Test procedures are described for measuring noise at specific receiver locations (passenger and cargo doors, and servicing positions) and for conducting general noise surveys around aircraft. Procedures are also described for measuring noise level and directivity at noise source locations to facilitate the understanding and interpretation of the data.Requirements are identified with respect to instrumentation; acoustic and atmospheric environment; data acquisition, reduction and presentation, and such other information as is needed for reporting the results.This document makes no provision for predicting APU or component noise from basic engine characteristics or design parameters, nor for measuring noise of more than one aircraft operating at the same time.No attempt is made to suggest acceptable levels of noise or suitable subjective criteria for judging acceptability. ICAO Annex 16 Volume I Attachment C provides guidance on recommended maximum noise levels. This document has been updated and expanded to reflect current instrumentation and test practices for measurement and analysis of noise from APUs and associated equipment.