The common scheduling problems related to all airlines are unplanned flight changes, delays and cancellations. These delays affect passengers' ability to make connections and, in extreme circumstances, negatively impact reservations at their final destinations.
Reorganization and mergers are responsible for the bulk of unplanned flight changes and cancellations. In order to offer to continue offering the best service and prices to passengers, airlines are constantly forced to re-evaluate their routes. When routes are no longer generating enough business for the airline to continue to earn revenue from them, the amount of flights that traverse them is reduced or eliminated altogether. Unfortunately, passengers who have book their tickets well in advance are sometimes negatively impacted. The end result is also overbooked flights, in which more passengers are able to book seats on a plane than what the plane has. Airlines do this in order to insure booked flights. They rely on the idea that some passengers are not traveling on a time sensitive itinerary and are willing to relinquish their seats on the overbooked flight for seats on a different flight in exchange for a voucher that often covers the cost of their next flight. Fewer flights also means tighter connection windows for passengers. A missed connection may result in lengthy delays for travelers.