During the Military Flight Aptitude Test, you can expect questions about the atmosphere and how it relates to the aviation world. The aircraft you pilot someday will penetrate the atmosphere somewhat like a boat paddle going through the water, so you want to know a little more about the makeup of the wild blue yonder than just “It’s made of air and stuff.”

The earth’s atmosphere is comprised of various elements; as a whole, it affects your aircraft and its performance. But aviators are primarily concerned with the oxygen in the atmosphere and the effect that element has on their bodies, as well as how temperature and humidity affect aircraft performance.

Just a little more than 20 percent of the atmosphere is made up of oxygen; this element is relatively heavier than most other gaseous elements in the atmosphere, so you find more of it below 30,000 feet. The higher you fly, the less oxygen pressure you have available, and that’s why pilots wear oxygen masks above a certain altitude.

Here’s an example of an atmosphere-type question you may encounter:

The most accurate description of earth’s atmosphere is that it is made up of
  • (A) 78 percent oxygen, 19 percent nitrogen, and 2 percent carbon dioxide, with trace amounts of water vapor and dust particles.

  • (B) 3 percent water vapor, 78 percent ozone, and 20 percent nitrogen.

  • (C) 20 percent oxygen, 77 percent hydrogen, 3 percent carbon dioxide, and some water vapor.

  • (D) 21 percent oxygen, 78 percent nitrogen, .03 percent carbon dioxide, trace amounts of rare gases, water vapor, and some dust particles.

  • (E) 77 percent oxygen, 21 percent hydrogen, and 2 percent carbon dioxide, with trace amounts of nitrogen, water vapor, and dust particles.

The correct answer is Choice (D).