What is qnh

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Term » Definition. Word in Definition. Freebase 0. Suggested Resources 0. How to pronounce QNH? Alex US English. David US English.

Mark US English. Daniel British. Libby British. Mia British. Karen Australian. Hayley Australian. Natasha Australian. Veena Indian. Priya Indian. Neerja Indian. Zira US English. Oliver British. Wendy British. Fred US English. Tessa South African. How to say QNH in sign language? 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 Pressure to height conversions in altimetry are based on ISA. In non-ISA conditions, altimeter readout may be significantly different than the true altitude of said altimeter.

Since cold air is denser than warm air, isobaric surfaces are vertically more constrained towards the ground. It is for flight in colder-than-ISA that particular attention must be paid to true altitude. The altimeter readout, being an underestimate of the actual altitude, may lead crews to think they are higher than they actually are, and can lead to serious incidents if not accidents.

Since all altimeters are based on ISA, notwithstanding instrument error, altitude readouts between aircraft will be similar.

Therefore with the notable exceptions of flight in mountainous terrain or at low altitudes near the ground, aircraft will fly consistent altitudes regardless of taking into account true altitude.

See also the article Altimeter Temperature Error Correction.