Converting to Pressure Altitude

[meritflyer]

I have a ground lesson with a new student pilot -

Just to confirm, when we're converting to pressure altitude, we take 29.92, subtract the current altimeter setting and multiply by 1000 to get the amount of altitude to subtract or add to the field elevation.

Example -

Current altimeter: 30.12
Elevation: 1000

29.92-30.12 = .2(1000) = -200'

So pressure altitude would be 800'.

Do I have that right? Its been a long time since I messed with this stuff.

 

[MattHansen]

I believe you are correct. That's how I do it, anyway. Another way to think of it is that when you twist to a lower altimeter setting, the indicated altitude decreases also, so as you turn from 30.12 to 29.92 the altitude indicated drops from 1,000 to 800. The decimal in the altimeter setting is like the comma in the altitude so an altimeter setting decrease of 00.20 is the same as and altitude decrease of 0,200'.

I don't know if that helps at all, but you've got it right.

-Matt

 

[MSNFlyer]

Yes, the higher the pressure the lower your pressure altitude will be.

I have found that drawing a picture helps your students with this concept. First draw sea level and your elevation and explain true altitude and how it is the same on a standard day. Then change your sea level pressure to 30.12 and ask them where they think 29.92" will occur--higher or lower than sea level? Once they get the concept down of 29.92 being closer to field elevation on a high pressure day it is simple math to figure out your pressure altitude.