Boston Logan Airport Noise Study
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A90 – Three letter identifier for the Boston Terminal RADAR Approach Control facility.

A-WEIGHTED SOUND LEVEL (dBA) - The ear does not respond equally to different frequencies of sound. It is less efficient at low and high frequencies than it is at medium or speech range frequencies. Thus, to obtain a single number representing the sound level of a noise having a wide range of frequencies in a manner representative of the ear's response, it is necessary to reduce the effects of the low and high frequencies with respect to the medium frequencies. The resultant sound level is said to be A weighted, and the units are decibels (dB); hence, the abbreviation is dBA. The A weighted sound level is also referred to as the noise level. Sound level meters have an A weighting network for measuring noise in A weighted decibels.

ABOVE GROUND LEVEL (AGL) - Altitude of aircraft in feet above the ground surface.

ABSORPTION - Absorption is a property of materials that reduces the amount of sound energy reflected. Thus, introduction of an “absorbent” into the surfaces of a room will reduce the sound pressure level in that room because sound energy striking the room’s surfaces will be partially absorbed rather than totally reflected. The process of absorption is different from that of transmission loss through a material, which determines how much sound enters a room via the walls, ceiling, and floor. Absorption reduces the resultant sound level in the room produced by energy that has already entered the room.

ACCEPTABLE - Relating to noise-Day-night average sound level (DNL) not exceeding 65 decibels Noise exposure may be of some concern, but common building construction will make the indoor environment acceptable, and the outdoor environment will be reasonably pleasant for recreation and play. As defined by Federal Aviation Regulations, Part 150, “Airport Noise Compatibility Planning” (see FAR PART 150). (See DAY-NIGHT AVERAGE SOUND LEVEL

ACOUSTICS - (1) The science of sound, including the generation, transmission, and effects of audible and inaudible sound waves.
(2) The physical qualities (such as size and shape) of a room or other enclosure that determine the audibility and perception of speech and music.

ADVISORY CIRCULAR (AC) - An external Federal Aviation Administration (FAA) publication consisting of non-regulatory material of a policy, guidance, or informational nature.

ANOMS - Airport Noise and Operations Monitoring System. A computer system that collects aircraft flight track data and noise event information for the analysis of flight patterns and resulting noise impacts.

AREA NAVIGATION (RNAV) - Method of navigation that permits aircraft operation on any desired course within the coverage of station-referenced navigation signals or within the limits of a self-contained system capability, or a combination of both. RNAV was developed to provide more lateral freedom and thus more complete use of available airspace. This method of navigation does not require a track directly to or from any specific radio navigation aid, and has three principal applications: 1) A route structure can be organized between any given departure and arrival point to reduce flight distance and traffic separation; 2) Aircraft can be flown into terminal areas on varied pre-programmed arrival and departure paths to expedite traffic flow; and 3) Instrument approaches can be developed and certified at certain airports, without local instrument landing aids at that airport. Accuracy and precision of an RNAV procedure depends greatly on the type of navaid, aircraft equipage and pilot training.

AFFECTED LOCAL GOVERNMENT AGENCIES - The local government agencies that have the authority to control land uses in areas that may be adversely affected by aviation activities.


AIR CARRIER, CERTIFICATED ROUTE - An airline company 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 contract with the U.S. Postal Service, certificated in accordance with Federal Aviation Regulations (FAR) Parts 121 and 127.

AIR CARRIER, COMMUTER - 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 contract with the U.S. Postal Service.

AIRCRAFT DELAY - The additional travel time, caused by airfield or airspace congestion, needed by an aircraft to move from point A to point B.

AIRCRAFT OPERATION - An aircraft arrival (landing) or an aircraft departure (takeoff) represents one aircraft operation. A low approach, below traffic pattern or a touch and go operation is counted as both a landing and a takeoff, i.e., two operations. The Federal Aviation Administration (FAA) records aircraft operations in four categories: air carrier, air taxi, general aviation, and military.

AIR CARRIER - Operations performed in revenue service by certificated route air carriers. (See AIR CARRIER, CERTIFICATED ROUTE and AIR CARRIER, COMMUTER).

AIR TAXI/COMMUTER - Operations performed by operators of aircraft holding an air taxi certificate. This category includes commuter airline operations (excluding certificated commuter airlines), mail carriers under contract with the U.S. Postal Service, and operators of nonscheduled air taxi service.

AIRFIELD CAPACITY (HOURLY) - Airfield capacity refers to the maximum number of aircraft operations (landings or takeoffs) that can take place on an airfield in one hour under specific conditions.

