What is qnh in flying

A site that includes everything related to civil aviation. The term of Q codes were set of 3 letters begging with a Q to make a clear method of communication. The Q letter basically signifies a question. Generally, QNH is Q nautical height which means indicating altitude at the height above sea level. Setting on altimeter on the ground, will read the correct elevation above sea level whereby QNH allows displaying the airfield elevation above mean sea level.

For example, if the airport which at feet above sea level, the altimeter shall read as well. Further, QNH also a common setting used during take-off and landing whereby used below the transition level. QNH also known as regional pressure settings because it ensures the aircraft safe terrain separations when cruising at lower altitudes. There is no mention of QNE at all. It reads zero when you are on the runway and gives your height above it when you are airborne.

FAA reference material. It reads runway elevation when you are on the runway and is based on an altimeter setting adjusted until the station's correct elevation above sea level is read. 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.

FAA sources. The terms "altimeter setting" and "barometric pressure" can be confusing but should not be. They are the same thing. You input barometric pressure into your altimeter and it produces altitudes.

Click photo for a larger image. There isn't a lot of source material on what you are setting in what is known as the "barometric scale" by some, but is more properly called the "Kollsman Window," in honor of Paul Kollsman the person who invented the first sensitive barometer. There are three choices, each of which is based on how high a column of mercury can be pushed up by atmospheric pressure in a vacuum tube. See: Altimetry Theory for a more indepth explanation. Most of us in the United States are accustomed to using inches for that scale.

Setting A hectopascal is equal to a millibar, which is one-thousandth of a "standard atmosphere" which is equal to 1, "dynes" which comes to about 0.

At other altitudes, the indicated altitude is likely to be in error, depending on the temperature of the atmosphere. QFE - The pressure set on the subscale of the altimeter so that the instrument indicates its height above the reference elevation being used. QFE is the isobaric surface pressure at the reference point. At other altitudes the altimeter will give an indication of the height above that reference point.

With the aerodrome QFE set in the subscale, your altimeter will read zero on the highest point on the runway and at other altitudes will read the height above the airfield elevation.

For precision approach runways or for instrument runways when the threshold is 7 ft or more below aerodrome elevation, the QFE may be based on the threshold elevation [ICAO Doc , 4. With the runway threshold QFE set in the subscale, your altimeter will read zero on the runway threshold.

QNE is different to the other altimetry Q codes in that it is an altitude not a pressure although it is commonly incorrectly described as such. With Standard Pressure