At altitudes above 35,000 feet, oxygen must be used by how many crew members?

• A. Both pilots
• B. No one
• C. Some single pilot
• D. One pilot

Answer: (D)

At very high altitude the air is too thin to breathe without supplemental oxygen, so crews must use oxygen to prevent hypoxia. For two-crew Part 135 operations, the rule sets the minimum that one pilot must be on oxygen when the aircraft is operating at or above 35,000 feet. This ensures that there is always at least one oxygenated pilot who can maintain control of the airplane if the other crew member is unable to function. While it’s common for both pilots to wear oxygen at these altitudes, the regulatory minimum is one pilot. The other options imply more or less than the required minimum, which is not correct.