Under what condition is density altitude equal to field elevation?

Density altitude represents the altitude at which the air density is equal to standard conditions at sea level, usually referenced at 29.92 inches of mercury (inHg) and 15 degrees Celsius (59 degrees Fahrenheit). Under standard atmospheric conditions, there is a direct correlation between density altitude and field elevation; in these conditions, the pressure, temperature, and humidity align with the International Standard Atmosphere (ISA) model.

When standard conditions exist, the air density at the field elevation corresponds to what is expected based on the standard atmospheric parameters. In other words, at sea level, density altitude is zero, and as you ascend, the density altitude will increase in a predictable manner if the atmospheric conditions remain standard.

Humidity, fog, and low temperatures affect density but do not create a scenario where density altitude equals the elevation of the field. High humidity causes air to become less dense, which increases density altitude above field elevation. Fog typically signals high moisture content in the air, which can also lead to an increase in density altitude. Lastly, when temperatures are below freezing, although the air is denser, the influence of temperature on density must be considered holistically with pressure and humidity to assess density altitude adequately.

Therefore, the condition that ensures density altitude