An AID cleanup was a type of maintenance performed on the impulse engines of Constitution-class starships. In 2268, while Montgomery Scott was performing an AID cleanup on impulse engine number two of the USS Enterprise, he left a hatch open. Pavel Chekov warned Captain James T. Kirk of this, but Kirk assured him that it wasn't an issue as they wouldn't be using the impulse engines to pursue the dikironium cloud creature. (TOS: "Obsession" )