Aeromedix was founded to introduce portable, economical pulse oximeters to general aviation. Prior to this advanced equipment, pilots were at the mercy of the FAA regulations to determine when and how much oxygen to use. Those regulations, originally developed in the 1950s, were based mostly on politics and economics and minimally on human physiology. Basically, the 12,500 and 14,000 MSL rules were instituted after the GA lobby convinced the FAA that anyone should be able to fly a GA airplane anywhere in the US without supplemental oxygen. Thus, this 12.5 for 30 minute rule made it possible for any pilot to fly across any mountain or mountain pass without the need for what was then, heavy, expensive oxygen equipment.
What we now know is that some pilots need oxygen at 8,000 feet and some younger, healthy ones, who live at 6,000 feet, might not need oxygen till much higher. Pulse oximetery gives a modern determination of when and how much oxygen a person needs. No more guessing (more about pulse oximeters later).
One caveat before I get into oxygen systems—everyone who flies high and certainly anyone who flies over 18,000 feet needs to undergo high altitude training in an altitude chamber. This is not for the commonly held reason that it teaches the pilot how to recognize hypoxia in their system. That is hog wash. The basic problem with early hypoxia is that it impairs cognitive thinking. No one who gets goofy is going to know when they are getting hypoxic and needs supplemental oxygen.
The purpose in altitude training is to prove to pilots that they too can get goofy when hypoxic. The best chambers video this display of hypoxic effects on each participant so when back to normal oxygen levels, the pilot can see exactly how dumb they got. Convincing each and every pilot that they too will be affected is the important part of this training.
There are many types of oxygen equipment but the bottom line is oxygen is oxygen. Probably the most significant issue for pilots is the hassle of filling the oxygen, how big a tank to buy, and whether conserving equipment is necessary which is based on the prior two issues.
Since the 1960s, all oxygen sources have been from liquid oxygen. There is no difference between aviator’s and medical oxygen. When oxygen was first used in hospitals, the gas was humidified in the tank which is a problem for aviation because water will freeze in oxygen plumbing in cold, high altitude aircraft environments. Since medical oxygen is humidified after it leaves the tanks, this is no longer an issue. However, getting something taken off the FAA regulation books requires undue time and energy so everyone uses whatever oxygen they can find and no one apparently cares. If you truly get “aviation” oxygen, you will find the only difference is that it is tested for water and is more expensive.
First, let me address built in oxygen systems. When an unpressurized aircraft is certified with oxygen, the oxygen system delivers oxygen at a flow rate which is set for the service ceiling of the aircraft. The FAA rule is 1 lpm for each 10,000 feet. If your turbo aircraft is certified for 25,000 feet, your oxygen system would deliver 2.5 lpm regardless of whether you were flying at 15,000 or 20,000 feet. (One disclaimer, there are some aircraft which have automatic pressure controllers but few work properly.) This is a true waste of oxygen. Although oxygen is dirt cheap, if you have to fill at an FBO, the mark up is ridiculous and you are supposed to have an A&P sign off the fill. Most people who have built in systems and use them frequently have gone to filling their systems themselves using readily available hose kits which fit large H cylinders which they keep in the hangar. Not quite legal but I have never heard of anyone being busted for it! Besides, you can always have your friendly A&P sign it off.
A big improvement for the built in systems was the Nelson flow meter introduced in the 1970’s which was essentially a medical flow meter with settings in thousands of feet instead of liters per minute (lpm). The pilot just dialed 15,000 feet into the device which had a floating metal ball and they received the FAA required 1.5 lpm and saved 1 lpm over the preset flow the unadulterated aircraft systems would have given them. These style flow meters are readily available from Aeromedix and others. Another improvement was the FAAs decision to allow the use of nasal cannulas instead of masks up to 18,000 feet. This allows the use of oxygen saving cannula and increased comfort (translates in to more willingness to use). More on cannula and mask later.
Pulse Oximetry
Pulse Oximetry is the biggest advance in oxygen use in aircraft since, well, the use of oxygen in aircraft. It brings the use of oxygen into the 21st century.
Pulse oximeters measure the oxygen saturation in the blood. They do this by comparing the red pulsation of ones pulse in the finger to the background red between pulses via a special red light emitted from the unit. Via a complicated formula embedded in a microchip in the unit, it calculates oxygen saturations. This system works with almost every finger but is impaired with black or some other deep colored nail polish, people with low blood pressure, cold fingers, Reynaud’s syndrome, and a surprisingly few other situations.
