Pale Rider,
Open up the .TMD file for the plane using Word or somthing similar,
there will be a VERSION number like the second line, and it might be 1.9.0
just change the 9 to an 8, so it's 1.8.0
the 1.9.0 is for the add on that you purchase, and 1.8.0 is without.
Then hit ctrl+S to save, and enjoy you new airplane
