GPS or any SatNav is
very susceptible to simple jamming,and with high powered jammers (fairly readily made) and suicidal terrorists a major TMA could be taken out for some time.
Everbody agrees there must be some backup, butno conclusion yet as far as I can see. E-Loran is a contender and DHS are seemingly backing that
(apparently the world banking falls apart again if ther is no timing to nano-
seconds!). Another possibility is mixed GPS/inertia where the INS is "calibrated" while the GPS is working--good enough to land.Nobody seems to be making up their mind
