Showing papers on "Aircraft noise published in 2003"

Noise pollution: non-auditory effects on health

Abstract: Noise is a prominent feature of the environment including noise from transport, industry and neighbours. Exposure to transport noise disturbs sleep in the laboratory, but not generally in field studies where adaptation occurs. Noise interferes in complex task performance, modifies social behaviour and causes annoyance. Studies of occupational and environmental noise exposure suggest an association with hypertension, whereas community studies show only weak relationships between noise and cardiovascular disease. Aircraft and road traffic noise exposure are associated with psychological symptoms but not with clinically defined psychiatric disorder. In both industrial studies and community studies, noise exposure is related to raised catecholamine secretion. In children, chronic aircraft noise exposure impairs reading comprehension and long-term memory and may be associated with raised blood pressure. Further research is needed examining coping strategies and the possible health consequences of adaptation to noise.

Noise sensitivity and reactions to noise and other environmental conditions

Abstract: This article integrates findings from the literature and new results regarding noise sensitivity. The new results are based on analyses of 28 combined datasets (N=23 038), and separate analyses of a large aircraft noise study (N=10939). Three topics regarding noise sensitivity are discussed, namely, its relationship with noise exposure, its working mechanism, and the scope of its influence. (1) A previous review found that noise sensitivity has no relationship with noise exposure. The current analyses give consistent results, and show that there is at most a very weak positive relationship. (2) It was observed earlier that noise sensitivity alters the effect of noise exposure on noise annoyance, and does not (only) have an additive effect. The current analyses confirm this, and show that the relation of the annoyance score with the noise exposure is relatively flat for nonsensitives while it is steeper for sensitives. (3) Previous studies showed that noise sensitivity also influences reactions other than noise annoyance. The current analyses of the aircraft noise study extend these results, but also indicate that noise sensitivity has relatively little influence on reactions to nonenvironmental conditions. © 2003 Acoustical Society of America.

Classroom experiments on the effects of different noise sources and sound levels on long-term recall and recognition in children

Abstract: A total of 1358 children aged 12–14 years participated in ten noise experiments in their ordinary classrooms and were tested for recall and recognition of a text exactly one week later. Single and combined noise sources were presented for 15 min at 66 dBA Leq (equivalent noise level). Single source presentations of aircraft and road traffic noise were also presented at 55 dBA Leq. Data were analysed between subjects since the first within-subjects analysis revealed a noise after-effect or a asymmetric transfer effect. Overall, there was a strong noise effect on recall, and a smaller, but significant effect on recognition. In the single-source studies, aircraft and road traffic noise impaired recall at both noise levels. Train noise and verbal noise did not affect recognition or recall. Some of the pairwise combinations of aircraft noise with train or road traffic, with one or the other as the dominant source, interfered with recall and recognition. Item difficulty, item position and ability did not interact with the noise effect. Arousal, distraction, perceived effort, and perceived difficulty in reading and learning did not mediate the effects on recall and recognition. Copyright © 2003 John Wiley & Sons, Ltd.

Jet Aeroacoustic Testing: Issues and Implications

Abstract: Issues that are important for jet aeroacoustic tests and the critical role of good data in the development of jet noise technology are reviewed and discussed. A major effort for improving the quality of aeroacoustic data acquired at the Boeing Low Speed Aeroacoustic Facility has been carried out. This extensive undertaking targeted all aspects of model-scale testing and acquisition of good quality data and covered issues of flow quality, nozzle performance, and acoustics. Significant improvements have been made in all of the named categories. Simultaneous measurement of nozzle aerodynamic performance and noise is important, especially for the development of noise suppression devices. The capabilities of a jet rig incorporated with a six-component force balance are described. It is clearly demonstrated that the measured thrust with the current rig is in excellent agreement with that obtained using a dedicated force balance over a wide range of nozzle pressure ratios. Results of the efforts at rig refurbishment, carried out over the last few years, are presented. The high quality of noise measurements is established through good spectral agreement with data obtained with a blowdown jet, for a wide range of nozzle conditions. An extensive study of available jet noise data from various jet noise facilities has been completed. Implications of contaminated data from most tests and the obligations of the experimental community for the advancement of jet noise technology are discussed.

