Airplane radios are generally broadcasting and receiving mono. There are modern headsets that can also play stereo, but only for onboard music or intercom purposes, if the plane supports it. But in planes with 2 radios you can usually configure their I/O individually. So you can listen (and also talk, although that makes sense less often) on two frequencies at the same time.

They are mono, but I was trying to say that with practice, you can process 2 independent audio streams simultaneously irrespective of whether they are mono or stereo. For example, I am able to keep track of 2 people talking at the same time. I obviously can't respond to both but can maintain independent contexts.