Gives a method for testing ducted fans. Applies to fans which emit steady, broadband, narrow-band and discrete-frequency sound. Applies to air temperatures between -50 °C and +70 °C. The test duct diameter range is from 0,15 m to 2 m. The maximum flow velocity is 30 m/s and the maximum swirl angle is 15°. An example of a method for determining the angle of swirl is given in annex F. The one-third octave band centre frequency range is from 50 Hz to 10 000 Hz.