"G.R. Patterson III" wrote in message
...


Robert Lyons wrote:

- Why would people be using two different altimeter settings anyway?

Because the regulations require it. In the States, all aircraft flying at
or
above 18,000' ASL are required to set their altimeters to 29.92. Aircraft
flying
below 18,000' are expected to set their altimeters to the local barometric
pressure.

I have occasionally idly wondered about one little detail. When it's a
significantly low or high pressure day, when do you change the altimeter
setting while climbing or descending? Maybe as you pass through FL180
descending, and as you pass through 18,000ft climbing?

Or maybe you do it when you get the clearance through the transition
altitude, to make it easier to plan the climb/descent (assuming the computer
isn't doing all that for you). Or maybe it takes you so long to twist the
knob that it doesn't much matter. What do you oxygen-suckers actually do?

-- David Brooks