Under Pressure

Tim Vasquez

Thursday, January 21, 2021 at 12:12 PM ET

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

Key Takeaways:

The article differentiates various atmospheric pressure values crucial for aviation and meteorology, including Station Pressure (QFE), Altimeter Setting (QNH), Sea Level Pressure (QFF), and Pressure Altitude (QNE).
Pressure reduction techniques are essential to convert raw readings from diverse elevations to standardized sea-level references, enabling comparable altimeter settings for pilots and accurate data for weather forecasting.
QFE represents the actual pressure at an airfield, QNH extrapolates to mean sea level for pilot altimeters (especially below 18,000 feet), and QNE uses a standard 29.92 inches of mercury reference for flight at higher altitudes.
Accurately understanding and setting the altimeter (especially QNH) is critical for flight safety, as errors or unusual weather conditions (e.g., low pressure, cold air) can cause altimeters to read artificially high, posing significant dangers.

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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.