AIR NAVIGATION FACILITY (NAVAID) - A facility designed for use as an aid to air navigation, including landing aids, lights, any apparatus or equipment for disseminating weather information; for signaling for radio direction finding or for radio or other electronic communication; and any other structure or mechanism having a similar purpose for guiding and controlling flight in the air or the landing or takeoff of aircraft.

AIRPORT APPROACH AND RUNWAY PROTECTION ZONE LAYOUT PLAN - A plan map showing the imaginary surfaces that specify the maximum height of structures, trees, and other phenomena around an airport and that is prepared in accordance with FAR Part 77, "Objects Affecting Navigable Airspace." The plan is required as part of an airport master plan.

AIRPORT ARRIVAL RATE (AAR) - A dynamic input parameter specifying the number of arriving aircraft which an airport or airspace can accept from the ARTCC per hour. The AAR is used to calculate the desired interval between successive arrival aircraft.

AIRPORT ELEVATION - The highest point of an airport's usable runways measured in feet above mean sea level (msl).

AIRPORT ENVIRONS - The area surrounding an airport that is considered to be directly affected by the presence and operation of the airport.

AIRPORT IMAGINARY SURFACES - Imaginary surfaces established at an airport for the purposes of identifying obstructions to air navigation. The imaginary surfaces consist of primary, approach departure, horizontal, vertical, conical, and transition surfaces.

AIRPORT IMPROVEMENT PROGRAM (AIP) - A program administered by the FAA to provide financial grants in aid for airport planning, airport development projects, and noise compatibility programs. The AIP was established through the Airport and Airway Improvement Act of 1982, which was incorporated as Title V of the Tax Equity and Fiscal Responsibility Act of 1982 (Public Law 97 248). Funds are appropriated by the U.S. Congress for the AIP annually.

AIRPORT LAYOUT PLAN (ALP) - A plan showing boundaries and proposed additions to all areas owned or controlled by the airport sponsor for airport purposes, the location and nature of existing and proposed airport facilities and structures, and the location on the airport of existing and proposed nonaviation areas and improvements thereon. The ALP is a required element of an airport master plan.

AIRPORT MASTER PLAN - An assembly of appropriate documents and drawings addressing the development of a specific airport from physical, economic, social, and political jurisdictional perspectives. The airport master plan includes forecasts of aviation demand, an airport land use plan, airport layout plan, airport approach and runway protection zone plan, terminal area plan, airport access and parking plan, staging plan, capital improvement plan, and financial plan.

AIRPORT NOISE AND CAPACITY ACT OF 1990 - Commonly referred to as the national noise policy; the Act was enacted on November 5, 1990 (Public Law 101 508). Two important provisions of the Act were the establishment of a national aviation noise policy (Sections 9308 and 9309) and the creation of a passenger facility charge (Sections 9110 and 9111), which enables airport sponsors to impose fees on the tickets issued to eligible enplaning passengers. An amendment to FAR Part 91, "Transition to an All Stage 3 Fleet Operating in the 48 Contiguous United States and the District of Columbia," and new FAR Part 161, "Notice and Approval of Airport Noise and Access Restrictions”, implement the national noise policy. New FAR Part 158, "Passenger Facility Charges," implements that portion of the Act authorizing the imposition of such a charge.

AIRPORT NOISE CONTROL AND LAND USE COMPATIBILITY (ANCLUC) STUDY - A study designed to minimize aircraft noise and maintain compatible land use around airports. Certain noise control and land use compatibility studies are eligible for federal funding participation. (See FAR PART 150.)

AIRPORT SPONSOR - A public agency or tax supported organization, such as an airport authority, 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.

AIRPORT SURVEILLANCE RADAR (ASR) - Radar providing aircraft position data in terms of azimuth and range. ASR does not provide altitude data. It is designed for range coverage up to 60 nautical miles and is used by terminal area air traffic control.

AIRPLANE APPROACH CATEGORY (AAC) - One of two design standards related to airport geometry. AAC is part of a system used by the FAA to relate airport design criteria to the operational and physical characteristics of the airplanes operating and expected to operate at an airport. The airplane approach category is based on approach speed requirements, which relates directly to the operational requirements of an airport design.

AIRPLANE DESIGN GROUP (ADG) - One of two design standards related to airport geometry. ADG is part of a system used by the FAA to relate airport design criteria to the operational and physical characteristics of the airplanes operating and expected to operate at an airport. The airplane design group is based on aircraft wingspan and is used to determine the physical requirements of an airport design.


