What is the maximum IFR altitude you may fly in an unpressurized aircraft without providing passengers with supplemental oxygen?

In operations involving unpressurized aircraft, there are specific regulations concerning the use of supplemental oxygen for passengers to ensure safety at higher altitudes where oxygen levels can become insufficient for normal respiration. According to FAA regulations, the maximum altitude that you may fly without providing supplemental oxygen to passengers is 14,000 feet. However, at altitudes above this threshold, it becomes necessary to provide supplemental oxygen for any duration of flight.

Flying above 14,000 feet without supplemental oxygen can lead to hypoxia, which is a condition caused by a deficiency of oxygen in the body. Since the answer given is 15,000 feet, it suggests a misunderstanding of the regulations, because at this altitude, passengers must have supplemental oxygen if flying for more than 30 minutes.

In summary, the correct altitude where passengers can fly without supplemental oxygen in an unpressurized aircraft is 14,000 feet, making this the answer to the question regarding maximum IFR altitudes under these conditions.