I lean towards discounting both rumors. I think the temptation to use said kill-switches would prove too great to resist, particularly for the authoritarian types involved.

We saw this a lot with provisions of the “PATRIOT Act”. It was championed as tools needed to combat terrorists and claimed to be reserved for such cases. In actuality, it was used to go after people running fan sites for sci-fi tv shows, among other things.

If such a kill switch existed in computer hardware, I’m sure it would have been used already. I’m less sure about a kill switch in the planes. On one hand, that’s a pretty situational tool, and you wouldn’t want to play that card until you really needed it.

OTOH, we didn’t hear about threats to throw the kill switch during the bluster over Greenland. If they had one, I think it would have been part of that bluster.