# 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 2.7.25: The weighted number of operations

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

The cumulative noise level is estimated by summing the contributions from all different types or categories of aircraft using the different flight routes which comprise the airport scenario.
To describe this summation process the following subscripts are introduced:
i index for aircraft type or category
j index for flight track or subtrack (if subtracks are defined)
k index for flight track segment
Many noise indices — especially equivalent sound levels — include time-of-day weighting factors gi in their definition (equations (2.7.56) and (2.7.57)).
The summation process can be simplified by introducing a ‘weighted number of operations’
Mij = (gday · Nij,day + gevening · Nij,evening + gnight · Nij,night )
(2.7.58)
The values Nij represent the numbers of operations of aircraft type/category i on track (or subtrack) j during the day, evening and night period respectively.
From equation (2.7.57) the (generic) cumulative equivalent sound level Leq at the observation point (x,y) is
L eq,W x,y = 10 × lg t 0 T 0 × ∑ i ∑ j ∑ k M ij × 10 L E,ijk x,y ∕ 10 + C
(2.7.59)
T 0 is the reference time period. It depends on — as well as the weighting factors gi — the specific definition of the weighted index used (e.g. LDEN ). LE,ijk is the single event noise level contribution from segment k of track or subtrack j for an operation of aircraft of category i. The estimation of LE,ijk is described in detail in Sections 2.7.14 to 2.7.19.

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Source: https://www.legislation.gov.uk/eudr/2015/996/annex/division/ASSESSMENT/division/2/division/2.7/division/2.7.25 (the official version)
Page: https://openlegislation.uk/eu-directive-2015-996/annex/division-ASSESSMENT/division-2/division-2.7/division-2.7.25
Contains public sector information licensed under the Open Government Licence v3.0. Source: legislation.gov.uk, The National Archives.