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Under Pressure

Evangelista Torricelli is credited with the invention of the barometer in the mid 17th century.
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Key Takeaways:

  • The article details various atmospheric pressure measurements used in aviation and meteorology, including Station Pressure (QFE), Altimeter Setting (QNH), Sea Level Pressure (SLP), and Pressure Altitude (QNE), explaining their derivations and specific applications.
  • A key challenge in interpreting pressure data is compensating for varying station elevations, leading to methods like QNH and SLP which "reduce" observed pressure to a common sea-level reference for consistent forecasting and altimetry.
  • The Altimeter Setting (QNH) is critical for pilots below 18,000 feet, providing altitude relative to sea level, and its accurate setting is vital for flight safety, as errors or unusual weather conditions (e.g., low pressure, cold air) can cause altimeters to read dangerously high.
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Dialing in the altimeter setting is perhaps one of the most universal, timeless rituals of aviation, spanning decades, continents, and cultures, and tying all pilots to one another. This underscores the importance of atmospheric pressure and its effect on flight safety. But how much do you know about where those numbers come from?

In this issue we’ll take an introductory look at barometers, pressure, and get a better look at where QNH, QFE, and other values come from. If you’ve found them mysterious or confusing, this article is for you.

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