"They can be moved into (but not through) as a noncombat move by land units of a power
that is at war. This moves the territory out of its neutral status, however. The
first friendly power to do so places its national control
marker on the former friendly neutral territory, and its
national production level is adjusted upward by the value
of the territory. With the territory’s loss of neutrality in
this way, its standing army is immediately activated.
In my defense, it does say the standing army is immediately activated, and also says the territory has lost neutrality, and was formerly a friendly neutral. Since it is no longer neutral, during the noncombat phase, and since there is no rule prohibiting air units from flying over territories that are not neutral, I think it was a good question.
As you pointed out, the rule says that LAND units can’t move THROUGH the friendly neutral during the noncombat move, but this gives even more reason to believe that air could fly over it because it is specifying that land units can’t move through.
But now I know what was intended and what the rule is, so I will write it in my rule book.
Thanks for the quick clarification as always!!