Up to 2015, Annex II of the END (Assessment methods for the noise indicators), recommended that the Member States which don't have national computation methods use ECAC Doc 29 "Report on Standard Method of Computing Noise Contours Around Civil Airports" (1997, 2nd edition) as the method to calculate the noise contours around their airports. Following this, most EU Member States have implemented 2nd or 3rd edition of ECAC Doc 29 to their national regulations. Thus, the three first rounds of Strategic Noise Maps were prepared mostly using ECAC Doc 29.
However, this guidance is not applicable where the noise exposure derives mainly from propeller-driven light aircraft or helicopters. Most countries do not have another regulation for light aircraft or helicopters. Consequently, most European countries did not include these kinds of operations in their noise contours for major airports, therefore, the contribution to noise exposure from those kinds of aircraft was not considered in the first three rounds.
Furthermore, the aircraft noise calculations in the ECAC Doc 29 only consider aircraft movements' noise. All ground noise sources such as taxiing aircraft, auxiliary power units and undergoing engine testing are excluded from the guidance. Consequently, most EU countries do not include these kinds of operations in their noise contours for major airports, which again excludes some noise sources from the contours that summarise overall noise exposure at airports.
The new European Commission's Directive 2015/996 established common noise assessment methods according to the END and has solved some of these omissions. The new Directive has revised Annex II of the END with an updated and common methodology. Noise from helicopters, taxiing, engine testing and use of auxiliary power units must be included in the new methodology of calculation, which has to be applied in the preparation of fourth round Strategic Noise Maps. Accordingly, in some cases, there will be an increase in the number of people exposed to noise as a result of these changes to Annex II. Some other airport-specific changes are expected because of changes to the way in which the number of people exposed is calculated, but in those cases, the noise contours will change homogeneously.