This document is divided into five parts. The first part deals with flotation analysis features and definitions to acquaint the engineer with elements common to the various methods and the meanings of the terms used. The second part identifies and describes the various methods used. To accomplish the minimum intent of this document, techniques could be limited to those needed for flotation analysis only; however, because of the close relation between flotation analysis and runway design, methods for the latter are also included. In fact, runway design criteria are used for flotation and evaluation in some cases, and are periodically the governing procedure in specific, if isolated, instances. From time to time, it may be necessary to deal with runways built to obsolete criteria. Therefore, a listing of most of these constitutes the third part. The fourth part of this document tabulates the recommended documents, categorizing them for commercial and civil versus military usage, by military service to be satisfied, and by type of pavement. The document concludes with brief elaborations of some concepts for broadening the analyst's understanding of the subject.
Aircraft flotation analysis is characterized by a variety of methods, and this leads to confusion. Sources of this variety are at least fourfold. First, the foundation of all runways and taxiways is soil, which is not a homogeneous material. Not only does it vary widely from place to place, but it also varies with time and/or as a function of the weather. Although soils have been classified into a limited number of groups, variability within each group prevents soil classification from providing a complete answer for defining properties of interest to the flotation analyst. A second source of flotation's varied nature stems from the diverse methods used by different agencies and countries in solving their particular problems with the materials they have at hand. Third, the economics involved dictates, and will continue to dictate, differences in methods applicable to a given pavement construction. Fourth, and finally, the military is particularly interested in operation on unpaved areas, such as mats, membranes, and unsurfaced soil.
Although technology has not produced a uniform methodology, efforts have been applied in this direction on an international scale. While the product of these efforts cannot provide a total focus in the foreseeable future, a uniform method of reporting aircraft flotation has been devised which provides a meaningful value. This method, termed ACN/PCN, has broad support in the western world; and has been adopted by the International Civil Aviation Organization (ICAO) as a single airfield weight bearing reporting method. ACN/PCN has been devised for conventional flexible and rigid pavements. It has not been made applicable to mat, membrane, and unsurfaced soil landing fields. Flotation analysis will continue to be concerned with the broad array of methods for design, evaluation, and weight bearing reporting of pavements and rapidly prepared unpaved landing areas. With the above in mind, the purpose of this document is to inform the aircraft flotation analyst of the various methods likely to be used and to characterize them for evaluating the capability of aircraft to operate on airport runways and taxiways.