So Many Altitudes

The one you should be concerned with depends on how you measure it, and how hot or cold conditions might be.

Jim Wolper

Friday, January 10, 2025 at 08:00 AM ET

Verified

Edited By: Omar Filipovic

Key Takeaways:

Aviation employs multiple types of altitude measurement, including barometric, radar, and GPS, each based on different principles and used for distinct purposes.
Barometric altimeters, the primary method, are susceptible to errors caused by variations in atmospheric pressure and temperature, necessitating correct altimeter settings to avoid significant inaccuracies, particularly in cold weather.
Radar altimeters provide accurate height above ground at low altitudes, independent of atmospheric conditions, while GPS altitude measures position relative to an Earth model and can differ notably from barometric readings.
Understanding the unique characteristics, advantages, disadvantages, and potential errors of these various altitude sources is critical for pilots to ensure flight safety and prevent collisions.

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I recently overheard a couple of pilots talking about various kinds of altitude. “How many altitudes are there?” one asked. I don’t recall the details of any answer he got but, alas, the answer is that there are many. If you use the wrong one, you might get into an uncomfortable situation.

Aviation Safety has discussed altimetry errors in numerous articles over the years. See November 2015’s “Your Altimeter Is Lying” for an example. Meanwhile, let’s stick to the more conceptual errors.