Which altitude metric is primarily used to describe the effect of air density on aircraft performance?

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

Answer: (B)

When thinking about how air density affects aircraft performance, the key measure is density altitude. It represents the altitude in the standard atmosphere at which the air density is equal to the current air density. In other words, it translates actual pressure and temperature conditions into a single altitude value that reflects how “dense” the air behaves for performance calculations. Higher density altitude means thinner air, which reduces engine power, propeller efficiency, and wing lift, leading to slower climbs and poorer overall performance. Lower density altitude means denser air and better performance.

Indicated altitude is simply what the altimeter shows, adjusted for local instrument error and pressure settings, and does not directly describe how density affects performance. Pressure altitude is the altitude corresponding to a pressure in the standard atmosphere and is used for certain routing and performance calculations, but it describes pressure conditions rather than density. True altitude is the actual height above mean sea level, not a density-related metric.