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phonometry

Aircraft noise

Aircraft noise is computed under internationally negotiated methods of two kinds. Certification fixes a single number per aircraft type to the last decimal, at reference points a standard places around the runway. Contour methods take that certified fleet and predict what an airport does to the ground around it. The four pages of this section cover both, and they share a common anatomy: a rigorously standardised source descriptor — a spectral time history, a noise-power-distance table or a noise hemisphere — plus standardised propagation adjustments that place the source at a receiver.

Aircraft noise: Effective Perceived Noise Level covers fixed-wing certification. The EPNL of ICAO Annex 16 condenses a one-third-octave time history of a flyover into a single EPNdB value through perceived noisiness, a tone correction and a duration correction; the page adds the IEC 61265 measurement-system verifier and the SAE ARP 5534 atmospheric absorption used in the certification chain. Airport Noise (ECAC Doc 29) picks the aeroplane up from there: the noise-power-distance tables, the per-segment corrections of a flight path (impedance, lateral attenuation, engine installation, duration, noise fraction and start-of-roll directivity) and the single-event contour over a ground grid.

Rotorcraft noise: the hemisphere method covers helicopters, whose strong directivity defeats a single-number source level. ECAC Doc 32 instead describes the source as a noise hemisphere (band levels on a grid of emission angles at a 60 m reference distance), propagates each ray with spherical spreading, atmospheric absorption and the Chien-Soroka ground effect, interpolates between the measured flight conditions along the track, and integrates the received history into the single-event SEL, LASmax and EPNL and their ground-grid contours.

The ANP fleet database closes the loop on the two above: the noise-power-distance tables and default trajectories EASA and EUROCONTROL publish for real aircraft types, ready to feed the Doc 29 chain without writing a table by hand.

The shared physics connects outward: atmospheric absorption comes from the same ISO 9613-1 model as Outdoor Sound Propagation, and the same type-testing logic governs Wind-turbine noise, which is filed with the other environmental sources: its IEC 61400-11 apparent sound power level and tonal-audibility chain answer the same question for a source that is not an aircraft. That tonality test is in turn a cousin of the methods in Psychoacoustics.

Start from the question. To check an aeroplane against a certification limit, or to understand where the published numbers for a type come from, start with the EPNL page. To predict what a movement does at a street address, use the Doc 29 page, with the ANP page supplying the aircraft data. For helicopters the hemisphere page replaces both. Read the fixed-wing pages in that order: the EPNL page defines the certified metric, the Doc 29 page turns certified aeroplanes into ground contours from tables written by hand, and the ANP page replaces those hand-written tables with the published fleet data. The rotorcraft page stands on its own — a different standard and a different source model — and can be read first if helicopters are what you came for.

The three metrics are not interchangeable. EPNL is a certification metric of one aeroplane at one prescribed point; SEL and LASmax are single-event assessment metrics at an arbitrary receiver; neither is the long-term index a land-use study is finally judged on.

Pages in this section

Section titled “Pages in this section”

What this section does not cover

Section titled “What this section does not cover”

  • Single events only. The Doc 29 chain builds single-event contours; it does not assemble the cumulative multi-event indices — an Lden-style sum over a full flight schedule — that a complete noise-contour study needs on top of them. That last step is where a land-use decision is actually made, and it is not here.

  • No aircraft is modelled from first principles. NPD tables and noise hemispheres are inputs: the library interpolates the tables published for a type and does not synthesise them from engine data, and the ANP database is read and never written (version 2.3 ships as-is). Of the ANP entries, only those with fixed-point profiles have a ready-to-use trajectory, because turning a procedural-step departure into a flight path needs the ICAO Doc 9911 flight-mechanics performance model, which is not implemented.

  • Three specific gaps. Rotorcraft hover, idle and taxi run on the Table 3 derived sources, but the guidance’s last resort for a type with no hover data at all (two side-line level-flight microphones corrected to the 150 m hover circle by the Annex 16 integrated method) is not modelled. The measurement-system verifier checks IEC 61265:1995 and not the superseding 2018 edition. And sonic boom is not touched anywhere in the library.

  • Finally, the CNOSSOS-EU aircraft source of sections 2.6 and 2.7 is not implemented: aircraft noise here is the ICAO and ECAC family, which is a different set of models from the road and rail sources of Environmental sources, and the two must not be mixed inside one strategic map without saying so.

Before and after these pages

Section titled “Before and after these pages”

Every level on these pages is built from band levels, so the filtering, weighting and calibration that produce them are in Signal analysis, and Build a sound level meter runs that chain end to end on one runnable page. The derivations for aircraft noise are not in the theory reference: they stay inside the guides above, beside the flight geometry that motivates them.

If you arrived here from a search and want the shape of the whole library, What do you need to measure? indexes it by the job and All guides lists every page with a line on each.

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