July 2003 Issue

Oxygen Oddities

Mounting tanks and filling with non-ABO complicate picture for supplemental oxygen

I just finished reading my May issue and I had two questions.

In “Burn, Baby, Burn” it says “the average daily consumption rate of automotive gas in 1999 was around 360 million gallons.” Is that in the U.S. alone, or worldwide? It’s a statistic I’d like to quote to (non-aviation) friends, but I want to get it right.

In “Roll your own O2 System” on page 5, when you mount the O2 tank in the baggage compartment, doesn’t that require an STC or form 337, at least? I have seen the FAA declare an aircraft unairworthy because it had a non-STC’d panel mount for a portable GPS, and this seems like a bigger modification to me. It affects the aircraft weight and balance and empty weight, at the very least. Perhaps that’s why some FBOs won’t fill the tank.

The same question applies, I guess, to the use of welding oxygen to fill the tank. Is there an FAR mandating “aviation oxygen?” Just because the distillers use the same method to manufacture the product doesn’t mean the sellers ship/contain/preserve its purity in the same way. Is there some governmental body that regulates welding equipment that would guarantee purity (as much as any governmental body “guarantees” anything)?

In these days when common sense has been replaced with by-the-book interpretations, I’d hate to see someone get violated for modifying their aircraft, trying to make it safer.

-B. Von Bevern
Via e-mail

First of all, the 360 million gallon figure is U.S. consumption of gasoline.

Second, you are probably being thrown off by the reference to “mount” the oxygen tank. If the tank is strapped down with cargo straps, it is nothing but luggage in the eyes of the FAA and therefore does not need approval of any kind. A more permanent mounting can involve brackets that hold the tank, which can simply be installed by 337. The tank itself then clips into the brackets but the FAA takes the position that this is no more its business than if you installed the brackets to securely hold scuba tanks on your flights to the Bahamas.

There is no FAR requiring aviation breathing oxygen for Part 91 operations because all references state “or equivalent.” That makes the “equivalence” of different oxygen sources subject to debate that is not likely to be resolved here – or anywhere for that matter – any time soon. There are those who contend welding is actually less tolerant of contaminants than the human body, but that’s not a can of worms we care to get into.

The whole question of using oxygen is generally not between ABO and “regular” oxygen, but between regular oxygen and not using supplemental oxygen at all. Pulse oximetric experience suggests that many pilots are hypoxic at 10,000 feet and make more errors at 10,000 feet. Slight enrichment with non ABO is likely much safer than not using supplemental oxygen at all in those circumstances.

No one is suggesting this for charter or scheduled traffic, and certainly not for 100 percent administration in the occlusive facemask designed for high altitudes.

The regulation regarding altitudes at which oxygen is required, 91.211, was a 1970s compromise between Colorado pilots and the FAA. It was not based on much data. Tom Nestus et. al. have since published a very nice study of aviation errors under just such circumstances (FAA/AM-97/9) which is available from the Civil Aeromedical Institute.

The fact is that any oxygen supply source will discourage you from using oxygen for any purpose other than what they’re selling it for. We think this is based more on potential legal liability than anything else.


Always High
I enjoyed the article on the hazards of high altitude flying [Medical Matters, May] and wonder whether you know of any studies that address pilots who live at altitude.

I live at 9,513 feet and fly out of Leadville, Colo., which has an altitude of 9,928. Checking my oxygen saturation with the Flightstat pulse oximeter, I find the value to vary from 91 to 93 percent. The general assumption of pilots in the area is that since we live at altitude we should have adapted by increasing the number of red cells, and we should therefore be able to function safely at altitudes that would be prohibitive for “lowlanders.”

I personally know of no studies that would give me guidelines for safe flying and therefore continue to adhere to the FAA rules. Any thoughts?

-Alvin Weiner
Via e-mail

There has been precious little aviation-specific research into this, but some generalizations apply. The adaptation you speak of is a chemical change that enables your body to remove more oxygen from the hemoglobin, ie. reduce the “unusable fuel” carried around in your bloodstream. The adaptation does not appear to give “highlanders” added protection above 14,000 feet, however, because the lungs cannot load enough oxygen into the hemoglobin in the first place. It’s best to use a pulse oximeter and go on supplemental oxygen or descend if saturation gets below 90 percent.


