An example is a question that often confronts airport operators: When will airside delays reach a level that will require a major expansion of an airport’s capacity (e.g., through the construction of a new runway)? Questions of this type, often requiring a look far into the future, are best answered through the approximate analytical models surveyed earlier, which permit easy exploration of a large number of alternative scenarios and hypotheses. Detailed simulation models, by contrast, cannot cope well with the massive uncertainty involved because they require inputs that are difficult to produce (e.g., a detailed schedule of aircraft movements at the airport for a