Normal saturation at sea level is 95 to 100%. In Jackson Hole, at 6,200 feet, normal is 90 to 95%. When and how much oxygen to use is an interesting question. There are no FAA recommendations based on oximetery. However, when we introduced pulse oximetery to aviation, we did some physiological testing and have made the following recommendations.
The pilot and passengers should take note their saturation levels at their home airport (obviously different if they live at sea level versus a ski town). We recommend that the person “should” use oxygen if their saturation drops five points below their home airport saturation. We recommend that the person “must” use oxygen if their saturation drops ten points below their home airport saturation. Now some pilots will require oxygen at 8,000 feet and other might not need it to much higher. Once the decision to use oxygen is made, the level should be titrated by adjusting the oxygen flow to bring the saturation close to the home field levels.
An important caveat to remember about pulse oximeters is one thing fools them—carbon monoxide (CO). CO actually falsely increases the saturation reading. It is one but not the only reason everyone should have a low level carbon monoxide detector. in their aircraft—high altitude flying or not. This silent killer is responsible for accidents every year and carbon monoxide accidents are completely preventable.
Portable Systems Fall between Cracks
Portable Systems fall between the regulatory cracks. Aviation systems are not regulated by the FDA and portable systems are not regulated by the FAA. For the most part, all oxygen equipment made in the US is of superior quality and can be trusted. Tanks do need hydrostatic testing every five years but that is about all the hassle besides filling the system.
Tanks can be filled at most medical, welding, or other gas suppliers. Some require a prescription but this is as variable as the TSA inspectors at airports. (I will be happy to provide a prescription for any of our customers.)
Generally the size of the tank is dictated by the normal mission length and altitude, the number of passengers usually taken, and the space on board the aircraft. Tanks come in different lengths and diameters and there never is a perfect choice. Systems have built in gauges showing their fill level and require a second regulator stage which lowers the pressure to the flow meter (if not built into the second stage itself).
Cannulas
One of the newest and cheapest oxygen saving devices to hit the market is the Oxymizer Cannula. This cannula has a thicker section which sits on the upper lip under the nose which contains a “bag” which collects oxygen during the exhalation and pause part of the breathing cycle. The normal breath cycle is inhalation, exhalation, and pause. With normal cannulas, the oxygen flowing during the exhalation and pause part of the cycle is wasted. With the Oxymizer cannula, the oxygen flow during these portions of the cycle is captured and the bag collapses during the inhalation portion of the cycle giving the “stored” oxygen to the pilot. This allows for lower oxygen settings to obtain the same inhaled amount of oxygen. This cannula can increase the oxygen tank duration up to 50%. For those who dislike the larger nasal portion under the nose, there is a pendant style Oximizer which has a “remote” storage “bag” and works the same way. We combine the pendant with the OxyArm cannula for a cross between convenience, comfort, and increased oxygen duration.
Although the FAA requires the use of oxygen masks above 18,000 feet, I have concerns about that. Depending on the individual, they may or may not be able to obtain a high enough saturation in the flight levels. (Anyone who flies unpressurized aircraft in the flight levels must have an oximeter. It is crazy to fly without one.) My concern with masks is that you have to take it off to drink water or to eat (hopefully, you have a built in mic). In the flight levels, even during a 15 second period of taking off the mask to drink some water, a pilot can get goofy and forget to put the mask back on. One great thing about nasal cannula is that they are kept on for eating and drinking. Besides, I have never seen a FAA inspector at 18,000 feet.
Find out more about our Oxyarm with Oxymizing Pendant Conserver here at Aeromedix.com
The Cirrus Problem
For Cirrus pilots only: The Cirrus Pilot Operating Handbook has presented an unusual problem dealing with oxygen. Cirrus has designated a specific portable system for the aircraft to be legal for oxygen use. This requirement is for the aircraft to be legal. For the pilot to be legal, they can use any source of oxygen. What this means is that to be totally legal, you must have the Cirrus required system on board but you can bring along any system you want to provide the oxygen. The only place you would have trouble with not having the designated system on board would be if you were ramp checked and told the FAA examiner you had just been flying above 12,500 feet MSL for more than 30 minutes or above 14K at all. Don’t you dare!