>> a single point of failure, is pretty concerning. If is it concerning, we must have a definition of "failure". Does failure mean the inability to fly a rout

>> a single point of failure, is pretty concerning. If is it concerning, we must have a definition of "failure". Does failure mean the inability to fly a route as planned? If so then we cannot fly any routes via GPS that we cannot fly without GPS. So GPS doesn't really add any efficiencies. But if we instead define failure as "danger to life" then we can accept that when GPS fails we will use the other systems to get aircraft to a safe landing, even if flights don't complete as planned. Under that definition we can still enjoy the efficiencies of GPS without maintaining a backup that can instantly replace all GPS functions. This is very important in a military context too. If you always need a 100% backup at the ready then you cannot ever use a novel system. Any new system won't have a backup that is 100% equal. So to leverage new tech you must accept the risk that you may loose some abilities should it fail. If you won't use the new toy until it has a 100% backup, you will end up never playing with any new toys/weapons.