Frequently Asked Questions : Noise Management

Operational Questions

Noise Complaint Questions

Acoustical Questions

Noise Study Questions

Airport Noise and Operations Monitoring System (ANOMS) Questions

Noise Abatement Questions

Why are planes flying over this area, we're not under a flight path?

The FAA (Air Traffic Control (ATC)), not DEN, has sole authority and responsibility for routing and separating aircraft throughout the national airspace system. ATC's first priority is always the safe and efficient separation and routing of aircraft throughout the national airspace system.

The Denver region experiences many types of aircraft over flights that may or may not be related to DEN. In the Denver airspace, at any point in time, there could be long haul flights en route (e.g. from Los Angeles to Chicago) traveling at very high altitudes; general aviation aircraft traveling to and from other local airports, military aircraft, other commercial aircraft traveling to nearby commercial airports and helicopter traffic for medical or traffic reasons.

If you live anywhere within the Denver metro area, you will likely experience aircraft over flights. How and to what frequency depends on, the weather, the runways being used, the type of aircraft, aircraft engine characteristics and relative distance from the airport.

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What is DEN responsible for?

DEN is responsible for operating and maintaining airport facilities and for ensuring runways (and taxiways) are in good working conditions and ensure FAA regulations are met.

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How does weather impact traffic operations and noise?

When Denver experiences pleasant and temperate springs and autumns, and neither air conditioners nor heaters are being operated, many citizens opt to leave windows and doors ajar. These actions, allow aircraft, vehicle traffic, and other exterior noise to permeate deeper into the home, hence increasing awareness of noise and its associated annoyance.

A greater number of noise complaints are received in the spring and autumn when people are outside and windows are open.

In addition, during warm temperatures, the air density (air molecules per cubic foot) decreases significantly, thereby reducing aircraft performance and lift. (Aircraft performance is dependent upon the number of molecules in the atmosphere. The fewer number of air molecules, the lesser the engine and airframe performance.) Consequently air density decreases as airport altitude increases.

Aircraft noise is also more noticeable on cloudy days. Low ceiling cloud cover tends to reflect or reverberate aircraft noise downward off the clouds, thus confining it.

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Can't you do something about the helicopters?

Typical complaints concerning helicopters tend to be related to the media, with medical flights, or with law enforcement and therefore, are not required to maintain any particular altitude. Take notice that most helicopter flights do not originate or terminate at DEN.  Helicopters may fly below these minimum altitude requirements if the operation is conducted without hazard to persons or property on the ground.

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Is there a minimum altitude requirement for aircraft flying over residential areas and school yards?

Airport managers and the Federal Aviation Administration (FAA) would prefer that aircraft did not fly over populated areas. The FAA and airline’s policy is to get DEN commercial flights up high.

Helicopters may fly below these minimum altitude requirements if the operation is conducted without hazard to persons or property on the ground.

Local and state authorities do not have jurisdiction over airspace regulations and, therefore, cannot mandate that aircraft and/or helicopters fly at higher altitudes.

Aircraft operating under visual flight rules outside or beneath the FAA Tower's airspace are not required to use air traffic's services and fly unrestricted. A pilot can freely select his or her route and altitude with no restrictions other than those flight rules establishing minimum altitudes for flights over populated areas and required separation distances from clouds and terrain.  The Federal Aviation Regulation (FAR) Part 91.119 indicates that, except when necessary for departure or landing, the minimum altitude over urban areas is 1,000 feet above ground level (AGL) and 500 feet AGL over rural areas.

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How is runway use determined at DEN?

Runway use is determined by variables such as weather, capacity, airport layout, aircraft performance, noise abatement procedures and aircraft density in the surrounding airspace. When wind conditions allow, traffic density and arrival/departure streams determine the runway use at the airport to ensure the most expeditious and safe flow of air traffic. 

Each morning at DEN, Air Traffic Control (ATC) sets the airport’s flow for the day, based on the prevailing winds. Due to the complexities of re-routing aircraft to alternative runway ends, the flow is not changed unless wind conditions require it.

