True altitude is the aircraft’s height above which reference point when using the described altimeter setting?

• A. Field elevation
• B. Mean sea level
• C. Ground level
• D. Aircraft altitude

Answer: (A)

True altitude is the vertical distance of the aircraft above mean sea level. When the altimeter is set with the local QNH (the current sea-level pressure adjusted for the area), the indicated altitude corresponds to height above mean sea level, giving you the true altitude (with small corrections for nonstandard temperature). Using field elevation as the setting would make the instrument show height above the field, not above sea level, so it wouldn’t represent true altitude. Ground level and aircraft altitude refer to different concepts or readings that don’t define the altitude relative to mean sea level.