Flight Level, Transition Layer and when to use it
Whilst doing all of the theory examinations I remember working on the transition layer. After 3000ft you changed to FL and switched the altimeter to 1013. There were also questions about whether FL30 existed on a particular day etc. All good fun.
However, thinking about it, I've not ever flown FL before. I put this down to the bad British weather, rarely having clouds higher than 3000ft. where I fly.
I was thinking though, when flying around the states at an altitude of 10,000ft and we still weren't on FL. I was then listening to the RT on United airlines today and coming into Heathrow we were at altitude 17,000ft., 5,000ft. The lowest FL I heard was FL250
So when do you switch to FL ? Or don't you ever ? Why did the books seem to suggest about 3000ft you switched to FL ?