AIRPORT DEPARTURE RATE - A dynamic parameter specifying the number of aircraft that can depart an airport and the airspace can accept per hour.

AIR TRAFFIC CONTROL (ATC) - A service operated by appropriate authority (the FAA) to promote the safe, orderly, and expeditious flow of air traffic.

AIRPORT TRAFFIC CONTROL TOWER (ATCT) - A central operations facility in the terminal area air traffic control system, consisting of a tower cab structure and an associated instrument flight rule (IFR) room if radar equipped, using air/ground communications and/or radar, visual signaling, and other devices, to provide safe and expeditious movement of terminal area air traffic.

AIR ROUTE TRAFFIC CONTROL CENTER (ARTCC) - A facility established to provide airport traffic control service to aircraft operating on an instrument flight rule (IFR) flight plan within controlled airspace and principally during the en route phase of flight.

AIRSPACE - Space in the air above the surface of the earth or a particular portion of such space,
usually defined by the boundaries of an area on the surface projected upward.

AMBIENT NOISE - The total of all noise in a system or situation, independent of the presence of the specific sound to be measured. In acoustical measurements, strictly speaking, ambient noise means electrical noise in the measurement system. However, in popular usage, ambient noise is also used to mean "background noise" or "residual noise."

APRON - A paved area that provides the connection between the terminal buildings and the airfield. The apron includes aircraft parking areas, called ramps, and aircraft circulation and taxiing areas for access to these ramps. On the ramp, aircraft park in locations typically designated as gate positions or gates.


AUTOMATED DEPENDENT SURVEILLENC BROADCAST (ADS-B) - A system by which airplanes constantly broadcast their location, speed, flight plan, type of aircraft and other information. This information is received by other aircraft and air traffic controllers. This system relies upon the Global Positioning System.

AUTOMATED RADAR TERMINAL SYSTEM (ARTS) - Computer aided radar display subsystems capable of associating alphanumeric data with radar returns.


AVIATION SAFETY AND NOISE ABATEMENT ACT OF 1979 - Public Law 96 193 enacted February 18, 1980. The purpose of the Act is to assist airport sponsors in preparing and carrying out noise compatibility programs and in assuring continued safety for aviation. The Act also contains provisions extending to January 1, 1988, the requirement for certain types of aircraft to comply with Part 36 of the Federal Aviation Regulations. (See FEDERAL AVIATION REGULATIONS (FAR) PART 36).

AVIGATION EASEMENT - A type of land acquisition that involves less-than-fee purchase (see also LESS-THAN-FEE ACQUISITION). One form of avigation easement grants the right to perform aircraft operations over the designated property, including operations that might cause noise, vibration, and other effects. A stronger form of easement is a deed restriction that may include (1) the right to perform aircraft operations over the property, and (2) public acquisition of a landowner’s rights restricting future development of the property in any use more intensive than that existing at the time of the transaction. This easement may also include specific prohibitions as to the uses for which the property may be developed. Maximum heights of structures and other objects may also be specified.

BACKBLAST - Noise generated by jet exhaust on takeoff characterized by high acoustic energy, low frequency, and high velocity air behind the aircraft engine.


BOSTON LOGAN AIRPORT NOISE STUDY - Phase 2 of the study is known by this name. Phase 1 of the study is known by BOSTON OVERFLIGHT NOISE STUDY.

BOSTON OVERFLIGHT NOISE STUDY - Phase 1 of the study is known by this name. Phase 2 of the study is known by BOSTON LOGAN AIRPORT NOISE STUDY.

BLANS - Acronym sometimes used in place of Boston Logan Airport Noise Study. See BOSTON LOGAN AIRPORT NOISE STUDY.

BONS - Acronym sometimes used in place of Boston Overflight Noise Study. See BOSTON OVERFLIGHT NOISE STUDY.

BUILDING CODE - A legal document that sets forth requirements to protect the public health, safety, and general welfare as they relate to the construction and occupancy of buildings and structures. The code establishes the minimum acceptable conditions for matters found to be in need of regulation. Topics generally covered are exits, fire protection, structural design, sanitary facilities, lighting, and ventilation. Sound insulation may also be included.

BUILDING PERMIT - A permit issued by a local political jurisdiction (village, town, city, or county) to erect or modify a structure.

