# 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 2.7.16: Determination of event levels from NPD-data

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

The principal source of aircraft noise data is the international Aircraft Noise and Performance (ANP) database. This tabulates Lmax and LE as functions of propagation distance d — for specific aircraft types, variants, flight configurations (approach, departure, flap settings), and power settings P. They relate to steady flight at specific reference speeds Vref along a notionally infinite, straight flight path.
How values of the independent variables P and d are specified is described later. In a single look-up, with input values P and d, the output values required are the baseline levels Lmax(P,d) and/or LE∞(P,d) (applicable to an infinite flight path). Unless values happen to be tabulated for P and/or d exactly, it will generally be necessary to estimate the required event noise level(s) by interpolation. A linear interpolation is used between tabulated power-settings, whereas a logarithmic interpolation is used between tabulated distances (see Figure 2.7.i).
Figure 2.7.i
Interpolation in noise-power-distance curves
If Pi and Pi + 1 are engine power values for which noise level versus distance data are tabulated, the noise level L(P) at a given distance for intermediate power P, between Pi and Pi + 1 , is given by:
L P = L P i + L P i + 1 − L P i P i + 1 − P i × P − P i
(2.7.19)
If, at any power setting, di and di + 1 are distances for which noise data are tabulated, the noise level L(d) for an intermediate distance d, between di and di + 1 is given by
L d = L d i + L d i + 1 − L d i lg d i + 1 − lg d i × lg d − lg d i
(2.7.20)
By using equations (2.7.19) and (2.7.20), a noise level L(P,d) can be obtained for any power setting P and any distance d that is within the envelope of the NPD data base.
For distances d that lie outside the NPD envelope, equation (2.7.20) is used to extrapolate from the last two values, i.e. inwards from L(d1) and L(d2) or outwards from L(dI – 1) and L(dI) where I is the total number of NPD points on the curve. Thus
Inwards:
L d = L d 2 + L d 1 − L d 2 lg d 2 − lg d 1 × lg d 2 − lg d
(2.7.21)
Outwards:
L d = L d I − 1 − L d I − 1 − L d I lg d I − lg d I − 1 × lg d − lg d I − 1
(2.7.22)
As, at short distances d, noise levels increase very rapidly with decreasing propagation distance, it is recommended that a lower limit of 30 m be imposed on d, i.e. d = max(d, 30 m).

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Source: https://www.legislation.gov.uk/eudr/2015/996/annex/division/ASSESSMENT/division/2/division/2.7/division/2.7.16 (the official version)
Page: https://openlegislation.uk/eu-directive-2015-996/annex/division-ASSESSMENT/division-2/division-2.7/division-2.7.16
Contains public sector information licensed under the Open Government Licence v3.0. Source: legislation.gov.uk, The National Archives.