The Federal Noise Compatibility Framework

Federal airport noise policy rests on a voluntary planning program, a mandatory noise certification standard, and a statutory restriction framework that together define how airports, airlines, and the FAA address aircraft noise exposure in communities surrounding airports. The three statutory pillars are:

• Aviation Safety and Noise Abatement Act of 1979 (ASNA) — Created the noise compatibility planning program, now codified at 49 U.S.C. §§ 47501–47510 and implemented through 14 CFR Part 150. This program establishes procedures for developing Noise Exposure Maps (NEMs) and Noise Compatibility Programs (NCPs).
• Airport Noise and Capacity Act of 1990 (ANCA) — Established the national aviation noise policy, required the phase-out of Stage 2 aircraft over 75,000 pounds by December 31, 1999, and created the process under 14 CFR Part 161 for FAA review of airport noise and access restrictions on Stage 3 aircraft.
• 14 CFR Part 36 — Prescribes noise certification standards for aircraft. The FAA Modernization and Reform Act of 2012 extended the Stage 2 prohibition to aircraft weighing 75,000 pounds or less.

The DNL 65 dB Threshold

All federal airport noise policy pivots on a single metric and threshold: the Day-Night Average Sound Level (DNL) at 65 decibels (dB). DNL is an annual average noise exposure measure that applies a 10 dB penalty to nighttime operations (10:00 PM to 7:00 AM) to reflect the greater intrusiveness of nighttime noise.

The land use compatibility table in 14 CFR Part 150, Appendix A, identifies which land uses are compatible at each noise level:

Land Use	Below 65 DNL	65–70 DNL	70–75 DNL	75–80 DNL	80–85 DNL	Over 85 DNL
Residential (non-mobile home)	Compatible	Not compatible	Not compatible	Not compatible	Not compatible	Not compatible
Schools, hospitals, nursing homes	Compatible	NLR 25 required	NLR 30 required	Not compatible	Not compatible	Not compatible
Offices, business, professional	Compatible	Compatible	NLR 25 required	NLR 30 required	Not compatible	Not compatible
Agriculture (except livestock)	Compatible	Compatible	Compatible	Compatible	Compatible	Compatible

NLR = Noise Level Reduction in dB. Standard residential construction provides approximately 20 dB NLR; a 25 NLR requirement means 5 dB of additional attenuation beyond standard construction.

The Annoyance Gap

The DNL 65 dB threshold was set in the early 1980s based on the Schultz Curve (1978), which predicted that 12.3% of the population would be "highly annoyed" at DNL 65 dB. The Federal Interagency Committee on Noise (FICON) revalidated the Schultz Curve in 1992.

The FAA's Neighborhood Environmental Survey (NES), released January 13, 2021, surveyed over 10,000 residents near 20 airports in 2016 and found a different relationship between noise exposure and annoyance:

DNL Level	1992 Schultz Curve (% highly annoyed)	2016 NES (% highly annoyed)
50 dB	1.7%	15.4–23.4%
55 dB	3.3%	27.8–36.8%
60 dB	6.5%	43.8–53.7%
65 dB	12.3%	60.1–70.9%

The FAA stated upon release that "additional research is needed to understand the reasons for those changes" and that it "will not make any determinations on implications" pending further review. The FAA commenced a Noise Policy Review following Congressional directive in the FAA Reauthorization Act of 2024. As of March 2026, the DNL 65 dB threshold remains unchanged.

14 CFR Part 150: The Study Process

A Part 150 study is a voluntary program administered by the FAA that allows airport operators to assess aircraft noise exposure and develop measures to reduce and prevent incompatible land uses. Participation in Part 150 is not required, but it is a prerequisite for AIP grant funding of noise mitigation projects.

1. Noise Exposure Maps (NEMs)

The NEM documents existing and forecast (minimum five years into the future) aircraft noise exposure at the airport and identifies noncompatible land uses within the noise contours.

The NEM is produced using the FAA's Aviation Environmental Design Tool (AEDT), which replaced the Integrated Noise Model (INM) as the required modeling software effective May 29, 2015. AEDT models noise exposure based on:

• Airport physical layout (runway configuration, orientation)
• Annual aircraft operations by type and time of day/night
• Fleet mix and aircraft noise certification data
• Flight tracks (derived from radar data where available)
• Runway use percentages and flight procedures

The output is a set of noise contours — lines connecting points of equal DNL — plotted at 65, 70, 75, 80, and 85 dB intervals over a base map showing land uses.

