"Vaughn Simon" wrote:
But changing to FM would require a new radio to be
simultaneously installed in every cockpit in the world. The only way
to accomplish that would be for every plane with a new radio to
transmit in "parallel" (as someone already suggested) for a period of
years on both the new mode and the old mode.

That need not be the case, as evidenced by dual-mode cell phones that allow
access to analog and digital cell sites, though not both at the same time.
Newer radios could certainly be made capable of either mode and a future
cutoff date X years in the future could be set for required switchover when
older model radios would be required to be replaced. This would certainly
ease the transition woes.

Actually, not much does change in aviation compared with other fields of
human endeavor.

It does seem that way. Unfortunately I don't think there is anyone in the
FAA or even the avionics industry who is both sufficiently knowledgeable
about recent advances in communications and has the clout and vision to
push for a radical improvement of aviation communication.