# 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: The finite segment correction ΔF (Exposure levels LE only)

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

The adjusted baseline noise exposure level relates to an aircraft in continuous, straight, steady level flight (albeit with a bank angle ε that is inconsistent with straight flight). Applying the (negative) finite segment correction ΔF = 10 · lg(F), where F is the energy fraction, further adjusts the level to what it would be if the aircraft traversed the finite segment only (or were completely silent for the remainder of the infinite flight path).
The energy fraction term accounts for the pronounced longitudinal directivity of aircraft noise and the angle subtended by the segment at the observer position. Although the processes that cause the directionality are very complex, studies have shown that the resulting contours are quite insensitive to the precise directional characteristics assumed. The expression for Δ F below is based on a fourth-power 90-degree dipole model of sound radiation. It is assumed to be unaffected by lateral directivity and attenuation. How this correction is derived is described in detail in Appendix E.
The energy fraction F is a function of the ‘view’ triangle OS1S2 defined in Figures 2.7.j to 2.7.l such that:
Δ F = 10 × lg 1 π α 2 1 + α 2 2 + arctan α 2 − α 1 1 + α 2 1 − arctan α 1
(2.7.45)
with
α 1 = − q d λ ;
α 2 = − q − λ d λ ;
d λ = d 0 × 10 L E∞ P,d p − L max P,d p ∕ 10 ;
d 0 = 2 π × V ref × t 0 .
where dλ is known as the ‘scaled distance’ (see Appendix E). Note that Lmax(P, dp) is the maximum level, from NPD data, for perpendicular distance dp , NOT the segment Lmax .
It is advised to apply a lower limit of – 150 dB to Δ F .
In the particular case of observer locations behind every takeoff ground-roll segment and every landing ground-roll segment, a reduced form of the noise fraction expressed in equation (2.7.45) is used, which corresponds to the specific case of q = 0. This is computed using
Δ F′ = 10 log 10 1 ∕ π α 2 ∕ 1 + α 2 2 + tan − 1 α 2 10 ΔSOR ∕ 10
(2.7.46)
where α2 = λ/dλ and ΔSOR is the start-of-roll directivity function defined by equations (2.7.51) and (2.7.52).
The rationale for using this particular form of noise fraction is further explained in the section below, as part of the start-of-roll directivity application method.

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Source: https://www.legislation.gov.uk/eudr/2015/996/annex/division/ASSESSMENT/division/2/division/2.7/division/2.7.19/division/6 (the official version)
Page: https://openlegislation.uk/eu-directive-2015-996/annex/division-ASSESSMENT/division-2/division-2.7/division-2.7.19/division-6
Contains public sector information licensed under the Open Government Licence v3.0. Source: legislation.gov.uk, The National Archives.