# 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: Segmentation of the initial climb segment

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

During the initial climb segment the geometry is changing rapidly particularly with respect to observer locations to the side of the flight track, where beta angle will change rapidly as the aircraft climbs through this initial segment. Comparisons with very small segment calculations show that a single climb segment results in a poor approximation of noise to the side of the flight track for integrated metrics. Calculation accuracy is improved by sub-segmenting the first lift-off segment. The length of each segment and number is strongly influenced by lateral attenuation. Noting the expression of total lateral attenuation for aircraft with fuselage-mounted engines, it can be shown that for a limiting change in lateral attenuation of 1,5 dB per sub-segment, that the initial climb segment shall be sub-segmented based on the following set of height values:
z = {18,9, 41,5, 68,3, 102,1, 147,5, 214,9, 334,9, 609,6, 1 0289,6} metres, or
z = {62, 136, 224, 335, 484, 705, 1 099, 2 000, 4 231} feet
The above heights are implemented by identifying which height in the set above is closest to the original segment endpoint. The actual sub-segment heights would then be calculated using:
z′i = z [zi/zN] (i = 1…N)
(2.7.15)
where z is the original segment end height, zi is the ith member of the set of height values and zN is the closest upper bound to height z. This process results in the lateral attenuation change across each sub-segment remaining constant, producing more accurate contours, but without the expense of using very short segments.
The speed and engine power values on the inserted points are interpolated using respectively equations (2.7.11) and (2.7.13)

---
Source: https://www.legislation.gov.uk/eudr/2015/996/annex/division/ASSESSMENT/division/2/division/2.7/division/2.7.13/division/4 (the official version)
Page: https://openlegislation.uk/eu-directive-2015-996/annex/division-ASSESSMENT/division-2/division-2.7/division-2.7.13/division-4
Contains public sector information licensed under the Open Government Licence v3.0. Source: legislation.gov.uk, The National Archives.