low altimeter and FL180

No intrusion, just a great question. Keep reading ...and posting.

Now you have the info others have (links). These resources are free online,
or you can buy a printed FAR/AIM 2004 book for under $20.

http://www1.faa.gov/ATPubs/AIM/index.htm
Aeronautical Information Manual
Official Guide to Basic Flight Information and ATC Procedures

http://www.landings.com/evird.acgi$pass*58241480!_h-www.landings.com/_landings/pages/regulations.html#aim
Federal Aviation Regulations

or

http://makeashorterlink.com/?L2EF42F56
(Same as long link above. Wait a few seconds for it)

These are from Landings.com. You can also get them from the FAA website.

--
Montblack
"Just the usual inanity"


("Robert Lyons" wrote)
I hope you'll forgive the intrusion from a lurker and non-pilot (well,
a wannabe-pilot). Would someone please explain a few points about this
to me?

I don't have any reference books mentioned in another post, so cannot
look up these answers myself. Thanks for any light you can shed.

"Peter Duniho" wrote in message
...
"Robert Lyons" wrote in message
...

- Why would this problem affect just FL180 and FL200? Why not FL160,
220,
and every other altitude?

It affects all flight above FL180. There is no "FL160" in the US, and I'm
not sure why you got the impression that flights at FL220 are unaffected.

It'd have to be a hell of a depression to affect FL220 though. The table in
the relevant regulation (14CFR91.121) doesn't allow for such sucky weather.

-- David Brooks

"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

"Ron Natalie" wrote in message
m...

To put it another way, flight levels don't exist below the transition
altitude
(18,000 Feet MSL In the US). If FL180 would be at 16950, it's not
available.

Is there a similar regulation in countries with lower transition altitudes?
On a really high pressure day, could you be cleared from 2,000ft to FL000?

-- David Brooks

"David Brooks" wrote in message
...
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?

Most of the planes flying in the flight levels, they climb quickly enough
that asking "when do you change the altimeter" is like asking "should I have
my dinner delivered at 5 minutes, 31 seconds past the hour, or 5 minutes 37
seconds past the hour".

For the rest of "us" (my plane is certified to 20,000', though it's not
worth the trouble to fly that high), I believe that you're supposed to
switch over to 29.92 during the climb when you actually reach FL180, and
switch back to the local altimeter during the descent when you leave FL180.

When you actually do switch is, of course, more a matter of practicality
than anything, since you won't be given vertical separation during the climb
or descent that might depend on your altimeter setting (not counting
separation at the top or bottom of the climb or descent, of course).

Pete

"David Brooks" wrote in message
...
It'd have to be a hell of a depression to affect FL220 though. The table
in
the relevant regulation (14CFR91.121) doesn't allow for such sucky
weather.

I guess that depends on your definition of "affect". The local barometric
pressure *always* affects FL220, just as it affects all other altitudes. If
you mean that FL220 is unlikely to be below 18,000' true altitude, sure.
But it moves around just as much as all the other flight level altitudes
(altitudes not really being discrete intervals).

Pete

"David Brooks" wrote
Maybe as you pass through FL180 descending, and as you pass through
18,000ft climbing?

You got it!

Bob Moore

The US uses 18,000 or FL180 as it's "transition" altitude.. other countries
us other altitudes, some as low as FL040 or 4,000ft MSL.

In the US: reset to 29.92 when climbing upon passing 18,000ft and climbing
to a FL
reset to the assigned local setting as soon as starting a descent when the
"altitude cleared to" is below FL180.

BT

"David Brooks" wrote in message
...
"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

3000ft here in the UK. Unless specified otherwise:

http://www.caa.co.uk/docs/64/DAP_ACD_8_Altimeter.pdf

Paul

"BTIZ" wrote in message
news:zqYnb.103692$La.22441@fed1read02...
The US uses 18,000 or FL180 as it's "transition" altitude.. other
countries
us other altitudes, some as low as FL040 or 4,000ft MSL.

In article , "David Brooks"
writes:

What do you oxygen-suckers actually do?

Reset the altimeter passing through FL180 going up or down. However, I hope I
am not sucking oxygen as this would be indicative of a major malfunction. :-)

G. Lee