The following are some commonly asked questions about the 14 CFR Part 150 Noise Study process.

Can you provide some background on Airport Noise Compatibility Planning Studies?

Title 14 of the Code of Federal Regulation Part 150 (“14 CFR Part 150” or simply “Part 150”) establishes a voluntary program, administered by the Federal Aviation Administration (FAA), that includes procedures for airports to assess aircraft noise and land use compatibility. It establishes a single system for evaluating aircraft noise, determining the exposure of individuals to aircraft noise, and standardizing airport noise compatibility planning programs. The Airport Noise Compatibility Planning program includes: (1) provisions for the development and submission to the FAA of the Noise Exposure Map (NEM) and Noise Compatibility Program (NCP) by airport operators; (2) standard noise units, methods, and analytical techniques for use in assessments; (3) identification of land uses that are normally considered compatible (or non-compatible) with various levels of aircraft noise based on federal guidelines; and (4) procedures and criteria for FAA approval or disapproval of airport-recommended NCP measures.

The current Centennial Airport (APA) Part 150 Study will update the NEM by assessing current aircraft noise and land use compatibility. The Study will develop a 5-year forecast of aircraft operations to assess future conditions. The NCP will contain recommendations for addressing non-compatible land uses identified in the NEM. NCP measures approved by the FAA could potentially be eligible for federal funding.

What is the objective of the Study?

The objective of this Part 150 Study is to update the Noise Exposure Map based on current and forecast future conditions, and to formulate a set of recommendations to include in the Noise Compatibility Program that addresses non-compatible land uses, as defined by the Day-Night Average Sound Level (DNL) of 65 decibels (dB). The goal of the overall program is for APA, in consultation with stakeholders, to develop a balanced program to minimize aircraft noise effects on surrounding non-compatible land uses.

How long will it take to complete?

Approximately two years. Work on the Part 150 Study started in late 2023. Completion is anticipated in 2026. Once the documents are accepted by the FAA and published in the Federal Register, it will take up to an additional six months for the FAA to issue their Record of Approval for the Airport-recommended Noise Compatibility Program measures.

Why is the current Part 150 Study being updated?

APA is updating its Part 150 Study in conjunction with ongoing efforts by the Centennial Airport Community Noise Roundtable (CACNR) and in collaboration with all stakeholders to assess noise from APA aircraft operations and land use compatibility with those operations. Since the last update, there have been changes to aircraft fleet mix and activity levels, and updates to the noise model used for analysis, which will all be addressed during the Study.

What is the difference between the Part 150 Study and the CACNR Study Group Committee?

The Part 150 Study and the work of the Centennial Airport Community Noise Roundtable (CACNR) Study Group Committee are separate, but complementary processes.

The Part 150 Study is a voluntary land use compatibility study funded by the FAA that takes approximately two years to complete. It will analyze, model, and examine a broad range of operational, land use compatibility, and program management alternatives, following the Part 150 Study federal requirements. For questions or comments about this Study, use the comment form on the Study website.

The CACNR Study Group Committee was formed prior to the kickoff of the Part 150 Study to work collaboratively with the Airport, CACNR, FAA, flight schools, and elected officials representing the community to address the noise exposure created by the extended traffic pattern. To contact the CACNR, visit centennialairportnoise.com.

How is aircraft noise exposure determined?

In 1981, the FAA officially implemented the Day-Night Average Sound Level (DNL) as the primary metric for assessing community exposure to aircraft-related noise. The DNL represents the yearly, 24-hour average sound level, measured in decibels (dB), derived from the cumulative noise levels of the annual-average aircraft operations. During the period from 10 p.m. to 7 a.m., an additional 10 dB are added to each aircraft noise event to account for nighttime noise intrusion. This adjustment recognizes that noise disturbances at night tend to be more disruptive due to lower ambient noise levels and people’s need for sleep. The 24-hour DNL is annualized to reflect noise generated by aircraft operations for an entire year and is identified by “noise contours” showing levels of aircraft noise in 5-dB increments.

