What defines pressure altitude?

Pressure altitude is defined as the altitude at which the atmospheric pressure is measured to be 29.92 inches of mercury (Hg) or 1013.25 hPa. This standardized setting allows pilots and air traffic controllers to communicate and operate under a common reference point, especially in conditions where weather can cause pressure differences.

When altimeters are set to 29.92 inches of mercury, they provide a reading of pressure altitude, which is particularly useful during high-altitude operations and when flying in controlled airspace. This adjustment eliminates the variables of local atmospheric pressure differences, thereby allowing for more accurate altitude readings across different aircraft.

The other options do not correctly define pressure altitude. The height above the ground level refers to elevation and does not take into account atmospheric pressure. Mean sea level is part of the definition, but pressure altitude specifically requires the setting to the standard pressure of 29.92 inHg. Lastly, aeronautical charts provide various types of altitude references, but they do not define pressure altitude specifically.