2. Noise Compatibility Program (NCP)

The NCP identifies measures the airport operator has taken or proposes to take to reduce existing noncompatible land uses and prevent the introduction of new noncompatible uses. NCP measures fall into three categories:

Noise Abatement Measures

Operational and procedural measures to reduce noise at the source or redirect it away from noise-sensitive areas:

• Preferential runway use programs
• Noise abatement departure and arrival procedures
• Restrictions on aircraft type or class (subject to ANCA/Part 161 requirements for Stage 3 aircraft)
• Flight path modifications (subject to FAA air traffic control authority)
• Engine run-up restrictions (location, time, duration)

Preventive Land Use Measures

Actions to prevent the introduction of new noncompatible development within the noise impact area:

• Zoning recommendations to local jurisdictions (airport operators do not control zoning; local governments exercise this authority under state police powers)
• Building code requirements for noise level reduction (NLR) in new construction
• Overlay zones requiring noise disclosures for real estate transactions
• Acquisition of vacant land in imminent danger of noncompatible development

Remedial Mitigation Measures

Actions to mitigate noise impacts on existing noncompatible land uses:

• Sound insulation of residential structures (windows, doors, ventilation systems)
• Sound insulation of schools, hospitals, churches, and other public-use buildings
• Voluntary acquisition (buyout) of noise-impacted properties
• Avigation easements

Under the FAA's Final Policy on Part 150 Noise Mitigation Measures (effective October 1, 1998), the FAA approves remedial measures only for incompatible development that existed as of that date. Incompatible development that occurred after October 1, 1998 may be addressed only through preventive measures.

FAA Review and Record of Approval

After the airport operator submits the NCP, the FAA has 180 days to approve or disapprove each measure. Failure to act within 180 days constitutes approval under the statute. The FAA issues a Record of Approval (ROA) that identifies each NCP measure and states whether it is approved, disapproved, or approved with conditions.

FAA approval of an NCP measure is a necessary condition for AIP funding of that measure, but it does not guarantee that AIP funds will be appropriated.

Sound Insulation Programs

Sound insulation — the retrofit of existing residential and public-use structures with acoustically rated windows, doors, ventilation systems, and building envelope treatments — is the predominant remedial measure implemented in Part 150 NCPs, as documented in FAA-approved Noise Compatibility Programs at major U.S. airports.

Eligibility Requirements

FAA AIP eligibility for sound insulation requires:

• The structure must be located within the DNL 65 dB or greater noise contour (or a lower locally adopted threshold with FAA concurrence)
• Existing interior noise levels must be 45 dB or greater with windows closed
• For residences, interior noise is calculated as the average of habitable rooms (living, sleeping, kitchen areas)
• The treatment must be part of an FAA-approved NCP measure or included in an FAA-approved environmental document

Funding

AIP funding for sound insulation is split 80% federal / 20% airport sponsor at most airports. The airport sponsor's 20% share comes from airport revenue, PFCs, or state/local grants.

Program Scale: Named Examples

Several airports operate sound insulation programs with documented scope:

• Seattle-Tacoma International Airport (SEA): Over 9,400 single-family homes sound insulated since 1985; seven condominium complexes (321 units); a $100 million agreement with the Highline School District ($50 million from the Port of Seattle, $50 million from FAA) covering 15 school buildings. The program is funded approximately 80% FAA AIP / 20% airport revenue.
• San Diego International Airport (SAN): The Quieter Home Program has retrofitted 5,929 homes since 2001. In 2025, the FAA awarded SAN $15 million in AIP funds for sound insulation of 250 additional eligible residences. Eligible homes are located within the 65 dB CNEL contour and must have average interior noise levels of 45 dB or greater with windows closed.
• Chicago O'Hare International Airport (ORD): The O'Hare Residential Sound Insulation Program (RSIP), administered by the O'Hare Noise Compatibility Commission, is funded by FAA AIP grants and Chicago PFCs. Eligible residences fall within the FAA's OMP Full Build-Out noise contour.
• Oakland International Airport (OAK): The Bay Farm Island sound insulation program insulated 558 of 629 eligible homes (89% participation rate), at a total cost of $18.7 million funded by AIP and PFCs. Post-installation testing of 82 homes showed average interior noise reduction of 5 to 7 decibels.

Land Acquisition Programs

For properties in the highest noise contours — generally DNL 75 dB and above — voluntary acquisition (buyout) may be included as an NCP measure. The airport acquires the property at fair market value, relocates the occupants, and either uses the land for airport purposes or maintains it as a noise buffer.

