INTRODUCTION ESDU 02020 provides an introduction to the main sources of aircraft noise@ aircraft noise transmission@ modifying effects and to subjective response. And the ESDU Aircraft Noise Series provides a range of methods for predicting the aircraft noise levels. The subjects covered include powerplant noise@ airframe noise@ propagation effects and cabin noise. Regarding powerplant noise@ gas-turbine engines are treated in considerably more detail than piston engines. Propellers are considered separately and helicopter rotors are included in that methodology. Aircraft noise sources and propagation effects are complex insofar as they can depend on many variables. It is often not straightforward to be certain of the applicability of a particular method to the circumstances for which a user may want to perform a prediction. It is the purpose of this Item to assist in this process@ particularly for those new to the subject. It should be made clear from the outset@ for example@ that all currently known methods only apply to an aircraft or an engine operating in steady-state conditions. That is@ the conditions are either stationary or at a constant flight speed along a linear path and there is thus no variation in the sound pressure levels with time. This applies to the noise source strengths@ their radiation patterns and to propagation effects through the atmosphere arising from@ say@ wind and/or temperature gradients. Of course@ for an aircraft in flight@ an observer on the ground will experience varying noise levels. Thus@ transient aircraft manoeuvres can only be predicted assuming a succession of steady-state conditions. Prediction methods generally are not structured so as to be able to deal readily with other than straight@ constant-speed flight paths. None of the prediction methods predict the noise in the region within a few wavelengths of the noise source@ the so-called ??acoustic near-field'@ except insofar as the prediction of the noise levels close to jets may include such effects in the database used. What are referred to as ??near-field' effects in propeller noise@ for example@ are not acoustic near-field effects but geometric effects related to the propeller diameter as described in Section 11.1. This Item provides an overview of the extent to which currently-available prediction methods can meet the particular circumstances for which a user may desire to perform a prediction. All of the methods incorporated into the ESDU Aircraft Noise Series are included in this survey. At the end of each section@ there is a list of references which are not references in the conventional sense but point the reader to other methods@ recent work or sources of information in the public domain which may be of help. These references are not necessarily referred to explicitly in the text. Each reference list is intended to cover the foregoing subject completely@ the same reference being repeated in different sections if required. The Item treats the various mechanisms arising in the context of aircraft noise prediction@ firstly by considering the several possible sources of noise (i) Gas turbine engine noise@ (ii) Piston engine noise@ (iii) Propeller noise and (iv) Airframe noise and then going on to consider the transmission effects along the path from the noise component to the observer@ whether through the atmosphere@ over the ground@ or into the aircraft cabin@ viz. (v) Propagation effects and (vi) Cabin noise. Engine noise from both gas turbine and piston engines is considered to be basically axisymmetric although the intake or nozzle geometry may alter this@ and@ apart from non-axial inflow effects@ propeller noise is also considered to be axisymmetric whereas airframe noise@ from any of its component sources@ is fundamentally non-axisymmetric. The noise of an aircraft is predicted by calculating separately the main source constituents which are applicable. As a consequence@ the noise from many particular aircraft configurations can be predicted by summing@ on a spectral basis@ the individual levels estimated for the particular sources. This summation process may be carried out using ESDU 08018.