Noise
Glossary
Abatement:
The method of reducing the degree of intensity of noise and the use
of such a method.
Air Carriers:
Airlines holding a certificate of public convenience and necessity
that operate aircraft designed to have a maximum seating capacity of
more than 60 seats or a maximum payload capacity of more than 18,000
pounds or conduct international operations.
Air
Taxi: Non-scheduled passenger aircraft with 50 or fewer
seats.
ANOMS: The Airport
Noise and Operations Monitoring System (ANOMS) is a sophisticated,
acoustical system which monitors aircraft flight tracks, fleet mix,
and noise levels by time of day, season and on an annual basis.
Commercial Aviation: The sum total of air carrier and air taxi flights.
Community Noise Equivalent (CNEL): A method fo rpredicting, by a single number rating, cumulative aircraft noise that affects communities in airport environs. The CNEL value represents noise as measured by an A-weighted sound level (see also) meter. The metric includes a 4.8-dcibel penalty for aircraft operations during evening hours (7 p.m to 10 p.m.) and a 10-decibel penalty for aircraft operations during nighttime hours (10 p.m. to 7 a.m.). This is equivalent to multiplying the number of operations occurring during the evening hours by 3 and multiplying th enumber of operations occuring during the nighttime hours by 10. The A-weighted decibel scale was developed to closely represent the response of the human ear to sound. CNEL is only used in the State of California and is similar to Ldn, which does not include the evening penalty.
Commuter Aircraft: Scheduled passenger aircraft with fewer than 50 seats.
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.
dBA:
The A-weighted Decibel (dBA) is the most common unit used for
measuring environmental sound levels. It adjusts, or weights, the
frequency components of sound to conform with the normal response of
the human ear at conversational levels. dBA is an international
metric that is used for assessing environmental noise exposure of all
noise sources.
DNL:
The Day-night Average Sound Level (DNL) is the level of noise
expressed (in decibels) as a 24-hour average. Nighttime noise,
between the hours of 10:00 p.m. and 7:00 a.m. is weighted; that is,
given an additional 10 decibels to compensate for sleep interference
and other disruptions caused by nighttime noise. An annual average of
DNLs is used by the Federal Aviation Administration to describe
airport noise exposure. Areas with noise impacts less than 65 dB DNL
are considered "compatible" with residential use; areas at
or above 65 dB DNL are designated "incompatible" with
residential use.
DNL is used by all Federal agencies (EPA,
HUD, DOE, DOD, etc.) and internationally in the assessment of
potential noise impacts. It is used interchangeably with DNL.
EPNdB: The
Effective Perceived Noise Level (EPNdB) is another unit of measure
for aircraft noise. It is based on how people judge the annoyance of
sounds they hear with corrections for the duration of the event and
for pure tones. The Federal Aviation Administration (FAA) uses EPNdB
in the certification of large transport planes for Federal Noise
Regulations (FAR Part 36).
General
Aviation: Non-commercial airline aviation - primarily
business aircraft and individuals traveling in private aircraft,
including those making connections to commercial flights.
Hertz
(Hz): The Hertz is a unit of measurement of frequency,
numerically equal to cycles per second of the measure of the rate of
the vibration of the sound. High frequencies can be thought of as
having a high pitch; like a whistle; low frequency sounds are more
like a rumble of a truck or airplane.
Huskkitted
Aircraft: Hushkitted Stage III aircraft are previously
Stage II aircraft that have been adapted to meet Stage III
requirements.
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.
Intensity:
The sound energy flow through a unit area in a unit time.
ILS:
An Instrument Landing System (ILS) is a precise landing aid
consisting of several components giving the pilot vertical and
horizontal electronic guidance. Elements usually include: 1. an outer
marker, a radio beam 4 to 6 miles from the touchdown point where the
electronic signal begins; 2. an approach lighting system at the
runway end; 3. a localizer radio beam which provides the horizontal
guide; and 4. a glide slope which provides vertical guidance on the
angle of descent for landing.
INM:
The Federal Aviation Administration's (FAA), Office of Environment
and Energy (AEE-100) has developed the Integrated Noise Model (INM)
for evaluating aircraft noise impacts in the vicinity of airports.
The INM has been the FAA's standard tool since 1978 for determining
the predicted noise impact in the vicinity of airports. The FAA
requires airports use the INM in assessing environmental impacts for
soundproofing, evaluating physical improvements to the airfield,
analyzing changes to existing or new procedures and in assessing land
use compatibility.
The INM Model utilizes flight track
information, aircraft fleet mix, standard and user defined aircraft
profiles and terrain as inputs. The INM model produces noise exposure
contours that are used for land use compatibility maps. The INM
program includes built in tools for comparing contours and utilities
that facilitate easy export to commercial Geographic Information
Systems. The model also calculates predicted noise at specific sites
such as hospitals, schools or other sensitive locations.
Lmax:
The Maximum Instantaneous Noise Level (Lmax) is the maximum level of
noise measured during a given measurement period.
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 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
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.
Peak
Level (in DB): The Peak Level is the highest level of
sound pressure measured during a noise event.
Preferential
Runway Use: Taking off or landing on specified runways
during certain hours to avoid residential areas.
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.
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.
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.
