FAA Ground School Practice Test

How does high altitude affect air density?

1. Air density increases

2. Air density decreases

3. Air density remains constant

4. Air density is unaffected by altitude

The correct answer is: Air density decreases

High altitude has a significant impact on air density, primarily causing it to decrease. As altitude increases, the atmosphere becomes thinner because there is a lower pressure of air molecules at higher elevations. This reduction in pressure results in fewer air molecules being present in a given volume of space, which leads to a lower density of air. At sea level, air is denser due to the weight of the air being pressed down by the atmosphere above it. However, as one ascends to higher altitudes, the number of air molecules decreases, along with the overall pressure of the air column, which in turn reduces the density of the air. This effect is critical for pilots and aviation operations, as lower air density affects aircraft performance characteristics such as lift, engine performance, and climb rates. Understanding the decrease in air density with increasing altitude is essential for safe and effective flight operations.