Noise Glossary

Massport's Primer on noise monitoring terms and their common abbreviations



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.

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 oscillation.

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

Noise-sensitive Receptor: A location where noise can interrupt on-going activities which can result in community annoyance, especially in residential areas. Examples of noise-sensitive receptors include schools, libraries, hospitals, residences, retirement communities and nursing homes.

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 period of time. An aircraft noise event begins when the sound level of an overflight 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. Massport uses the FAA computer model, the Integrated Noise Model, to calculate noise contours in intervals of 5 DBA from 65 to 80 Ldn.

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 submitted to the Federal Aviation Administration and other government agencies (state and local). The Integrated Noise Model (INM) is the most commonly applied aviation noise model. Massport uses INM adjusted for Logan-specific topography.

NPSI: The Noise Per Seat Index (NPSI) is an index value used in the Massport Noise Rules to represent total noise emissions per seat for commercial turbojet aircraft operations at Logan. It is based on the total EPNdB for takeoff and landing, as certified by the FAA, divided by (on an energy basis) the number of seats in the aircraft.

NR: The Noise Reduction (NR) between two areas is the numerical difference, in dBA, of the average sound levels in those areas. NR is a measure of the complete construction (including all of the elements, such as window and wall).

NRC: The Noise Reduction Coefficient (NRC) is the measure of the acoustical absorption performance of a material, calculated by averaging its sound absorption coefficients at 250, 500, 1000 and 2000 Hz, expressed to the nearest multiple of 0.05. NRC is used in calculating soundproofing benefits.

Peak Level (in DB): The Peak Level is the highest level of sound pressure measured during a noise event.

PRAS: Preferential Runway Advisory System (PRAS) is a computer program that recommends to the FAA air traffic controllers runway configuration options that both will meet weather and demand requirements and will provide an equitable distribution of the airport's noise impacts on surrounding airports. Its primary objectives are to distribute the noise in accordance with (annual) runway utilization goals and to provide short-term relief from continuous operations over the same neighborhoods located at the ends of runways.

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

ROI: The Region of Influence (ROI) for noise impacts includes areas near Logan International Airport and its operations. This includes surrounding communities, the inner harbor and the routes that would be used by trucks hauling cargo.

RMS: Remote noise monitoring sites (locations).

Run-ups: An aircraft maintenance procedure; a "revving" of the engine.

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 and Stage 3 Aircraft: Commercial jet engines currently meet either Stage 2 or Stage 3 noise standards. 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 noise; 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. Aircraft less than 75,000 lbs that are Stage 2 aircraft are not allowed to arrive or depart from Logan between the 11:00 pm and 7:00 am.

Time Above: The Time Above is a measure identifying the number of minutes in a day which exceed a certain noise level. For example, a location may experience 10 minutes a day when the noise level exceeds 65 dBA.

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.