You could try
#Loop
Plane setpos [getpos plane select 0, getpos plane select 1, 200]
~0.1
goto "Loop"
That would keep it at 200m (even if it was destroyed though)
Alternativly:
#Loop
?(getdammage plane > 0.9):goto "End"
Plane setpos [getpos plane select 0, getpos plane select 1, 200]
~0.1
goto "Loop"
#End
exit
Would allow the plane to fall out of the sky when it was killed.