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Why do some aircraft seem louder than others?

Aircraft operating at DEN have a diverse range of noise levels. These noise levels primarily depend on the type of engine used by the aircraft, the size of the aircraft and whether the aircraft is taxiing on the airfield, landing or taking off.  Current versions of Stage 3 aircraft tend to be the quietest aircraft in the fleet. Older aircraft with Stage 3 "hush kitted" engines tend to be the loudest. Departures tend to be louder than arrivals since the pilot is using more power to the engine to achieve lift.

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Will filing a noise complaint change how the airport operates?

The Federal Aviation Administration (FAA) has the sole authority in determining where aircraft will fly and how the airport will operate. These decisions are made solely on standard air traffic control procedures. Noise complaints are not considered when making these decisions.

However, considerable time and effort are spent on a daily basis in handling and analyzing complaints. 

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What happens when I file a noise complaint on the Noise Complaint Hotline or the online Noise Complaint?

Citizens are concerned about aircraft noise and complain because they would like to see changes occur. Filing a complaint will not bring about an individual's desired change, rather it provides a means for DEN to report and disseminate information to the Federal Aviation Administration (FAA), airlines, public, and local representatives. Complaints are logged and reported quarterly.

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How are noise complaints addressed?

DEN has maintained a 24-hour noise hotline for several years. The hotline allows citizens to leave a recorded message containing detailed information concerning aircraft noise events. Staff perform daily checks of the hotline and calls are returned, if requested by the individual, as soon as possible.  The hotline phone number is (303) 342-2360.

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What are the rules for reporting noise complaints?

Only one inquiry per call will be accepted. Multiple times and ranges of times will not be accepted, all aircraft operational inquires need to be reported within one week of the occurrence.  Each call/email should include name, address, date and time of the overflight. If you would like a call-back, please include telephone number and a request for call-back.  Abusive language or comments will not be tolerated. Threats involving aircraft and or the airport will result in notification of the proper authorities.  Please note, all calls are recorded, and recordings are subject to disclosure under the Federal Freedom of Information Act and the Colorado Open Records Act.

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What is Day-Night Average Sound Level (DNL or Ldn)?

DNL (Ldn) stands for Day-Night Average Sound Level and is used to describe the cumulative noise exposure during an average annual day. Ldn does not represent the sound level heard at any particular time, but rather represents the total sound exposure. DNL (Ldn) stands for Day-Night Average Sound Level and is used to describe the cumulative noise exposure during an average annual day. Ldn does not represent the sound level heard at any particular time, but rather represents the total sound exposure.

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How is sound generated?

As air moves through a jet engine, past a propeller, or over the aircraft’s wing or fuselage, air is defected and accelerated resulting in turbulence as it mixes with the surrounding air. These changes in airflow can generate significant sound levels. While these sound levels can be measured in many different ways, the Federal Aviation Administration (FAA) provides guidelines for the measurement and presentation of data. 

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What is decibel?

The average human ear begins sensing at a pressure of only 20 micropascals and begins to experience pain at approximately 100 pascals.  Because the human ear perceives pressure changes logarithmically over a large range, sound pressure level (SPL) is measured in decibels (dB). The decibel is logarithmic in relation to sound pressure (sound pressure is measured in pascals) giving us a more manageable scale.

Because of this logarithmic relationship, one cannot simply arithmetically add, subtract, or average decibel levels. For example if you have two 60 dB noise sources occurring simultaneously they combine to equal 63 dB. While a 3 dB change is generally just perceptible, a ten decibel change, either up or down, is approximately twice or half as loud.

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What is frequency and how is it weighted?

The healthy young person’s ear senses tones (frequencies) in the range of 20 and 20,000 Hertz (Hz). Because the human ear doesn't respond to all of these frequencies equally, weightings are applied to more accurately quantify what the ear is actually sensing.  

A-weighting (dBA) is the approximate response of the human ear therefore, A-weighting is the most commonly used by airports as directed by FAA Part 150 guidelines.

