Density

the aircraft is considered unsafe for IFR flight. Indicated altitude corrected for instrument

error is called Calibrated Altitude.

DENSITY

In order to calculate True Altitude, which is the height of the aircraft above Mean Sea

Level (MSL), calibrated altitude must be corrected for density. The two major factors

affecting air density are temperature and pressure.

TEMPERATURE

Outside Air Temperature (OAT) or Indicated Air Temperature (IAT) is measured with

aircraft instruments. These temperatures may or may not be corrected for aircraft

instrument error. Aircraft instruments are calibrated for standard lapse rates. An incorrect

instrument indication will result if the temperature deviates from the standard.

For every 11 C that the temperature varies from the standard lapse rate, the altimeter will

be in error 4%. If the air is colder than the standard atmosphere, the aircraft will be lower

than the altimeter indicates; if the air is warmer than standard, the aircraft will be higher

than the altimeter indicates. For purposes of this course always assume a standard lapse

rate.

Temperature's effects on pressure and density translate directly to corresponding affects

on TAS.

4.6-90