The art of defining a new airplane to suit the requirements of a particular airline involves a mixture of science, technical judgment, and business acumen. The same considerations are involved in evaluating new manufacturer designs, although somewhat more refined analytical tools are available to decrease the dependence on the human element.This paper highlights some of the important problems that an airline faces in determining its new aircraft needs, and using historical data, it illustrates some of the analytic methods used. Interpretations of the analyses are made to focus on the most basic requirement of any new airplane, the transportation of revenue payload at a profit. Constraints which the operator's system imposes on the design of new aircraft, along with a brief discussion of their potential effect on cost (or profitability), are included.The paper discusses the risks and potential payoffs which are inherent in any new airplane program. It also discusses some of the key elements involved in the evaluation and selection process of new manufacturer airplane designs. Analytic tools used for evaluation of critical characteristics are described, and illustrations of the use of some of these tools are shown.