'Amplitude modulation is used with ATC communications because... '
Not so.
Engineer Edwin Armstrong invented Frequency Modulation (FM) in 1932 but commercial development of FM was strenuously opposed by commercial interests with major investments in AM, including Radio Corporation of America and the British Marconi Company. The corporations knew that public acceptance of and demand for static-free FM broadcasting would destroy their heavy investment in AM transmission equipment and they prevented FM's widespread usage till the '50s. Tired of battling against major corporations for years to establish FM, Armstrong suicided in 1954.
By the time the patent and commercial battles had subsided, Amplitude Modulation (AM) was well established for aviation use and the benefits of of interference- free reception for aviation were not seen to outweigh the cost of equipment conversion to FM.
Fortunately the commercial interests behind internal combustion engines were unable to prevent the development of jet engines.
Don
