DFW is the nation's 2nd largest airport in terms of space (behind Denver). Its operations lag at #3 behind Atlanta and Chicago. DFW is an excellent O & D airport with its unique half-circle terminals. As a hub airport, it can lead to long walks. The 4 terminals, from the 1973 era, are being remodeled in and out with the addition of an elevated People Mover train system to replace the subterranean Tram systerm. An international terminal, Terminal D, opened in late 2005. It is about the worst place in the country to photograph ramps, aircraft, and terminals due to numerous obstructions. DFW is the headquaters and main hub of American Airlines, since 1981, replacing hometown carrier Braniff which liquidated initally in 1982 and then deserted the DFW hub by 1987 in its second carnation.