Download and unzip the aircraft files below to your PC; the unzipped folder will be
LewisAire-1
Install the folder to your Flight Simulator 9/Aircraft folder, same as you'd do with any other add-on plane. It will appear on your Flight Sim aircraft listing under Manufacturer: LewisAire.
(Aircraft Download Page)
There are also two gauges that must be added to your main Flight Simulator 9/Gauges folder.