Aircraft Overflight Glossary and Acronyms

Aircraft Overflight: An air flight that passes over a specific area, country or territory.

Air Traffic Control (ATC): A federal government service operated by the Federal Aviation Administration that facilitates the safe and efficient movement of aircraft in the air and on the ground by receiving and processing data from radar and devices that monitor local weather conditions and by maintaining contact with pilots.

Altitude (AGL): Height above ground level

Altitude (MSL): Height above mean sea level

Ambient Noise: Also known as background noise. A composite of all noise sources in an area.

Area Navigation (RNAV): A method of navigation that allows aircraft to choose any course within a network of navigation beacons, rather than navigating to/from the beacons.

Arrival: The process of an aircraft landing at an airport, usually by a series of air traffic control procedures, and navigational aids.

Day-Night Sound Level (DNL, symbol Ldn): The day-night average sound level is the average noise level over a 24-hour period. The noise level measurements between the hours of 10 p.m. and 7 a.m. are artificially increased by 10 dB before averaging. The FAA established the DNL as the primary metric for aircraft noise analysis and expressing aircraft noise exposure in the United States.

DBA (A-weighting, dBA): A-weighted decibel scale adjusts (weights) low frequency ranges to model the response perceived by the human ear. The A-weighting scale is commonly used in the measurement of aircraft and environmental noise.

Decibel (dB): A numerical expression of the relative loudness of a sound. The difference in decibels between two sounds is ten times the common logarithm of the ratio of their power levels.

Departure: The process of an aircraft leaving an airport usually by a Standard Instrument Departure Route (SID) or through ATC directives.

Federal Aviation Administration (FAA): The agency of the United States Department of Transportation responsible for the regulation and oversight of civil aviation within the U.S., as well as operation and development of the National Airspace System. Its primary mission is to ensure safety of civil aviation and enforce the rules of air safety.

Federal Aviation Regulations (FAR): Federal Aviation Regulations are enacted by the Department of Transportation, under the statutory authority of the Federal Aviation Act and published in Title 14 Code of Federal Regulations (CFR).

Glideslope (GS): Vertical guidance provided by a radio beacon as the proper path (angle) for an aircraft approaching a landing strip.

Instrument Approach: Series of predetermined maneuvers for the orderly transfer of an aircraft under instrument flight conditions from the beginning of the initial approach to a landing, or to a point from which a landing may be made visually or the missed approach procedure is initiated.

Instrument Flight Rules (IFR): Instrument flight rules govern flight procedures during limited visibility or other operational constraints. Under IFR, pilots fly under the guidance of radar.

Instrument Landing System (ILS): An electronic system installed to guide aircraft to runways during adverse weather conditions or when visibility is limited.

Land Use Compatibility: Land uses identified in FAR Part 150 as normally compatible with the outdoor noise environment adjacent to an airport within a specific noise contour level (or an adequately attenuated noise level reduction for any indoor activities involved).

Localizer (LOC): A component of the ILS that provides runway centerline guidance (lateral) to aircraft, but not the glideslope information (vertical).

Loudness: Subjective assessment of the intensity of sound.

National Airspace System (NAS): The common network of U.S. airspace, air navigation facilities, equipment, services, airports or landing areas; aeronautical charts, information and services, rules, regulations and procedures; technical information, manpower and materials, all of which are used in air navigation.

Noise: Any unwanted sound that is considered annoying or undesirable that interferes with speech or hearing.

Noise Abatement: A procedure or action that minimizes noise exposure.

Noise Contour: A noise contour is a line on a map representing equal noise exposure, typically for an annual average.

Noise Event: Measured sound for a particular period of time. An aircraft noise event is recorded when the sound level exceeds a threshold for a specified period of time.

Noise Level: For airborne sound, unless specified to the contrary, it is the A-weighted sound level.

Part 150 Noise Study: Sets forth the methodology and procedures to be followed when preparing aircraft noise exposure maps and developing airport/airport environs land use compatibility programs.

Preferential Runway Use: Aircraft using specified runways for arrivals and departures during certain hours to avoid residential and other noise-sensitive areas. Airports sometimes use this for overflight mitigation or noise abatement initiatives.

Required Navigation Performance (RNP): A type of performance-based navigation that allows an aircraft to fly a specific path between defined points in space. A RNP requires that aircraft are equipped for navigation performance monitoring and alerting.

Sequencing: An Air Traffic Control procedure used to merge air traffic into a single flow while maintaining specific time and distance separations.

Sound: Sound is the result of energy (vibration waves) traveling through a medium to a receptor. The vibration spreads spherically away from the source.

Terminal Radar Approach Control (TRACON): An FAA ATC facility that communicates and issues navigational instructions to aircraft approaching and departing the specific airspace of one or more airports. The TRACON typically assumes control of departing aircraft shortly after leaving an airport and approaching aircraft between 5 and 50 miles of the airport.

Turbo-jet: An aircraft powered by one or more jet turbine (turbofan) engines.

Turbo-prop: An aircraft powered by one or more propeller engines. This aircraft type is commonly used when flying shorter distances.

Vector: Compass heading used to provide navigational guidance by radar.

Visual Approach: A visual approach is an ATC authorization for an aircraft on an IFR flight plan to proceed visually and clear of clouds to the airport of intended landing.

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