The movement of passengers and cargo by aircraft such as airplanes and helicopters. Air transportation has become the primary means of common-carrier traveling. Greatest efficiency and value are obtained when long distances are traveled, high-value payloads are moved, immediate needs must be met, or surface terrain prevents easy movement or significantly raises transport costs. Although the time and cost efficiencies obtained decrease as distance traveled is reduced, air transport is often worthwhile even for relatively short distances. Air transportation also provides a communication or medical link, which is sometimes vital, between the different groups of people being served.