Message-ID: <367E0541.FF3FF659@his.com>
Date: Mon, 21 Dec 1998 03:22:25 -0500
From: Jeff Cook <jcook@his.com>
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Subject: Re: Finding Pressure Altitude
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Possum169 wrote:
> Is there a calculation for determining pressure altitude when given variables
> such as current barometric pressure and temps?...If so, how do you do it?


Here's the routine I go through on my flight plan. During a stage check,
the asst chief flight instructor copied it for himself (of course, he
never said why):


PRESSURE ALTITUDE:

 29.98 (Current Pressure)
-29.92 (Standard Pressure)
------
   .06 = 60 FEET

 4500 (intended Indicated Altitude)
-  60 (actual altitude adjustment; subtract because pressure is higher
than normal)
-----
 4440 (PRESSURE ALTITUDE)




Then you need to get 
DENISTY ALTITUDE:

Temp (degrees C)
----------------
 15C (std Sea Level Temp)
- 9C (std lapse = 2C x 4.5)
----
  6C (std @ 4500)
 18C (current @ 4500)
----
+12C (actual temp at 4500 is 12C warmer)

IF PRESSURE ALTITUDE IS 4500 AND TEMP IS 18C (+12C FROM STANDARD),
USE CLUNKY E6B OR ELECTRONIC CALCULATOR TO GET APPROX:

 5100 (DENSITY ALTITUDE)


Anybody see a problem with this? Seems to work fine for me. Of course
the difference between 4500 and 5100 feet is hardly worth mentioning,
but it's nice to get in the number crunching habit.

-- 
Jeff Cook
jcook@his.com
Washington DC area
