What is pressure altitude?

• A. Altitude above mean sea level.
• B. Altitude above the standard 29.92 inHg plane.
• C. Indicated altitude corrected for nonstandard pressure.
• D. Altitude at which air pressure equals 1 atm.

Answer: (B)

Pressure altitude is the altitude in the standard atmosphere that corresponds to the current ambient pressure. In practice, it’s the height above the standard datum plane where the pressure is 29.92 inches of mercury. When you set the altimeter to 29.92, the instrument reading is the pressure altitude, which lets you compare altitude and performance under different weather conditions independent of the actual sea-level pressure. The other ideas describe true altitude (height above mean sea level, possibly corrected for nonstandard pressure) or aren’t meaningful for altitude in aviation (a pressure of 1 atm corresponds to sea level, not an altitude).