Under AIP Handbook Section 5-68, if AIP-funded noise land is later determined to be no longer needed for airport purposes (including noise buffer), the airport sponsor must apply the federal share of the fair market value in the following order of precedence:

1. Reinvestment in an approved noise compatibility project
2. Reinvestment in a project eligible under 49 U.S.C. § 47117(e)
3. Reinvestment in other approved airport development at the airport
4. Transfer to another public airport for noise compatibility
5. Repayment as directed by FAA

ANCA and Part 161: Restrictions on Stage 3 Aircraft

The Airport Noise and Capacity Act of 1990 (49 U.S.C. §§ 47521–47534) established the framework for FAA review of airport-imposed noise and access restrictions that affect Stage 3 aircraft operations. 14 CFR Part 161 implements ANCA's restriction review program.

Six Conditions for Approval

For a Stage 3 restriction to receive FAA approval, the airport proprietor must demonstrate, on the basis of substantial evidence, that:

1. The restriction is reasonable, nonarbitrary, and nondiscriminatory
2. The restriction does not create an unreasonable burden on interstate or foreign commerce
3. The restriction is not inconsistent with maintaining the safe and efficient use of the navigable airspace
4. The restriction does not conflict with any existing federal statute or regulation
5. The restriction provides adequate opportunity for public comment
6. The restriction does not create an undue burden on the national aviation system

All six conditions must be met for approval. The evidentiary burden is on the airport proprietor. The Part 161 application requires an analysis of costs and benefits, a description of alternative measures considered, and evidence that the proposed restriction is the minimum necessary to address the noise problem.

Restrictions Not Subject to Part 161

ANCA exempts certain pre-existing restrictions from Part 161 review:

• A restriction in effect on November 5, 1990 (the date of ANCA enactment)
• A local action to enforce a negotiated airport noise agreement executed before November 5, 1990
• An intergovernmental agreement with a noise restriction in effect on November 5, 1990
• A subsequent amendment to a pre-ANCA restriction that does not reduce or limit aircraft operations or affect aircraft safety

Financial Dimensions

AIP Funding

AIP grants for noise compatibility projects carry the same federal share as other AIP-eligible projects: 90% federal for most airports; 75% for large and medium hub primary airports (subject to adjustments under the FAA Reauthorization Act of 2024). Sound insulation programs are funded at 80% federal / 20% local at airports that collect PFCs.

In September 2024, the FAA announced over $2 billion in AIP grants, including noise-specific awards: $15.8 million to LAX for sound insulation of 400 homes; $2.2 million to Key West for design and installation; $555,019 to Chicago Midway for 12 homes; and $539,910 to Tweed New Haven for design of 12 residences.

PFC Revenue

PFC revenue may be applied to noise mitigation projects upon FAA approval of a PFC application. PFC-funded noise projects do not require a Part 150 NCP, though an approved NCP provides the analytical basis for the project's justification.

Bond-Funded Noise Mitigation

Noise mitigation costs — particularly land acquisition — may be financed through airport revenue bonds. Bond-funded noise mitigation enters the debt service calculations and affects airline rates through the same flow-of-funds mechanics as other capital projects.

Analytical Considerations

• Noise Policy Review timeline. The FAA's ongoing Noise Policy Review, initiated in January 2024, may result in a change to the DNL 65 dB threshold or the adoption of supplemental noise metrics. A lower threshold would expand the geographic area of noncompatible land use and the number of properties eligible for remedial mitigation, with corresponding cost implications for airport noise programs.
• Part 150 study timing. Because Part 150 NCP measures that receive FAA approval become eligible for AIP funding, the timing of a Part 150 study relative to the Noise Policy Review carries financial implications. An NCP approved under the current 65 dB standard defines the universe of AIP-eligible properties at that threshold.
• Part 161 burden. No airport has successfully completed the Part 161 process to impose a new Stage 3 restriction that was not agreed to by the affected carriers. The six-condition test and the evidentiary standard of "substantial evidence" establish a demanding standard that requires the airport proprietor to prove all six conditions on the basis of evidence in the record. Airports that wish to address noise through operational restrictions may instead pursue voluntary agreements with carriers.
• Interaction with airline rates. Noise mitigation costs funded from airport operating revenue or bond proceeds are passed through to airlines under compensatory or residual rate structures. An airport planning a multi-year sound insulation program may wish to model the cost-per-enplanement (CPE) impact within its financial feasibility framework.