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Atmospheric pressure

  • What is Atmospheric pressure? Standard pressure, Pressure levels, QNH, QFE, Pressure Altitude
  • Atmospheric pressure or barometric pressure; Is the unit force applied by the atmospheric column on a given surface. The atmospheric pressure is usually measured by bar and aneroid (liquid-free) barometers. In other words; The gases that make up the atmosphere have a certain weight. The pressurized atmosphere that the gases apply to the objects on earth is called the press.


  • When expressing the atmospheric pressure, a wide variety of units that vary according to the country or purpose are used:
  • Millimeter mercury (MmHg)
  • Inches of mercury (InHg)
  • Inch-pound (psi)
  • Dyne affecting square centimeter (dyne / cm2)
  • Milibar (mb)
  • Standard atmosphere (atm)
  • Pascal (kilopascal or hectopascal)


  • Standard pressure
  • Standard atmospheric pressure at sea level is 760 MmHg; 29.92 InHg; 14.70 psi; 1013.25 x 10 & lt; 3 & gt; dyn / cm & lt; 2 & gt ;; 1013,25 mb (or hPa); 1 standard atmosphere or 101,325 kilopascals. Atmospheric pressure on the sea level does not show much difference. The highest value recorded so far is 32,01 InHg (1084 mb) in Siberia and 25,90 InHg (877 mb) in a spectrum in the South Pacific. These small pressure differences determine the Earth’s storm and wind patterns.


  • As the atmospheric pressure increases around the earth (3.5 mb per 30 meters), it decreases. However, as the density of cold air is higher, the rate of decrease in pressure with height is higher in cold regions. At a height of 270,000 meters, the pressure drops to 10-6 mb, which is the lowest pressure achieved with vacuum. Between 1500 and 3000 meters (5000 to 10,000 feet), the pressure drops to such an extent that it causes altitude discomfort and other serious physiological disturbances and climatic adaptation techniques must be applied.


  • Atmospheric pressure

    Atmospheric pressure

  • The atmosphere is reduced as the pressure of the pressurized air increases from sea level. The increase in the dark blue color of the diagram and the expansion of the column as the height of the column symbolize the decrease in the density of the air.






  • Pressure levels
  • The decrease in atmospheric pressure as height increases is commonly used to calculate the elevation (altitude) of air vehicles relative to any reference point. The pressure submeter used in air vehicles is an aneroid barometer with a scale of altitude values. Any pressure value is entered in the setting window of the submometer. The altimeter indicates the height of the vehicle from this pressure line, which is entered into the window.


  • The most common Q codes used to specify pressure levels are QNH, QFE, and QNE. These codes are not abbreviation.


  • QNH
  • QNH is the atmospheric pressure value at the mean sea level (MSL). When the regional QNH value is entered into the altimeter, it indicates the height of the vehicle over the average sea level. The QNH value is widely used in close proximity to earth because the altitudes used in the maps are also based on the mean sea level.


  • QFE
  • QFE is the pressure value measured at any point. When the QFE value of the square is entered into the altimeter of an aircraft in the ground, the altimeter gives an approximate zero height value. QFE is used especially during landing and take-off, as the value is sensitive to the challenge altitude. However, when you are away from the square, the altitude of the manners on the ground will be different from the sky, so flying with the QFE value is not safe.


  • Pressure Altitude
  • The pressure altitude is the value read from six digits when the QNE value (standard pressure) is connected to the altimeter. The QNE value is 1013.25 millibar or 29.92 InHg and is constant. The QNE line is an imaginary line at this pressure. Especially in high-level flights (above transitional altitude) they use this value to provide standardization of aircraft. Otherwise, it is difficult to distinguish the safe altitude between aircraft because QNH and QFE values ​​are not constant values.
Atmospheric pressure
Author: wik Date: 1:03 am

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