Smoke (Black with or without Fireball Effect) Particle System attached to burning vehicles is always generated on the Ground !!!
It Seems that Z Axis always Defaults to 0 for Black Smoke Particle Generator....
Attached a screenshot of burning Hunter on a bridge in Agia Marina showing that Smoke gets generated below the Bridge.
I've also attached a simple mission with two AH-9 Helicopters:
First one has a "test_EmptyObjectForSmoke" attached to it and demonstrates same exact Problem. Second one has "test_EmptyObjectForFireBig" attached to it and shows that Fireball gets attached at correct assigned level and smoke stays on the GROUND !!!
TAKE A QUICK FLIGHT!