Noise Abatement Glossary of Terms

A | B | C | D | E | F | G | H | I | K | L | M | N | O | P | R | S | T | V | W

A

Acoustics – The science of sound, including the generation, transmission, and effects of sound waves, both audible and inaudible.

Ambient Noise Level – The level of noise that is all-encompassing within a given environment for which a single source cannot be determined. It is usually a composite of sounds from many and varied sources near to and far from the receiver.

Arithmetic Average Sound Pressure Level – The sum of a series of sound pressure levels divided by the number of levels included in the sum.

A-Weighted Sound Level – A quantity, in decibels, read from a standard sound level meter with A-weighting circuitry. The A-weighting scale discriminates against the lower frequencies below 1000 Hertz according to a relationship approximating the auditory sensitivity of the human ear. The A-weighted sound level is approximately related to the relative "noisiness" or "annoyance" of many common sounds.

Advisory Circular - A series of FAA publications consisting of all non-regulatory material of a policy, guidance, and informational nature.

Air Cargo - All commercial air express and air freight except air mail and air parcel post.

Air Carrier - Aircraft operating under Certificates of Public Convenience and Necessity issued by the FAA authorizing the performance of scheduled air transportation over specified routes and a limited amount of non-scheduled operations.

Air Carrier Airport - An airport (or runway) designated by design and/or use for air carrier operations.

Aircraft Types - An arbitrary classification system that identifies and groups aircraft having similar operational characteristics for the purpose of computing runway and terminal area capacity.

Air Freight - A system or service set up for the carrying of freight by air.

Air Route Traffic Control Center (ARTCC) - An FAA facility established to provide air traffic control service to aircraft operating on an IFR flight plan within controlled airspace above 18,000 feet during the en route portion of a flight. The facility also provides air traffic control service to IFR and VFR aircraft at lower altitudes.

Air Taxi - An air taxi operator that - (1) performs at least five round trips per week between two or more points and publishes flight schedules that specify the times, days of the week and places between which such flights are performed; or (2) transports mail by air pursuant to a current contract with the US Postal Service.

Air Traffic - Aircraft operating in the air or on an airport surface, exclusive of loading ramps and parking areas. (FAR Part 1)
Air Traffic Control (ATC) - Division of the Federal Aviation Administration responsible for the safe, orderly, and expeditious flow of air traffic in their transit of airspace and on the ground at towered airports.

Air Traffic Control Center (ATCC) – The service operated by appropriate authority to promote the safe, orderly, and expeditious flow of air traffic.

Aircraft Operations - The airborne movement (landing or taking off) of aircraft. There are two types of operations - local and itinerant.

1. Local operations are performed by aircraft that -

a. Operate in the local traffic pattern or within sight of the airport,

b. Are known to be departing for, or arriving from, flight in local practice areas within a 20-mile radius of the airport,

c. Execute simulated instrument approaches or low passes at the airport.

2. Itinerant operations are all aircraft operations other than local operations.

Air Taxi - An air taxi operator which - (1) performs at least five round trips per week between two or more points and publishes flight schedules which specify the times, days of the week and places between which such flights are performed; or (2) transports mail by air pursuant to a current contract with the U.S. Postal Service.

Airport Traffic Control Tower (ATCT) - The air traffic control facility located on an airport and responsible for traffic separation within the Class D-controlled air space that surrounds an airport. This area generally consists of the airspace within a 5 statute mile radius of the airport and from the surface up to but not including 2,500 feet above the surface. Aircraft within this area must be in communication with the ATCT.

Airport - An area of land or water that is used or intended to be used for the landing and take-off of aircraft, including its buildings and facilities. (FAR Part 1)

Airport Elevation - The highest point on an airport’s usable runways expressed in feet above mean sea level (MSL).

Airport Imaginary Surfaces - Imaginary surfaces established at an airport for obstruction determination purposes.

Airport Master Plan - Appropriate documents and drawings concerning the development of a specific airport from a physical, economic, social, and political jurisdictional perspective. The airport layout plan is a part of this plan.

Airport Reference Point (ARP) - The airport reference point is the latitude and longitude of a point that is the approximate center of all existing and proposed landing and take-off areas.

Airport Sponsor - A public agency or tax-supported organization such as an airport authority, that is authorized to own and operate an airport, obtain property interests, obtain funds, and be legally, financially, and otherwise able to meet all applicable requirements of current laws and regulations.

