fly by the seat of one's pants

verb2

1. •
   To pilot an aircraft without the aid of instruments and without a flight plan, using only instinct, visual observation, and practical judgment.

   • Between world wars, when Douglas Bader was a cocky, teen-age R.A.F. cadet . . . a man could navigate by eye and the nearest railroad track and fly by the seat of his pants. — 1955
2. •
   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.

   • “Unlike Obama and his methodical process, McCain was flying by the seat of his pants,” the authors observe. — 2010