PREFACE TO AIRCRAFT NOISE SERIES Noise@ from whatever source@ has become a matter of wide concern. Those responsible for the design@ certification and operation of aircraft of many different types need to apply their skills more and more to minimizing the health hazards@ annoyance@ reduction in environmental amenity and the costs which these may incur. To do this@ while at the same time maintaining efficient and socially desirable technological progress@ requires the provision of authoritative and reliable data relating to the estimation of noise. Such data must identify the many parameters involved@ the relationships between them and lead to the various means of attenuating noise at source and elsewhere. The data on noise prediction and sound propagation@ in common with many other phenomena relating to noise@ are of concern to engineers and scientists. However@ these data are often widely scattered and when located may be of variable quality and relevance to the practical application. The designer or operator does not@ generally speaking@ have the facilities or time required to collect and evaluate all the data available which may be applicable. These data need to be vouched for by a significant cross section of the engineering and scientific community@ concerned both with their derivation and application@ and need to be evaluated under as impartial circumstances as can be arranged. A number of Data Items@ relating to aircraft noise@ were prepared by the Engineering Sciences Data Unit (ESDU) under contract to the Ministry of Defence (Procurement Executive). Her Majesty??s Government has agreed to the public issue of these Items@ within the ESDU Series@ as a service to all who are concerned with noise. ESDU has continued to add to those Data Items to increase the range of noise sources covered and extend the range of application of the Series. These data are prepared by ESDU for use by the designer and equally his or her customer and by all others who may be concerned with noise problems; by serving the needs of many the task will be accomplished at much lower overall cost and result in an independently derived and@ it is hoped@ a universally acceptable database. A qualified staff is employed by ESDU to collect and evaluate the data. In carrying out this work@ the staff have the assistance of many individuals drawn from industry and research and educational establishments throughout the world. Data which are irrelevant or unreliable are discarded and the remainder are correlated and distilled into an authoritative working tool for practical application. Throughout@ the work of the staff is guided and monitored by an expert group and ad hoc working parties. The Series on Aircraft Noise is prepared under the guidance of the Aircraft Noise Committee which has the following constitution.