{
  "url": "https://openlegislation.uk/eu-directive-2015-996/annex/division-ASSESSMENT/division-2/division-2.7/division-2.7.19/division-1",
  "json_url": "https://openlegislation.uk/eu-directive-2015-996/annex/division-ASSESSMENT/division-2/division-2.7/division-2.7.19/division-1.json",
  "legislation": "eudr/2015/996",
  "legislation_title": "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)",
  "legislation_url": "https://openlegislation.uk/eu-directive-2015-996",
  "path": "annex/division/ASSESSMENT/division/2/division/2.7/division/2.7.19/division/1",
  "kind": "division",
  "number": null,
  "heading": "The duration correction DV (Exposure levels LE only)",
  "text": "This correction accounts for a change in exposure levels if the actual segment groundspeed is different to the aircraft reference speed Vref to which the basic NPD-data relate. Like engine power, speed varies along the segment (groundspeed varies from V1 to V2) and it is necessary to define an equivalent segment speed Vseg remembering that the segment is inclined to the ground; i.e.\nVseg = V/cosγ\n(2.7.32)\nwhere here V is an equivalent segment groundspeed (for information, see equation B-22 which expresses V in terms of calibrated airspeed, Vc and\nγ = tan − 1 z 2 − z 1 s 2 − s 1\n(2.7.33)\nFor airborne segments, V is taken to be the groundspeed at the closest point of approach S — interpolated between the segment end-point values assuming it varies linearly with time; i.e. if the observer is alongside the segment:\nV = V 2 1 + q λ × V 2 2 − V 2 1\n(2.7.34)\nIf the observer is behind or ahead of the segment, it is that at the nearest end point, V1 or V2 .\nFor runway segments (parts of the take-off or landing ground rolls for which γ = 0) Vseg is taken to be simply the average of the segment start and end speeds; i.e.\nVseg = (V1 + V2 )/2\n(2.7.35)\nIn either case the additive duration correction is then\nΔV = 10 · lg(Vref/Vseg )\n(2.7.36)",
  "extent": "E+W+S+N.I.",
  "status": null,
  "version": "current",
  "annotations": [
    {
      "type": "footnote",
      "label": "f1",
      "text": "This is known as the duration correction because it makes allowance for the effects of aircraft speed on the duration of the sound event — implementing the simple assumption that, other things being equal, duration, and thus received event sound energy, is inversely proportional to source velocity."
    }
  ],
  "outstanding_effects": [],
  "provenance": {
    "source": "legislation.gov.uk",
    "source_url": "https://www.legislation.gov.uk/eudr/2015/996/annex/division/ASSESSMENT/division/2/division/2.7/division/2.7.19/division/1",
    "retrieved_at": "2026-11-01T15:21:38.862218+00:00"
  },
  "licence": "Open Government Licence v3.0",
  "licence_url": "https://www.nationalarchives.gov.uk/doc/open-government-licence/version/3/",
  "attribution": "Contains public sector information licensed under the Open Government Licence v3.0. Source: legislation.gov.uk, The National Archives."
}