OpenLegislation

Division Segment event level Lseg

United Kingdom

Original text. Later amendments are not shown.

The segment values are determined by applying adjustments to the baseline (infinite path) values read from the NPD data. The maximum noise level from one flight path segment Lmax,seg can be expressed in general as

(2.7.25)

and the contribution from one flight path segment to LE as

(2.7.26)

The ‘correction terms’ in equations (2.7.25) and (2.7.26) — which are described in detail in Section 2.7.19 — account for the following effects:

Δ V

  • Duration correction: the NPD data relate to a reference flight speed. This adjusts exposure levels to non-reference speeds. (It is not applied to Lmax,seg .)

    • Δ I (φ)

  • Installation effect: describes a variation in lateral directivity due to shielding, refraction and reflection caused by the airframe, engines and surrounding flow fields.

    • Λ(β,ℓ)

  • Lateral attenuation: significant for sound propagating at low angles to the ground, this accounts for the interaction between direct and reflected sound waves (ground effect) and for the effects of atmospheric non-uniformities (primarily caused by the ground) that refract sound waves as they travel towards the observer to the side of the flight path.

    • Δ F

  • Finite segment correction (noise fraction): accounts for the finite length of the segment which obviously contributes less noise exposure than an infinite one. It is only applied to exposure metrics.

    • If the segment is part of the take-off or landing ground roll and the observer is located behind the segment under consideration, special steps are taken to represent the pronounced directionality of jet engine noise that is observed behind an aircraft about to takeoff. These special steps result in particular in the use of a particular form of the noise for the exposure level:

    (2.7.27)
    (2.7.28)
    Δ′ F

  • Particular form of the Segment correction

    • Δ SOR

  • Directivity correction: accounts for the pronounced directionality of jet engine noise behind the ground roll segment

    • The specific treatment of ground roll segments is described in Section 2.7.19.

    Sections below describe the calculation of segment noise levels.