On 15/01/16 10:45, Recliner wrote:
The Real Doctor wrote:

"Flight level - "A fancy way of telling you how many thousands of feet
you are above sea level. Just add a couple of zeroes. Flight level
three-three zero is 33,000 feet.""

Is that wrong? [Yes, I know it's the barometric altitude, but that's not
something that's normally mentioned.]

Flight levels are done with the altimeter at 1013hPa, and since the
actual pressure at sea level can be +/- 50hPa and atmospheric pressure
changes at ~30 feet per hPa, FL250 (say) could be anything from 23,500 -
26,500 feet above sea level. Things have hit other things because they
got this wrong.

Ian