然而，这种纯粹的视觉系统在恶劣天气下毫无用处，到了20世纪30年代，无线电通信开始用于空中交通管制。

However, this purely visual system was useless in bad weather, and, by the 1930s, radio communication was coming into use for ATC.

youdao

然而，这种纯粹的视觉系统在恶劣天气下毫无用处，到了20世纪30年代，无线电通信开始用于空中交通管制。

However, this purely visual system was useless in bad weather, and, by the 1930s, radio communication was coming into use for ATC.

youdao