The infrastructure of the global aviation system consists of two principal elements, airports and air traffic management (ATM) systems. Airports can be further subdivided into airside facilities (runways, taxiways, aprons, aircraft stands) and landside facilities (passenger and cargo buildings, curbside), while ATM systems are now viewed as being comprised of a tactical subsystem—air traffic control (ATC)—and a strategic one—air traffic flow management (ATFM).