Im from Germany
Ok, that's enough to help you:
First of all: where you've got the plane from (might help if the following general solution doesn't work)?
Then check if the SimObjects/Aircraft/*nameofaircraft* folder contains:
Model-, Panel-, (at least one) Texture- and Sound-folder plus the aircraft.cfg and a *.air file.
Report and we'll see.
...for the germans! ;)