From Longman Dictionary of Contemporary Englishon automatic piloton automatic pilotdoing something without thinking about it, especially because you have done it many times before Moving on automatic pilot, she tidied the room. → automatic pilot
Examples from the Corpus
on automatic pilot• I wasn't really asleep - I was just kind of running on automatic pilot.• Tommy Blue was on automatic pilot.• I was on automatic pilot, doing what I do best. 