Noise Characteristics of Aircraft High Lift Systems

Abstract: The characteristics of far-field noise from aircraft high lift systems are discussed. Analyses are made of the data from an airframe noise test conducted in the 40 by 80 ft wind tunnel at NASA Ames Research Center, using a 4.7% DC-10 aircraft model. Discussions are given on both far-field free microphone data and measurements from a phased microphone array. Major trends are revealed and discussed from the free microphone data, which include far-field frequency characteristics, dependence of the acoustic radiation on flow Mach numbers, effects of flap and/or slat deployment, and far-field directivity. Data from the phased microphone array are used to identify locations of major noise sources. Four subregions on the wing are identified as important source locations, namely, the leading-edge slat region, the inboard and outboard side edges of the outboard flap, and the inboard flap region close to the hub of the wing. The source strength distributions in these subregions are integrated to reveal dependencies of various noise sources on flow conditions and high lift system configurations. The effects of flap side edge fences on far-field noise are also discussed, which shows a reduction of a few decibels in flap-related noise.

A Review of the Effects of Aircraft Noise on Wildlife and Humans, Current Control Mechanisms, and the Need for Further Study

Abstract: Military and civilian aircraft overflights are an issue that may impact the quality of life for millions of United States residents. Aircraft noise annoys many people worldwide and is generally thought to adversely affect some wildlife species. In light of increasing demands being placed on airspace, and because of technological improvements in acoustical testing, there is a need to reexamine the effects of aircraft noise exposure on humans and wildlife. This paper reviews past research, current laws and legislation, and presents an argument for the need to revisit the effects of aircraft noise on humans and wildlife. Some evidence suggests that noise may adversely impact wildlife and humans, however, many of the past studies were inconclusive and based on relatively small sample sizes. Given that aircraft noise abatement legislation has been enacted and because of the recent promulgation of community-based noise awareness programs, future studies should be conducted to resolve public policy problems and debates associated with aircraft noise. The need to further study the effects of aircraft noise on humans and wildlife is critical for creating sustainable land use policies near aircraft installations. Data derived from these studies will be used to create sound public policies that enhance the operational capacity of military and civilian aircraft while reducing the opportunity for human and wildlife exposure to aircraft noise.

Effect of Slat Gap on Farfield Radiated Noise and Correlation with Local Flow Characteristics

Abstract: Significant source noise reduction efforts are needed to cope with the "Visions 2020" of the "group of personalities" in Europe. This vision defines an aircraft noise reduction goal of 15 dB per operation until 2020, which inherently requires a reduction of airframe noise, and thus of high lift devices noise, by this same amount during landing approach. Since high lift devices noise is known to be dominant by slat noise, the aerodynamic optimization of slat-wing configurations must also account for noise aspects. Therefore the effect of slat gap variations on slat noise generation was investigated through a scale model high lift devices experimental wind tunnel study. In parallel CFD calculations (2D RANS) were performed for all test configurations to correlate measured slat noise characteristics with flow field data. Broadband slat noise levels were found to scale best with the local flow velocity at the pressure (cove) side close to the upper slat trailing-edge. Relative to the reference slat gap width a broadband noise reduction of up to 10 dB was achieved for reduced gap width (up to 15%), accompanied by an up to 4% degradation in maximum lift. For high angles-of-attack slat noise spectra were governed by a complex tone pattern, which do not follow a simple harmonic scheme but approximately scale with inflow velocity.

Qualitative responses of children to environmental noise.

Abstract: Results from recent quantitative research consistently demonstrate that children are a high risk group, vulnerable to the adverse effects of noise exposure, especially effects on cognitive performance, motivation and annoyance. The aims of the two qualitative studies reported in this paper are to explore children's a) perception of noise exposure; b) perceived risk of and attitudes towards noise pollution; c) coping strategies; and d) the annoyance response. The Millennium Conference Study involved focus group interviews with an international sample (n=36) unselected by exposure. The West London Schools Study involved individual interviews, conducted with a purposively selected sample (n=18) exposed to aircraft noise. The children in the focus groups reported being most affected by neighbours' noise and road traffic noise, whereas children exposed to aircraft noise were most affected by aircraft noise. As expected, the impact of noise pollution on everyday activities (e.g. schoolwork, homework and playing) was larger for the children exposed to high levels of aircraft noise compared with the low noise exposed children and focus group samples. The range of coping strategies that children employed to combat noise exposure in their lives was dependent upon the amount of control they had over the noise source. The emotional response of children describing the annoyance reaction to noise was consistent with adult reactions and it would seem that child noise annoyance is the same construct. Future research should employ qualitative methods to supplement quantitative investigations.

