Originally Posted by
pinniped
I take it as merely well wishes,
So do I, as I described in the beginning of my post…
not a concern that my flight is somehow unsafe.
… and the phrase may be tending towards a stylistic conventionality, in the same way that “Goodbye” originally came from “God be with ye”.
But I still think it hasn’t become as fossilized as that, linguistically, and so it still carries a literal resonance of unnecessary concern about plane crashes, terrorism, hijacking, etc which are all highly unlikely phenomena, even if there was a period of time decades ago when they perhaps were more commonplace.