Section 9, Lesson 1
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Pressure Altitude

Pressure Altitude

Somewhere in the atmosphere, the pressure is 29.92″ Hg. Pressure altitude is our height above that area of standard pressure. Pressure altitude is important because it directly influences atmospheric performance, and is a component of density altitude, which is an even better performance metric.

Lesson Notes

Pressure altitude is the height above standard pressure, the line (or theoretical line) where the atmospheric pressure is 29.92’’ Hg. Or, said differently, pressure altitude is the altitude displayed in an altimeter that is set to 29.92.

Pressure altitude allows us to understand how the air pressure compares to a standard day.

On average, around the world, atmospheric pressure is 29.92’’, but local weather patterns cause this to change regularly. Pressure in the atmosphere always decreases with height at a rate of 1″ mercury for every 1,000 feet. This means at 1,000 feet MSL the standard atmospheric pressure is 28.92’’. However, a standard altimeter setting for an airport at 1,000 MSL would still be 29.92’’. That’s because the altimeter shows the difference between the pressure set in the Kollsman window and the actual atmospheric pressure. If we set the actual atmospheric pressure, the altimeter would indicate 0, which is immediately not helpful to us as soon as we takeoff. Weather stations at airports measure the pressure, correct for height by applying a standard lapse rate of 1’’ per 1,000 feet and then transmit the corrected value to pilots in text or radio reports.

Additional Resources

Flashcard Questions

What is pressure altitude?

What is standard pressure at 3,000′ MSL?

If the current altimeter is 29.90, and you are at 1,000 feet MSL, what is your pressure altitude?