DNL is the most widely accepted descriptor for aviation noise because of the following characteristics:

  • DNL is a measurable quantity.
  • DNL can be used by airport planners and the public who are not familiar with acoustics or acoustical theory.
  • DNL provides a simple method to compare the effectiveness of alternative airport scenarios.
  • DNL is based on a substantial body of scientific survey data regarding how people react to noise.

The DNL incorporates A-weighted noise events and/or hourly noise levels. The so-called “A” filter (“A weighting”) generally does the best job of matching human response to most environmental noise sources, including natural sounds and sound from common transportation sources. Because of the correlation with our hearing, the U.S. Environmental Protection Agency (EPA) and nearly every other federal and state agency have adopted A-weighted decibels as the metric for use in describing environmental and transportation noise because surveys have shown that it best mimics how our ears perceive common environmental sounds. Other metrics are used to measure aircraft noise and the supplemental metrics used in the Study are described below; however, only DNL is acceptable as defined by regulation for the Study process.

Will other noise metrics be used?

Sometimes the Day-Night Average Sound Level (DNL) noise metric used in Part 150 Studies is criticized because it averages noise over a 24-hour period for an entire year, which does not accurately portray what people hear on a day-to-day basis. It is true that because the DNL represents noise for an annual-average day, it does not represent what people hear when an aircraft flies over.

Some additional metrics that will be studied include LMAX contours (the maximum sound level) for single aircraft landing-takeoff cycles in each traffic flow direction for critical aircraft that operate at APA today and in the future. Another metric is the number of events that generate a maximum noise level above above 75 decibels (dB), known as the N75 noise metric. This metric is helpful in illustrating how many times per day noise events occur that can result in some degree of interference. Finally, representative receptor analysis will be completed, which presents the noise levels in terms of various metrics at example sites around the Airport. These sites will be the existing permanent noise monitoring locations used in the noise measurements. The metrics above will be presented for each of these locations. However, these metrics will be used for informational purposes only. The DNL metric is required to be used in the Part 150 analysis. The noise mitigation measures within this Study are approved or disapproved based on DNL alone.

What is considered a non-compatible land use?

In accordance with FAA guidance, a Part 150 Study relies on the Day-Night Average Sound Level (DNL) noise metric to assess land use compatibility. The FAA considers all land uses compatible with aircraft noise below 65 decibels (dB) DNL. The Part 150 Study will assess land uses exposed to a DNL of 65 dB or greater to identify non-compatible land uses according to Table 1 of Appendix A of the Part 150 regulation. Noise-sensitive land uses exposed to a DNL of 65 dB or greater could be eligible for federal funding for noise mitigation measures. Such measures and potential eligibility will be assessed in the Part 150 Study.

What are noise contours and how are they used?

Noise contours are digitally generated lines that depict either the existing noise exposure levels or forecasted future noise exposure levels represented by a cumulative noise metric. Essentially, a noise contour graphically represents the annual-average aircraft noise exposure (expressed by the Day-Night Average Sound Level, or DNL, metric) through the connection of points with equivalent noise exposure around the airport. They are like geographic contour lines that connect points of equal elevation.

A Part 150 Study uses the DNL contour of 65 decibels (dB) to represent the FAA-defined threshold for identifying non-compatible land uses. Certain noise-sensitive land uses (such as residences, schools, places of worship, etc.) within the DNL contour of 65 dB and greater are non-compatible with aircraft noise. Therefore, noise-sensitive land uses within the 65 dB DNL contour could be eligible for federal funding for FAA-approved noise mitigation measures.

A variety of information is gathered during the Part 150 Study to create an accurate set of aircraft noise exposure contours including: the number of operations, flight paths, type of aircraft, type of aircraft engines, time of day or night, weather conditions, and runway use.

This data is used to generate aircraft noise exposure contours that are overlaid on land use base maps depicting jurisdictional boundaries to create the formal Noise Exposure Map submitted to the FAA for review and acceptance.

What is the FAA’s noise model?

