# Fleet mix problem

### From Glossary

To determine how many of each type of aircraft should be in a fleet to meet demands and minimize total cost. Here is an integer linear program model:

where is the number of aircraft of type available; is the capacity of aircraft type for mission ; is the least number of missions of type that must be flown; is the greatest number of missions of type that must be flown. The variables are are the number of aircraft of type in the fleet, and is its maintenance cost. If the aircraft must be purchased, binary variables are introduced, as , with a fixed charge, , in the objective . There could be additional constraints, such as a budget on total purchases or on total maintenance .