Pressure altitude is the height above the standard datum plane when the altimeter is set to what value?

• A. 29.92 inches of mercury
• B. 30.00 inches of mercury
• C. 28.92 inches of mercury
• D. 29.50 inches of mercury

Answer: (A)

Pressure altitude is the height above the standard datum plane, and that plane is defined by a standard sea-level pressure of 29.92 inches of mercury. When the altimeter is set to 29.92 inHg, it is calibrated to read altitude relative to that standard plane, so the indicated value is the pressure altitude.

Setting the altimeter to a value higher or lower than 29.92 changes the reference pressure and thus the reading: a higher setting makes the altitude indication appear lower than the true pressure altitude, while a lower setting makes it appear higher. The other options use pressures different from the standard 29.92 inHg, so they do not yield the defined pressure altitude.