(1) Schedule design: Defining which markets to
serve and with what frequency, and how to schedule
flights to meet these frequencies.
(2) Fleet assignment: Specifying what size aircraft to
assign to each flight.
(3) Aircraft maintenance routing: Determining how
to route aircraft to ensure satisfaction of maintenance
requirements.
(4) Crew scheduling: Selecting which crews to assign
to each flight to minimize crew costs.
Suboptimal, yet feasible aircraft and crew plans are
constructed by solving the subproblems in order, constraining
the solutions to subsequent problems based
on the solutions to preceding problems. Although
smaller and simpler than the overall problem, these
subproblems are still large-scale and rich in complexity.
In fact, OR theoreticians and practitioners have
been developing models and algorithms to solve them
for decades and, in so doing, have had significant successes
and impacts.