When would density altitude equal pressure altitude?

• A. When the temperature is standard.
• B. When the temperature is extremely warm.
• C. When humidity is high.
• D. When altitude is sea level.

Answer: (A)

Density altitude and pressure altitude line up only when the air temperature matches the standard atmosphere at that height. In that case, the air density is the same as the ISA value for that pressure level, so the altitude that corresponds to that density in the standard atmosphere is the same as the pressure altitude.

If the air is much warmer than standard, it becomes less dense, so density altitude becomes higher than pressure altitude—the air behaves as if you were at a higher altitude. Humidity can also reduce density a bit, which pushes density altitude higher, but the equality only holds when the temperature is the standard ISA value for that height. Being at sea level doesn’t guarantee equality by itself; you’d still need the temperature to be standard at that location.