Why don't voice radio communications use FM?

Perhaps this is a naive question, but: Why don't voice radio
communications for aviation use FM radio instead of AM radio? I
realize there's substantial inertia in the installed base of AM
equipment, but surely one could allocate some new frequencies to FM
and use them in parallel for some years to ease the transition.

The reason I ask is that improper and misunderstood radio
communication is a leading cause of accidents, and so it seems that
anything that can make that communication clearer would greatly
improve safety. I can barely understand what I hear on the radio. It
is true that the communication is very standardized, making it easier
to guess what is being said, but the results are pretty unpleasant if
one guesses wrong.

On a related note, it has occurred to me that one could develop
voice-recognition systems that understand the speech of a pilot and
then repronounce what he says in an extremely standard synthetic
voice. This could also improve understanding, especially for
non-Anglophone pilots who speak with heavy accents. The same systems
could clean up the speech so that it is absolutely standard, with no
missing or added words. Of course, the issue here is that the system
would be stuck if it cannot recognize what is being said, or if a
completely non-standard utterance is made by the pilot. A natural
extension of this would be systems that recognize standard phrases in
one language and translate them to another, but that would be even
more dangerous if the system ever failed.

Still another idea is special training systems that listen to a
pilot's speech and transcribe it, and point out any problems with
understandability. Again, this would be most useful for
non-Anglophone pilots, but it would work for anyone. If a machine can
understand a pilot's speech clearly, then a human being should
certainly be able to understand it that much more easily.

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