What’s happening here is that you’re changing the type of data being returned by get_queryset.
If your Airport_FrequencyListView is supposed to be a list of Airport_Frequency, then that’s what get_queryset is supposed to return. (You don’t show here what model is associated with Airport_FrequencyListView - if one is even defined.)
However, what you’re returning from get_queryset is a set of Airport objects - a different model entirely.
You should be able to refer to that data in your template as airport_list.