#### uwochris

##### Flightinfo's sexiest user

- Joined
- Dec 21, 2001

- Posts
- 381

- Total Time
- 2500+

I seem to get confused when reading about PA and its significance.

From what I understand, PA is simply indicated altitude corrected for non-standard pressure. This all goes back to the fact that the altimeter is calibrated to a standard atmosphere, so when the atmosphere isn't standard, there will be some error. So, by calculating the PA, you are in fact determining the pressure that the a/c thinks it's flying at (or the altitude it thinks its at), assuming standard temperatures. And since all charts are based on PA, it is very important to determine it.

Is my understanding correct? The thing that gets me confused is that we should be more interested in Density Altitude, as it correctes for non-standard temps. I mean, how often can the atmosphere be standard, especially now? Why not worry about DA only, and discard PA? It seems DA is far more relevant, because it gives the altitude the a/c thinks its at, corrected for non-standard temps.

Also, just one more question. I assume that a lower PA is better; is this correct? For instance, if I calculate the PA to be 600' today, but 3000' tomorrow (I know, an xtreme example), it seems that the 600' would give better performance: lower altitudes= more dense air= better performance. Is this correct?

Thanks a lot for the help!