As used in this part, unless the context requires otherwise, the following terms have the following meanings.

Airport means any public use airport, including heliports, as defined by the ASNA Act, including: (a) Any airport which is used or to be used for public purposes, under the control of a public agency, the landing area of which is publicly owned; (b) any privately owned reliever airport; and (c) any privately owned airport which is determined by the Secretary to enplane annually 2,500 or more passengers and receive scheduled passenger service of aircraft, which is used or to be used for public purposes.

Airport noise compatibility program and program mean that program, and all revisions thereto, reflected in documents (and revised documents) developed in accordance with appendix B of this part, including the measures proposed or taken by the airport operator to reduce existing noncompatible land uses and to prevent the introduction of additional noncompatible land uses within the area.

Airport Operator means, the operator of an airport as defined in the ASNA Act.

ASNA Act means 49 U.S.C. 47501 et seq.

Average sound level means the level, in decibels, of the mean-square, A-weighted sound pressure during a specified period, with reference to the square of the standard reference sound pressure of 20 micropascals.

Compatible land use means the use of land that is identified under this part as normally compatible with the outdoor noise environment (or an adequately attenuated noise level reduction for any indoor activities involved) at the location because the yearly day-night average sound level is at or below that identified for that or similar use under appendix A (Table 1) of this part.

Day-night average sound level (DNL) means the 24-hour average sound level, in decibels, for the period from midnight to midnight, obtained after the addition of ten decibels to sound levels for the periods between midnight and 7 a.m., and between 10 p.m., and midnight, local time. The symbol for DNL is Ldn.

Noise exposure map means a scaled, geographic depiction of an airport, its noise contours, and surrounding area developed in accordance with section A150.1 of Appendix A of this part, including the accompanying documentation setting forth the required descriptions of forecast aircraft operations at that airport during the fifth calendar year (or later) beginning after submission of the map, together with the ways, if any, those operations will affect the map (including noise contours and the forecast land uses).

Noise level reduction (NLR) means the amount of noise level reduction in decibels achieved through incorporation of noise attenuation (between outdoor and indoor levels) in the design and construction of a structure.

Noncompatible land use means the use of land that is identified under this part as normally not compatible with the outdoor noise environment (or an adequately attenuated noise reduction level for the indoor activities involved at the location) because the yearly day-night average sound level is above that identified for that or similar use under appendix A (Table 1) of this part.

Regional Airports Division Manager means the Airports Division Manager having responsibility for the geographic area in which the airport in question is located.

Restriction affecting flight procedures means any requirement, limitation, or other action affecting the operation of aircraft, in the air or on the ground.

Sound exposure level means the level, in decibels, of the time integral of squared A-weighted sound pressure during a specified period or event, with reference to the square of the standard reference sound pressure of 20 micropascals and a duration of one second.

Yearly day-night average sound level (YDNL) means the 365-day average, in decibels, day-night average sound level. The symbol for YDNL is also Ldn.

[Doc. No. 18691, 49 FR 49269, Dec. 18, 1984, as amended by Amdt. 150-1, 53 FR 8724, Mar. 16, 1988; 53 FR 9726, Mar. 24, 1988; Amdt. 150-2, 54 FR 39295, Sept. 25, 1989; Amdt. 150-4, 69 FR 57625, Sept. 24, 2004]