Source Attribution of Helicopter Noise in Pristine National Park Landscapes

Abstract: Aircraft overflight noise from helicopter tours is frequently encountered in such national parks as Grand Canyon, Hawaii Volcanoes, Haleakala, and Bryce Canyon. Noise is an environmental stressor and is associated with a variety of physiological and psychological effects, some of which are long-lasting. Psychologically, attributing a stressor to a nonhostile origin (e.g., a helicopter rescue mission) could mitigate stress effects. In this study, 200 undergraduates rated National Park scenes while exposed to either natural sounds (birds, brooks, wind), helicopter noise attributed to tourist overflights, helicopter noise attributed to back country maintenance operations, or helicopter noise attributed to the rescue of a back country hiker. Regardless of the source, 60 decibel (dB(A)) helicopter noise resulted in lower ratings of scenic beauty, solitude, tranquility, freedom, naturalness, and preference, and higher ratings of annoyance. These effects occurred across all types of scenery. Results suggest that park management-related overflight noise is just as disturbing as tourist aircraft noise, and that the impact of this noise is substantial across demographic variables and across types of vistas.

In Search of the Physics: The Interplay of Experiment and Computation in Airframe Noise Research: Flap-Edge Noise

Abstract: The LaRC investigative process for airframe noise has proven to be a useful guide for elucidation of the physics of flow-induced noise generation over the last five years. This process, relying on a close interplay between experiment and computation, is described and demonstrated here on the archetypal problem of flap-edge noise. Some detailed results from both experiment and computation are shown to illustrate the process, and a description of the multi-source physics seen in this problem is conjectured.

In Search of the Physics: The Interplay of Experiment and Computation in Slat Aeroacoustics

Abstract: The synergistic use of experiments and numerical simulations can uncover the underlying physics of airframe noise sources. We focus on the high-lift noise component associated with a leading-edge slat; flap side-edge noise is discussed in a companion paper by Streett et al. (2003). The present paper provides an overview of how slat noise was split into subcomponents and analyzed with carefully planned complementary experimental and numerical tests. We consider both tonal and broadband aspects of slat noise. The predicted far-field noise spectra are shown to be in good qualitative (and, to lesser extent, good quantitative agreement) with acoustic array measurements. Although some questions remain unanswered, the success of current airframe noise studies provides ample promise that remaining technical issues can be successfully addressed in the near future.

Noise control problems of passenger airplanes (A review)

Abstract: The consequences of the introduction of new international standards and regulations that impose limitations on the community noise of passenger airplanes and restrict the operation of noisy airplanes are analyzed. The need in developing new methods for reducing the aircraft noise is stated. The main noise sources inherent in passenger airplanes of different types are considered. The ways of increasing the efficiency of noise-suppressing systems used in power plants and the ways of reducing the intensity of airplane noise sources are determined. The methods for reducing the noise both inside and outside an airplane are described.

Adaptive real-time optimization algorithm for noise abatement approach procedures

Abstract: Aircraft noise is a major obstacle to the growth of aviation. This paper presents an adaptive real-time optimization algorithm that uses dynamic programming, nonlinear optimization, and receding horizon control to generate approach procedures that simultaneously minimize approach noise and meet air traffic control targets and restrictions. Inputs to the optimization algorithm include flight states, waypoints, and air traffic control (ATC) commands, as well as the set of feasible noise abatement procedures. The resulting noise abatement trajectory compensates for environmental uncertainties, provides more flexibility to both air traffic controller and pilot, and improves airport efficiency while lowering community noise. The examples also illustrate the potential for a wider application of this methodology.

