It's demonstrated fact that GPS is not 100% reliable, which would be required to meet the "on its own" requirement. See the article you're commenting under, and documentation about it from the FAA [1].
reply[1] https://www.faa.gov/about/office_org/headquarters_offices/av...
100% reliable is not a requirement per FAA regs cited. Legacy navigation equipment fails too.
replyThen I think you should re-read the original comment, with this revelation in mind.
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