All airlines have complex route networks that connect the passengers and freight between airports. An airline could have more than 1000 routes in the network for any one season. The performance of each route is measured in terms of profitability which airlines monitor on a regular basis.  Capacity on profitable routes is often increased and can be crucial to the airline. However, not all routes are successful and underperforming routes may have the capacity reduced or may even be dropped altogether. Route performance is dynamic and can change quickly due to changes in passenger demand, variations in operating costs and changes to competition on the route due to other airline operators