Why is pressure altitude inportant?

Question

I am a student pilot and I am wondering why pressure altitude is important. Is it just so I know how the airplane will respond?

Answer 1

Two things I can think of...

1) Performance calculations: Aircraft response is indeed related to pressure.

2) Common Reference: Radio Altitude is with reference to local datum. In situations where altitude needs to be communicated (i.e to the ATC), we cannot use a local reference. So the Pressure Altitude is used.

Answer 2

You use pressure altitudes when flying at FL180 or above.. its important for vertical seperation

Answer 3

Nobody ever gets this one right as is evident with the answers so far but you got it paul. So as a student you get an A and I give everybody else here a C-. Better put would be so you'll know how the airplane will perform. PA is what matters when considering takeoff performance for instance because it indicates the true density of the airmass. So just dial in 29.92 in your kolsman window and read the PA. That's usually where you'll enter the the performance chart.

Answer 4

Wing and engine performance depend much on density altitude, which can be found by correcting pressure altitude for nonstandard temperature and humidity.  (There are density altitude tables and a Denalt circular computer for that).  Aircraft performance tables which have pressure altitude and temperature as inputs accomplish about the same thing.

Pressure altitude, not indicated altitude, is what is encoded and transponded.  That altitude is then corrected, using the local altimeter setting.

Answer 5

In aviation, pressure altitude is the indicated altitude when an altimeter is set to an agreed pressure setting. This setting, 101.325 kPa - equivalent to 1013.25 millibar, or 1013.25 hectopascals, or 29.92 inches Hg, is a baseline pressure setting equivalent to the International Standard Atmosphere (ISA) at sea level. It is primarily used in aircraft performance calculations, and in high-altitude flight (Class A airspace in the United States, which is controlled airspace at or above 18,000 feet MSL. In radio communication, it is referred to by the Q code QNE.

The relationship between static pressure and pressure altitude is defined in terms of the properties of the International Standard Atmosphere.

Answer 6

Can you imagine what will happen above there when many aircraft flying, using different altitude referrence/setting ?

Answer 7

It is a standardised altimeter setting above FL 180 so that the controllers can be aware that all aircraft are being flown at heights which are universally understood and accepted. It especially caters for the 'Quadrantal Height Separation' system under which pilots are flying headings and heights according to that system. The controllers do not have to worry that different aircraft are flying with different altimeter settings.