FAQ

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Below you will find answers to frequently asked questions about the Noise Exposure Map (NEM) update being conducted at Fresno Yosemite International Airport (FAT) in accordance with Title 14 of the Code of Federal Regulations Part 150. Title 14 noise and land use compatibility projects are often referred to as “14 CFR Part 150” or more simply “Part 150.” The present update includes only the NEM portion of Part 150.  As the NEM update project progresses and as other questions are received, we may add to this section to address questions of general interest.

What is an NEM update?

When applying for a federal grant to implement noise compatibility measures at an airport, such as residential sound insulation programs, the Noise Exposure Map (NEM) is used to determine the area of eligibility.  The NEM is most often thought of as a map that shows the noise exposure from aircraft operations using contours similar to a topographical map that uses contours to display ground elevations.  An NEM update is a voluntary, in-depth re-evaluation of aircraft noise and land use compatibility as prescribed by the Federal Aviation Administration (FAA) in Part 150 regulations.

Over time, airport operations may change, technological advancements may reduce aircraft noise, and/or land uses may be altered to accommodate growth and development in the region.  The current effort at FAT is an update to the NEM previously accepted by the FAA in 2005 and will be based on current (2016) and forecast (2021) aircraft operational activity at the airport.  The FAA has provided funding assistance to complete this NEM update at FAT.

Why is the NEM being updated?

FAA regulations require periodic review of NEM’s to verify that the maps reflect the current conditions at an airport and current land uses in the vicinity of an airport. With the recent runway extensions, the change in primary aircraft from F-16 to F-15 for the California Air National Guard, and changes in airline operations, the FAA has mandated an update to the FAT NEM. The NEM is the primary vehicle used to determine eligibility for participation in the Airport’s residential sound insulation program (locally known as the SMART Program).

What will the FAT NEM update mean to residents near the airport?

What the NEM update means to residents can be determined only when all the data are analyzed. The current NEM used for noise mitigation eligibility near the airport is based on the 2009 forecast NEM, accepted by the FAA in 2005.  The FAA currently requires NEMs to be updated at least every five years.  Also, since 2009 there have been many changes to aircraft technology and aircraft operations. Therefore, it is necessary to determine what changes have occurred with respect to aircraft noise and incompatible land uses, based on current and updated forecast operations and aircraft types.  It is too early to know how these changes will affect the resulting noise contours provided in the NEM, but the NEM update will likely result in a change to the eligibility area for noise mitigation programs where some residents, currently eligible in the 2009 NEM, may no longer be eligible for noise mitigation programs like the SMART program.

How often must an NEM be updated?

The regulation requires that updates be conducted when there is likely to have been a change in airport operations that would either: (1) increase the yearly CNEL by 1.5 dB or greater in a land area which was formerly compatible but is thereby made incompatible or in a land area which was previously determined to be incompatible and whose incompatibility is significantly increased, or (2) reduce noise by the same margin (CNEL reduction of 1.5 dB or more) over existing incompatible uses. In both cases, the land areas to be considered are those addressed by both the existing and forecast Noise Exposure Maps on file with the FAA.

According to the recent update of the Airport Improvement Program (AIP) Handbook, FAA Order 5100.38D, the FAA requires by policy that if the FAA-accepted NEM used to document project eligibility (e.g., residential sound insulation and land acquisition) is more than five years old, airport sponsors are to confirm that the noise exposure map upon which noise compatibility is based continues to be a reasonable representation of current and/or forecast conditions at the airport.

How is noise exposure described in an NEM update?

Part 150 requires that airports describe noise exposure using a measure of cumulative noise exposure over an entire calendar year, in terms of a metric called the Day-Night Average Sound Level (DNL). In California, the State Department of Transportation, Division of Aeronautics, uses a more conservative substitute for the DNL metric known as the Community Noise Equivalent Level (CNEL). While DNL is the primary metric FAA uses to determine noise impacts, FAA accepts the CNEL metric in California to assess noise effects.

DNL and CNEL are measures of cumulative noise exposure over a 24-hour period, with adjustments to reflect the added intrusiveness of noise during certain times of the day. DNL includes a single adjustment period; each aircraft noise event at night (defined as 10 p.m. to 7 a.m.) is adjusted equal to increasing the noise levels during that time interval by 10 dB.  CNEL adds a second adjustment period; in addition to the nighttime adjustment, each aircraft noise event in the evening (defined at 7 p.m. to 10 p.m.) is adjusted equal to increasing the noise levels by 4.77 dB.

