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This document describes a practical system for a user to determine observer-to-aircraft distances. These observer-to-aircraft distances can be either closest point of approach (CPA) distances during field measurements or overhead distances during acoustic certification tests. The system uses a digital camera to record an image of the subject aircraft. A method of using commercial software to obtain the distance from such an image is presented. Potential issues which may affect accuracy are discussed.

This document presents a practical method for calculating atmospheric absorption for wide-band sounds analyzed with one-third octave-band filters, called the SAE Method. The SAE Method utilizes pure-tone attenuation algorithms originally published in ISO 9613-1 and ANSI S1.26-1995 to calculate path-length attenuation at mid-band frequencies. The equations introduced in this standard transform the pure-tone, mid-band attenuation to one-third octave-band attenuation. The purpose of this guidance document is to extend the useful attenuation range of the Approximate Method outlined in ANSI S1.26-1995, and to replace ARP866A. Calculation of sound attenuation caused by mechanisms other than atmospheric absorption such as divergence, refraction, scattering due to turbulence, ground reflections, or non-linear propagation effects, is outside the scope of this document.

ARP876 is intended to provide specific recommended procedures for the prediction of gas turbine jet exhaust system noise sources. Procedures are issued as separate sections, to allow for future updating as additional methods, consistent with state-of-the-art, become available.

Recommendations presented in this document are intended primarily for the acquisition of far-field noise data. The test engine is to be appropriately configured and operated so that the sound pressure levels obtained are consistent with the specific objectives of the test. The principal output of the data reduction system is one-third octave band sound pressure levels. However, when appropriate, data may be recorded for purposes of broader or narrower bandwidth analysis.

This SAE Aerospace Recommended Practice (ARP) provides engineering methods that can be applied to monitoring aircraft noise and operations in the vicinity of airports using either attended or unattended monitoring systems, as well as methods for validation of measurement results from permanent systems. Part 1 provides guidance on the components, installation and administration of permanent systems and guidance on analysis of data collected from temporary monitoring of aircraft noise. A separate document, Part 2, describes both system screening tests and detailed test methods for validating the data reported by permanently installed systems. This document is intended as a guide toward standard practice and is subject to change with experience and technical advances.

This method estimates noise for both single and tandem main rotor helicopters except for approach where it applies to single rotor designs only. It does not apply to coaxial rotor designs. Due to lack of available data, application of the method has not been evaluated for application to tiltrotor, or other VTOL configurations, when operating in the helicopter mode. Since there are substantial differences between helicopter rotors included in the data base, and tiltrotor rotors, application to VTOL configurations other than helicopters is not advised. Application is limited to helicopters powered by turboshaft engines and does not apply to helicopters powered by reciprocating engine, tip jets or other types of power plants. It provides noise information using basic operating and geometric information available in the open literature. To keep the method simple, it generates A-weighted sound levels, and Sound Exposure Levels precluding the necessity for spectral details.

The primary measurement procedure recommended in this ARP includes the recording of sound pressure signals in the interior of an airplane during steady state cruise conditions with analysis after the flight into octave band (or one-third octave band) sound pressure levels.

Test procedures are described for measuring noise at specific locations (passenger and cargo doors, and servicing positions) and for conducting general noise surveys around aircraft. Requirements are identified with respect to instrumentation; acoustic and atmospheric environment; data acquisition, reduction and presentation, and such other information as is needed for reporting the results. Recommended procedures involve recording data on magnetic tape for subsequent processing. The use of tape-recorder/time-integrating analyzer systems avoids the need to average by eye the variations associated with manual readings from sound level meters and octave band analyzers and, therefore, yields more accurate results. This document makes no provision for predicting APU noise from basic engine characteristics, nor for measuring noise of more than one aircraft operating at the same time.

This SAE Aerospace Recommended Practice (ARP) provides engineering methods that can be applied to monitoring aircraft noise and operations in the vicinity of airports using either attended or unattended monitoring systems, as well as methods for validation of measurement results from permanent systems. Part 1 provides guidance on the components, installation and administration of permanent systems and guidance on analysis of data collected from temporary monitoring of aircraft noise. A separate document, Part 2, describes both system screening tests and detailed test methods for validating the data reported by permanently installed systems. This document is intended as a guide toward standard practice and is subject to change with experience and technical advances. Potential users include: airport proprietors, airport neighbors, federal, state and local government agencies, equipment vendors and other public bodies and officials.

ARP876 is intended to provide specific recommended procedures for the prediction of gas turbine jet exhaust system noise sources. Procedures are issued as separate Sections, to allow for future updating as additional methods, consistent with state-of-the-art, become available.

Recommendations presented in this document are intended primarily for the acquisition of far-field noise data. The test engine is to be appropriately configured and operated so that the sound pressure levels obtained are consistent with the specific objectives of the test. The principal output of the data reduction system is one-third octave band sound pressure levels. However, when appropriate, data may be recorded for purposes of broader or narrower bandwidth analysis.

Because of the special circumstances under which these tests were conducted, it is necessary to carefully define the limitations on the validity of the results. The measurements and the comparisons reported here apply only to the specific locations of the noise sources and microphones and only for the specific weather and ground-surface conditions existing at the time of the tests. It cannot be assumed that these conditions are representative of most field measurements of aircraft exterior noise.