fly是飞，fly by the seat of one's pants“摸着石头过河，凭感觉试试看”。

【例句】
It's during a time like this you must fly by the seat of your pants.
在这种时候，你只能摸着石头过河。

When Mike started up business in the town, he didn't know anybody, so he had to fly by the seat of his pants.
当迈克在这个镇子开始做生意时，他一个人都不认识，所以只好全靠自己摸索。