fly by the seat of one's pants

fly by the seat of one's pants

1. To pilot an airplane by feel and instinct rather than by instruments: The old-time barnstormers had to fly by the seat of their pants (1930s+ Aviators)
2. To proceed or work by instinct and improvisation, without formal guides or instructive experience: The teachers are not trained to recognize it. They're flying by the seat of their pants/ Every case is different, and every investigator ends up flying by the seat of his (or her) pants (1970s+)

seat-of-the-pants