There comes a time in every commercial airliner's life where it's just too old to keep flying. Boeing's famous 747 jumbo jet, the workhorse of the aviation industry, has been transporting passengers around the world since its first commercial flight in 1970.
A recent BBC documentary called Engineering Giants took a close look at the process of a 747 refit, and also at what happens when one of these jumbos reaches the end of its working life, which could be after 25 years or so.
