In the early game with Standard rules, Aircraft don't have facing. You can point them in any direction you want -- it makes no difference. Only Vehicles have facing.
But with the expanded rules, the aircraft must face one hex side. And LOS would pass through the hex side. Enemies suffer -1 Range if they arent in front.
Forumini Q: Suppose Player A places an Aircraft as seen in the diagram above its’ nose pointing towards hex side 2. Then Player B places his in hex number five facing the tail of Player A’s plane. Would Player A’s Aircraft be able to fire at Player B’s in the air strike phase?
Forumini A: Yes it would. Facing is not determined until the Aircraft actually fires. Here is how it works:
1. In the flight phase, Player A places his Aircraft first. He opts to face it towards hex side 2.
2. Now Player B places next and opts to put his Aircraft behind Player A’s facing hex side 5.
3. It’s now the air strike phase and Player A moves first. He decides to rotate his Aircraft around and face it in direction 5. He now has the option of either firing at Player B’s Aircraft or any target in his forward firing arc.
4. During Player B’s portion of the airstrike phase he can keep his current facing or change it to any other direction of his choosing. If he keeps it pointing towards hex side 5, he can either fire at Player A’s Aircraft or any target in his forward firing arc.