INTRODUCTION: The sound exposure level produced at a fixed location near the ground by an airplane operation is dependent on a number of factors. Primary factors are: airplane and engine type; power, flap, and airspeed management procedures; distance from the location near the ground to the flight path of the airplane; and the effects of local topography and weather on sound propagation. Airport operations generally include different types of airplanes, various flight procedures, and a range of operational weights. Cumulative average sound levels computed by the procedure described in this AIR are suitable for land-use planning purposes.

In this document, noise from individual airplane operations is described in terms of sound exposure level (SEL, symbolized LAE) while the cumulative noise from a series of airplane operations is described in terms of day-night average sound level (DNL, symbolized Ldn), in conformance with Reference 1. Recommendations for measurement of airplane sound levels, data normalization to reference atmospheric conditions, and extrapolation of the measured data to propagation distances normally occurring in contour constructions are included in this AIR. The method described for extrapolating the SEL may be applicable to other types of noise descriptors.

Airplane performance is estimated from simplified equations which require airplane-dependent coefficients. This provides a practical method of including in the SEL modeling process the effects of changes in flight profile which result from changes in operational procedure or mission weight.

This AIR describes the step-by-step method for calculating SEL at any point near the ground in the vicinity of an airport. The total procedure for calculation of a single-event or cumulative noise contour is best accomplished by a computer. The description of computer programs to perform contour calculations is not a part of this AIR. Noise contours formed by connecting points of equal sound exposure level produced by one airplane during a single take of for approach operation have been generally referred to as single-event contours or "footprints." An example contour is shown schematically on Fig. 1. Contours formed by connecting points of equal cumulative average sound level produced by a series of airplane operations that have occurred over a specified time period, such as 24 hours, are called cumulative noise contours. In this AIR the computation of airplane noise contours is simplified by establishing a single set of airport reference conditions (temperature, humidity, airport altitude, and wind speed) based on yearly average conditions at several major world airports. Ranges of average annual environmental conditions are specified for which the noise levels resulting from the procedures can be considered sufficiently accurate for the purpose of land-use planning.

For a particular airplane, the relevant manufacturer should be consulted for the basic aerodynamic, engine-performance, and acoustical data needed to perform the computations in accordance with the recommendations of this AIR.

Application of the techniques presented herein to uses other than estimating airplane/airport cumulative noise levels was not considered.