MAXIMUM SOUND LEVEL (Lmax) – The maximum a-weighted sound level, in dBA, for a given noise event.
MEAN SEA LEVEL - Altitude in feet compared to the average sea level (referenced with a 0 altitude). Altitudes reported by controllers and pilots use mean sea level as a reference.
MISSED APPROACH - An approach that is not completed with a landing due to lack of visual reference (see MISSED APPROACH POINT), the presence of other aircraft on or too near the runway, instructions from air traffic control to execute a missed approach, or other reasons.
MISSED APPROACH POINT (MAP) - A point during an instrument approach procedure at which, if the visual reference to continue the approach does not exist (i.e., the pilot cannot see the runway or visual guidance to the runway), a missed approach procedure must be executed.
MITIGATION MEASURE - An action that can be planned or taken to alleviate (mitigate) an adverse environmental impact. Mitigation includes:
(1) Avoiding the impact altogether by not taking a certain action or parts of an action.
(2) Minimizing the impact by limiting the degree or magnitude of the action and its implementation.
(3) Rectifying the impact by repairing, rehabilitating, or restoring the affected environment.
(4) Reducing or eliminating the impact over time by preservation and maintenance operations during the life of the action.
(5) Compensating for the impact by replacing or providing substitute resources or environments.
A proposed airport development project or alternatives to that project may constitute a mitigation measure.
NA See NUMBER OF EVENTS ABOVE (NA).
NAVAID See AIR NAVIGATION FACILITY.
NEPA - National Environmental Policy Act of 1969. (Public Law 91 190.)
NIGHTTIME AVERAGE SOUND LEVEL (NL)- The average sound level during nighttime hours between 10:00 pm and 6:59 a.m. Sometimes symbolized Ln.
NOISE - Noise is any sound that is considered to be undesirable because it interferes with speech and hearing, or is intense enough to damage hearing, or is otherwise annoying.
NOISE ABATEMENT PROCEDURES - Changes in runway use, flight approach and departure routes and procedures, and other air traffic procedures that are intended to shift adverse aviation effects away from noise-sensitive areas (such as residential neighborhoods).
NOISE ATTENUATION OF BUILDINGS - The use of building materials to reduce noise through absorption, transmission loss, and reflection of sound energy.
NOISE CONTOURS - Lines drawn on a map that connect points of equivalent noise exposure levels. For aircraft noise analyses conducted using DNL (see DAY-NIGHT AVERAGE SOUND LEVEL), noise contours are usually drawn in 5 DNL intervals, such as connections of DNL 75 exposure, DNL 70 exposure, DNL 65 exposure, and so forth.
NOISE CONTROL PLANS - Documentation by an airport sponsor of actions to be taken to reduce the effect of aviation-related noise. These actions are to be taken by the sponsor either alone or in cooperation with the FAA, airport users, and affected units of local government, and are developed and implemented considering appropriate comments from affected citizens. Alternative actions should be considered; particularly where proprietary use restrictions (see also) on aircraft operations are involved.
NOISE EXPOSURE MAP (NEM) - A map prepared in accordance with FAR Part 150 or other FAA environmental regulation that depicts actual (existing or historical conditions) or anticipated (future conditions) aircraft noise exposure and the affected land uses. NEMs for future conditions may take into account anticipated land use changes around the airport.
NOISE LEVEL REDUCTION (NLR) - The noise reduction between two areas or rooms is the numerical difference, in decibels, of the average sound pressure levels in those areas or rooms. Noise reduction is measured by combining the effect of the transmission loss performance of structures separating the two areas or rooms and the effect of acoustic absorption in the receiving room.
NOISE SENSITIVE LAND USE - A land use that can be adversely affected by high levels of aircraft noise. Residences, schools, hospitals, religious facilities, libraries, and other similar uses are typically considered to be noise-sensitive.
