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IAD Dulles Int'l - Aircraft Noise Terminology
Definitions and Abbreviations
Acoustics: 1) The scientific study of sound and sound waves. 2) The characteristics of a room that determine the audibility of sound within it.
Advisory Circular (AC): An FAA informational publication for non-regulatory policy and guidance material.
Air Traffic: Aircraft operating in flight or on airport runways.
Air Traffic Control (ATC): A federal government service operated by the FAA that facilitates the safe and orderly movement of aircraft within and between airports by receiving and processing data from radar and devices that monitor local weather conditions and by maintaining contact with pilots.
Airport Layout Plan (ALP): The plan of an airport showing the layout of existing and proposed airport facilities. ALPs are used by many organizations for planning, verifying airport data, obstruction evaluation, project coordination, and other studies.
Airport Operations: Arrivals or departures to/from an airport.
Airport Surveillance Radar (ASR): Radar system used at airports to detect and display the position (distance & direction) of aircraft in the airport terminal area.
Altitude (AGL): Height above ground level.
Altitude (MSL): Height about mean sea level - 0 feet.
Ambient Noise: Also known as Background Noise. A composite of all noise sources in an area. For aviation studies, aircraft noise is not included as a noise source.
Area Navigation (RNAV): Formerly called Random Navigation. 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: Landing at an airport.
Arrival Procedure: A series of air traffic control procedures, using navigational aids, to direct an aircraft landing at an airport.
Attenuation: Loss of sound energy as it travels through a medium from the source to a receiver. Intensity diminishes due to factors such as distance, scattering, absorption, i.e. - atmospheric conditions, geography, insulation etc.
Avigation Easement: An easement, or right of overlight, in the airpsace above or in the vicinity of a particular property. It permits aircraft, operating to/from an airport, to fly at low altitudes above private property.
A-Weighting: See dBA.
Background Noise: See Ambient Noise.
Capacity: The number of aircraft that can arrive or depar from an airport under specific conditions during a specified time. It is determined by several factors including available runways and gates, runway length, air traffic rules, aircraft fleet mix and weather.
Commuter Aircraft: Smaller aircraft ranging from turboprop aircraft with 19 or less seats to regional jets with 70 or less seats.
Contour: See Noise Contour.
Day-Night Sound Level (DNL, symbol Ldn): Land-use planning metric which logarithmically calculates the average A-weighted sound level over a 24 hour period, with a 10 dB correction applied to nighttime (22:00 - 07:00 local time) sound levels.
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: Taking off from an airport.
Disclosure Statement: A statement citing that a property is in the vicinity of an airport and it will be exposed to aircraft noise. Disclosure statements are typically attached to Deeds of Conveyance, sales brochures, subdivision plats, homeowner association documents etc.
Displaced Threshold: A runway threshold that is located at a point other than the physical beginning or end of the runway.
DNL: See Day-Night Average Sound Level
Easement: The legal right of one party to use a piece of real estate belonging to another party. This may include the right of passage over, on or below the property. See Avigation Easement.
Enplanements: Number of passengers boarding an aircraft.
Enroute: Section of flight path between departure and arrival terminal areas.
Enroute Air Traffic Control System: FAA facilities that provide enroute service, typically for Instrument Flight Rules aircraft, when they are flying at higher altitudes between their departure and arrival airports.
Equivalent Sound Level (Leq): Equivalent Sound Level represents the average sound energy over a specified time period. Leq logarithmically averages the total sound energy experienced over a specified time period, during which multiple noise events may have occurred, and computes it as a continuous or equivalent sound exposure level. An Leq value may be calculated for any measurement period, however, it is typically calculated for: 1 second, 1 hour, 8 hours or 24 hours.
Federal Aviation Administration (FAA): The responsible for the safe and efficient use of the nation's airspace. The FAA
Federal Aviation Regulations (FAR): Federal regulations enacted by the Department of Transportation, under the statutory authority of the Federal Aviation Act and published in Title 14 of the Code of Federal Regulations (CFR).
Flight Plan: Aircraft information filed with Air Traffic Control that is associated with a specific flight.
Glideslope (GS): Vertical guidance provided by a radio beacon as the proper path (angle) for an aircraft approaching a landing strip.
Hertz (Hz): Metric to measure frequency, the rate at which something vibrates or oscillates.
