How High Am I Really?

While I have been confused often while learning new aviation skills, one item I have a hard time wrapping my head around is altitude.  Yes, I understood altitude meant how high the aircraft was, but what troubled me the most is there are several types of altitude. 

Indicated altitude is the altitude measured by the aircraft’s altimeter, the one most used during flight.

Absolute Altitude is the difference between the aircraft and the surface you are flying above.  While this is important information, it is not as practical to be used.  During level flight, the altitude would change based upon the terrain over which the plane is flying.  To maintain a consistent altitude, the pilot would have to consistently adjust.  Also, it is not as easy to measure as other types of altitude.  Absolute altitude is also referred to as the height above ground level (AGL).

True Altitude is the actual height above mean sea level (MSL).  On aviation charts, heights of ground obstacles will be displayed as true altitude.  During level flight, true altitude would not change based upon what you are flying over.  Also called actual altitude.

Pressure altitude is the altitude indicated when set to 29.92 in Hg.  This is the altitude above the standard datum plane, which is a theoretical plane when air pressure (corrected to 15 degrees C) equals 29.92 in.  Pressure altitude is used to compute density altitude, true altitude, true airspeed and other performance data.

Density Altitude is pressure altitude corrected for non-standard temperature.  It is where the aircraft “feels” like it’s flying.  If the density altitude is at 2,000 feet on the ground, then the aircraft feels like it is at 2,000 feet already and this will have an impact on it performance.  If density altitude is too high for the plane’s requirements, it could prevent flight.

My explanation may not of provided a clear understanding of the differences, but the different types of altitude have a greater impact when flying cross country.  As you fly from one region to another the barometric and temperature may change.  This has an effect on the closeness of the air molecules which can impact the altimeter readings. 

I’m sure there will be more to come. I found the below video which may help.