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What is an acoustic metric?

It simply a measurement derived through the use of a mathematical formula for a specific purpose. The following metrics are those most commonly used in airport noise. These metrics are A-weighted unless otherwise noted.

Ldn (day-night average sound level)
The average sound level over an entire day, with 10 dB being added between 10 p.m. and 7 a.m. to account for the added intrusiveness of noise during these hours. Ldn contours used for mitigation purposes generally represent an average day that is calculated or modeled using a full year of data.

Leq (equivalent-continuous sound level)
An equivalent-continuous sound level is simply an average level (without 10 dB weighting) over a stated time-period.

SEL (sound exposure level)
SEL is similar to Leq. The difference between the two is that SEL represents the entire noise event as though it occurred within a duration of one second. With the SEL metric we can directly compare two noise events having different durations.

Lmax (maximum sound level)
This is the highest level displayed on a sound level meter during a noise event or time period.

Lmin (minimum sound level)
This is the lowest level displayed on a sound level meter during a noise event or time period.

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I live several miles away from DEN, why can I still hear the rumble of departures?

Lack of attenuation is a large factor. Attenuation is the reduction of sound energy by the absorption (via trees, buildings etc.) or divergence of sound waves. The amount of attenuation due to absorption varies with the substance through which the sound waves are being transmitted, or propagating. Generally speaking, through air, noise decreases by six decibels for a doubling of distance when sound emanates from a single point in space. In contrast, noise emanating from a line, such as a train or constant road traffic, decreases by only three decibels per doubling of distance. 

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What is a Part 150 Study and what is its purpose?

14 CFR Part 150 provides a means for airports to accomplish land use compatibility, noise reduction goals and develop a comprehensive set of noise abatement actions and mitigation measures that will work effectively together. Part 150 is a federal program appropriating aviation-generated funds for the purpose of aircraft noise mitigation measures in communities surrounding an airport.

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What is NOMS and what does it do?

The Noise and Operations System (NOMS) is designed to provide DEN officials with accurate runway use counts specific to aircraft type, aircraft flight path information and 24-hour noise monitoring data at selected sites within residential communities. The Federal Aviation Administration (FAA) has agreed to provide DEN with computer-processed Automated Radar Terminal Systems (ARTS IIIE) data from the Denver Terminal Radar Approach Control (TRACON). In addition to providing reliable airport operations data, NOMS archives data for future airport decisions, validates complaint information, tracks effects of air traffic routing procedures and validates computer-generated noise models.

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What resources do concerned citizens have in the noise abatement process?

As a resource for concerned citizens, DEN has developed this informational web site and a Noise Complaint Hotline.  It provides an outlet for citizens to vent airport noise frustrations by registering a complaint.  A complaint can be registered online or via telephone by calling (303) 342-2380 or (800) 417-2988.  Concerned citizens may also tour the Noise Abatement office, please call the above numbers to set up an appointment. 

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Glossary of Noise Terms

Air Carriers: Airlines holding a certificate of public convenience and necessity that operate aircraft designed to have a maximum seating capacity of more than 60 seats or a maximum payload capacity of more than 18,000 pounds or conduct international operations.

Air Taxi: Non-scheduled passenger aircraft with 50 or fewer seats.

NOMS: The NOMS is an acronym for Noise and Operations Monitoring System which is designed to provide DEN officials with accurate runway use counts specific to aircraft type, aircraft flight path information and 24-hour noise monitoring data at selected sites within residential communities.  In addition to providing reliable airport operations data, NOMS archives data for future airport decisions, validates complaint information, tracks effects of air traffic routing procedures and validates computer-generated noise models.

dB: The Decibel (dB) is the unit used to measure the magnitude or intensity of sound. The decibel uses a logarithmic scale to cover the very large range of sound pressures that can be heard by the human ear. Under the decibel unit of measure, a 10 dB increase will be perceived by most people to be a doubling in loudness, i.e., 80 dB seems twice as loud as 70 dB.

dBA: The A-weighted Decibel (dBA) is the most common unit used for measuring environmental sound levels. It adjusts, or weights, the frequency components of sound to conform to the normal response of the human ear at conversational levels.

