Unless one of you knows differently for a fact, I'm not sure there would be a 'locked down' position. If they operated hydraulically in both directions, then there would be. But according to Flyjack, they drop down by gravity, and the hydraulics are just used to pull them back up. If that is the case, then in their normal usage on the ground, they would just drop either to full extension or till they come to rest on the ground. There would not need to be a 'locked' down position.