Airspace - Navigable area used by aircraft for purposes of flight.

Alignment (Azimuth) - The azimuth or actual magnetic bearing of a course.

Alignment (Elevation) - The actual angle above a horizontal plane, originating at a specific point of a course used for altitude guidance.

Alternate Airport - An airport where an aircraft may land if a landing at the intended airport becomes inadvisable. (FAR Part 1)
Altitude - Height expressed in feet above a reference point, either Mean Seal Level or Above Ground Level.

Approach Area - The defined area over which landing and take-off operations are made.

Approach Lighting System (ALS) - An airport lighting facility that emits radiating light beams in a directional pattern by which the pilot aligns the aircraft with the runway on his final approach and landing.
Arrival – The act of an aircraft ceasing flight and landing at an airport.

Arrival Procedure - A series of directions from air traffic control, using fixes and procedures, to guide an aircraft from the en route environment to an airport for landing.

B

Blast Fence - A barrier used to divert or dissipate jet blast or propeller wash.

Block - Census blocks are small areas bounded on all sides by visible features such as streets, roads, streams, and railroad tracks, and by invisible boundaries such as city, town, township, and county limits; property lines; and short, imaginary extensions of streets and roads. Blocks are numbered uniquely within each census tract or block numbering area (BNA). A block is identified by a three-digit number, sometimes with a single alphabetical suffix.

Block Group (BG) - A cluster of blocks having the same first digit of their three-digit identifying numbers within a census tract or Block Numbering Area (BNA). For example, BG 3 within a census tract or BNA includes all blocks numbered between 301 and 397. In most cases, the numbering involves substantially fewer than 97 blocks. Geographic BGs never cross census tract or BNA boundaries, but may cross the boundaries of county subdivisions, places, Native American and Alaska Native areas, urbanized areas, voting districts, and congressional districts. BGs generally contain between 250 and 550 housing units, with the ideal size being 400 housing units.

C

Ceiling - Means the height above the surface of the earth of the lowest layer of clouds or obscuring phenomena that is reported as "broken," "overcast," or "obscuration." (FAR Part 1)

Commuter Airline - Aircraft operated by an airline that performs scheduled air transportation service over specified routes using light aircraft. Light aircraft means an aircraft having 30 seats or less and a maximum payload capacity of 7,500 pounds or less.
Controller – See Air Traffic Controller.

Crosswind - A wind blowing across the line of flight of an aircraft.

Crosswind Runway - A runway that provides for wind coverage not adequately provided by the primary runways.

D

Day-Night Average Sound Level (DNL) - A measure of the annual average noise environment over a 24-hour day. It is the 24-hour, logarithmic- (or energy-) average, A-weighted sound pressure level with a 10-decibel penalty applied to the nighttime event levels that occur between 10 p.m. and 7 a.m.

Decibel (dB) - The term used to identify 10 times the common logarithm of two like quantities proportional to power, such as sound power or sound pressure squared. Commonly used to define the level produced by a sound source.Declared Distances - The distances the airport owner declares available and suitable for satisfying the airplane’s take-off run, take-off distance, accelerate-stop distance, and landing distance requirements. The distances are - (see TORA, TODA, ASDA, and LDA).

Departure - The act of an aircraft taking flight and leaving an airport.

Descent – The process of decreasing altitude.

Displaced Threshold - A threshold that is located at a point on the runway other than the beginning.

Dwelling Unit - See "Housing Unit."

E

Environmental Impact Statement (EIS) - A document required by federal (if federal funds or properties are involved) and state law for proposed projects that could have potentially significant adverse impacts on the social, economic and natural environments. The EIS must address the environmental impacts of all reasonable alternatives, including the "no action" alternative, and commit to measures that would mitigate those adverse impacts that cannot be avoided.

Environmental Noise - Unwanted sound from various outdoor sources that produce noise. Environmental noise sources include aircraft, cars, trucks, buses, railways, industrial plants, construction activities, etc.

Equivalent Sound Level (Leq) - The level of a constant sound which, in the given situation and time period, has the same average sound energy, as does a time-varying sound. Specifically, equivalent sound level is the energy-averaged sound pressure level of the individual A-weighted sound pressure levels occurring during the time interval. The time interval over which the measurement is taken should always be specified.

