Hofy,
do you have the correct Mode mapped? You need BOTH Mode1 set up for plane control, and Mode2 for Vehicles (there are some buttons I have differing for the two modes, but the analog axis are all mapped the same).
Also make sure that the box "Autoselect Mode at start of flight" is checked and that when you launch a plane you get the "Control Mode 1 selected" message in the text buffer.
Ill be online in the Training Arena after 8pm GMT (thats 3pm EST), look for me there if you still have trouble.