Commuter Aircraft: Scheduled passenger aircraft with fewer than 50 seats.

Commercial Aviation: The sum total of air carrier and air taxi flights.

General Aviation: Non-commercial airline aviation - primarily business aircraft and individuals traveling in private aircraft, including those making connections to commercial flights.

Husk kitted Aircraft: Hush kitted Stage III aircraft are previously Stage II aircraft that have been adapted to meet Stage III requirements, typically by means of engine modification.

IFR: Instrument Flight Rules govern flight procedures during limited visibility or other operational constraints. Under IFR, pilots must file a flight plan and fly under the guidance of radar.

Intensity: The sound energy flow through a unit area in a unit time.

INM: The Federal Aviation Administration's (FAA), Office of Environment and Energy (AEE-100) has developed the Integrated Noise Model (INM) for evaluating aircraft noise impacts in the vicinity of airports. The INM has been the FAA's standard tool since 1978 for determining the predicted noise impact in the vicinity of airports. The FAA requires airports use the INM in assessing environmental impacts for soundproofing, evaluating physical improvements to the airfield, analyzing changes to existing or new procedures and in assessing land use compatibility.

Ldn: The Day-Night Average Sound Level (Ldn) is the level of noise expressed (in decibels) as a 24-hour average. Nighttime noise, between the hours of 10:00 p.m. and 7:00 a.m. is weighted; that is, given an additional 10 decibels to compensate for sleep interference and other disruptions caused by nighttime noise.

Ldn is used by all Federal agencies (EPA, HUD, DOE, DOD, etc.) and internationally in the assessment of potential noise impacts. It is used interchangeably with DNL.

Lmax: The Maximum Instantaneous Noise Level (Lmax) is the maximum level of noise measured during a given measurement period.

NMT: Noise Monitoring Terminals, DEN has 26 NMTs placed strategically throughout the Denver metro area.

Noise: 1. Unwanted sound. 2. Any sound not occurring in the natural environment, such as sounds emanating from aircraft, highways, industrial, commercial and residential sources. 3. An erratic, intermittent, or statistically random fluctuation.

Noise Abatement: A procedure or technique used by aircraft at an airport to minimize the impact of noise on the communities surrounding an airport.

Noise Study: Investigation of existing noise conditions, flight patterns and land use surrounding an airport.

Noise Event: A Noise Event is the measured sound produced by a single source of noise over a particular duration of time. An aircraft noise event begins when the sound level of a flight operation exceeds a noise threshold and ends when the level drops down below that threshold.

Noise Contour: A Noise Contour is a line on a map that represents equal levels of noise exposure.

Noise Models: Noise Models are computer models used to predict the impacts of aircraft noise over a geographic area. Such models are used to develop the noise exposure contours and noise exposure maps.

Preferential Runway Use: Taking off or landing on specified runways during certain hours to avoid residential areas.

RMT: Remote Monitoring Terminals, DEN has 26 RMTs placed strategically throughout the Denver metro area.

SEL: The Sound Exposure Level (in dB) is computed by converting the total noise energy measured during a noise event to an equivalent dBA level for a single event that would only be one second in duration. The SEL accounts for both the magnitude and the duration of the noise event; noise analysts use SEL to calculate the day-night average noise level.

Stage 2 vs. Stage 3 Aircraft: Stage 2 engines are older and noisier than Stage 3 engines. Stage 3 aircraft incorporate the latest technology for suppressing jet-engine noise and, in general, are 10 dB quieter than Stage 2 aircraft. This represents a halving of perceived reduction in noise levels; however, actual noise reduction varies by aircraft. All aircraft greater than 75,000 lbs had to meet Stage 3 noise standards as of January 1, 2000.

VFR: Visual Flight Rules (VFR) are air traffic rules allowing pilots to land by sight without relying solely on instruments. VFR conditions require good weather and visibility.

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