The way I see it, the flames shouldn't trail behind THAT far. I know it's an AH thing, but of all the photos I've seen of planes on fire, I don't recall seeing them trailing that far back.
As is, the smoke does appear a little thick towards it's tail, and may do for a little thinning. If you are going to stick with the AH Default fire, the transition between the flameballs and the smoke needs a little more attention. Not much, but a little more "poofy" between the two could make it a more smooth transition. In your 3rd shot, right where your LA is at, that is where I think you could add a little more "poofy".

Kind of like a smokey fire thing.

Either way, VERY nicely done.

Hey HiTech, could you make this the new smoke?

Ranger, I know you had played with fire before, have you thought about combining that with what you have done with the smoke? Or will you stick to the default fire?