NONDIRECTIONAL RADIO BEACON (NDB) - A low/medium frequency radio beacon transmitting nondirectional signals whereby the pilot of an aircraft equipped with direction-finding equipment can determine the aircraft’s bearing to or from the radio beacon and track to or from the station.
NON-PRECISION INSTRUMENT APPROACH PROCEDURE - A standard instrument approach procedure for which no glide slope guidance is provided. Typical non-precision instrument approach procedures include VOR (see VERY HIGH FREQUENCY OMNIDIRECTIONAL RANGE), GPS (see GLOBAL POSITIONING SYSTEM), NDB (see NONDIRECTONAL RADIO BEACON), and LOC (see LOCALIZER) approach procedures. (See PRECISION INSTRUMENT APPROACH PROCEDURE.)
NORMALLY UNACCEPTABLE DNL - Higher than 65 but not higher than 75 decibels (see UNACCEPTABLE) the noise exposure is significantly more severe; barriers may be necessary between the site and prominent noise sources to make the outdoor environment acceptable; special building construction may be necessary to ensure that people indoors are sufficiently protected from outdoor noise.
NUMBER OF EVENTS ABOVE (NA)- A noise metric that shows the total number of aircraft noise events above a certain threshold during a specific time period.
OBJECT FREE AREA (OFA) See RUNWAY OBJECT FREE AREA.
OBSTACLE FREE ZONE (OFZ) - The OFZ is a three dimensional section of airspace that supports the transition of ground-to-airborne-aircraft operations (and vice versa). The OFZ clearing standard precludes taxiing and parked airplanes and object penetrations, except for frangible NAVAIDS, the location of which is fixed by function. The runway OFZ; when applicable, the inner approach OFZ; and the inner transitional OFZ compose the obstacle free zone.
OBSTRUCTION - An object that exceeds a limiting height or penetrates an imaginary surface described by FAR Part 77.
OVERFLIGHT - An aircraft flight over a particular area.
PATTERN - The configuration or form of a flight path flown by an aircraft, or prescribed to be flown, as in making an approach for landing.
PC See PROJECT CONSULTANT (PC).
PEAK MONTH AVERAGE WEEKDAY (PMAWD) -
PRECISION APPROACH PATH INDICATOR (PAPI) - An airport lighting facility in the terminal area navigation system used under VFR conditions (see also), through a single row of two to four lights, radiating high intensity red or white beams to indicate whether the aircraft is on, above, or below the required runway glide slope. (See VISUAL APPROACH SLOPE INDICATOR.)
PRECISION INSTRUMENT APPROACH PROCEDURE - A standard instrument procedure for a pilot to approach an airport, in which both electronic course guidance and an electronic glide scope are provided. For example, an approach using an ILS is considered a precision instrument approach.
PREFERENTIAL RUNWAY ADVISORY SYSTEM (PRAS) - A preferential runway use program operated by FAA ATC and monitored by Massport to assist in distributing aircraft traffic around the airport. In the 1990's, PRAS became a computer supported system that helps air traffic controllers select preferred runways to minimize community noise.
PREFERENTIAL RUNWAY USE (PROGRAM) - A noise abatement action whereby the FAA Air Traffic Division, in conjunction with the FAA Airports Division, assists the airport sponsor in developing a program that gives preference to the use of a specific runway(s), unless weather or other conditions prevail, to reduce overflights of noise sensitive areas.
PROJECT CONSULTANT (PC) - Project Consultant. For this project, the Project Consultant is Ricondo & Associates, Inc. Ricondo is the consultant to the Federal Aviation Administration (FAA) and Massport. A second team (see Landrum & Brown, Inc.) is responsible for peer review, working with the Community Advisorty Committee (CAC), and acting as a technical resource.
PROPRIETARY USE RESTRICTIONS - Restrictions by an airport sponsor on the number, type, class, manner, or time of aircraft operations at the airport. The ability of an airport sponsor to impose proprietary use restrictions was significantly affected by passage of the Airport Noise and Capacity Act of 1990 (see also).