The FAA requires use of its Aviation Environmental Design Tool (AEDT) to generate noise exposure contours from aircraft operations to assess land use compatibility around airports. AEDT is a software system that models aircraft performance in space and time to estimate fuel consumption, emissions, noise, and air quality consequences. The AEDT uses the following aircraft operational data when generating noise exposure contours from aircraft operations:

  • Total number of aircraft operations
  • Aircraft operations by type of aircraft
  • Aircraft operations by time of day
  • Aircraft operations by runway use
  • Aircraft operations by flight track
  • Aircraft operational procedures, including touch-and-go operations
  • Aircraft auxiliary power unit and ground power unit usage

The FAA requires the latest available AEDT model be used to generate the noise contours for use in Part 150 Studies, which at the onset of noise modeling for this APA Part 150 Study was version 3f.

How does noise measurement differ from noise modeling?

To ensure consistency among all U.S. airports, the FAA requires the use of its noise model, Aviation Environmental Design Tool (AEDT), to generate aircraft noise exposure contours. The noise algorithms in AEDT use the results of measurement data provided to them via the aircraft certification process.

Noise measurements typically occur at a relatively small number of discrete monitoring locations not intended to generate contours but rather to monitor changes in noise levels over time. For consistency purposes, the FAA does not allow noise measurements to validate or calibrate the model. The Airport uses noise measurements from their noise monitoring system for reporting to the Centennial Airport Community Noise Roundtable.

What are federal grant assurances?

Grant assurances are contract obligations that airport owners agree to when they accept funds from FAA-administered airport financial assistance programs. These are meant to protect the government’s investment and the public’s interest in using public airports. For example, some of the 39 grant assurances are:

  • The airport will be open to the public and not discriminate against anyone who wants to use it.
  • The airport will charge reasonable fees and not give unfair advantages to any airlines or businesses.
  • The airport will maintain and operate the facilities safely and efficiently.
  • The airport will use the money or land only for airport purposes.
  • The airport will follow environmental laws and regulations.
  • The airport will cooperate with the government in case of emergencies or national security issues.

These grant assurances become legally binding when the airport owners accept the funds or property. The government can enforce these grant assurances by withholding future funds, taking back the property, requiring repayment of funds, or declaring the airport in noncompliance, along with other measures.

Can landing fees for touch-and-go operations be implemented at APA?

The Arapahoe County Public Airport Authority is a quasi-government entity that owns and operates Centennial Airport. The airport receives federal and state grants for its capital improvement projects, which are subject to certain grant assurances that protect the public interest in using the airport. Some of these grant assurances require the airport to be open to the public, charge reasonable fees, and not discriminate against any users. Landing fees for touch-and-go traffic might violate some of these grant assurances or create legal challenges from the users and FAA.

Why do aircraft not have to follow county noise ordinances?

The regulation of aircraft noise levels has been preempted by the federal government as aircraft are integral to the National Air Transportation System. The FAA has exclusive authority to certify aircraft and pilots, and to control aircraft in flight and on the ground, along with regulating aircraft noise levels and emission levels. Local governments can promote compatible land use through zoning, prohibit non-compatible land uses, and require real estate disclosure. They cannot directly restrict aircraft operations or regulate the routes, rates, or service of air carriers.

Does the Study consider non-aircraft operations?

No. The Study includes aircraft in the air that operate from APA. The Study does not include sources of non-aviation noise, such as roadway traffic.

Can the Study examine and change flight patterns?

Flight tracks will be examined as part of the Study. The Study may make recommendations on flight track changes; however, flight pattern procedures are under the sole purview of the FAA, considering operational, safety, and air traffic control procedures. The airport operator does not have authority to regulate flight patterns. Full development of new procedures would be completed by the FAA after the completion of the Study.

Who will be involved in the Study?

