ECAC.CEAC Doc 29 3rd Edition Report on Standard Method of Computing Noise Contours around Civil Airports Volume 2: Technical Guide This second volume, a Technical Guide, is written for modellers themselves, those who develop and maintain the computer models and their databases. It fully describes a specific noise contour modelling system which is considered by ECAC to represent current best practice. It does not prescribe a computer programme but rather the equations and logic that need to be programmed to construct a physical ‘working model’. Any physical model that complies fully with the methodology described can be expected to generate contours of aircraft noise exposure around civil airports with reasonable accuracy. The methodology applies only to long-term average noise exposure; it cannot be relied upon to predict with any accuracy the absolute level of noise from a single aircraft movement and should not be used for that purpose.