To use one's judgment, initiative, and perceptions as events unfold in order to improvise a course of action without a predetermined plan or without the desirable data inputs to decision making.
To pilot an aircraft without the aid of instruments and without a flight plan, using only instinct, visual observation, and practical judgment.
To do by guessing, intuition, or trial and error; to react to events as they occur; improvise
To play guided by one's musical ear, rather than from a written score.