Where does Class A start (was IGC Rejects Garmin GPS)

In article ,
"ADP" wrote:

"Bruce Hoult" wrote in message
...
In article ,
"ADP" wrote:

In the US FL180 is always MSL as measured on a standard day.
Thus the altimeter is set to 29.92.

That is correct.


In the US, you can never be at or above FL180 unless you have an
IFR clearance, or have a waiver. A wave window is a waiver.

That is incorrect. What you may not be in without an IFR clearance is
Class A airspace.

...Snip...

No, you can never fly above 17,999.999999999999999999 ft
in the US without your altimeter set to 29.92 inches.
Consequently, you can never fly at FL 180 with out an IFR
clearance or a waiver. It doesn't matter how high you are AGL.
You are always in Class A airspace at FL 180. So there!

Do you not agree that you can fly at 17,999 ft and not be in Class A
airsapce?

If so, do you not then realize that 18,000 ft and FL180 are at the same
place *only* when the pressure at sea level is 29.92?

When the pressure at sea level is less than 29.92 (101.3), FL180 is
*lower* than 18,000 ft, but you may still fly at 17,999 with your
altimeter set for the actual conditions and not be in Class A airspace.

You may contradict me again if you wish, but I'm not going to reply due
to advice my mother once gave me about the danger of people not being
able to tell the difference.

-- Bruce