Thank you Dave ! I will do it but I could give you more details now.
To start, I was on RWY23 at LFBD with CNA2P departure. After right turn, airplane didn't caugt the next point. I tried a direct to BD ndb but it was crazy and started to turn left heading273.
With autopilot HDG no problem but when I engeged the NAV mode it start aigain. NAV SOURCE was on FMS1.
Another point, when I want a direct to on FMC, it's the same problem... It seems lost in the air.
I fly on IVAO with IVAO real waether. FSX acceleration, Window 7 64 bit SP1.
I had updated my AIRAC from NAVIGRAPH AIRAC 1709
I'll take pictures of my next flight for you.
Many thanks for your help.