The Airport, FAA, stakeholders, and the public can all be involved in the Part 150 Study process. A Study Advisory Committee (SAC) has been formed to work closely with airport staff and the consultant team. The SAC includes representatives from the local jurisdictions, aviation stakeholders, businesses, and the communities. The role of the SAC is to review information, provide feedback, discuss noise abatement alternatives, and advise the Airport on the adoption of Noise Compatibility Program (NCP) measures to address noise and land use compatibility. Additionally, public information meetings/workshops will be held at key points throughout the Study. Public meetings will be announced on this website under Events. The public can also provide feedback at any time through the comment form on this website. All comments will be sent to the Study team.

How can I be involved?

Public information meetings will be held at key times during the Study process. These meetings will primarily be conducted in an “open house” format to allow attendees to ask questions of the subject matter experts to better understand the information being presented. Various alternatives will be presented, and draft recommendations will be available for review. You will have the opportunity to ask questions and express any concerns or comments to the Study team during meetings and on this website at any time. Meeting dates will be advertised through newspaper advertisements, email outreach, social media and posted on the Study website. This website will also be updated at key points in the Study. The Study team will continually refine the community engagement plan and look for ways to get the information out to a broader audience.

All comments formally submitted will be taken into consideration during this Study. Those submitted during the official public comment period for the Noise Exposure Map and Noise Compatibility Program during and following the public hearing will be formally included and responded to in the final report documents. Individual comments provided throughout the process but outside of the public comment period will not be responded to directly; rather, the most frequently asked questions will be addressed as part of these FAQs and all comments are reviewed by the Study team and integrated continually in the process as it moves forward.

What is Title 14 CFR Parts 36, 161, and 91 and how do they relate to aircraft noise?

CFR Parts 36, 161, and 91 are all parts of Title 14 of the Code of Federal Regulations (CFR), which deals with aeronautics and space. These parts specifically relate to aircraft noise in the following ways:

  • CFR Part 36: Titled “Noise Standards: Aircraft Type and Airworthiness Certification,” Part 36 defines the U.S. noise standards for aircraft. It prescribes the noise measurement and evaluation procedures, noise limits, and documentation requirements that must be met for certification for different types of aircraft, including transport category large airplanes, jet airplanes, propeller-driven small airplanes, helicopters, and tiltrotors. The FAA publishes certified noise levels in Advisory Circular 36-1H, Noise Levels for U.S Certificated and Foreign Aircraft.
  • CFR Part 161: Titled “Notice and Approval of Airport Noise and Access Restrictions,” Part 161 implements the Airport Noise and Capacity Act (ANCA) of 1990. It prescribes the notice requirements and procedures for airport operators who wish to implement noise and access restrictions on Stage 2 and Stage 3 (and greater) aircraft. To date, there have been no approved Part 161 Studies in the nation that restrict Stage 3 and greater aircraft, which account for most, if not all, aircraft flying today. There are very few, if any, Stage 2 aircraft certified prior to 1977 remaining in the U.S. aircraft fleet.
  • CFR Part 91: Titled “General Operating and Flight Rules,” Part 91 prescribes general operating and flight rules, including noise limits for aircraft operations. It is less restrictive compared to other parts of the Federal Aviation Regulations and primarily applies to general aviation, non-commercial, and private flights. Subpart I of CFR Part 91 specifically prescribes operating noise limits and related requirements for the operation of civil aircraft in the United States.

These parts of the CFR provide the regulatory framework for managing aircraft noise in the United States, balancing the operational needs of the aviation industry with the noise exposure on communities surrounding airports.

What is the FAA NES?

The Neighborhood Environmental Survey (NES), conducted by the Federal Aviation Administration (FAA), is a key component of the FAA’s ongoing research into aircraft noise. This nationwide survey aims to gauge the level of annoyance caused by aircraft noise. The FAA is currently working through comments submitted on the NES; the FAA’s plans for the results of the NES remain uncertain at this point. For purposes of this Study, DNL of 65 decibels is the threshold for non-compatibility that is required for alternatives analysis. The study team will examine other contours specifically for land use planning purposes and will continue to monitor any developments that may be released from the FAA regarding the NES.

Will the Part 150 include traffic from other airports or medical facilities like Sky Ridge?

