Flying along in my Cessna 172 and I can't shake the feeling something is wrong. The last two times there was a faint smell in the cockpit, but not like exhaust, not like fuel, but something rather important. Important enough to cancel any future flights that involved passengers. So it smelled of something familiar, like butane or kerosene. Anyone guess what it was? There's no crazy modifications or anything out of the ordinary in the plane. I actually can't believe I didn't know immediately.