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Altitude: Difference between revisions
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The code [http://en.wikipedia.org/wiki/QNH '''QNH'''] is how a pilot would request the "atmospheric pressure at sea-level". In reply [[ATC]] will repeat QNH followed with the pressure. These days QNH is also transmitted automatically on [[ATIS]]. | The code [http://en.wikipedia.org/wiki/QNH '''QNH'''] is how a pilot would request the "atmospheric pressure at sea-level". In reply [[ATC]] will repeat QNH followed with the pressure. These days QNH is also transmitted automatically on [[ATIS]]. | ||
To use | To use a barometer as a tool to measure the altitude, the altimeter, means it must be corrected for weather influences. For that the airfield has an accurate barometer and they know the height of the airfield above [[Mean Sea Level]]. From those two they will calculate the barometric pressure at [[Mean Sea Level]], the QNH. It will transmit the QNH and with that the altimeter in the aircraft can be corrected for weather influences and will display the [[#True height]]. This way the [[#Indicated altitude]] will be accurate for a certain area around the airfield as long as the weather remains stable. | ||
QNH is a vital tool to use a height map of an area, hence it is vital during approach of an airfield. | QNH is a vital tool to use a height map of an area, hence it is vital during approach of an airfield. | ||