He's not entirely wrong.

Above 18,000 you use 29.92 for your altimeter setting.

Bob

> -----Original Message-----
> From: Nate Duehr [mailto:nate@NATETECH.COM]
> Sent: Wednesday, September 04, 2002 5:23 PM
> To: PICLIST@MITVMA.MIT.EDU
> Subject: Re: [EE]:Barometer & Altimeter
>=20
>=20
> This is way off-topic on this response, but in this day and age of
> e-mail list archives ending up on Google...
>=20
> Dave... you're going to end up hurting someone if you use 29.92 every
> time you're IMC like that.
>=20
> You're actually supposed to use the closest known correct altimeter
> setting to your location.  And ATC has requirements to make sure that
> you have that setting if you're in the IFR system unless you're in
> uncontrolled airspace (rare even out here in the "West" anymore), then
> it's the Pilot-in-Command's responsibility to get.
>=20
> I'm too lazy to go to the basement to get the FAR, AIM, and=20
> Controller's
> Handbook references right now, but please... don't just use 29.92
> blindly.
>=20
> You're friendly neighborhood aviation safety warning guy...
>=20
> Nate
>=20
> On Wed, 2002-09-04 at 15:46, Dave King wrote:
> > >If I am driving up a mountain and a storm is approaching=20
> then what? The
> > >pressure drops from the storm and changes the
> > >barometric pressure changing the altimeter, which is=20
> changing because I am
> > >driving up the mountain.
> > >
> > >The MPX4115A is calibrated and compensated. Then pressure=20
> measured is
> > >correct, so how do I know when the change if from
> > >the altitude or a storm? If I am not moving then no=20
> problem. The altitude
> > >is the constant, If there is no storm then the
> > >relative barometric pressure is the constant.
> > >
> > >Gordon Varney
> >
> > You can't know what is affecting what. In aircraft altimeters the
> > barometric pressure is set to local pressures as you go
> > along if you are low level and to 29.92 inches of mercury=20
> if you are ifr.
> > The idea is that everyone in the same area/altitude
> > will at least be using the same base setting and be able to=20
> know what
> > altitude they are at.
> >
> > With a fixed station position you can set the altimeter to=20
> a known altitude
> > and derive the current pressure. With your setup
> > unless you have access to a local/regional report or can=20
> set it to a known
> > altitude its as good as you can get.
> >
> > Dave
> >
> > --
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> >
>=20
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>=20
>=20
>=20

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