.01 Definitions.

A. Acoustic Terminology.

(1) "Annual day-night (average) sound level (Ldn)" means for locations in the neighborhood of an airport, the day-night (average) sound level, in decibels, resulting from the effective annual average daily traffic and the utilization of runways and flight paths that affect the noise exposure at the location in question.

(2) "Average sound (noise) level (Leq)" means the constant sound level, in decibels, which, in a given situation and time period, would convey the same sound energy as does the actual time-varying sound during the same period. A-weighting is understood. Unless otherwise qualified, the average is reckoned over a 24-hour day, from midnight to midnight. The mathematical formulation of average sound level is as follows: If LA(t) represents the value of instantaneous A-weighted sound pressure level fluctuating with time, (See Formula Table below) where t1 and t2 are, respectively, the times marking the beginning and end of the observation period over which the average is reckoned.

(3) "Contours of equal noise exposure" means the locus of points on the ground with a given noise exposure.

(4) "Data range" means for a set of 24-hour measurements of Ldn, the difference between the highest value and the lowest value of Ldn in decibels.

(5) "Day-night (average) sound level (Ldn)" means the average sound level, in decibels, reckoned over a 24-hour day with a 10 decibel weighting applied to the noise occurring during the nighttime period; that is, noise levels occurring at night are treated as though they were 10 dB higher than they actually are. The mathematical formulation of day-night sound level is as follows:

See Formula Table below.

(6) "Daytime (average sound level (Ld)" means the average sound level, in decibels, for the 15 hour time period between 0700 and 2200 (7a.m. to 10p.m.). The mathematical formulation for daytime sound level is as follows:

See Formula Table below.

(7) "Decibel (dB)" means a division of the logarithmic scale customarily used to express the ratio of two like quantities proportional to power or energy.

(8) "Decibel scale" means a logarithmic scale used to express the ratio of two like quantities proportional to power or energy. The ratio is expressed on the decibel scale by multiplying its common logarithm by ten.

(9) "Hourly (average) sound level, (Lh)" means the average sound level, in decibels, for a 1-hour period, usually reckoned between integral hours. There would be 24 such values per day. The mathematical formulation of hourly sound level is, for example:

See Formula Table below.

(10) "Level (L)" means the ratio, expressed on the decibel scale, of two like quantities, the second of which is a standard reference quantity.

(11) "Nighttime (average) sound level (Lp)" means the average sound level, in decibels for the 9 hour period from 2200 to 0700 the next morning (10 p.m. to 7 a.m.). The mathematical formulation for nighttime sound level is as follows:

See Formula Table below.

(12) "Sound level (noise level) (LA)" means the quantity in decibels measured by an instrument satisfying the requirements of American National Standard Specifications for Sound Level Meters, S1.4-1971, or its latest revision; that is, the frequency-weighted sound pressure level obtained with the standardized "fast" dynamic characteristic and the "A" frequency weighting of the sound level meter.

(13) "Sound pressure (p)" expressed in micropascals, means a fluctuating pressure superimposed on the static atmospheric pressure in the presence of sound. Unless qualified, the term means root-mean-square sound pressure.

(14) "Sound pressure level (Lp)" means the squared ratio, expressed the decibel scale, of the sound pressure under consideration to the standard reference pressure of 20 micropascals (= 20 micronewtons/square meter or 0.0002 dynes/square centimeter).

B. Airport Terminology. The following terms refer to physical and operational characteristics of airports:

(1) "Airport" means any airport licensed by the Administration.

(2) "Airport operator" means the licensee, or any person who is designated by the licensee as airport operator and who is made responsible to the licensee for the supervision and operation of the airport.

(3) "Effective annual average daily traffic "EAADT" means the standard daily volume of air traffic typifying airport operations, which is determined as follows:

(a) Calculate the average number of airport operations for the 10 busiest days of the year:

See Formula Table below.

N1 through N10 being the number of operations on the 10 busiest days;

(b) Eliminate from further consideration the number of days and the number of operations at the airport which are less than N/2;

(c) The effective annual average daily traffic is the average number of daily operations for all the remaining days of the year.

(4) "Flight operation" means a single take-off, landing or flyby. (A "touch-and-go" counts as two operations.)

(5) "Licensee" means the person, firm, agency, or political subdivision to whom the airport license is issued by the Executive Director.

(6) "Start of takeoff roll" means the position on a runway where an aircraft starts to accelerate in taking off.

(7) "Threshold" means that position on a runway, seen from the approach end, designated as the first point where a landing is permitted. The first point does not necessarily coincide with the start of paving.

(8) "Utilization" means the percentage of the total number of a specific category of operations, on an annual basis, that uses a particular runway or flight track.

C. Other Terminology. Other terms concerning airport noise regulation, but not specifically related to airports or acoustics, are as follows:

(1) "Certified noise abatement plan" means a noise abatement plan accepted by the Executive Director for implementation by an airport operator.

(2) "Daytime" means 0700 to 2200 hours (7 a.m. to 10 p.m.).

(3) "Nighttime" means 2200 to 0700 hours (10 p.m. to 7 a.m.).

(4) "Noise abatement plan" means a detailed program of changes in airport operation which has as its goal the reduction or elimination of impacted land use areas.

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