Comment Re:Inertial Navigation Systems (INS) (Score 3, Informative) 108
It's not the "entire" problem. INS updates from GPS because it has to update from something. You can't INS your way from New York to Paris.
Why not? "Doc" Draper INS'ed his way from Hanscom Field outside Boston to Los Angeles in a B-29 in 1953. With only one planned human course correction en route, the INS was only 10 miles off after a 2,600 mile trip. JFK-CDG is 40% longer, so you should be good to within 15 miles... you are using a 70-year-old INS, right? If you can't flat-out eyeball the airport at that distance, any kind of beacon the airport itself has should be pretty helpful.
(Of course, Draper and his folks hadn't had time to test that version of the INS before their flight. And they made the flight to attend a top-secret conference the government was hosting with University of California researchers to discuss the possibility of inertial guidance... where Draper promptly ruined everything by explaining that it wasn't just possible; they had used it to get there.)