Whats the weather like in the missions they don't want to fly? is it raining? Planes back then were almost literally made of cardboard cutouts and couldn't fly in a storm. When you call a plane in do you click to deploy it in the middle of the map or off the map.
Have your planes refueled or are they still on cooldown?
Did you get the "harassment" research upgrade? Fighter planes don't have the option to strafe (which I think is a bit foolish but I'm not responsible for balance) Bomber planes will only target emplacements such as mgs, mortars, tanks, and artillery. they won't bomb soldiers in trench lines (This I really don't understand but again, not responsible for balance)
