It really does depend what effect you want. To get a smoke shell and "attach" it to a plane you can just use a repeating script. Name your plane and then make a script like thus;
smoke = "SmokeShell" CamCreate (Getpos PlaneName)
#Smokey
smoke Setpos (Getpos PlaneName)
~0.01
Goto "Smokey"
And Tadaaaaa, once the script is called it makes a smoke shell and holds it in place at your plane. Now as you fly along it will look like you have some nasty grey smoke billowing out the back of your plane.
If this isnt the effect you want, then you are probably looking at a drop command, (assuming you have resistance).