However, this is only a static version of a problem
which in truth is a dynamic one: Over time the
pool of aircraft available to land changes, as some
aircraft reach the runway while new aircraft join
the arrivals queue. Moreover, minimizing the “latest
landing time” (or maximizing “throughput”) should
not necessarily be the objective of optimal sequencing.
Many alternative objective functions, such as minimizing
the average waiting time per passenger, are
just as reasonable. A further complication is that the
very idea of “sequencing” runs counter to the traditional
adherence of ATM systems to a first-come,
first-served (FCFS) discipline. Deviations from FCFS
raise concerns among some airside users about the possibility of systematic discrimination against certain
classes of aircraft operators (e.g., general aviation)
when it comes to runway access. In a dynamic
environment, this may even result in a compromise
of safety, if some aircraft are indefinitely relegated to
the end of the queue as new aircraft show up to land.