Antonio P wrote on Feb 27^th, 2012 at 3:10am:

Hi: I would like to ask you if you think if CIVA INS is worth to be installed in a short-medium hauler as B727 is. I'm flying 707 from a long year now, and the 727 more recently. Let me explain my question. The need of an inertial system arised when crossing long distances over the water with no VOR NDB or whatever radio stations. Although LORAN stations where usefull, AFAIK signal was not allways available. So INS was usefull for the 707 (although a little unaccurate, though risky as veterans may remeber for KAL flights over USSR border). But...Was it so usefull for a plane overflying the continent full of navaids? What do you think about this? Perhaps Lou can tell us something.

INS useful if you crossing Australia. huge region around YBAS dont have any beacons. if you planning to use Radio nav only, then you'll have to make a big detours instead of straight route. if you plan strait beacon to beacon route, then you'll get leg lengths about 300 nm between NDB (no VORs there). So you gotta arrive within 60nm of NDB. Add changing winds and you can be badly offcourse, and waste a lot of fuel.  IFR and ground control helps. INS very handy in this situation. Same for Africa. Plus, with INS you can go Australia to New Zealand and oceania routes. They not long, but over sea.
I dont use INS on 727, and i fly over desert, and thats hard. im thinking to get one for AU-NZ routes.