Side scrolling game - gravity

[TriXteR]

what I have for gravity is

onClipEvent (enterFrame) {
    if (ground == "true") {
    } else {
        setProperty ("/bird", _y, Number(getproperty("/bird", _y))+10);
        x_value = getproperty("/bird", _x);
        y_value = getproperty("/bird", _y);
    }
}

where "bird" is the character and "ground" is turned on by a looped 2 frame hittest in all my ground objects

flag = this.hitTest("/bird");
if (flag == true) {
    tellTarget ("/") {
        gotoAndStop ("hit");
    }
}
if (flag == true) {
    tellTarget ("/grav") {
        ground = "true";
    }
}

to either side of the ground object are invisable ground objects that do the same thing except turn "ground" off

now... this works... but it's not very effective... I can't ever make enemies affected by gravity... I was hoping there is an easier, more practical way....

can any body help?