No. It is important to note that the 14 CFR Part 150 guidelines stipulate that only aircraft operations that originate or end at the Study airport can be incorporated into the Study process. Overflight operations from other airports or facilities are not included.

Will the Study look at air quality?

No. The focus of the Study is land use compatibility.

Who makes flight decisions at APA, and can aircraft be restricted as an outcome of the Study process?

While the Arapahoe County Public Airport Authority operates the Airport, it does not have the ability to control the number or type of aircraft that operate at the Airport, to dictate the runways aircraft use, to control aircraft flight paths, or to limit the time of day or night that aircraft take off or land. The FAA and the pilots determine which runways and aircraft flight paths are used. The aircraft operators determine the number of flights and the types of planes that are flown. Additionally, federal law prevents the Authority from limiting the hours of the day or night when aircraft are allowed to operate.

Will you evaluate previous Noise Compatibility Program measures?

Yes. Any available information on the measures from the 2008 NCP has been assessed and included in the present Study. The preliminary results are shown in the table below and additional information regarding implementation challenges are being researched for those measures not implemented.

Why was the 2008 Part 150 Study recommendation “Implementation of 170° departure heading to four DME or 8,000 MSL, plus or minus 20°” disapproved?

APA operates within a complex airspace system, characterized by multiple types of airspace, various airports, and altitude constraints. The effective management of this intricate control area demands precise coordination. As aircraft navigate this airspace—whether during approach, departure, or maneuvering—air traffic controllers meticulously ensure safe separation while optimizing operational efficiency. Importantly, this responsibility extends beyond the air traffic control tower at APA; it encompasses all air traffic controllers within the Denver metropolitan area. Their collaborative efforts integrate not only the flow of aircraft to and from APA but also those traversing Denver International Airport (DEN) and other regional airports. Departing flights from APA frequently adhere to specific departure procedures to accommodate the broader air traffic utilizing DEN. This recommendation was not deemed compatible with the complex airspace.

What effects did the midair collision of 2021 have on the traffic pattern at APA?

On May 12, 2021, a midair collision occurred between a Cirrus aircraft and a Metroliner while both aircraft were inbound to Centennial Airport. The Cirrus was on a right base turn for Runway 17R and the Metroliner was flying straight in for Runway 17L. Subsequent to the collision, the Metroliner continued and landed on Runway 17L, and the Cirrus landed in Cherry Creek State Park utilizing the pilot’s airframe parachute. While the collision did not result in injuries or fatalities, the FAA conducted an evaluation of safety regarding Centennial Airport’s two closely separated parallel runways. The FAA’s continuing mission is to provide the safest, most efficient aerospace system in the world.

The FAA identified the following data for operations between June 24, 2019, and June 24, 2021 (including the time frame in which the collision occurred):

  • Wrong Surface Landing: APA had 5 wrong surface landings and 4 reports of aircraft lined up for the wrong runway and corrected by ATC.
  • Pilot Initiated Go Around due to Traffic Collision Avoidance System Resolution Advisory (TCAS RA): APA had 37 go arounds due to aircraft responding to a TCAS RA for traffic on the parallel runway.
  • Suspected Surface Loss Involving Two Aircraft: APA had 14 reports of suspected loss of surface separation between two aircraft.

After evaluating these events, the FAA determined that air traffic controllers must implement the use of Positive Control, which staggers arrivals between the two closely separated parallel runways, 17R/35L and 17L/35R. This procedure protects aircraft that fly through their final approach and has successfully enhanced safety at Centennial Airport.

What is included in the Airport Influence Area?

The Airport Influence Area (AIA) is a designated region surrounding an airport, within which current or future airport-related factors such as aircraft noise, overflight, safety, or airspace protection may affect land uses or necessitate restrictions on those land uses. The existing AIA delineates the Day-Night Average Sound Level (DNL) thresholds, commencing with 75 DNL at the core of the airfield and reducing to 55 DNL at the outermost ring. Any modifications to this AIA will be thoroughly examined and incorporated in the Noise Compatibility Program update as part of this Study.