"Military-grade" systems use complicated techniques like frequency-hopping spread spectrum. They're designed to be encrypted and resistant to jamming. The jamming resistance is not something we care about (if someone is jamming the signal you just make them turn off their radio), and the whole point of encryption is to prevent interoperability when you don't have the right key.
So sure, you could pay a bunch of extra money for military features and end up with a product that is even less what you want than AM radio. And then you'd have to retrofit everything with these systems.
AM is wonderful. You put a bunch of people on the same channel and it just works.
> "Military-grade" systems use complicated techniques like frequency-hopping spread spectrum
Note that that technology has been around since World War II. And fun fact, while we're on that topic, this page is worth a read: https://en.wikipedia.org/wiki/Hedy_Lamarr
"The jamming resistance is not something we care about (if someone is jamming the signal you just make them turn off their radio)"
Evie might know this, too, so I think you should be concerned about jamming. Luckily, AM provides jamming resistance, since Evie would have to bring a powerful transmitter to be loud enough to drown out the other signals.
Nevertheless, I think large airports should have fast response teams who can rapidly fix the position of a jammer and silence it, if needed. If Evie could effectively take out, say, the main airports of LA and SF for a few hours with a few strong AM transmitters, I doubt all will end well.
Evie? I honestly have no idea who that is. But the more powerful the jamming, the easier it is to find the source. These days even hobbyists play around with cheap off-the-shelf RF analyzers and directional antennas, so I can't imagine that someone jamming airport signals would be able to evade arrest for very long.
So sure, you could pay a bunch of extra money for military features and end up with a product that is even less what you want than AM radio. And then you'd have to retrofit everything with these systems.
AM is wonderful. You put a bunch of people on the same channel and it just works.