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 are a set of regulations that dictate how aircraft are to be operated when the pilot is unable to navigate using visual references under visual flight rules. In order for the aircraft to be flown in instrument meteorological conditions (IMC), it must be fitted with the necessary instrumentation and certified by the regulatory authority. In addition to this, the pilot must hold an instrument rating.
Instrument Landing System (ILS): An electronic system installed to guide aircraft to runways during adverse weather conditions or when visibility is limited.
Instrument Meterological Conditions (IMC): Weather conditions expressed in terms of visibility and cloud ceilings during which aircraft are required to operate using Instrument Flight Rules.
Integrated Noise Model (INM): The INM is an FAA computer model used to predict aircraft noise exposure in the vicinity of airports.
Knot (KT): Airspeed measured as one (1) nautical mile per hour.
Localizer (LOC): A component of the ILS that provides runway centerline guidance (lateral) to aircraft, but not the glideslope information (vertical).
Localizer-Type Directional Aid (LDA): A navigational aid used for non-precision instrument approaches with utility and accuracy comparable to a localizer. It is not part of a complete ILS and its signal is not typically aligned with the runway.
Loudness: Subjective assessment of the intensity of sound.
Maximum Noise Level (Lmax): The maximum noise level during a measurement period.
Mean Sea Level (MSL): Average height of the surface of the sea for all stages of the tide; used as a reference for elevations.
Mitigation: To avoid or minimize an adverse impact.
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 aerial navigation.
Noise: 1) Unwanted sound. 2) Any sound that is considered annoying or undesirable that interfers with speech or hearing.
Noise Abatement: An procedure or action that minimizes aircraft noise exposure on communities surrounding an airport.
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 Monitoring System: A comprehensive system to provide measured aircraft and community noise levels, as well as flight track data.
Nautical Mile: A measured distance equal to 6076 feet.
Required Navigation Performance (RNP): A type of performance-based navigation that allows an aircraft to fly a specific path between defined points in space. An RNP requires that aircraft are equipped for navigation performance monitoring and alerting.
RNAV: See Area Navigation.
RNP: See Required Navigation Performance.
Runway: A level, man-made or natural, surface prepared for arriving and departing aircraft. Runways are numbered relative to their compass heading divided by 10, e.g. - Runway 19 points to a compass heading of 190 degrees.
Runway Threshold: The beginning of the usable portion of a runway.
Sequencing: An Air Traffic Control procedure used to merge air traffic into a single flow while maintaining specific time and distance separations.
Single Event: One noise event. The sound from a sing event is often expressed as using the Sound Exposure Level metric. See SEL.
Slant Range Distance: The straight line distance between a point on the ground and the aircraft position.
Sound: Sound is the result of energy (vibration waves) traveling through a medium to a receptor. The vibration spreads spherically away from the source.
Sound Exposure Level (SEL): Sound Exposure Level represents the total sound energy of a single event within 10 dB of the peak level (Lmax) that is logarithmically calculated as 1 second. For noise events longer than 1 second, SEL will always be greater than Lmax.
Sound Pressure Level (SPL): A measure of loudness. SPL is typically expressed in decibels, with respect to the threshold of human hearing. The threshold of hearing is defined as 20 microapascals, which is assigned a value of 0 decibels.
Stage 2 and Stage 3 Aircraft: Aircraft that meet the noise levels prescribed by the Federal Aviation Regulations Part 36 (14CFR36). The Airport Noise and Capacity Act of 1990 required the phase-out of all Stage 2 aircraft over 75,000 pounds by January 1, 2000. Stage 3 aircraft incorporate technology for suppressing jet-engine noise and, in general, are 10 dB quieter than Stage 2 aircraft.
Standard Instrument Departure Route (SID): A published instrument departure route.
Standard Terminal Arrival Route (STAR): A published instrument arrival route.
Statute Mile: A measured distance equal to 5, 280 feet.
Terminal Radar Approach Control (TRACON): An FAA Air Traffic Control facility that communicates and issues navigational instructions to aircraft operating within the specific airspace of one or more airports.
Terminal Radar Service Area: Airspace surrounding airports where Air Traffic Control provides full-time radar vectoring, sequencing and separation for all aircraft flying Instrument Flight Rules.
Threshold: 1) Physical beginning or end of the runway. 2) Baseline noise level above which microphones record a noise event.
Time Above (TA): Amount of time that sounds exceeds a specified threshold during 24-hours.
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.