ALP, or Airport Layout Plan is the official, FAA approved map of airport facilities.

APU, or Auxiliary Power Unit is a small engine supplying power to aircraft when the main engines are not running.

ATC, or Air Traffic Control - Federal Aviation Administration air traffic controllers are responsible for giving directions to pilots both departing and landing at airports.

Avionics - Navigation, communication and data display equipment.

Altitude MSL - Mean Sea Level - Aircraft altitude is measured in feet above mean sea level.

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

Decibel (dB) - The unit of sound pressure used to measure noise. Decibel means 1/10 of a Bell, after Alexander Graham Bell (thus the capital B). Because decibels are such a small measure, they are computed logarithmically and cannot be added arithmetically. An increase of 10 dB is perceived by human ears as a doubling of noise.

dBA - A-weighted decibels adjust the sound pressure to conform with the frequency responses of the human ear. Airport noise is almost always measured in dBA.

dBC - C-weighted decibels adjust the sound pressure towards the low frequency end of the spectrum. Although less consistent with human hearing than A-weighting, dBC can be used to consider the impacts of certain low frequency operations such as reverse thrust and take-off roll noise.

Displaced Threshold - A threshold is the designated point on the runway, usually near the beginning, where an aircraft touches down. Displacing a threshold moves this touchdown point further along the runway, thus keeping the aircraft higher over residential areas under the approach path.

DME - Distance Measuring Equipment - Navigational equipment on the ground and on the aircraft, which measures the distance between the aircraft and the ground station. It is often used to define the point where an aircraft turns.

DNL - Day/night noise level, previously known as Ldn. This is a 24-hour average hourly noise level with a 10 decibel (dB) penalty for nighttime noise events between 10 PM and 7 AM.

DNL Contour - The "map" of noise exposure around an airport. It is computed through an FAA model called the Integrated Noise Model (INM), which calculates the annual noise exposure from an input consisting of the actual fleet operated at the airport, the runway use, number of operations, and time of day. FAA defines significant noise exposure as any area within the 65dB DNL contour; that is the area within an annual average noise exposure of 65 decibels or higher.

Duration - The length of time in seconds that a noise event lasts. Duration is usually measured in time above a specific noise threshold.

FAA - The Federal Aviation Administration - agency responsible for aircraft safety, movement and controls.

FMS - Flight Management System - Refers to a computer installed aboard newer aircraft to aid in navigation. Installation is not mandatory but at the airlines' discretion.

GA - General Aviation - Non-commercial airline aviation. Primarily business aircraft and individuals traveling in private aircraft.

GIS - Geographic Information Systems are computerized maps allowing several layers of information to be used simultaneously.

Glide Slope - See ILS

GPS - Global Positioning System uses satellites to precisely define the position of aircraft in flight.

GPU - Ground Power Unit - source of power, generally from the terminals, for aircraft to use while their engines are off.

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.

ILS - Instrument Landing System - A precise landing aid consisting of several components giving the pilot vertical and horizontal electronic guidance. Elements usually include:

An outer marker, a radio beam 4 to 6 miles from the touchdown point where the electronic signal begins;
An approach lighting system at the runway end;
A localizer radio beam which provides the horizontal guide;
A glide slope which provides vertical guidance on the angle of descent for landing.

Lmax - The peak noise level reached by a single aircraft event.

Localizer - See ILS

Missed Approach - Sometimes called a "go around", this is a maneuver where a pilot cannot execute a landing due to weather or inadequate separation of aircraft. The pilot then climbs the aircraft and circles on a pre-determined path before approaching the runway again.

Outer Marker - See ILS

Preferential Runways - The most desirable runways from a noise abatement perspective to be assigned whenever weather and traffic volumes allow.

Radar Vector - A radar heading (compass direction) issued by air traffic control to a pilot on for navigation on departure.

Reverse Thrust - When landing, pilots reverse the direction of jet engine airflow towards the front of the aircraft slowing it down. Reverse thrust is the major method of reducing airspeed when landing.

Run-ups - After routine maintenance, aircraft engines must be tested or run-up, usually at partial power, to ensure that they operate properly during flight.

Run-up Locations - Specified areas on the airfield where scheduled run-ups may occur. These locations are sited, so as to produce minimum noise impact in surrounding neighborhoods.

SID - Standard Instrument Departure - A pre-determined departure route for a specific airport. An airport is likely to have a SID for each runway. SIDs are published for pilots' reference, but also assigned verbally by Air Traffic Control.

SENEL - Single Event Noise Exposure Level is the total noise emitted by one flight. Each single event will have a total noise level over the duration of the event and a peak, which is the highest noise level reached by that event.

It is important to distinguish single event noise levels from cumulative noise levels such as CNEL. Single event noise level numbers are often higher than CNEL numbers, because CNEL represents an average noise level over a period of time, generally a whole year.

SOIA - Simultaneous Offset Instrument Approach is a navigational system permitting simultaneous landings at airports with staggered parallel runways.

Time Above - An expression of the amount of time noise exceeds a threshold level. The threshold can be set at any point, for instance, 65 or 75 dBA. Generally time above is expressed in minutes per day that the threshold is exceeded.

VFR - Visual Flight Rules allow pilots to land by sight without relying solely on instruments. VFR conditions require good weather and visibility.

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