How to stop this plane from flipping?

Help and Feedback Scripting Support
1

Here’s the visual: https://gyazo.com/21de6c51c8410f74987fb9810d2658e6
You can see how the plane flips half way.

Script:

while wait() do
		local Y = workspace.Earth.Position.Y + math.cos(start)*magnitude
		local X = workspace.Earth.Position.X + math.sin(start)*magnitude
		local partX, partY = workspace.Earth.Position.X + math.sin(partstart)*magnitude, workspace.Earth.Position.Y + math.cos(partstart)*magnitude
		print(partY.."-YPOS")
		print(partX.."-XPOS")
		start += 0.05
		print(workspace["Lion Air B737 MAX 8"].PrimaryPart.Position.Z)
		partstart += 0.05
		workspace["Lion Air B737 MAX 8"]:SetPrimaryPartCFrame(CFrame.new(Vector3.new(X, Y, workspace["Lion Air B737 MAX 8"].PrimaryPart.Position.Z), Vector3.new(partX, partY, workspace["Lion Air B737 MAX 8"].PrimaryPart.Position.Z)))
	end

The script isn’t the most efficient, but I am not attempting to make it so. How do I fix the plane flipping issue?
Here’s the visual again: https://gyazo.com/21de6c51c8410f74987fb9810d2658e6