Overgangshøyder

Overgangshøyder, which translates to "transition altitudes" in English, are critical safety altitudes used in aviation. They represent the altitude at which pilots are required to transition between two different altimeter setting systems. Specifically, it is the altitude at which the altimeter is changed from setting the local QNH (which provides true altitude above sea level) to the standard atmospheric pressure setting of 1013.25 hectopascals (hPa) or 29.92 inches of mercury (inHg).

The purpose of overgangshøyder is to ensure that all aircraft operating in a given airspace are using the same altimeter reference. This prevents dangerous altitude conflicts, particularly when aircraft are climbing or descending through this altitude band. Above the transition altitude, all aircraft will display the same altitude readings if they are at the same true altitude, as they are all referencing a common pressure setting. This creates a "flight level" system, where altitudes are referred to as flight levels (e.g., Flight Level 350).

Conversely, the "transition level" is the altitude at which aircraft descending below the transition altitude change their altimeter setting back to the local QNH. This ensures that aircraft are aware of their precise altitude above ground level or sea level in relation to terrain and obstacles as they approach the airport. The specific values for transition altitude and transition level are determined by air traffic control authorities for each country or region and are published in aeronautical information publications (AIPs).