A three-dimensional virtual simulator for aircraft flyover presentation

Abstract: This paper presents a system developed at NASA Langley Research Center to render aircraft flyovers in a virtual reality environment. The present system uses monaural recordings of actual aircraft flyover noise and presents these binaurally using head tracking information. The three-dimensional audio is simultaneously rendered with a visual presentation using a headmounted display (HMD). The final system will use flyover noise synthesized using data from various analytical and empirical modeling systems. This will permit presentation of flyover noise from candidate low-noise flight operations to subjects for psychoacoustical evaluation.

Aircraft Noise Impact Under Diverse Weather Conditions

Abstract: Weather affects both the performance of aircraft and the propagation of noise. Thus, the impact of aircraft noise on communities surrounding airports can vary with changes in the weather at or around an airport. This paper explores the magnitude of these effects for aircraft departing from Runway 4R at Boston Logan International Airport, and illustrates how the noise impact can be significantly reduced by changing the departure procedure to capitalize on changes in the weather.

Evaluation criteria for aircraft noise.

Abstract: Based on extensive and detailed reviews the present paper suggests evaluation limits for aircraft noise for the prediction of noise effects and for the protection of residents living in the vicinity of (newly constructed or extended) civil airports. The protection concept provides graded assessment values: Critical Limits indicate noise loads that shall be tolerated only exceptionally during a limited time. Protection Guides are central assessment values for taking actions to reduce noise imission. Threshold values inform about measurable physiological and psychological reactions due to noise exposures where long term adverse health effects are not expected. Evaluation limits are provided for various protection goals. Apart from hearing damage, evaluation limits are provided for the avoidance of primary extraaural effects on communication and on sleep, for the avoidance of annoyance as a secondary effect and for the avoidance of suspected cardiovascular diseases. Such limits enable authorities to outline the areas around airports, where appropriate measures are mandatory to protect residents against the deleterious effects of noise. Protecting residents is a dynamic process that must be followed up. The evaluation limits must be repeatedly tested in view of new scientific findings and adapted, if necessary.

Numerical study of n-wave propagation using optimized compact finite difference schemes

Abstract: Among the aircraft noise sources, the fan is a dominant one in the high-bypass engine, especially during takeoff and landing. The fan noise can be classified into three types: blade passage frequency (BPF) tonal noise, multiple pure tonal (MPT) noise, and broadband noise. MPT noise levels can exceed the BPF tonal noise during takeoff and landing because shock waves are generated at the rotor tip in the today’s high-bypass engine when the revolutions per minute of the engine shaft is increased to get maximum thrust. Hawkings analyzed the shock wave coalescence by using one dimensional saw-toothed shock models. His analysis describes how an initial nonuniform wave train evolves to become increasingly irregular with distance. However, this type of analysis cannot be directly related to the irregularities in the fan geometry.

Relationship between Aircraft Noise Contour Area and Noise Levels at Certification Points

Abstract: The use of sound exposure level contour area reduction has been proposed as an alternative or supplemental metric of progress and success for the NASA Quiet Aircraft Technology program, which currently uses the average of predicted noise reductions at three community locations. As the program has expanded to include reductions in airframe noise as well as reduction due to optimization of operating procedures for lower noise, there is concern that the three-point methodology may not represent a fair measure of benefit to airport communities. This paper addresses several topics related to this proposal: (1) an analytical basis for a relationship between certification noise levels and noise contour areas for departure operations is developed, (2) the relationship between predicted noise contour area and the noise levels measured or predicted at the certification measurement points is examined for a wide range of commercial and business aircraft, and (3) reductions in contour area for low-noise approach scenarios are predicted and equivalent reductions in source noise are determined.

Audio noise detection using hidden Markov model

Abstract: Simple noise level monitoring systems, which are currently used to create noise map in residential areas, are unable to identify source of environmental noise. The proposed automatic noise recognition (ANR) system can be used in conjunction with simple noise level monitoring to create an intelligent noise monitoring system (INMS). The presented system which is focused on aircraft noise detection, consists of two parts: feature extractor and training-recognition. We append linear prediction coefficients to Cepstrum coefficients to make a rich feature extractor. The hidden Markov model (HMM) is used for training and recognition. The required observation sequence is obtained by means of a vector quantization method based on fuzzy C-mean clustering. 15 signals are used for training and 28 signals are used in test phase. An overall 83% accuracy in classification is achieved.

