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Re[3]: correct air pressure and aircraft altimeter settings
>Content-Description: cc:Mail note part
>Date: Thu, 26 Mar 1998 13:46:49 -0500
>Reply-To: Medical Physics Mailing List <MEDPHYS@LISTS.WAYNE.EDU>
>Sender: Medical Physics Listserver <medphys@lists.wayne.edu>
>From: James Burns <Jim.Burns@PROMEDICA.ORG>
>Subject: Re[3]: correct air pressure and aircraft altimeter settings
>To: Multiple recipients of list MEDPHYS <MEDPHYS@LISTS.WAYNE.EDU>
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>Subject: Re: correct air pressure
>Author: Bob Flood <bflood@SLAC.Stanford.EDU> at internet_smtp
>Date: 3/26/98 11:55 AM
>
>
>Well, those mis-spent years as a meteorologist finally become useful!
>
>The local weather service determines pressure in 2 ways, each for a
>different purpose.
>
>Naturally, pressure varies dramatically with elevation. A pilot trying to
>land needs to know the actual air pressure so s/he can set the altimeter
>for local conditions. Thus, the pressure value must reflect actual
>conditions including current weather AND altitude.
>
> ....
>
> ----------------------------------------------------------------------
>
> But a pilot needs to set the altimeter to the local pressure corrected
> to sealevel. The altimeter measures the pressure at its location and
> calculates the altitude based on the difference between the measured
> pressure and the pressure setting. As he wants to know his altitude
> above sea level, not above the ground, that setting needs to be the
> sea level corrected reading. However, all pilots above about 20,000
> set altimeters to a standard value around 29.92 so everyone in a small
> area will be at the same altitude for the same reading.
>
> radar altimeters are used to measure distance above the ground.
>