By the way, French aircraft can be under german airstrikes threat for the very first turn. I've rebased it to Le Havre so that it can intercept german air on the northern part of the front.
If the Germans air strike the French, it would trigger the West Invaded Conditional Event. That is not something they want to do on the first turn.
If you are playing the full campaign game, I strongly recommend you review the Conditional Events, both their triggers and events. They are important in providing play balance and to deal with things such as the above.