CNEL is the noise metric used in the FAT NEM update to determine potential areas of noise annoyance and may be substituted for any DNL references.

How is noise exposure determined for the NEM update?

An NEM update requires computer-generated CNEL estimates developed using the most current release of the FAA’s “Aviation Environmental Design Tool” (AEDT).  The CNEL must be depicted in terms of equal-exposure noise contours (much as topographic maps have contours of equal elevation).  Part 150 requires that the 65, 70, and 75 dB CNEL contours be modeled and depicted.  Information on the noise model can be found via the following link to the FAA’s website: AEDT.

CNEL values can also be measured.  However, measurements are practical only for obtaining CNEL values for relatively limited numbers of points.  The FAA does not permit adjustments of the noise modeling process using permanent or portable noise measurement monitors.

Noise terminology, modeling, and other analytical topics will be discussed in detail in public workshops, and within the FAT NEM update documentation. Related presentations and documents will be posted on this website as they are developed to permit all interested parties to learn as the update progresses.

How are the forecasts for aircraft operations developed?

The forecasts for aircraft operations are prepared for separate market sectors: passenger airline, cargo airline, and general aviation (GA).  The 2016 base year forecasts reflect current activity and recent trends, as well as views expressed by airport officials and key operators at FAT regarding potential short-term changes in airport activity.  In addition to these factors, the 2021 forecast takes into account longer-term trends including economic growth, aviation industry strategic developments, and planned or likely changes in the aircraft fleet mix.  The research draws heavily on aviation data compiled by the airport, the US Department of Transportation, and the Federal Aviation Administration.

How is land use compatibility determined?

The FAA, other federal agencies, and several states have used available data on community reaction to noise to create guidelines for identifying the land uses that are compatible with specific noise exposure levels – the more noise-sensitive the land use, the lower the noise exposure should be in order to achieve compatibility. The FAA guidelines, as defined in Part 150, state that all identified land uses, even the more noise-sensitive ones (e.g., residential, schools, places of worship, hospitals), normally are compatible with aircraft noise at CNEL levels below 65 dB (Part 150, Appendix A, Table 1).  These noise/land use compatibility guidelines were adopted by the City and other local land use control jurisdictions for the previous NEM and are again used for this update.

When was the existing NEM completed?

The NEM in existence today was completed along with the Noise Compatibility Program (NCP). The NEM was accepted by the FAA in 2005.

What is the NEM update schedule?

The NEM update began in the second quarter of 2015, and is anticipated to be submitted to the FAA for acceptance in the second quarter of 2016. A more detailed schedule is posted on the Schedule tab of this website which will be updated as appropriate. Dates, times, and locations of public involvement opportunities will be announced on the Public Involvement tab.

Who is involved in the NEM update and what are their roles and responsibilities?

All interested parties are encouraged to participate in the study. Please use the information provided in the Contacts tab on the Home Page for information on submitting any comments or questions.

Several groups have pre-defined roles and responsibilities, based on Part 150 regulatory requirements, as summarized below:

    • The City of Fresno: As the airport operator, the City has overall responsibility for all Part 150 related actions at FAT.
    • Federal Aviation Administration: FAA involvement includes participation by staff from several agency offices.
      • FAA Air Traffic Control Tower: The FAA tower staff at FAT provides significant input in several areas, including: operational data from their files. The tower staff also may solicit input from other FAA air traffic control entities with which it coordinates regularly.
      • FAA San Francisco Airports District Office (ADO): The FAA’s San Francisco ADO will review the Noise Exposure Map submission for compliance with Part 150, notify the City of their determinations, prepare a formal Letter of Acceptance of the NEMs, publish related notices in the Federal Register, and provide opportunity for public comment on the acceptance.
      • Other FAA Offices and Divisions: The ADO may solicit review and input on more complex technical, regulatory, legal, or other matters from FAA’s Washington headquarters or from other FAA divisions on a local or regional level
    • Consulting Team: The City has retained the services of HMMH, along with C&S Engineers and CommuniQuest, to prepare the NEM update.

How can I participate in the NEM update?

All interested parties are encouraged to participate in the process through the avenues outlined on the Contact Tab of this project website. Dates, times, and locations of public involvement opportunities will be announced on this website.