(Flint Craig, 1991)
Southwest Airlines (SWA) is required by the FAA to maintenance their fleets based on flight hours. There are five
levels of checks that constitute the maintenance program; the service check, ``A'' check, ``B'' check, ``C'' check, and
structural sampling.
Currently, there are problems with variability in the time it takes to perform a ``C'' check because of structural
corrosion or cracks often found in this check. These findings lead to excess work time and delays or cancellations of
flights in the SWA routing schedule - a major economic drain.
It has been proposed that a new ``MOD'' check be introduced to relieve the variability in the ``C'' check. A ``MOD''
check would constitute stripping the plane down and checking for structural faults such as corrosion, cracks, and
other major problems.
The proposal analysis first took the form of a simulation. The ``C'' check was simulated to determine delays in terms
of minutes per day. After further consultation with SWA, it was decided that there is too much delay in the ``C''
check and that economic options on the ``MOD'' check were to be considered. These options are to either hire out
for the ``MOD'' or perform the work in-house.
This analysis was done on a spreadsheet because of the uncertainty involved in the ``MOD'' related variables. As
``MOD'' check data becomes available, the model can be updated with relative ease.
Based on ``ballpark'' estimations by SWA Maintenance management,
the least expensive of the two options is to perform the ``MOD''
check in-house.