INTRODUCTION This Item allows the user to estimate the noise generated by axial-flow fans or compressors in turbojet and turbofan engines with and without inlet guide vanes. Throughout the rest of this Item@ the term ??fan' will be used to describe both configurations. Sound pressure levels in one-third octave bands in the frequency range of 50 Hz to 10 000 Hz are calculated for lossless free-field ambient conditions with no temperature gradient or wind. These results can be corrected for the effects of a real atmosphere and for ground reflection using other ESDU Data Items (References 6@ 7 and 8). The main input parameters that need to be specified are the mass flow rate@ the total temperature rise associated with a fan stage@ both the design point and the operating point values of the rotor tip relative inlet Mach number and certain data about the fan geometry. The total temperature rise@ if not readily available@ may be estimated using Reference 5. The method allows the user to estimate fan noise radiated (i) from both intake and discharge ducts@ (ii) from only the intake duct or (iii) from only the discharge duct. For the first case@ the distance@ @ from @ is required as input and is determined as shown in Sketch 1.1. For the second case@ is measured from the reception point to point A in Sketch 1.1. Similarly@ for the third case is measured from the reception point to point B.