Types of Altitudes in Aviation


When it comes to flying airplanes, there are numerous types of altitudes a pilot must consider. Here's what they all mean, including examples of where you might come across each one.

Indicated Altitude

Indicated altitude is what is indicated on the altimeter in your airplane. 


True Altitude

True altitude is the height of the airplane above Mean Sea Level (MSL). Area forecasts (FAs) report cloud height in MSL and airport elevations, terrain and obstacle clearance altitudes listed on the VFR sectional charts are often given in MSL, or true altitude.


Pressure Altitude

Pressure altitude is the altitude above the standard datum plane and is also the altitude that your altimeter reads when it's set to 29.92, which is the standard pressure setting. Pressure altitude is important when it comes to computing aircraft performance data like takeoff and landing distances. It's also the altitude that operators use while flying in Class A airspace, where everyone is required to set their altimeter to 29.92 in order to standardize the indicated altitudes. You can actually determine the pressure of the air by calculating the difference between the pressure altitude and the current altimeter setting. 


Density Altitude

Density altitude is important for determining the performance of an aircraft, or how the aircraft will "act" under certain conditions. Density altitude is pressure altitude corrected for nonstandard temperature - and, since the temperature is always nonstandard, it's important to know the density altitude.

 At sea level, the standard temperature is 15 degrees celsius. It decreases, on average, about 2 degrees per 1,000 feet increase in elevation. At sea level, the pressure altitude will be the same as the density altitude when the temperature is standard - or 15 degrees celsius. Density altitude is what your aircraft "feels like" it's at.

If the airport elevation is 5,000 feet MSL and the temperature is above standard, as it might be in Prescott, Arizona on a summer day, then your airplane might "act like" it's at 7,000 feet instead of 5,000 feet, meaning there could be a substantial decrease in performance characteristics and an increase in takeoff and landing distances.  


Absolute Altitude (AGL)

Absolute altitude is the height above ground level or the actual height above the earth's surface. METARs and TAFS report cloud cover in AGL, and if you have a radar altimeter on your airplane, it will depict an AGL altitude.