QNH
From Wikipedia, the free encyclopedia.
QNH is a
Q code used by
pilots,
air traffic control (ATC) and
low frequency weather beacons to refer to the barometric
altimeter setting which will cause the altimeter to read altitude
above mean sea level within a certain defined region. This region may be fairly widespread, or apply only to the airfield for which the QNH was given. In the latter case, an altimeter calibrated to the QNH will read the runway elevation above sea level on landing. The lowest forecast value of QNH for an altimeter setting region is called the "regional pressure setting" and may be used to ensure safe terrain separation when cruising at lower altitudes. A
mnemonic for the code is "Query Newlyn Harbour".
Newlyn Harbour is home to the
Newlyn Tidal Observatory which is a reference for Mean Sea Level. Another mnemonic sometimes used is "Q - Not Here" meaning it refers to the pressure setting that applies away from the airfield. This is to distinguish it from QFE, which novices sometimes confuse.