An airline is a civilian organisation providing aviation services to fare-paying passengers and/or cargo. It owns or leases airliners with which to supply these services and may form partnerships or alliances with other airlines for reasons of mutual benefit.
In view of the congestion apparent at many international airports, the ownership of slots at certain airports (the right to take-off or land an aircraft at a particular time of day or night) has become a significant tradeable asset in the portfolios of many airlines. Clearly take-off slots at popular times of the day can be critical in attracting the more profitable business traveller to a given airline's flight and in establishing a competitive advantage against a competing airline. If a particular city has two or more airports, market forces will tend to attract the less profitable routes, or those on which competition is weakest, to the less congested airport, where slots are likely to be more available and therefore cheaper. Other factors, such as surface transport facilities and onward connections, will also affect the relative appeal of different airports and some long distance flights may need to operate from the one with the longest runway. Where an airline has established an engineering base at an airport then there may be considerable economic advantages in using that same airport as a preferred focus (or "hub") for its scheduled flights.
Each operator of a scheduled or charter flight uses a distinct airline call sign when communicating with airports or air traffic control centres. Most of these call-signs are derived from the airline's trade name, but for reasons of history, marketing, or the need to reduce ambiguity in spoken English (so that pilots do not mistakenly make navigational decisions based on instructions issued to a different aircraft), some airlines and air forces use call-signs less obviously connected with their trading name. Click on the previous link to discover some of these less obvious radio call-signs.
Bilateral airline treaties/Alliances/Codeshares/International airline regulation/Transport of goods and passengers/Airline personnel/Airline security/Maintenance policy