How would I go about moving an entire model after another script is triggered?

It's sort of hard to explain, but I want to make one of those things that when you pull down on the trapped door, a ladder extends outwards for you to go into the attic. I have it to where if you press 'F' the trapdoor comes down, but I can't figure out how to make the second part extend like a ladder. I know it isn't much of a script, but I was wondering why this wasn't working. I tried to make it see when the main part is already rotated (after the trapped door opens) and then run a piece of the script to make the ladder come down.

local ladder = script.Parent
if script.Parent.MainPart.Position = Vector3.new(39.778,7.378,-12.766) then
	wait(.5)
	for i = 0,1,.001 do
		ladder:SetPrimaryPartCFrame(ladder:GetPrimaryPartCFrame() * CFrame.new(0,0,-i))
		wait()
end

Thanks!

Not enough information but here.

local ladder = script.Parent
if script.Parent.MainPart.Position = Vector3.new(39.778,7.378,-12.766) then
    wait(.5)
    for i = 0,1,100/10000 do
        ladder:SetPrimaryPartCFrame(ladder:GetPrimaryPartCFrame() * CFrame.new(0,0,-i))
        wait()
end