Pressure Altitude (PA)
Calculates the Pressure Altitude (PA) based on field elevation and QNH setting.
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PA (Pressure Altitude)
Pressure Altitude (PA) is the altitude in the International Standard Atmosphere (ISA) where the air pressure is equal to the current atmospheric pressure. It is a critical metric used by pilots and aeronautical engineers to determine aircraft performance, as standard performance charts are based on pressure altitude rather than indicated altitude.
Why Use This Tool?
Indicated altitude only matches your actual height above sea level when the barometric pressure is standard (29.92 inHg or 1013.25 hPa). Since pressure varies with weather, you must correct your elevation using the current QNH setting to find your Pressure Altitude. This value is the first step in calculating Density Altitude, which determines how much lift your wings generate and how much thrust your engine produces.
Practical Applications
- Flight Planning: Use PA to determine takeoff and landing distances from aircraft manuals.
- Engine Performance: Accurate pressure altitude helps in leaning the engine and estimating fuel flow.
- Safety: Understanding PA is vital for high-altitude operations where engine performance significantly degrades.
live_help Frequently Asked Questions (FAQ)
What is the difference between Altitude and Pressure Altitude?
Altitude (indicated) is your height above mean sea level as shown by your altimeter after setting it to the local pressure (QNH). Pressure Altitude is your height above the theoretical 29.92 inHg (1013.25 hPa) pressure level. PA is used for performance calculations because aircraft engines and wings respond to pressure, not actual height.
When should I use the 29.92 inHg (1013.25 hPa) setting?
In aviation, you switch to the standard pressure setting (29.92/1013.25) when climbing through the “Transition Altitude” (which varies by country). Once above this altitude, you operate in “Flight Levels,” which are essentially increments of Pressure Altitude.
Why is my Pressure Altitude lower than my actual elevation?
This happens when the atmospheric pressure is higher than standard (high-pressure system). High pressure “pushes down” the theoretical standard pressure level, making the air denser and your Pressure Altitude lower, which generally improves aircraft performance.
How does PA relate to Density Altitude?
Pressure Altitude is the first step in finding Density Altitude (DA). DA is simply PA corrected for non-standard temperature. If the temperature is standard for your altitude, PA and DA will be the same.