>Is it just that we standardized on AM before the 60s This one mostly. As otherwise mentioned, there is some advantage in the case of multiple transmissions at

>Is it just that we standardized on AM before the 60s This one mostly. As otherwise mentioned, there is some advantage in the case of multiple transmissions at once for AM, but in practice both are often entirely garbled. The loud tone caused by any slight difference in transmit frequencies is the big indicator that something has gone wrong. If one signal is much stronger than the other then that tone will be very faint and will likely be missed. So AM has something like FM capture effect in that case. AM has allowed for very narrow channels on the aviation band. In Europe mostly, the channels are only 8.33 kHz apart. Typical narrow band FM voice communication requires 12.5 kHz. Since the end points in aviation are usually within line of sight of one another, radio communication is very easy. Any modulation method would work well. Of course in practice this means that the equipment is allowed to degrade that much more before anyone gets around to fixing it...