At other altitudes the altimeter will give an indication of the height above that reference point. QFE is the isobaric surface pressure at the reference point. In the PANS-OPS Doc 8400, see Q-Codes, QFE is referred to as “Atmospheric pressure at aerodrome elevation (or at runway threshold)” QFE - The pressure set on the subscale of the altimeter so that the instrument indicates its height above the reference elevation being used. At other altitudes, the indicated altitude is likely to be in error, depending on the temperature of the atmosphere. As your altimeter is calibrated using ISA, it will indicate altitude correctly at the airfield reference point. The altimeter will read runway elevation when the aircraft is on the runway.Īirfield QNH is obtained by correcting a measured QFE to sea level using ISA regardless of the temperature structure of the atmosphere. QNH - The pressure set on the subscale of the altimeter so that the instrument indicates its height above sea level. Three references for barometric pressure are in common usage: QNH, QFE and Standard Pressure. Millimetres of mercury (CIS and some other south-east European States).Inches of mercury (inHg) (in particular North America).
Variations from the standard shown in the Supplement to ICAO Annex 5 include: The SI or metric unit of measurement for barometric pressure is the hectopascal (hPa) and this is adopted in respect of altimeter pressure settings in ICAO Annex 5. Sound altimeter setting procedures are an essential tool in ensuring safe separation from the ground and from other aircraft. The datum selected depends on the barometric pressure set on the altimeter sub-scale. Aircraft pressure altimeters indicate the elevation of the aircraft above a defined datum.
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