Division Terms
United Kingdom
Aeronautical Information Publication
The positions of slats, flaps and landing gear
An arrival, departure or other aircraft action that affects noise exposure around an aerodrome
Data describing the acoustic and performance characteristics of different aeroplanes types that are required by the modelling process. They include → NPD relationships and information that allows engine thrust/power to be calculated as a function of → flight configuration. The data are usually supplied by the aircraft manufacturer although when that is not possible it is sometimes obtained from other sources. When no data are available, it is usual to represent the aircraft concerned by adapting data for a suitably similar aircraft — this is referred to as substitution
Height above mean sea level
The Aircraft Noise and Performance database included in Appendix I
Basic sound/noise level scale used for measuring environmental noise including that from aircraft and on which most noise contour metrics are based
A representative or nominal ground track which defines the centre of a swathe of tracks
The noise event level read from an NPD database
→ Start of roll
At a given power setting (e.g. EPR or N 1) net thrust falls with air density and thus with increasing aircraft altitude; corrected net thrust is the value at sea level
A decibel measure of the noise received over a specified period of time, at a point near an airport, from aeroplane traffic using normal operating conditions and flight paths. It is calculated by accumulating in some way the event sound/noise levels occurring at that point
Sometimes referred to elsewhere as ‘energy’ or ‘logarithmic’ (as opposed to arithmetic) values. Used when it is appropriate to sum or average the underlying energy-like quantities; e.g.
Ratio of sound energy received from segment to energy received from infinite flight path
Value of the → noise related power parameter used to determine noise emission from the NPD database
A measure of long-term sound. The level of a hypothetical steady sound, which over a specified period of time, contains the same total energy as the actual variable sound
A decibel measure of the finite quantity of sound (or noise) received from a passing aeroplane → sound exposure level
= → Aircraft configuration + → Flight parameters
Aircraft power setting, speed, bank angle and weight
The path of an aeroplane through the air, defined in three dimensions, usually with reference to an origin at the start of take-off roll or at the landing threshold
Part of an aircraft flight path represented for noise modelling purposes by a straight line of finite length
The sequence of operational steps followed by the aircraft crew or flight management system: expressed as changes of flight configuration as a function of distance along the ground track
Variation of aeroplane height along the ground track (sometimes includes changes of → flight configuration too) — described by a set of → profile points
(Or Nominal Ground Plane) Horizontal ground surface through the aerodrome reference point on which the contours are normally calculated
Aircraft speed relative to a fixed point on the ground
Vertical projection of the flight path onto the ground plane
Vertical distance between aircraft and → ground plane
Otherwise termed → single event sound exposure level
International Standard Atmosphere — defined by ICAO. Defines variation of air temperature, pressure, and density with height above mean sea level. Used to normalise the results of aircraft design calculations and analysis of test data
Excess attenuation of sound with distance attributable, directly or indirectly, to the presence of the ground surface. Significant at low angles of elevation (of the aircraft above the ground plane)
The maximum sound level reached during an event
The standard earth surface elevation to which the → ISA is referred
The propulsive force exerted by an engine on the airframe
Noise is defined as unwanted sound. But metrics such as A-weighted sound level (LA ) and effective perceived noise level (EPNL) effectively convert sound levels into noise levels. Despite a consequent lack of rigour, the terms sound and noise are sometimes used interchangeably in this document, as elsewhere — especially in conjunction with the word level
A line of constant value of a cumulative aircraft noise level or index around an airport
The adverse effect(s) of noise on its recipients; importantly it is implied that noise metrics are indicators of noise impact
A measure of long term, or cumulative sound which correlates with (i.e. is considered to be a predictor of) its effects on people. May take some account of factors in addition to the magnitude of sound (especially time of day). An example is day-evening-night level LDEN
A decibel measure of sound on a scale which indicates its loudness or noisiness. For environmental noise from aircraft, two scales are generally used: A-weighted sound level and Perceived Noise Level. These scales apply different weights to sound of different frequencies — to mimic human perception
An expression used to describe any measure of quantity of noise at a receiver position whether it be a single event or an accumulation of noise over extended time. There are two commonly used measures of single event noise: the maximum level reached during the event, or its sound exposure level, a measure of its total sound energy determined by time integration
Noise event levels tabulated as a function of distance below an aeroplane in steady level flight at a reference speed in a reference atmosphere, for each of a number of → engine power settings. The data account for the effects of sound attenuation due to spherical wave spreading (inverse-square law) and atmospheric absorption. The distance is defined perpendicular to the aeroplane flight path and the aircraft wing-axis (i.e. vertically below the aircraft in non-banked flight)
Parameter that describes or indicates the propulsive effort generated by an aircraft engine to which acoustic power emission can logically be related; usually taken to be → corrected net thrust. Loosely termed ‘power’ or ‘power setting’ throughout the text
The contribution from a flight path segment is ‘noise significant’ if it affects the event noise level to an appreciable extent. Disregarding segments that are not noise-significant yields massive savings in computer processing
→ Receiver
Prescription for flying a profile — steps include changes of speed and/or altitude
Height of flight path segment end point — in vertical plane above the ground track
A recipient of noise that arrives from a source; principally at a point on or near the ground surface
A tabulation of sound absorption rates used to standardise NPD data (see Appendix D)
A set of atmospheric conditions on which ANP data are standardised
A nominal time interval used to standardise single event sound exposure level measurements; equal to 1 second in the case of → SEL
Aeroplane groundspeed to which NPD → SEL data are normalised
→ Sound Exposure Level
The sound level an event would have if all its sound energy were compressed uniformly into a standard time interval known as the → reference duration
A ground surface that is acoustically ‘soft’, typically grassy, that surrounds most aerodromes. Acoustically hard, i.e. highly reflective, ground surfaces includes concrete and water. The noise contour methodology described herein applies to soft ground conditions
Energy transmitted through air by (longitudinal) wave motion which is sensed by the ear
The decrease in sound intensity with distance along a propagation path. For aircraft noise its causes include spherical wave spreading, atmospheric absorption and → lateral attenuation
A measure of total sound energy immission over a period of time
(Acronym SEL) A metric standardised in ISO 1996-1 or ISO 3891 = A-weighted single event sound exposure level referenced to 1 second
The strength of sound immission at a point — related to acoustical energy (and indicated by measured sound levels)
A measure of sound energy expressed in decibel units. Received sound is measured with or without ‘frequency weighting’; levels measured with a weighting are often termed → noise levels
Distance to first destination of departing aircraft; taken to be an indicator of aircraft weight
The point on the runway from which a departing aircraft commences its take-off. Also termed ‘brake release’
Actual speed of aircraft relative to air (= groundspeed in still air)
An modified version of Leq in which different weights are assigned to noise occurring during different period of the day (usually day, evening and night)