Exit Taxiway - A taxiway used as an exit from a runway to another runway, apron, or other aircraft operating area.

F

Federal Aviation Regulations (FAR) - The procedures, standards, and methodology governing the development, submission, and review of the airport noise exposure maps and airport noise compatibility programs, including the process for evaluating and approving or disapproving those programs, required by FAA to be eligible for federal funds. The FAR Part 150 is the body of

Federal regulations relating to aviation (published as Title 14 of the Code of Federal Regulations).

Fleet Mix - The proportion of aircraft types or models expected to operate at an airport.

Flight Track - The path along the ground followed by an aircraft in flight.

Frequency - The number of oscillations per second completed by a vibrating object.

G

General Aviation (GA) - All civil aviation except passenger and cargo airlines.

H

Hertz - The unit used to designate frequency; specifically, the number of cycles per second.

Household - A household includes all the persons who occupy a housing unit. The occupants may be a single family, one person living alone, two or more families living together, or any other group of related or unrelated persons who share living arrangements.

Housing Unit - A housing unit is a house, apartment, a mobile home or trailer, a group of rooms or a single room occupied as separate living quarters or, if vacant, intended for occupancy as separate living quarters.

I

Instrument Approach - An approach to a landing area guided by instruments in the aircraft and on the ground, as opposed to a visual approach.

Instrument Flight Rules (IFR) – Rules governing the procedures for conducting flight via aircraft-based and ground-based

Instruments. Also a term used by pilot and controllers to indicate type of flight plan. The International Civil Aviation Organization defines IFR as a set of rules governing the conduct of flight under Instrument Meteorological Conditions (IMC).

Instrument Landing System (ILS) - A system that provides the lateral, longitudinal, and vertical guidance necessary for a landing.

Instrument Meteorological Conditions (IMC) - Weather conditions expressed in terms of visibility, distance from clouds, and cloud ceilings during which all aircraft are required to operate using Instrument Flight Rules (IFR).

K

Knots (kts) – Airspeed measured as the distance in international nautical miles covered in one hour.

L

Localizer (LOC) - An ILS navigation facility providing horizontal guidance to the runway centerline during approach and landing.

Logarithmic (or energy-averaged) Sound Pressure Level - Ten times the common logarithm of the arithmetic average of the squared pressure ratios from which the individual levels were derived.

Loudness - The attribute of an auditory sensation, in terms of which sounds may be ordered on a scale extending from soft to loud. Loudness depends primarily upon the sound pressure of the source, but it also depends upon the frequency and waveform of the source.

M

Mean Sea Level (MSL) - The average height of the surface of the sea for all stages of the tide, used as a reference for elevations. Also called sea level datum.

N

Nautical Mile – A measure of distance equal to one-minute arc on the earth’s surface (approximately 6,076 feet)

Noise - Any sound that is undesirable because it interferes with speech and hearing, or is intense enough to damage hearing, or is otherwise annoying.

Noise Abatement - Measures taken to reduce the off-airport impacts of aircraft noise.

Noise Contour - Continuous lines of equal noise level usually drawn around a noise source. The lines are generally drawn in 5-decibel increments so that they resemble elevation contours found in topographic maps except that they represent contours of equal noise level. Noise contours are generally used in depicting the noise exposure around airports, highways, and industrial plants.

Noise Exposure - The cumulative acoustic stimulation reaching the car of a person over a specified period of time (e.g., a work shift, a day, a working life, or a lifetime).

Noise Exposure Map (NEM) – A scaled, geographic depiction of an airport, its noise contours, and surrounding area developed in accordance with 14 CFR Part 150 regulations, including the accompanying documentation setting forth the required descriptions of forecast aircraft operations at that airport during the fifth calendar year beginning after submission of the map, together with the ways, if any, those operations will affect the map (including noise contours and the forecast land uses).

O

Operation - A landing or a take-off by an aircraft.

Overflights -Aircraft whose flights originate or terminate outside the controlling facility’s area that transit the airspace without landing.

P

Pink noise - Noise with a continuous frequency spectrum and with equal power per constant percentage bandwidth, for example, equal power in any one-third octave band.

R

Radar (primary and secondary) - A device which, by measuring the time interval between transmission and reception of radio pulses and correlating the angular orientation of the radiated antenna beam or beams in azimuth and/or elevation, provides information on range, azimuth, and/or elevation of objects in the path of the transmitted pulses.

