Ever wonder what happens to all the old airplanes that the airlines don't want? You would be surprise? Most old airplanes don't go to scrap metal. Some go to the airline bone yard were they're stripped for parts. Many of these airliner grave yards are in Arizona, or places like Roswell , New Mexico.  Many old airplanes go to cargo carriers like FedEx, UPS, US Postal , Atlas, Polar & a few other companies. These carriers can get these aircraft very cheap. In some cases companies like FedEx will rebuilt the aircraft cockpit with a new makeover & call it a different  model of aircraft. One such example is the DC-10. The DC-10 has been retired since the last 8 years & has flown for 35 years. However, Fed Ex has over 70 DC-10 that were converted & are now called MD-10's. They updated the cockpit avionics( cockpit instruments)  to make it more modern. Airplanes can be flown for a long time if they are well maintained.  In some cases art collectors have purchased old airplanes for various project.