BrianG asked...

Back to my original question, in a real 707 or 727 would you ever find both doppler and INS. And if so, in what instances would you use one over the other? Would one just be a back up and one of those two be the primary nav system, say on trans oceanic flights where VOR is not available?

Brian,

Doppler was OK in its time, but even Loran C was sometimes better. I guess you could still find an old 707 with Doppler and a single INS and/or GPS installed. INS like the Delco Carousel were a big deal in the 70's. The IRS nav system using a ring laser was a lot better and less maintenance. Using the doppler shift of light, the ring laser had less moving parts and produced a more accurate track.

Some detail information on the IRS system...
http://www.biggles-software.com/software/757_tech/flight_management_navigation/irs.htm

As for the question by pj747 - That sounds like too much work to me!  ;)  TWA never had the 777 on its list of planes. The 747 fleet was well established and the 767 fleet was slowly replacing the big bird. By the time AA bought TWA our fleet was pretty much all 2 engine both domestic and international. With MD-80 and commuters feeding the long haul stuff which were 767-200 and -300's.

It is a sissy plane compared to the old 707 and even the 747 where you need to know which foot to use if an engine fails. The 777 and most of the sissy planes put the rudder in for you... too much computer stuff in the flying department for me. Push a button marked START and the engine either starts or it tries again. What happened to all the careful watching of the start procedure? Too much like my Hybrid car.  :-?