Doesn't look like it's been mentioned yet, but engine fires don't exist in Aces High. If you look (which is impossible in online fighters), it's a fuel fire from the fuselage when you think it's an engine fire. On bombers you can see the fire off to one side of the engine. (I think the B-17 is an exception; one bomber in the game has fires that look like they're in the engine.)
In short, all Aces High fires are currently burning fuel tanks.
