thanks :)
I added
{combos = {{key = 'JOY_BTN50'}} ,down = iCommandPlane_FLAPS_UP, up = iCommandPlane_FLAPS_MNR_from_UP,name = _('Toggle Flaps Up'), category = _('Systems')},
{combos = {{key = 'JOY_BTN52'}} ,down = iCommandPlane_FLAPS_DN, up = iCommandPlane_FLAPS_MNR_from_DN,name = _('Toggle Flaps Dn'), category = _('Systems')},
to a file Thrustmaster Combined.lua in DCS World OpenBeta\Mods\aircraft\A-10C\Input\A-10C\joystick
the command appears in Controls menu, but in red, and does'nt work in game.
I surely did something wrong