what is pressure altitude
Pressure altitude is the height above a standard datum plane (SDP), which is a theoretical level where the weight of the atmosphere is 29.92 Hg (1,013.2 mb) as measured by a barometer. An altimeter is essentially a sensitive barometer calibrated to indicate altitude in the standard atmosphere.If the altimeter is set for 29.92 Hg SDP, the altitude indicated is the pressure altitude. As atmospheric pressure changes, the SDP may be below, at, or above sea level.ore widely, this is also the PRESSURE ALTITUDE, which is alternatively defined as the height of any level in the international standard atmosphere (ISA-see above), above the level corresponding to a pressure of 1013.2 hPa.
In aviation, pressure altitude is the indicated altitude when an altimeter is set to an agreed baseline pressure setting under certain circumstances where the aircraft's altimeter would be unable to give a useful readout of altitude.ircraft transponders report the pressure altitude; corrections for atmospheric pressure variations are applied on the ground. The relationship between static pressure and pressure altitude is defined in terms of the properties of the International Standard Atmosphere.