What is Flight Level (FL) – A surface of constant atmospheric pressure which is related to a specific pressure datum, 1013.2 hectopascals (hPa), and is separated from other such surfaces by specific pressure intervals.

What is Altitude – The vertical distance of an object measured from mean sea level.

What is Height – The vertical distance of an object measured from a specified datum (eg. Airport or Runway).

To obtain height, altitude and flight level of an aircraft from a datum (ground or from mean sea level), the most practised technique is by feeding the Pressure at the desired location into the aircraft system which will process and provide the exact height, altitude and flight level of the location from respective datums.

Meaning of QNH QFE QNE :

A pressure type altimeter calibrated in accordance with the Standard Atmosphere:

  • when set to a QNH altimeter setting, will indicate altitude above Mean Sea Level;
  • when set to a QFE altimeter setting, will indicate height above the QFE reference datum; and
  • when set to a pressure of 1013.2 hPa, may be used to indicate flight levels(FL).

Height Above Ground (QFE): A local altimeter setting equivalent to the barometric pressure measured at an airport altimeter datum, usually signifying the approach end of the runway in use. At the airport altimeter datum, an altimeter set to QFE indicates zero altitude meaning on the airport, the altimeter will read “0” feet.

Altitude (QNH): A local altimeter setting equivalent to the barometric pressure measured at an airport altimeter datum and corrected to sea level pressure. At the airport altimeter datum, an altimeter set to QNH indicates airport elevation above mean sea level (MSL).

Standard Altimeter Setting (QNE): QNE is a pressure setting at 1013 hPa that will produce a standard atmosphere altitude and provides the basis for flight levels. The term does not appear to be used by the ICAO, though the concept itself is used to produce flight levels. QNE is explicitly defined in U.S. FAA sources.

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