[CamperBob2]

All true, except that a key reason they still use AM for voice communications is precisely because it's obvious if multiple users are trying to transmit at once.

AM is obviously not the way a "CSMA/CD" system would be designed today, but it does get the job done, and has for a long time.

[cperciva]

AM is good for instructions because its broadcast nature allows everyone to hear everyone, but arguably coordinates-over-voice-over-AM is dangerously error-prone. My sense is that the ideal system might look something like "AM with a digital side band" where ATC can press buttons to transmit data (e.g. authorized altitudes and vectors) to a plane but metadata is still carried over AM.

A lot of fatalities have been avoided thanks to a pilot overhearing ATC giving takeoff or landing clearance to another plane, but quite a few incidents could also have been avoided if plane cockpits had a big red light "authorized to enter runway" which could only be turned on by ATC. In an industry which is designed around so many redundant systems, it's rather astonishing that an error in a single communication channel can lead to disaster.