Cardinal Altitude

What Is a Cardinal Altitude?

Cardinal altitudes are flight levels expressed in thousand-foot intervals or in flight levels. For example, a flight level of 250 (FL250) is equal to 25,000 feet. Cardinal altitude is used to maintain a safe flying distance between planes as they approach and depart from an airport. Each aircraft is assigned a specific flying level in order to avoid collisions with other aircraft. Cardinal altitude is based on local air pressure because differences in altimeter calibration can result in planes flying at the same flight level as each other. Thus, near the ground, aircraft will use cardinal altitude and switch to standard flight levels once they have reached a high enough altitude.