Recent aeroacoustics research in the United States

Abstract: It is expected that with the projected increase in air travel aeroacoustics research will be very critical in meeting increasingly stringent aircraft noise certification standards. In the United States aeroacoustics research has steadily progressed toward enhanced safety, noise benefits and lower costs. This report provides a brief summary of selected recent aeroacoustics activity in the US. Four topics of great interest to the aerospace industry are: (1) Advanced Subsonic Technology (AST) for future subsonic aircraft, (2) High Speed Research (HSR) for future supersonic commercial aircraft, (3) Rotorcraft noise control efforts, and (4) Weapons bay and other noise control applications for the military. Examples of good progress in the areas of jet, fan, airframe and helicopter noise as well as liner design and weapons bay noise suppression are provided herein. In the next few years we look forward to seeing major strides in noise reduction technology and our ability to predict situations of aeroacoustics i...

Aircraft noise and child blood pressure.

Abstract: . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . xxi GLOSSARY OF TERMS AND ABBREVIATIONS . . . . . . . . . . . . . . . . . . . xxiii CHAPTER 1 -INTRODUCTION . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 1.1 Setting . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2 1.2 Review of studies of aircraft noise and non-aural health effects . . . . . . . . . . . . 6 1.2.1 Blood Pressure: historical antecedents, definitions . . . . . . . . . . . . . . . 6 1.2.1.1 Brief historical sketch of blood circulation, pulse and blood pressure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6 1.2.2 Meaning and definitions of blood pressure and blood pressure variability . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13 1.2.2.1 Blood pressure regulation . . . . . . . . . . . . . . . . . . . . . . . . . 13 1.2.2.2 Haemodynamicity/BP variability . . . . . . . . . . . . . . . . . . . . 20 1.2.2.3 A candidate mechanism from human studies for noise stimulus to affect resting blood pressure . . . . . . . . . . . . . . 23 1.2.2.4 Issues of measurement of blood pressure . . . . . . . . . . . . . . 24 1.3 Determinants of child resting blood pressure . . . . . . . . . . . . . . . . . . . . . . . . . 32 1.3.1 Activity and fitness levels . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32 1.3.2 Diet and eating habits . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33 1.3.3 Ambient temperature . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33 1.3.4 Childhood conditioning factors . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34 1.3.4.1 Age . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34 1.3.4.2 Sex . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34 1.3.4.3 Race/Ethnicity . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34 1.3.4.4 Body mass, height, adiposity and growth stage . . . . . . . . . 35 1.3.4.5 Hormonal/metabolic factors . . . . . . . . . . . . . . . . . . . . . . . 36 1.3.4.6 ‘Tracking’ of BP levels . . . . . . . . . . . . . . . . . . . . . . . . . . . 36 1.3.4.7 Pulse rate . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 37 1.3.5 Effect modifiers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 37 1.3.5.1 BP and sodium (Na) intake/excretion/sensitivity . . . . . . . . 37 1.4 Noise . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 38 1.4.1 Definitions of noise . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 38 1.4.2 Human perception of, and reaction to, noise . . . . . . . . . . . . . . . . . . 40 1.4.3 Mechanical measurement of noise . . . . . . . . . . . . . . . . . . . . . . . . . . 41 1.4.3.1 Development of the dB(A) scale . . . . . . . . . . . . . . . . . . . . 41 1.4.3.2 The Effective Perceived Noise Level (EPNL) . . . . . . . . . . 43

