To function or do something automatically, without thinking about one's actions, generally because one has done something many times in the past. Also used in the shortened form, "be on autopilot." By the second week of data entry, I felt like I was on automatic pilot. Making bottles, changing diapers, and putting the baby to sleep were all challenging at first, but now I feel like I'm on automatic pilot when I do it. Sometimes I arrive at work without remembering how I got there, like I was on automatic pilot the whole time.