Occasionally I see pictures of 747s carrying a fifth engine to a remote location, such as http://www.airliners.net/open.file/379580/M/. Have any other jets routinely used a similar ability? Was this needed for 747s because their engines were (for the time) just too big to be hauled as cargo on any commonly available planes? For that matter, how do spare (or replacement) 777 engines get where they're going these days? Nick