A discussion of possible uses and limitations of systems analysis as an aid in air transportation planning. Following general remarks on the subject, consideration is given to the application of systems analysis to a few arbitrarily selected nonmilitary air transportation planning problems, to illustrate various pertinent points. The emphasis is on the important initial steps in formulating the analysis, beginning with the identification and definition of the problem. The need for realistic and relevant inputs is stressed. No attention is given to particular analytical or computational models or techniques. It is suggested that systems analysis can be anything from very useful to worse than useless in air transportation planning, depending on the quality of the analysis.