In addition to the possibility of generating infeasible solutions, a disadvantage of the sequential
solution approach to aircraft and crew planning is
that aircraft routing solutions limit possible crew
scheduling opportunities, potentially causing crew
costs to increase significantly. The linkage between
aircraft routing and crew scheduling occurs because
a crewmember can connect between two flight legs
separated by less than the minimum required connection time only if the same aircraft is assigned to both
legs. To account for this, Klabjan et al. (2002) swap
the order of the problems and solve the crew pairing problem before the maintenance routing problem.
This approach has the advantage of generating optimal crew solutions, but it does not ensure that for
the optimized crew solution there is a corresponding maintenance-feasible solution. To achieve crew
optimality and maintenance feasibility, Cordeau et al.
(2000) and Cohn and Barnhart (2003) integrate the
basic maintenance routing and crew pairing models.