Lee,

On Tue, 27 Jul 2004 02:22:49 -0700, Lee Jones wrote:

> At and above 18,000 feet MSL (flight level 180), you set the
> altimeter to 29.92 inches of mercury (standard pressure) [in
> the US, see FAR 91.121].  Your altitude is no longer exact, but
> everyone at a given altitude, say 35,000 feet, is at the same
> relative height above ground.

In the UK it's rather lower than FL180 - perhaps because we have very little land that's higher than 3,000ft.
As far as I remember you set 1013.2hPa (hectopascals, formerly known as millibars) whenever you are in an
airway (which can be quite low around here!), and always above 10,000 ft.  Below that you set either the
regional QNH (air pressure at Mean Sea Level) or QFE (air pressure on the ground of the aerodrome concerned).
The latter is particularly useful when landing, as it means your altimeter will read zero as you touch down,
even in Denver, CO, which is about 5,000ft above sea level!

Something that a lot of films and TV programmes get wrong is the terminology - "Flight Level" means you are
referring to the 1013.2 setting, and it's in hundreds of feet (so FL180 is 18,000 ft), "Altitude" means in
relation to Sea Level with QNH set, and "Height" is in relation to the aerodrome level with QFE set, and the
latter two are given in feet.  So the next time you hear a pilot or controller say "twenty thousand feet" or
"flight level twenty thousand" it indicates the scriptwriters aren't pilots, and didn't check their facts!
:-)

Incidentally, in the run-up to the first unpleasantness in the Gulf, a UK controller was contacted by a US
aircraft arriving from across the Atlantic, which reported "above FL600" (the height that Concorde used to
fly).  On being asked: "Report your flight level" the pilot responded: "You don't need to know that" !  :-)

Cheers,


Howard Winter
St.Albans, England

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