If you find yourself grounded from OFF for whatever reason (I'm currently on the road, for instance), but still want a WWI aerial combat fix, you might try Wings Over France. It's a PC version of an old board game and recreates Bloody April from the perspective of an RFC squadron commander. You manage your crews, assign patrols, and "fly" the various missions from a 2D perspective. It's a very simple, but very interesting recreation of the WWI air war.
Link to the game is here.
Link to a nice description and review posted on the Aerodrome forum is here.
May be old news to many of you, but I'm enjoying it while waiting to get back in the air.