GIS mapping and analysis of aircraft noise at Cape Town International Airport

Abstract: The noise produced by aircraft during operations around airports represents a senous social, technical, economic and environmental problem which is only going to get worse as air traffic volumes increase. Rapid urbanisation, development encroachment and poor planning in the past have resulted in noisy airport runways being situated too close to residents' living space. Rapid industrial growth and lack of funding exacerbate noise problems in developing countries. Moreover, developing countries and especially South Africa tend to have moderate climates and open-window living, which makes insulation an ineffective solution to the noise problem. This study aims at employing GIS to establish the potential noise exposure of various sensitive land use categories and population groups in the noise-controlled area at Cape Town International Airport. Firstly, options for the demarcation of a noise-controlled area were evaluated. Thereafter, incompatible land uses and priority areas for land use compatibility projects were identified and recommendations made for urban renewal projects for these areas. Lastly, the noise-exposed population were profiled according to vulnerability characteristics and vulnerable groups identified and located. A recommendation was made that Cape Town International Airport set up an interactive map-based website to disseminate information to the public about noise and any other important issues concerning the airport. An Internet GIS application would empower citizens by providing them with a dynamic and interactive tool for improved public participation and a better understanding of the potential environmental and socio-economic effects of the airport. Noise complaints could also be investigated through the website and prompt feedback given to the communities complaining about aircraft noise. At the local community level where people are being annoyed every day and night resulting in negative health effects, the problem of aircraft noise demands urgent attention, and measures should be put in place to reduce vulnerability to noise and improve the overall quality of life of noiseweary residents.

Aircraft and road traffic noise and childrenʼs cognition and health: preliminary results on dose-response relationships from the ranch study

Abstract: Introduction Many studies have found associations between exposure to aircraft noise and children’s cognition in terms of reading comprehension, long-term memory and motivation (Cohen et al, 1980; Evans et al, 1995; Haines et al, 2001a,b; Haines et al, 2002; Hygge et al, 2002). Associations have also been found between aircraft noise exposure and psychophysiological indices of arousal such as levels of catecholamines and elevated blood pressure. With a few exceptions (Green et. al, 1982; Haines et. al, 2002), most studies have compared high and low noise exposed groups and have not examined dose-response relationships. Moreover, most studies in children have focussed on aircraft noise rather than traffic noise and have not examined the effects of the combination of aircraft and road traffic noise.

Beamforming for aircraft noise measurements

Abstract: Phased array beamforming for aircraft noise source location has a long history, including early work on jet noise, wind tunnel measurements, and flyover testing. In the last 10 years, advancements in sparse 2‐D and 3‐D arrays, wind tunnel test techniques, and computer power have made phased array measurements almost common. Large aerospace companies and national research institutes have an advantage in access to major facilities and hundreds of measurement microphones, but universities and even consulting companies can perform tests with electret microphones and PC data acquisition systems. The type of testing remains a blend of science and art. A complex noise source is approximated by a mathematical model, and the microphones are deployed to evaluate the parameters of the model. For example, the simplest, but often the best, approach is to assume a distribution of mutually incoherent monopoles. This leads to an imaging process analogous to photography. Other models include coherent distributions of multipoles or duct modes. It is sometimes important to simulate the results that would have been obtained from single microphone measurements of part of the airplane in an ideal environment, had such measurements been feasible.

En Route Noise Levels From Propfan Test Assessment Airplane

Abstract: The en route noise test was designed to characterize propagation of propfan noise from cruise altitudes to the ground In-flight measurements of propfan source levels and directional patterns were made by a chase plane flying in formation with the propfan test assessment (PTA) airplane Ground noise measurements were taken during repeated flights over a distributed microphone array The microphone array on the ground was used to provide ensemble-averaged estimates of mean flyover noise levels, establish confidence limits for those means, and measure propagation-induced noise variability Even for identical nominal cruise conditions, peak sound levels for individual overflights varied substantially about the average, particularly when overflights were performed on different days Large day-to-day variations in peak level measurements appeared to be caused by large day-to-day differences in propagation conditions and tended to obscure small variations arising from operating conditions A three-dimensional ray-tracing method was used to account for atmospheric propagation of sound and predict sound levels on the ground from repeated flights performed at three representative cruise conditions A parametric evaluation of the sensitivity of this prediction method to weather measurement and source level uncertainties was also performed In general, predictions showed good agreement with measurements However, the method was unable to predict short-term variability of ensemble-averaged data within individual overflights Although variations in absorption appear to be the dominant factor in variations of peak sound levels recorded on the ground, accurate predictions of those levels require that a complete description of operational conditions be taken into account The comprehensive and integrated methods presented in this paper have adequately predicted ground-measured sound levels On average, peak sound levels were predicted within 3 dB for each of the three different cruise conditions