Why Often-Overlooked Atmospheric Pressure Is Critical for Every Pilot

Altimeter settings vary wildly in mountainous terrain, so lean on a lifesaving habit.

Scott Dennstaedt, Ph.D

Friday, November 21, 2025 at 08:00 AM ET

Verified

Edited By:

Travis Tingle

There is a way to understand the crude science of sea-level pressure reduction and how high-elevation airports can throw off your flight's most critical number. [Credit: Adobe Stock]

Key Takeaways:

Atmospheric pressure, specifically the altimeter setting, is a critical and accurately measured weather element that enables pilots to determine their height above the Earth's surface.
In mountainous areas, altimeter settings can vary significantly between nearby stations, even with weak pressure gradients, due to the complex reduction-to-sea-level calculation which introduces larger potential errors at higher elevations.
Pilots must always use the local altimeter setting provided by Air Traffic Control (ATC) or the field's Automated Surface Observing System (ASOS) to prevent substantial altitude errors (potentially hundreds of feet) and ensure flight safety.
Verifying the altimeter setting against the known airport elevation during pre-flight checks is crucial, as even minor mistakes can lead to significant and dangerous altitude discrepancies.

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No, this doesn’t address the anxiety you might feel while shooting an instrument approach to minimums or the intense pressure to keep your speed up after a slam-dunk vector to the final approach course into a busy airport.

In this case, I am talking about atmospheric pressure. Pressure is not something we ordinarily dwell on before or during a flight. But if you fly in a location where the mountain peaks are plentiful, then you should become better acquainted with how much the altimeter setting can truly vary in mountainous areas even when the weather is tranquil.