Why does this Script Work in Test Mode Only?

I know it's a free model, but I've always wondered WHY it stopped working. I know some ROBLOX update broke it around a year ago. It caused most vehicle tool scripts to break and not do anything when commanded. Can anyone look at it and see what's wrong with it please? It works fine in Test mode, just not in online

Here's the script:

fly = false
turn = false
fire = true
a = 25
hover = false

function onFire(gun)
    local b = Instance.new("Part")
    b.Parent = game.Workspace
    b.CFrame = gun.CFrame + (gun.CFrame.lookVector * 10)
    b.formFactor = 2
    b.Size = Vector3.new(1,1,2)
    b.TopSurface = 0
    b.BottomSurface = 0
    b.BrickColor = BrickColor.new(24)
    b.Reflectance = 0
    b.Name = "Rocket"
    local bv = Instance.new("BodyVelocity")
    bv.velocity = gun.CFrame.lookVector * 400
    bv.Parent = b
    local s = script.Parent.Rocket:Clone()
    s.Disabled = false
    s.Parent = b
end

function onButton1Down(mouse)
    if fly == true then
        turn = true
        while turn == true do
            if heli ~= nil then
                if heli.Parts:FindFirstChild("Engine") ~= nil then
                    heli.Parts.Engine.BodyGyro.cframe = mouse.Hit
                end
            end
            wait(0.1)
        end
    end
end

function onButton1Up()
    turn = false
end

function onKeyDown(key)
    key:lower()
    if key == "y" and fly == false and script.Parent.Parent.Parent.Character:FindFirstChild("Helicopter") ~= nil then
        fly = true
        heli = script.Parent.Parent.Parent.Character.Helicopter
        if heli.Parts:FindFirstChild("Motor1") ~= nil then
            heli.Parts.Motor1.BottomSurfaceInput = "Constant"
        end
        if heli.Parts:FindFirstChild("Motor2") ~= nil then
            heli.Parts.Motor2.BottomSurfaceInput = "Constant"
        end
        if heli.Parts:FindFirstChild("Engine") ~= nil then
            heli.Parts.Engine.BodyVelocity.maxForce = Vector3.new(1e+009,1e+009,1e+009)
            heli.Parts.Engine.BodyVelocity.velocity = Vector3.new(0,5,0)
            wait(4)
            heli.Parts.Engine.BodyVelocity.velocity = Vector3.new(0,0,0)
        end
    elseif key == "x" and fly == true then
        fly = false
        if heli ~= nil then
            if heli.Parts:FindFirstChild("Engine") ~= nil then
                heli.Parts.Engine.BodyVelocity.maxForce = Vector3.new(0,0,0)
                heli.Parts.Engine.BodyVelocity.velocity = Vector3.new(0,0,0)

            end
            if heli.Parts:FindFirstChild("Motor1") ~= nil then
                heli.Parts.Motor1.BottomSurfaceInput = "NoInput"
            end
            if heli.Parts:FindFirstChild("Motor2") ~= nil then
                heli.Parts.Motor2.BottomSurfaceInput = "NoInput"
            end
        end
    elseif key == "w" and fly == true then
        hover = false
        while fly == true do
            if hover == false then
                if heli ~= nil then
                    if heli.Parts:FindFirstChild("Engine") ~= nil then
                        heli.Parts.Engine.BodyVelocity.velocity = heli.Parts.Engine.CFrame.lookVector * a
                    end
                end
            end
            wait(0.1)
        end
    elseif key == "s" and fly == true then
        hover = true
        if heli ~= nil then
            if heli.Parts:FindFirstChild("Engine") ~= nil then
                heli.Parts.Engine.BodyVelocity.velocity = Vector3.new(0,0,0)
            end
        end
    elseif key == "d" then
        if a < 100 then
            a = a + 5
        end
    elseif key == "a" then
        if a > 5 then
            a = a - 5
        end
    elseif key == "f" and fly == true then
        if fire == true then
            fire = false
            local gun1 = heli.Parts:FindFirstChild("Gun1")
            local gun2 = heli.Parts:FindFirstChild("Gun2")
            local gun3 = heli.Parts:FindFirstChild("Gun3")
            local gun4 = heli.Parts:FindFirstChild("Gun4")
            if gun1 ~= nil then
                onFire(gun1)
            end
            wait(0.1)
            if gun2 ~= nil then
                onFire(gun2)
            end
            wait(0.1)
            if gun3 ~= nil then
                onFire(gun3)
            end
            wait(0.1)
            if gun4 ~= nil then
                onFire(gun4)
            end
            wait(1.5)
            fire = true
        end
    elseif key == "e" and fly == true then
        hover = true
        if heli ~= nil then
            if heli.Parts:FindFirstChild("Engine") ~= nil then
                heli.Parts.Engine.BodyVelocity.velocity = Vector3.new(0,5,0)
            end
        end
        wait(4)
        if heli ~= nil then
            if heli.Parts:FindFirstChild("Engine") ~= nil then
                heli.Parts.Engine.BodyVelocity.velocity = Vector3.new(0,0,0)
            end
        end
    elseif key == "q" and fly == true then
        hover = true
        if heli ~= nil then
            if heli.Parts:FindFirstChild("Engine") ~= nil then
                heli.Parts.Engine.BodyVelocity.velocity = Vector3.new(0,-5,0)
            end
        end
        wait(4)
        if heli ~= nil then
            if heli.Parts:FindFirstChild("Engine") ~= nil then
                heli.Parts.Engine.BodyVelocity.velocity = Vector3.new(0,0,0)
            end
        end
    end
end

function onSelect(mouse)
    mouse.Icon = "http://www.roblox.com/asset/?id=8599980"
    mouse.Button1Down:connect(function() onButton1Down(mouse) end)
    mouse.Button1Up:connect(onButton1Up)
    mouse.KeyDown:connect(onKeyDown)
end

script.Parent.Selected:connect(onSelect)