add on planes missing

Hello,

I have a problem that I don't know why is happening.

I downloaded a Airbus 320 Air Canada, I then installed in my FSX airplane folder, I started FSX the plane is there, beautiful, then I download an Airbus like a 319 another plane
from a different airline, why when I install the folder which it has a different name and number it removed the
plane that I already have installed, in this case the Airbus 320.

Can you help me with this?

Thank you

Henry