Adrian von Bidder wrote:
Do you have more info on this? I heard (but that may be outdated) that precisely because the US wouldn't commit to uphold civilian GPS globally, commercial airtraffic was forbidden to rely on GPS for navigation.
Commercial and civil aviation does rely on GPS for navigation. However, all planes are required to have redundant navigation methods. In the US a VOR approach with a glide slope ILS is usually the alternative. In fact at least in my friend's little plane we don't use GPS to land because GPS isn't good for measuring altitude without expensive equipment. Redundancy is common in aviation; it's not just that the US may turn off or degrade GPS; the GPS unit may fail so you need an alternative. In other words, were GPS suddenly to go away planes wouldn't fall out of the sky. But you can imagine a bunch of lazy pilots would complain.
As a practical matter, I think GPS would likely only be turned off in case of a severe global military emergency. I certainly wouldn't worry about relying on GPS as a sole source of time for an NTP server. If the worst happens and GPS is turned off, you'll probably have more important things to worry about than whether your local clock has drifted 10ms.
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