N-Z


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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.

Slant Range: is the line-of-sight distance between two points which are not at the same level relative to a specific datum.  In Aviation, slant range can be described as the distance of an aircraft at a high altitude relative to a radar antenna.

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.