Handheld Antenna Mount
R.G. Copeland raises some good points regarding the use of handheld radios (Unicom, May). A major point Copeland makes is that many of the problems have more to do with the antenna than the radio itself. The fix that Copeland suggests, is to move the antenna outside the airplane.

Attached are two photos of a nice, reasonably priced antenna mount, that I found at my local Radio Shack store. I purchased this for use with my Sporty’s SP-200 Nav/Com radio. The mount utilizes the same BNC connectors that are furnished with the radio, enabling the re-use of the antenna supplied with the radio. The bracket end clips over one of the hinged side windows typical of Cessna light singles.

I realize that other, similar mounts, may also be available.

-Wayne Hansen
Milford, Mass.

Moving the antenna outside the airplane is one step toward a cure, but it’s not a complete solution because the short antenna is optimized for portability, not for the frequency range of the signals the radio is expected to process. The kind of remote antenna mount you use is similar to the one used by Bruce Chien at the time of the incident he relates in his March article “Rescue Heroes?” except his mounts via suction cup to the window.


Not Recommended by Whom?
I would like to take exception to Brian Johnson’s statement in “VFR the Sane Way” [Airmanship, April] that “if the briefer tells you VFR is not recommended, consider that an automatic no-go unless you and the airplane are instrument capable.”

For 35 years I have flown VFR from British Columbia to Arizona and California, using only VFR sectionals and never using VORs or any other navaids, with what I considered safe ceilings and visibilities, despite advisories that VFR was not recommended because of showers, mountain obscuration, etc.

For those who use direct point-to-point navigation via VORs or GPS, the “VFR is not recommended” admonition is very appropriate because showers or mountain obscuration do preclude direct VFR routing. For those like myself who are quite prepared and comfortable with flying circuitous valley routes, the “VFR not recommended” qualifier need not be an automatic no-go.

Reading the American flying publications suggests that American pilots are more likely to be trained and encouraged to use electronic navigation aids and to upgrade to instrument ratings, whereas where I learned to fly in the Yukon Territory a map and a compass heading were all that were available.

Therein lies the different approach and philosophy to VFR flying in western Canada and the USA.

-Morton Doran
Cranbrook, B.C.

The problem with any blanket statement such as “automatic no-go” is that there are always exceptions. Over your career you’ve determined what you consider safe ceilings and visibilities, and your success speaks for itself. However, most pilots are not forced to do this kind of flying as you were and therefore don’t have the experience or knowledge base to determine what those ceilings and visibilities are.

You’re proof that it’s not impossible to fly VFR when the weather is marginal, but the high number of accidents in such conditions makes it clear that not everyone shares your combination of skills, judgment and luck.


The Friendly Aviation Administration
As a born-and-bred Californian, it may surprise some that I do what I can to spread my views that less is better when it comes to government. However, I believe there are certain factions of the government that are very necessary to preserve public safety and our way of life. One such faction is the FAA and air traffic control.

Recently, I was leaving Tahoe-Truckee airport in the late afternoon on the way home. I picked up flight following after climbing through 8,500 feet and was headed for 10,500 feet. Upon reaching cruise, I was queried by Oakland Center as to my altitude. The airplane was on autopilot and was dead-on 10,500 feet. I informed them of my altitude, and they gave me a new altimeter setting that only changed the altimeter 20 feet or so. It seems my transponder was showing 10,800 feet. I was asked to turn off the Mode C squawk, and did so.

Later on we tried it again and it was only off 200 feet, a legal (though maybe unsafe) discrepancy. I subsequently forgot about the issue and flew several IFR flights without a known problem.

Last week, I was surprised to find a letter in the mailbox from the FAA. My N-number was listed, along with a description of the issue, the time and date of the problem, and the exact reported altitudes and discrepancy. This letter was written in an informative, friendly and helpful way, and in the spirit of helping me become aware of a problem I may not know existed.

In my opinion, this valuable safety service (someone else could have been flying my plane and not told me) is something that only a well-run and organized service could provide. I doubt very much that this type of communication would take place properly were the ATC facilities privatized.

Thank you to the FAA and the ATC facility that did a great job of initiating the report. You have helped to reinforce to me the importance of organization and the service you provide.

-Al Browne
Salinas, Calif.

Like you, we’ve come across a number of controllers who have taken constructive and non-threatening approaches to dealing with problems. We hope that continues because, face it, pilots need all the friends they can get right now.