FAA Military Competency Practice Exam

According to 14 CFR part 91, when must supplemental oxygen be used by the minimum flight crew?

1. Above 10,000 feet MSL

2. At cabin altitudes exceeding 14,000 feet MSL

3. When cabin altitude exceeds 12,500 feet MSL for over 30 minutes

4. At all altitudes above 18,000 feet MSL

The correct answer is: When cabin altitude exceeds 12,500 feet MSL for over 30 minutes

Supplemental oxygen usage rules are critical for maintaining pilot and crew safety at higher altitudes. According to 14 CFR part 91, the requirement for supplemental oxygen begins at specific altitudes due to the decrease in atmospheric pressure and the associated risks of hypoxia. When the cabin altitude exceeds 12,500 feet MSL for more than 30 minutes, it is necessary for the minimum flight crew to use supplemental oxygen. This regulation is in place because the body can start to experience ill effects from the reduced oxygen available at these altitudes, and prolonged exposure can exacerbate these effects. The 30-minute threshold is a crucial differentiator because it recognizes that brief excursions above this altitude may not pose a significant risk, but extended duration increases the likelihood of hypoxic conditions. In contrast, other altitude thresholds provided in the options relate to general guidelines for oxygen use, but they do not specifically pertain to the minimum flight crew requirements in the same way this option does. Thus, understanding the importance of the specific cabin altitude and duration in relation to the regulations helps clarify when supplemental oxygen must be utilized in compliance with aviation safety standards.