Unfortunately, these models are frequently misused
in practice, at great cost to the client organization.
This happens when they are applied to the study
of “macroscopic” issues that can have only approximate
answers because of the uncertainty inherent in
the input data. 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
typical day 10 or 15 years hence) and lack credibility
under the circumstances.