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Abatement: The method of reducing the degree of intensity of noise and the use of such a method.

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. There are four different types of air carriers: majors, nationals, medium regionals and large regionals.

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

ANMS: The Airport Noise Monitoring System (ANMS) is a sophisticated, acoustical system which monitors noise impacts by time of day, season and on an annual basis. ANMS also monitors noise levels generated by a variety of outside aircraft activities and obtains accurate data of aircraft flight tracks and fleet mix. Massport's NMS (Noise Monitoring System) uses ENOMS (Environmental Noise and Operations System) to collect and process the same information in a similar manner as ANMS. The NMS has 29 locations in the Logan area and 6 locations at Hanscom.

dB: The Decibel (dB) is the unit used to measure the magnitude or intensity of sound. Decibel means 1/10 of Bel (named after Alexander Graham Bell). 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 with the normal response of the human ear at conversational levels. dBA is an international metric that is used for assessing environmental noise exposure of all noise sources.

dBC: The C-weighted Decibel (dBC) is the method of measuring sound which takes into account the low frequency components of noise sources, such as aircraft operations, and reflects their contribution to the environment.

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

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

EPNdB: The Effective Perceived Noise Level (EPNdB) is another unit of measure for aircraft noise. It is based on how people judge the annoyance of sounds they hear with corrections for the duration of the event and for pure tones. The Federal Aviation Administration (FAA) uses EPNdB in the certification of large transport planes for Federal Noise Regulations (FAR Part 36).

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

Hertz (Hz): The Hertz is a unit of measurement of frequency, numerically equal to cycles per second of the measure of the rate of the vibration of the sound. High frequencies can be thought of as having a high pitch; like a whistle; low frequency sounds are more like a rumble of a truck or airplane.

Huskkitted Aircraft: Hushkitted Stage III aircraft are previously Stage II aircraft that have been adapted to meet Stage III requirements.

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.

ILS: An Instrument Landing System (ILS) is a precise landing aid consisting of several components giving the pilot vertical and horizontal electronic guidance. Elements usually include: 1. an outer marker, a radio beam 4 to 6 miles from the touchdown point where the electronic signal begins; 2. an approach lighting system at the runway end; 3. a localizer radio beam which provides the horizontal guide; and 4. a glide slope which provides vertical guidance on the angle of descent for landing.

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.

The INM Model utilizes flight track information, aircraft fleet mix, standard and user defined aircraft profiles and terrain as inputs. The INM model produces noise exposure contours that are used for land use compatibility maps. The INM program includes built in tools for comparing contours and utilities that facilitate easy export to commercial Geographic Information Systems. The model also calculates predicted noise at specific sites such as hospitals, schools or other sensitive locations.

The INM model used by Massport for Logan Airport has been updated to reflect local topographical conditions such as water and hills.

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. An annual average of DNLs is used by the Federal Aviation Administration to describe airport noise exposure. Areas with noise impacts less than 65 dB DNL are considered "compatible" with residential use; areas at or above 65 dB DNL are designated "incompatible" with residential use.

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.

Logan Noise Rules: The principal aim of Logan's noise rules is to keep cumulative noise at or below the 1986 level, regardless of fluctuations in the number of passengers and operations. The rules entirely eliminated the oldest and noisiest Stage I aircraft in 1988, and of Stage II aircraft in 2000. Noise rules limit the time period (Midnight to 7 AM) during which engine maintenance "run-ups" can occur. Airlines have the option of complying with two standards: either a Stage III percentage or a Noise Per Seat Index (NPSI). These standards are determined by Massport each July for the upcoming year.