Cirrus Braking Systems: A Hot Topic

Need To Breath

ByRyne Bergren March 28, 2019April 30, 2019

I got a call today from a friend asking me about oxygen requirements.  That got my brain pondering about the different items the FAA would like all pilots to know. I did a little refreshing and found several other tidbits directly from the FAA that I thought worth sharing. No matter what you’re flying, I think these apply to all of us. 

First off, what are our general oxygen requirements? If you jump on over to the FAR’s and take a look at 91.211 you’ll see: 

1. At cabin pressure altitudes above 12,500ft MSL to 14,000ft MSL, pilots
required to use oxygen unless the segment is less than 30 minutes of flight.

2. At cabin pressure altitudes above 14,000ft MSL, the crew is required to use
oxygen.

3. At cabin pressure altitudes above 15,000ft MSL, each occupant must be
provided the use of oxygen. This doesn’t necessarily mean they have to use it.

Things get a little more in depth when you get to pressurized aircraft.

These requirements are also listed in 91.211: 

1. If you’re flying above Flight Level 250, a 10 minute supply of oxygen is
required for each person onboard.

2. If you’re flying above Flight Level 350-410, and one pilot leaves their seat, the other pilot will be required to wear an oxygen mask, unless both seats are equipped with quick-donning oxygen masks.

There are three basic components to any oxygen system in an aircraft:  the storage system, the delivery system, and the mask or cannula. First, there are several types of storage systems. 

Gaseous aviators breathing oxygen is the first. This is the standard green tank that everyone is familiar with. There are two types of tanks. Either the high- pressure with 1800-2200 psi or the low pressure tank with 400-450 psi. The major issue with these and General Aviation aircraft is weight. Some of these tanks can get bulky and heavy and therefore don’t work for everyone. 

Liquid aviators breathing oxygen or LOX is another form of storage. The major advantage of LOX is that it has a 900 to 1 expansion ratio, meaning that 1 liter of liquid oxygen can be expanded into 900 gaseous liters of Aviators Breathing Oxygen. The disadvantages of LOX are they are extremely volatile and have to be stored at -197F. If it comes in contact with exposed skin, severe frost bite can occur. 

Sodium chlorate candles or oxygen generators have a weight advantage like LOX. They’re essentially a canister that when activated mix sodium chloride and iron powder and produce oxygen. They general have a 600 to 1 expansion ratio, which goes back to the weight savings. However, once these are started they are very hard to stop. Another disadvantage is these devices produce a fair amount of heat, so proper precautions need to be taken. 

Next are the delivery systems. The main systems are Continuous Flow, Diluter Demand, and Pressure Demand. Continuous Flow, is exactly as it sounds. The oxygen is allowed to flow continuously from the tank to the user. The benefits of continuous flow are you don’t need a complicated mask or regulator. The downside to this system is since it continuously pumps oxygen, you’re wasting oxygen when you exhale. Most of continuous flow systems are used on aircraft that generally fly below 28,000 feet. 

Diluter Demand was designed to fix the negative of the Continuous Flow systems. Diluter Demand only sends oxygen to the user when the user inhales. The system also allows cabin air to be introduced in, sending the perfect mixture of oxygen to the user when needed. These systems are very efficient and generally tend to be used up to 40,000 feet. 

Pressure Demand is designed to essentially “over inflate” the users lungs. This will basically pressurize the the users lugs and allow the user to fly above 40,000 feet. This is needed at flights above FL400 because 100% oxygen without positive pressure will not suffice. 

The final portion of the oxygen system is the mask or cannula. Nasal cannulas generally are more comfortable and are regulated to 18,000 feet service altitude. Masks come in a couple different variants. From re-breathers to quick-donning, most masks accomplish the same task with a few small differences. Quick-donning must be able to be put on within five seconds and are rated up to FL400. 

Since that was a lot of information, what does all of it mean to you? Most fair weather flyers will never run into any of this. However, the high performance owner/operator will run into oxygen use situations a fair amount. Taking the family up to Colorado on a ski trip, jumping up to 12,500 feet to get above some weather, or flying above 5,000 feet at night on a long xc are all situations where you may want to have oxygen on board. 

If you are planning on doing any of this type of flying or are currently doing these types of flights, training is a must. If you’ve never been in an altitude chamber, I would highly recommend it. In college, I went with a group to Oklahoma City to the FAA’s headquarters where they hold a class on Hypoxia and High Altitude flying. It’s very informative to be in the chamber as it simulates being oxygen deprived. You get to see how you’ll react and what kind of symptoms you’ll have when in a loss of oxygen situation. Each person has different symptoms, so it’s important to see how you will react.

It’s also good to fly with an experienced instructor. Finding an instructor who will allow you to learn in a safe environment is worth its weight in gold. 

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Ryne Bergren is currently a First Officer with Mesa Airlines in the CRJ 900. Ryne has experience in many different areas of aviation, from corporate to airlines to teaching to ferrying across the Atlantic Ocean. His passion is for all things that travel across the big blue sky.