BUILDING RESTRICTION LINE (BRL) - The BRL should be located on an Airport Layout Plan to identify suitable locations for building areas on airports. It is recommended that the BRL encompass the runway protection zones, the runway visibility zone, areas required for airport traffic control tower clear lines of sight, and all airport areas with less than 35 foot clearance under the FAR Part 77 surfaces.

CATEGORICAL EXCLUSION (CATEX) - A category of actions that do not individually or cumulatively have a significant effect on the human environment and that have been found to have no such effect in procedures adopted by a federal agency in implementation of federal regulations and for which, therefore, neither an environmental assessment nor an environmental impact statement is required. An agency may decide in its procedures, or otherwise, to prepare environmental assessments for reasons stated under federal regulations even though it is not required to do so. Any procedures under federal regulations shall provide for extraordinary circumstances in which a normally excluded action may have a significant environmental effect.

CEILING - The height above the earth’s surface of the lowest layer of clouds or obscuring phenomena that is reported as “broken,” “overcast,” or “obscuration,” and not classified as “thin” or “partial.”

CEQ (COUNCIL ON ENVIRONMENTAL QUALITY) REGULATIONS CEQ - Regulations implementing the National Environmental Policy Act of 1969 (NEPA) were published in the Federal Register on November 29, 1978. References to the regulations in FAA Order 5050.4A (Airport Environmental Handbook) identify specific sections, e.g., CEQ 1500 or CEQ 1508.8. (See IMPACT.)


COMMUTER AIRCRAFT – Aircraft that may be in regularly scheduled passenger or cargo service, seating 72 passengers or less. A typical commuter aircraft flies trip distances less than 300 miles.


DAYTIME AVERAGE SOUND LEVEL (DL) - The average sound level during daytime hours between 7:00 am and 9:59 pm. Sometimes symbolized Ld. Used to calculate DNL.

DAY NIGHT AVERAGE SOUND LEVEL (DNL) - A measure used to predict, by a single number rating, cumulative aircraft noise that affects communities in airport environs. DNL represents decibels of noise as measured by an A weighted sound level meter (see also). In the DNL procedure, the noise exposure from each aircraft takeoff or landing is calculated at ground level around an airport, and these noise exposure levels are accumulated for a typical 24 hour period. (The 24 hour period often used is the average day of the peak month for aircraft operations during the year being analyzed.) Daytime and nighttime noise exposure is considered separately. A weighting factor equivalent to a penalty of 10 decibels is applied to operations between 10 p.m. and 7 a.m. to account for the increased sensitivity of people to nighttime noise. DNLs can be expressed graphically on maps using either contours or grid cells.


DE MINIMIS - Below the level of significance.

DECIBEL (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.

Sound level measurements in decibels are generally referenced to a standard threshold of hearing at 1000 Hz for the human ear, which can be stated in terms of sound intensity. This value has wide acceptance as a nominal standard threshold and corresponds to 0 dB. The actual average threshold of hearing at 1000 Hz is more like 2.5x10-12 watts per square centimeter or about 4 dB, but 0 dB is a convenient reference. Normal speech from 3 feet away has a sound level of approximately 60 dB. Sound levels above 120 dB may cause physical discomfort, and sounds maintaining a level above 140 dB can cause permanent hearing damage.

Sound levels cannot be arithmetically added or subtracted due to the logarithmic nature of the decibel unit. Some simple rules are useful in understanding sound levels. First, if a sound’s intensity is doubled, the sound level increases by 3 dB regardless of the initial sound level. For example:

60 dB + 60 dB = 63 dB, and

80 dB + 80 dB = 83 dB.

Second, the total sound level produced by two sounds whose levels differ by 10 dB or more is slightly more than the higher of the two. For example:

60.0 dB + 70.0 dB = 70.4 dB.

Adding the noise from a relatively quiet event (60 dB) to a relatively noisy event (70 dB) results in a value of 70.4 dB. The quieter event has only one-tenth the sound energy of the noisier event. As a result, the quieter noise event is “drowned out” by the noisier one. Therefore, the human ear perceives no discernible increase in the overall noise level.

Finally, when different sounds are averaged together, the result is dominated by the highest sound level. The average of 50 dB and 100 dB, assuming equal duration of each, is 97 dB.

Research indicates that a person can detect a change as small as 1 dB under very carefully controlled laboratory conditions. However, the minimum change in an individual event’s sound level that an average human ear can detect under normal conditions is about 3 dB. In general, a person perceives a 10 dB change in sound level as a doubling (or halving) of the sound’s loudness. A 10 dB decrease in sound level actually represents a 90 percent decrease in sound intensity, but only a 50 percent decrease in perceived loudness. Sound energy is linear, but perceived loudness to the human ear is nonlinear.