Receiver - The listener or measuring microphone that detects the sound transmitted by the source.

Reliever Airport - An airport to serve general aviation aircraft that might otherwise use a congested airport served by air carriers.

Runway Orientation - The magnetic bearing of the centerline of the runway.

Runway Protection Zone (RPZ) - The trapezoidal area at the end of a runway (formerly referred to as the clear zone) that must be acquired to afford a safety zone for aircraft landings and take-offs. The FAA requires that RPZs be a part of airport property.

Runway Safety Area (RSA) - A defined surface surrounding the runway prepared or suitable for reducing risk of damage to airplanes in the event of an undershoot, overshoot, or excursion from the runway.

S

Separation - The spacing of aircraft to achieve safe and orderly movement in flight and while landing and taking off.

Sound Exposure Level (SEL) - A time-integrated metric (i.e., continuously summed over a time period) which quantifies the total energy in the A-weighted sound level measured during a transient noise event. The time period for this measurement is generally taken to be that between the moments when the A-weighted sound level is 10 dB below the maximum (i.e., the 10-dB-down points).

Sound Insulation - Reducing the sound level inside a building through the installation of specific building construction materials, and component assemblies that provide increased noise reduction characteristics.

Sound Pressure Level - A measure, in decibels, of the magnitude of the sound. Specifically, the sound pressure level of a sound that, in decibels, is 10 times the logarithm to the base 10 of the ratio of the squared pressure of this sound to the squared reference pressure. The reference pressure is usually taken to be 20 micropascals.

Source - The object that generates the sound.

Spectral Characteristics -The frequency content of the noise produced by the source.

Structure - A structure is a separate building that either has open spaces on all sides, or is separated from other structures by dividing walls that extend from ground to roof.

T

Tactical Air Navigation (TACAN) - A navigational system used by the military. TACAN provides both azimuth and distance information to a receiver on board an aircraft.

Taxiway - A defined path established for the taxiing of aircraft from one part of the airport to another.

Terminal Radar Approach Control (TRACON) - An FAA Air Traffic Control Facility which uses radar and two way communication to provide separation of air traffic within a specified geographic area in the vicinity of one or more airports.

Turboprop Aircraft - An aircraft whose main propulsive force is provided by a propeller driven by a gas turbine. Additional propulsive force may be provided by gas discharged from the turbine exhaust.

Threshold - The designated beginning of the runway that is available and suitable for the landing of aircraft. When the threshold is located at a point other than at the beginning of the pavement, it is referred to as either a displaced threshold or a relocated threshold depending on how the pavement behind the threshold may be used.

Time Above (TA) – The TA noise metric provides the duration in minutes for which aircraft-related noise exceeded specified A-weighted sound levels. Further, TA can be related directly to some "threshold activated" physiological or annoyance events.

Tower - See Airport Traffic Control Tower (ATCT).

V

Very High Frequency Omni-directional Radio Range Station (VOR) - A ground-based electronic navigation aid transmitting very high frequency navigation signals, 360° in azimuth, oriented from magnetic North. Used as a basis for navigation in the National Airspace System.

Very High Frequency Omni-directional Range with Tactical Air Navigation (VORTAC) - A navigational radio station that provides magnetic bearing and distance (DME) from the station. VORTAC is the most common form of radio navigation currently in use. Each station has a three-letter identifier, i.e., SBG for Solberg and COL for Colts Neck

Visual Approach - An approach to a landing area following Visual Flight Rules.

Visual Flight Rules (VFR) – Rules that govern the procedures for conducting flight under visual conditions. In addition, pilots and controllers use it to indicate type of flight plan. Generally, pilots operating under VFR are not required to fly with reference to radio navigational aids but to visual reference to the ground and are not under positive control by Air Traffic Control.

Visual Meteorological Conditions (VMC) - Weather conditions equal to or greater than those specified in 14 CFR 91.155 for aircraft operations under Visual Flight Rules (VFR).

W

Wavelength - The physical distance between identical points on successive waves.

Weighting - An additive (or subtractive) factor by which the sound pressure level at certain frequencies in an acoustic measurement is increased (or reduced) in order for that measurement to be more representative of certain simulated conditions.

White Noise - Noise with a continuous frequency spectrum and with equal power per unit bandwidth. For example, equal power in any band of 100 Hz width.