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