Supplemental Oxygen in Unpressurized Aircraft (Part 91)

Supplemental Oxygen in Unpressurized Aircraft (Part 91)

by Gustin Robinson, FAA CFI-I ASEL

The body needs oxygen to regulate bodily functions and supply the brain with the power to process information. As pilots, we often fly at altitudes where the oxygen supply to our bodies is limited. Many student pilots have heard of §91.211 in the far/aim, but what exactly does it mean, and why do we need to use supplemental oxygen?

§ 91.211 Supplemental oxygen.

(a) General. No person may operate a civil aircraft of U.S. registry -
(1) At cabin pressure altitudes above 12,500 feet (MSL) up to and including 14,000 feet (MSL) unless the required minimum flight crew is provided with and uses supplemental oxygen for that part of the flight at those altitudes that is of more than 30 minutes duration;
(2) At cabin pressure altitudes above 14,000 feet (MSL) unless the required minimum flight crew is provided with and uses supplemental oxygen during the entire flight time at those altitudes; and
(3) At cabin pressure altitudes above 15,000 feet (MSL) unless each occupant (passengers included) of the aircraft is provided with supplemental oxygen. Note: They are not required to use it, but it must be available!

Why Should We Use Supplemental Oxygen?

Contrary to popular belief, the amount of oxygen remains fairly constant in the troposphere of the Earth. As you ascend in altitude, it is actually the pressure change that causes hypoxia—oxygen starvation—to the body. At high altitudes, the low atmospheric pressure disables the lungs from its ability to perform a positive gas exchange, which is why you may find yourself breathing hard and fast at higher altitudes.

The danger of flying in high altitude environments as pilots is the “time of useful consciousness,” the period of time that you can perform your tasks correctly and efficiently. At 18,000 feet, this time is around 25 minutes, but at 30,000 feet, it is reduced to only one minute, and at 40,000 feet it’s only a few seconds.

When Should We Use Supplemental Oxygen?

You should use it whenever you experience the symptoms of hypoxia, (increased breathing rate, headache, lightheadedness, dizziness, tingling or warm sensations, sweating, poor coordination, impaired judgment, tunnel vision, and euphoria) or when you reach the altitudes as prescribed by the FAA. It is important to note that these symptoms can occur before you reach 12,500 feet, there are several factors that determine your level of hypoxia resistance like health, atmospheric conditions, obesity, etc.

Personally, I have experienced hypoxic symptoms as low as 10,000 feet during a cross-country flight during my commercial training. It started out as general fatigue, then hyperventilation, and a sense of euphoria. Luckily, I was able to recognize the symptoms, as did my safety pilot, and we advised air traffic control that we would like to descend to 8,000 feet. If you have the chance, I highly recommend that you get the chance to understand how hypoxia affects you. Go with another pilot with supplemental oxygen onboard and understand your symptoms. Additionally, try to avoid flying above 10,000 feet in an unpressurized aircraft, especially without another pilot with you, as they will probably recognize your symptoms before you do! If you experience these symptoms and do not have supplemental oxygen available to you, descend the airplane immediately and notify Air Traffic Control of your intentions if required.

It is important that you stay alert and able to perform your duties at all times!
AIM 8-1-2 notes that you should use supplemental oxygen at 10,000 feet during the day, and 5,000 feet at night, due to your brain requiring more oxygen to process lights and cues at night.

by Gustin Robinson, FAA CFI-I ASEL

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