Ian Blair Fries, MD Senior FAA HIMS Medical Examiner
Let’s take hypoxia seriously It has been a difficult season for those of us who fly TBM 900 aircraft. Larry Glaser and his wife were lost in an accident after he and Atlanta Air Traffic Control last spoke. His pressurized TBM 900 turboprop continued on the last altered course at FL 250 until it ran out of fuel just north of the island of Jamaica. Based upon the best information available, it appears they succumbed to hypoxia. While we might be pleased the range of the TBM 900 can take us from Rochester NY to just short of Jamaica, there was nothing else to celebrate.
I was due to fly to from Florida to Denver the day after the accident but acquiesced to my family’s request and temporarily grounded my TBM 900 and myself. Unfortunately, we do not know much more since. For all of us who fly pressurized aircraft the accident should be impetus to review our pressurization and oxygen systems. Pressurized aircraft are so comfortable most of us forget we are flying in an extremely hostile environment.
FAA regulations include dangerously lax oxygen requirements for non-pressurized aircraft. Do you truly believe you can fly for an unlimited time at 12,500 or 14,500 ft for 30 minutes without any physiologic effects from hypoxia? While the FAA allows nasal cannula to supply necessary supplemental oxygen up to FL 180, I cannot condone hanging your life on thin easily kinked plastic tubing, unsecured fittings and inaccurate flow indicators.
Let’s talk turkey. At FL 250 textbooks tell us that the time for useful consciousness without oxygen is 2 to 5 minutes. I suspect the original research was on healthy young US Air Force pilots. I won’t ask your age if you don’t ask mine, but studies confirm the time for useful consciousness without oxygen substantially decreases with age. Add smoking, a lung condition, lack of exercise, anxiety and stress, and these liberal estimates evaporate.
Being usefully conscious may not be sufficient to save your life. Your judgment vaporizes well before the effect on loss of consciousness. We cannot determine we are hypoxic, though if somebody tells us to put on a mask we could do it.
Hypoxia training reduces risks. My friend Dr Paul Buza, who owns and operates his own altitude chamber in Melbourne FL, trains pilots to recognize hypoxia and take the appropriate steps. He also places controllers outside the chamber so they can recognize when communications between them and the pilots suggests hypoxia. In that golden period, when there are signs of hypoxia but not yet loss of useful consciousness, controllers can forcefully advise a pilot to don an oxygen mask.
There are designs for rapidly downed oxygen masks that are touted as being fully functioning within 5 seconds. However, to meet that standard takes practice. Have you thought about whether you will remove your headset first, and with which hand? Have you actually donned the mask recently? How you position your hand and which hand you use when removing the mask from its docking position may be time critical.
If the mask has not been properly packed, the headbands may inflate in a knot. They need to be untangled before the mask can be properly fitted. And then, have you considered communications? Typically the headset will be replaced over the mask but the microphone won’t operate and the alternative mask mic should be switched on. You may not know if intercom remains active and if you can talk to your copilot and passengers. There could be further complications if you also need to don smoke goggles and adjust the mask to flush them.
We traditionally depend upon a cabin altimeter and a cabin pressure warning system to alert us about impending hypoxia. However, those are indirect measurements. The only measurement that really counts is how much oxygen is within your body. This is measured using an oximeter with a sensor attached to a fingertip. Considering the low cost and easy availability of this device, there is little excuse not to have one aboard your aircraft and to use it routinely.
In an emergency it is never wrong to don an oxygen mask first. There will be time to sort out the problem later. Trouble shooting before putting the mask on may result in a disaster. Why create an additional emergency as ATC scatters traffic to allow you to descent rapidly when using oxygen is the correct antidote and will buy time?
We should all take seriously FAR Part 135 and 121 regulations that include the requirements that a single pilot seated at the controls above FL 250 should be wearing an oxygen mask, and at least 1 of the 2 pilots in the cockpit should wear an oxygen mask at all times above FL 350. These reasonable regulations should also apply to Part 91 operations. Hypoxia does not discriminate.
Lack of oxygen is the greatest single danger to man at high altitudes, despite the importance of pressure and temperatures. The shortage of oxygen in the human body results in a condition called hypoxia, which simply means oxygen starvation. When a pilot inhales air at high altitudes, there isn't enough oxygen pressure to force adequate amounts of this vital gas through the membranes of the lungs into the blood stream, so that it can be carried to the tissues of the body. The function of various organs, including the brain, is then impaired.
Unfortunately, the nature of hypoxia makes you, the pilot, the poorest judge of when you are its victim. The first symptoms of oxygen deficiency are misleadingly pleasant, resembling mild intoxication from alcohol. Because oxygen starvation strikes first at the brain, your higher faculties are dulled. Your normal self-critical ability is out of order. Your mind no longer functions properly; your hands and feet become clumsy without being aware of it; you may feel drowsy, languid, and nonchalant; you have a false sense of security; and, the last thing in the world you think you need is oxygen.
As the hypoxia gets worse, you may become dizzy or feel a tingling of the skin. You might have a dull headache, but you are only half aware of it. Oxygen starvation gets worse the longer you remain at a given altitude, or if you climb higher. Your heart races, your lips and the skin under the fingernails begin to turn blue, your field of vision narrows, and the instruments start to look fuzzy. But hypoxia - by its nature, a grim deceiver - makes you feel confident that you are doing a better job of flying than you have ever done before. You are in about the same condition as the fellow who insists on driving his car home from a New Year's Eve party when he can hardly walk. Regardless of his acclimatization, endurance, or other attributes, every pilot will suffer the consequences of hypoxia when he is exposed to inadequate oxygen pressure.
What do you do about it? There is one general rule: Don't let hypoxia get a foot in the door. Carry oxygen and use it before you start to become hypoxic. Don't gauge your "oxygen hunger" by how you feel.
24 PROFESSIONAL PILOT / November 2014