Which altitude is used for flight levels and is derived from setting 29.92?

• A. Absolute altitude
• B. Indicated altitude
• C. Pressure altitude
• D. True altitude

Answer: (C)

Pressure altitude is used for flight levels because it provides a constant reference surface based on standard atmosphere. When the altimeter is set to 29.92 inches of mercury, it reads the pressure level rather than actual height above the ground or sea level. In standard atmosphere, that pressure level corresponds to a fixed altitude, so flight levels (like FL180) are essentially pressure altitude readings, meaning 18,000 feet of pressure altitude. This uniform reference is essential for vertical separation between aircraft regardless of local weather or terrain.

Other altitude types describe different references: absolute altitude is height above the terrain, indicated altitude is what you read on the altimeter with the local setting, and true altitude is height above mean sea level corrected for nonstandard temperature and pressure. For flight levels, the standard reference is pressure altitude using the 29.92 setting.