Nothing to do !!
I've desinstalled FSDT Scenery, search for flatten in scenery.cfg, reinstalled simflyers scnerey that is properly OK, but so poor in front of FSDT !!!! , then desinstalled simflyers, search once more for flatten, then reinsatlled FSDT...the result is the same !!!
I'm sad, but I'm fed up... I'm an old 36 years old simmer, and I get tired for now, I do not have the strength to uninistall my FS for now, I'll do with what I have, and I'll wait for the AES compatibility...maybe, one day, I'll reinstall all...
I still think it's a good work, and may be my problem will be solved by a future update...I stay on line
Thank you for all !!!