must be considered in Noise Criteria, and NPS Geospatial sound modeling. 2013-2015. Project-2217356

Ambient Noise Levels should be considered in Noise Criteria

The Noise Criteria Threshold is too high above ambient Noise Levels. The threshold needs to factor in aircraft’s noise contribution to ambient noise levels.

The EA presents aircraft noise and only considers noises above DNL 45 dB as relevant to the Noise Criteria. The Noise Criteria should include existing neighborhood ambient noise levels as a baseline to compare against the aircraft noise contribution level.  This will demonstrate the amount of noise aircraft contribute above the existing ambient noise.

Most Southern California neighborhoods have  ambient noise levels (without aircraft) below a DNL 45 dB threshold. In these neighborhoods aircraft noise is already louder than other ambient noise prior to the proposed changes.  In some places  ambient noise is so low that even a small increase in air traffic noise could be disturbing to people and become a source of public concern.
The DNL 45 dB threshold was put forth 10 years ago in the Environmental Impact Statement (EIS) for the Expanded East Coast Plan (EECP). This level was recommended on the rationale that “even distant ambient noise sources and natural sounds such as wind in trees can easily exceed this [DNL 45 dB] value.” [1]

Map of natural conditions

Ambient Noise Level in Natural Conditions.

Southern California’s ocean breezes are not as strong as the wind in Chicago and off the Potomac where this standard originated. Our climate lacks the water sources that allows an abundance of vegetation and animals. The palm trees and desert chaparral that rustle in Mediterranean/sub-tropical Southern California are not a significant contributor of noise.

Map of existing conditions

Ambient Noise Level in existing Conditions.(including Aircraft Noise)

A 2015 National Park survey[2] of ambient noise levels recognizes the Southwest United States up to 10 dB quieter than Central and Eastern US – and up to 15 dB quieter after subtracting man-made noise sources.

The Socal Metroplex area’s existing ambient noise is as low as 36 dB in urban areas and 22 dB in non-urban areas. [3]

The EA should be considering the effect that an incremental increase in aircraft noise has on the cumulative impact of aircraft noise “when added to other past, present, and reasonably foreseeable future actions regardless of what agency … or person undertakes such other actions.”[4] Use of existing natural ambient noise levels allows comparing the project to an environmental baseline of natural quiet.

The EA’s Noise Criteria should include levels as low as DNL 25 dB for rural areas. There are communities where aircraft noise significantly exceeds ambient noise levels. They are at, or exceed, an overflight annoyance threshold. A noise analysis that wants to predict community annoyance should include the total difference between non-aircraft and aircraft sources and not just the change in aircraft noise.
DNL is not an adequate measure of annoyance at lower noise levels. Except at the highest noise levels, annoyance is related to the difference between the new noise and the existing ambient noise, not total noise. A more descriptive noise metric would express the difference in noise between the proposed actions and natural ambient, and the number of events above dB levels of 20. Aircraft noise from the proposed action needs to be compared against existing non aircraft ambient noise to predict annoyance.

[1] U.S. Department of Transportation, Federal Aviation Administration, Expanded East Coast Plan – Changes in Aircraft Flight Patterns Over the State of New Jersey, Pp. 5-9. 1995.
[2] National Park Service, Geospatial sound modeling. 2013-2015. Project-2217356
[3] A-weighted hourly L50 sound pressure level dB re 20 uPa on a typical summer day at 270m resolution.
[4] Title 40 C.F.R. § 1508.7- Cumulative Impact.

60 day extension granted

Ryan Weller of the FAA has just sent me this public notice about the OAPM’s Environmental Assessment document. This gives all of us more time to refine additional comments:

The FAA has extended the public comment period on the Draft EA by 60 calendar days.  The comment period will now close on September 8, 2015.

Public Notice:  Federal Aviation Administration (FAA) Southern California Optimization of Airspace and Procedures in the Metroplex (SoCal Metroplex OAPM) Draft Environmental Assessment (EA) Document