Defects
I'm not an instructor, just a PPL, who recently took off with another PPL in an aircraft in which there was a slight smell of fuel in the cockpit. We had agreed during the checks that the smell had been caused by a spillage onto his clothing when he was refuelling. Half an hour later we were both feeling seriously woozy from breathing in fumes. We ended up declaring an emergency and landing at an RAF base. It turned out that the fuel primer line was leaking. We’d done the A check and everything had checked out as fine. I have since wondered whether and how we could have known about the defect before departing.