Altimeter 3066

ATC computer converts the pressure altitude with local altimeter
setting. If ATC knows everyone is using 3100 as their altimeter setting
(can be by regulation in high pressure 31" situation, such as in
Canada), the computer can do similar converson, so the IFR separation
would not be unaffected.

Wade Hasbrouck wrote:


I thought the Mode C transponder reports Pressure Altitude and is basically
fixed at 29.92?

J. Severyn wrote:
"M" wrote in message
oups.com...


I can hardly see how it should affect VFR flights.


Well pattern altitudes might be one problem. How about easterly/westerly
odd/even +500 altitudes?

So you're a couple hundred feet off, that's no big deal. As for pattern
altitudes I always use 1000 agl, plus or minus depending on how I round
the field elevation.

M wrote:

ATC computer converts the pressure altitude with local altimeter
setting. If ATC knows everyone is using 3100 as their altimeter setting
(can be by regulation in high pressure 31" situation, such as in
Canada), the computer can do similar converson, so the IFR separation
would not be unaffected.

If the pressure gets above the limit IFR flight would not be allowed,
simple as that. That happened 10 or 15 years ago in Alaska. Very rare.

"
A very high pressure settled in Pacific NW:

KPSC 020453Z 31006KT 6SM BR BKN007 BKN075 M07/M08 A3066 RMK AO2
SLP389 T10671078

That's the highest that I've ever remember seeing.


Yeah with terrible smog to go along with it. Once you get to 1-1.5K and look
down it's almost like a fog bank it's so dense.
We're getting as bad as Los Angeles :-(

Cheers:

Paul
N1431A
1S0

You are flying VFR at 17,500 MSL with an altimeter setting of 30.66. You
pick up an IFR clearance and are given FL190. You begin a slow climb. As
soon as you pass 18,000 MSL you set your altimeter to 29.92. It now reads
17,300 so you set it back to 30.66. It now reads 18,000, so you set it back
to 29.92. I now reads 17,300 ...

Conclusion: It's impossible to get above 18,000 MSL if the altimeter setting
is 30.66.