{
  "url": "https://openlegislation.uk/eu-directive-2015-996/annex/division-ASSESSMENT/division-2/division-2.7/division-2.7.19/division-8",
  "json_url": "https://openlegislation.uk/eu-directive-2015-996/annex/division-ASSESSMENT/division-2/division-2.7/division-2.7.19/division-8.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/8",
  "kind": "division",
  "number": null,
  "heading": "The start-of-roll directivity function Δ SOR",
  "text": "The noise of jet aircraft — especially those equipped with lower by-pass ratio engines — exhibits a lobed radiation pattern in the rearward arc, which is characteristic of jet exhaust noise. This pattern is the more pronounced the higher the jet velocity and the lower the aircraft speed. This is of special significance for observer locations behind the start of roll, where both conditions are fulfilled. This effect is taken into account by a directivity function Δ SOR .\nThe function Δ SOR has been derived from several noise measurement campaigns using microphones adequately positioned behind and on the side of the SOR of departing jet aircraft.\nFigure 2.7.r shows the relevant geometry. The azimuth angle ψ between the aircraft longitudinal axis and the vector to the observer is defined by\nψ = arccos q d SOR .\n(2.7.47)\nThe relative distance q is negative (see Figure 2.7.j) so that ψ ranges from 0° in the direction of the aircraft forward heading to 180° in the reverse direction.\nFigure 2.7.r\nAircraft-observer geometry at ground for estimation of directivity correction\nThe function Δ SOR represents the variation of the overall noise emanating from the takeoff ground roll measured behind the start of roll, relatively to the overall noise from takeoff ground roll measured on the side of the SOR, at the same distance:\nLTGR(dSOR,ψ) = LTGR(dSOR,90°) + ΔSOR(dSOR,ψ)\n(2.7.48)\nwhere LTGR (dSOR ,90°) is the overall takeoff ground roll noise level generated by all takeoff ground roll segments at the point distance dSOR to the side of the SOR. At distances dSOR less than a normalising distance dSOR,0 , the SOR directivity function is given by\nΔ 0 SOR = 51,47 − 1,553 × ψ + 0,015147 × ψ 2 − 0,000047173 × ψ 3\nif 90° ≤ ψ < 148,4°\n(2.7.49)\nΔ 0 SOR = 339,18 − 2,5802 × ψ − 0,0045545 × ψ 2 + 0,000044193 × ψ 3\nif 148,4° ≤ ψ ≤ 180°\n(2.7.50)\nIf the distance dSOR exceeds the normalising distance dSOR,0 , the directivity correction is multiplied by a correction factor to account for the fact that the directivity becomes less pronounced for greater distances from the aircraft; i.e.\nΔ SOR = Δ 0 SOR\nif dSOR ≤ dSOR,0\n(2.7.51)\nΔ SOR = Δ 0 SOR × d SOR ,0 d SOR\nif dSOR > dSOR,0\n(2.7.52)\nThe normalising distance dSOR,0 equals 762 m (2 500 ft).",
  "extent": "E+W+S+N.I.",
  "status": null,
  "version": "current",
  "annotations": [],
  "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/8",
    "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."
}