The following is from Table B.1 from Federal Agency Review of Selected Airport Noise Analysis Issues [page B-6] published by the Federal Interagency Committee on Noise (August 1992) Source of the information is attributed to a publication titled Outdoor Noise and the Metropilitan Environment by M.C. Branch, et al. Los Angeles California: Department of City Planning, City of Los Angeles, 1970

Table B.1 Sound levels (dB) and relative loudness of typical noise sources in indoor and outdoor environments
dB(A)Overall LevelCommunity Noise Levels (Outdoors)Home and Industry Noise LevelsSubjective Loudness (Relative to 70 dB)
120Uncomfortably LoudMilitary jet aircraft take-off from aircraft carrier with afterburner at 50 ft . . . 130 dBOxygen Torch . . . 121 dB32 times as loud
110 Turbo-fan aircraft at takeoff power at 200 ft . . . 118 dBRiveting machine . . . 110 dB

Rock band . . . 108 - 114 dB

16 times as loud
100Very loudBoeing 707 or DC-8 aircraft at one nautical mile (6080 ft) before landing . . . 106 dB

Jet flyover at 1000 feet . . . 103 dB

Bell J-2A helicopter at 100 ft . . . 100 dB

 8 times as loud
90 Boeing 737 or DC-9 aircraft at one nautical mile (6080 ft) before landing . . . 97 dB

Power mower . . . 96 dB

Motorcycle at 25 ft . . . 90 dB

Newspaper press . . . 97 dB4 times as loud
80 Car wash at 20 ft . . . 89 dB

Propeller plane flyover at 1000 ft . . . 88 dB

Diesel truck 40 mph at 50 ft . . . 84 dB

Diesel train 45 mph at 100 ft . . . 83 dB

Food blender . . . 88 dB

Milling machine . . . 85 dB

Garbage disposal . . . 80 dB

2 times as loud
70Moderately loudHigh urban ambient sound . . . 80 dB

Passenger car 65 mph at 25 ft . . . 77 dB

Freeway at 50 ft from pavement edge 10 a.m. . . . 76 dB

Living room music . . . 76 dB

Radio or TV-audio. vacuum cleaner . . . 70 dB

70 dB(A)
60 Air conditioning unit at 100 ft . . . 60 dBCash register at 10 ft . . . 65-70 dB

Electric typewriter at 10 ft . . . 64 dB

Dishwasher (Rinse) at 10 ft . . . 60 dB

Conversation . . . 60 dB

1/2 as loud
50QuietLarge transformers at 100 ft . . . 50 dB 1/4 as loud
40 Bird calls . . . 44 dB

Lowest limit of urban ambient sound . . . 40 dB

10 Just audible  
0 Threshold of Hearing  

DECISION HEIGHT (DH) - The height at which a decision must be made during an instrument approach to either continue the approach or to execute a missed approach.

DEPLANED PASSENGERS - The passengers inbound to an airport on an arriving aircraft. The total annual number of passengers at an airport is the total of deplaned and enplaned passengers (see also).

DEREGULATION ACT - Airline regulatory reform act of 1978. Designed, among other things, to encourage competition among domestic airlines, the Act allows an airline greater freedom to enter and leave any given market.

DEVELOPMENT PLAN - A detailed land use plan for all or specific areas of an airport. The plan usually includes a plot map depicting parcel size and configuration, access, land use categories, utilities, improvements, and performance standards for each parcel and use category.

DEVELOPMENT RIGHTS - Rights of landowners to develop a parcel of land according to the zoning of that parcel. Land is often assessed on a combination of its “resource” value and its “commodity” value. The resource value is the value of the property in its natural state; while the commodity value is an artificial value placed on it by the marketplace (that is, its value for development purposes). In less-than-fee acquisition (see also), the airport sponsor may purchase only the development rights; the ownership of the land remains unchanged.

DISPLACED THRESHOLD - A runway threshold that is located at a point other than the designated beginning of the runway.

DISTANCE MEASURING EQUIPMENT (DME) - Equipment (ground and airborne) used to measure and report to the pilot the slant range distance, in nautical miles, of an aircraft from the DME navigational aid.



DURATION - The length of time that a noise event, such as an aircraft flyover, is experienced (typically reported in seconds) . “Duration” may also refer to the length of time that the noise event exceeds a specified threshold noise level.

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