# Commission Directive (EU) 2015/996 of 19 May 2015 establishing common noise assessment methods according to Directive 2002/49/EC of the European Parliament and of the Council (Text with EEA relevance), Division: Reference conditions for NPD data

Extent: E+W+S+N.I.

(1) Atmospheric pressure 101,325 kPa (1 013,25 mb)
(2) Atmospheric absorption Attenuation rates listed in Table D-1 of Appendix D
(3) Precipitation None
(4) Wind Speed Less than 8 m/s (15 knots)
(5) Groundspeed 160 knots
(6) Local terrain Flat, soft ground free of large structures or other reflecting objects within several kilometres of aircraft ground tracks.
Standardised aircraft sound measurements are made 1,2 m above the ground surface. However no special account of this is necessary as, for modelling purposes, it may be assumed that event levels are relatively insensitive to receiver height.
Comparisons of estimated and measured airport noise levels indicate that the NPD data can be assumed applicable when the near surface average conditions lie within the following envelope:
Air temperature less than 30 °C
Product of air temperature (°C), and relative humidity, (percent) greater than 500
Wind speed less than 8 metres per second (15 knots).
This envelope is believed to encompass conditions encountered at most of the world's major airports. Appendix D provides a method for converting NPD data to average local conditions which fall outside it, but, in extreme cases, it is suggested that the relevant aeroplane manufacturers be consulted.

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Source: https://www.legislation.gov.uk/eudr/2015/996/annex/division/ASSESSMENT/division/2/division/2.7/division/2.7.6/division/6/division/1 (the official version)
Page: https://openlegislation.uk/eu-directive-2015-996/annex/division-ASSESSMENT/division-2/division-2.7/division-2.7.6/division-6/division-1
Contains public sector information licensed under the Open Government Licence v3.0. Source: legislation.gov.uk, The National Archives.