Minecraft wiki entry for Flying_machines, associated text: Starting the engine of a flying machine often involves updating a piston or observer. Braking, on the other hand, isn't as straightforward to do in survival because a piston-immovable block must be present to stop the engine. A reliable braking method that was first popularized by SethBling is to attach a noteblock (or any similar redstone component movable by pistons) to the "face" of an observer that powers a piston. The piston is placed on the front of the engine, and since extended pistons cannot be pushed by other pistons, activating the noteblock at the right time will stop the engine.