from The American Heritage® Dictionary of the English Language, 4th Edition
- adj. Slang Based on or using intuition and experience rather than a plan or method; improvised: "Each has already moved beyond seat-of-the-pants management to more professional operating procedures” ( Business Week).
- adj. Slang Performed without using instruments: a seat-of-the-pants landing of the aircraft.
from Wiktionary, Creative Commons Attribution/Share-Alike License
- adj. Done by feel, guess, or trial and error rather than by careful planning, thought or technique.
From seat + of + the + pants. (Wiktionary)