I had another issue yesterday, that is solved now, that reminded me of this thread here where I was pulling my hair out trying to solve a yaw issue and it ended up being a loose screw. So, I take off yesterday and my 5" freestyle quad is jerking about pretty bad, then I could't land it! Reducing the throttle to idle it kept flying :O Eventually I got it low and disarmed it into the tall grass. I couldn't see anything obviously wrong so I'm pushing the wires around and thinking something is loose again. I get everything tucked away and try to fly it line of sight, throttle control is really sketchy, like disconnected a bit. Well hell! I am carrying it back to the pits and just happened to notice a big split in a prop hub. These are pretty new props, not a scratch on them, loosening the prop nut the crack closed up but it was definitely cracked right through vertically. I replaced the set of props and the quad is flying great again. It is amazing how a beat up quad can fly OK sometimes but a loose screw or crack can cause havoc. Next time a good quad suddenly goes bad on me I'm looking for a mechanical cause first. There's a lesson in there somewhere