Altitude – definition and calculation
10.01 Definitions
HEIGHT= Vertical distance above ground, Altimeter scale is set to QFE.
ALTITUDE = Vertical distance to MSL, (MSL = Mean Sea Level), Altimeter scale is set to QNH.
PRESSURE ALTITUDE = The indicated height if the altimeter scale is set to 1013.2 hPa. (1013.25 hPA = 1013.25 mbar = 29.92 inch HG)
= ISA (International Standard Atmosphere).
10.02 General
Density Altitude and True Altitude are calculated with the Pressure Altitude as a base. If the indicated air pressure does not comply with ISA, it needs to be converted to obtain the Pressure Altitude. Pressure Altitude is lower for pressures above 1013.2 hPA and vice versa (subtract or add 30 feet per millibar).
10.04.01 Density Altitude DA
The Density Altitude (DA) is very important for the performance of an aircraft. The data in the flight manual
are based on ISA conditions for the current temperature at the altitudes indicated. If the temperature
deviates from ISA then the DA is different. This means that if the temperature is higher than the DA is also higher
and vice versa.
Correction factors are given in most flight manuals, should this not be the case they can be calculated with the Aviation Calculator.
