Re: A venerable workhorse
A good ROI, but also a harbinger of enourmous problems for GE, RR, NASA, USAF, and a few other niche operators of the 747. For some jobs; you really do need 4 engines.
For GE and Rolls Royce, they absolutely need a 4 engine aircraft for engine testing. Everyone has been using 747 because it is ideal. Yet with today's trend for large twin jets, one day there will be no large 4 jet airframes left flying. Even the A380 will one day stop operating. So how then would GE and RR flight test an engine?
NASA uses an old 747 as a flying telescope, SOFIA. This is a remarkable piece of kit, extremely useful for a lot of astronomers across the world. The higher it flies, the better it works. A 747 can fly surprisingly high, thanks in part to having 4 engines (lots of surplus power). I don't think that any modern 2 jet airliner gets anywhere near as high, so SOFIA will one day be diminished.
Airforce 1 is supposed to have 4 jets for all sorts of reasons, mostly related to the USA's nuclear chain of command.
Anyway, there's a few operators for whom 4 engines is an imperative, who have been able to pick up 747s (and maybe A340 and A380s) cheaply and easily, and who have gone on to have a truly beneficial impact on our lives (please feel free to reserve judgement about the merits of AF1). When we stop flying 4 engine aircraft commercially, those niche operators are going to be in difficulty; where's their next one coming from?
Anyone got a plan for that?