January 1, 2000
The crash of a Learjet 35 carrying golfer Payne Stewart brought renewed interest in high-altitude flight physiology. How is it that all of those on board the airplane failed to realize that they were becoming hypoxic? Perhaps it was one of hypoxia’s side effects—fatigue and lethargy, or euphoria and giddiness—that assured the crew and passengers of the Learjet that things were fine as they barreled up to the flight levels.
Regardless of the cause, the accident illustrates the need for pilots to recognize the onset of hypoxia and to understand how the body reacts to altitude. The U.S. Air Force conducts an excellent all-day course in flight physiology that should be considered a must for pilots, especially those who regularly venture above 10,000 feet. Contact your local Air Force base for information.
A week after the Payne Stewart crash, Tim Devlin, national sales director of White Mountain Products Group Inc., stopped by AOPA’s headquarters in Frederick, Maryland, to demonstrate the company’s Breath of Life emergency oxygen kit designed for pilots of light aircraft. Breath of Life comes with two 12-ounce bottles of aviation-grade oxygen and a simple regulator with a built-in mask that fits over the nose. The bottles are tiny and can be stored in a seat pocket with the regulator installed and ready to use. When finished, simply throw the bottles away and put the regulator on a new one.
White Mountain also sells a self-contained pulse oximeter that simply clips on to your fingertip to provide a nearly instantaneous readout of your blood-oxygen saturation level and pulse rate. The device can tell you whether your oxygen saturation level has dropped below the optimum range. Oxygen saturation should be 97 percent or better. When saturation levels slip below 90 percent, you can consider the hypoxia-warning flag to be officially raised.
We brought the pulse oximeter and emergency oxygen kit along on a 4.5-hour nonstop cross-country flight at a VFR cruising altitude of 9,500 feet. On the ground, our tester registered a 99-percent saturation level with a pulse of 64. More than an hour into the en route portion of the trip at 9,500 feet msl on this relaxing VFR night flight, our subject scored an 88- to 90-percent saturation level with a pulse of 100. After a deep breath from the Breath of Life oxygen bottle, the saturation level quickly returned to 99 percent. After 3.5 to 5 minutes, the saturation level would trickle back down to 90 percent, where he would take another hit to keep saturation levels above 90 percent. For the next three hours, we repeated this cycle until the canister ran out a few minutes before the planned descent into the destination airport. Our subject was a 29-year-old male in good physical condition. Those who are elderly, overweight, smokers, or are in generally poor health could expect worse results, but as always it depends on the individual.
Just as interesting to note from our experiment was the steady pulse of 100. Ever wonder why you feel fatigued after a long trip? The body’s unconscious reflex is to increase heart rate to facilitate an increase in respiratory exchange rate. A pulse of 100 for our tester would typically only be seen during a light workout at his normal just-above-sea-level altitude. Flying several hours at altitude with a 100-beat-per-minute pulse is akin to a light workout for as many hours as you’re flying. After seeing the results of the testing, our guinea pig admitted that he would be far more careful about flying higher than 10,000 feet without supplemental oxygen, especially when solo or during night or instrument conditions. During the test, he said he felt normal and wouldn’t have suspected hypoxia to be a problem at any altitude below 10,000 feet.
For those in pressurized airplanes, the emergency oxygen canisters can be a lifesaver in the event of a rapid cabin depressurization. Pilots and passengers can quickly grab a bottle and begin using it as the airplane descends to a breathable altitude. Without supplemental oxygen, the time of useful consciousness at 25,000 feet—the certified ceiling for many turbo-charged/pressurized GA airplanes—is only 2.5 minutes. In other words, if your pressurization system or its source (the engine) gives up the ghost, you don’t have much time to get down to a breathable altitude before you become dopey or simply pass out. Of course it would be foolish not to have a standby oxygen supply ready in an airplane that routinely flies higher than 10,000 feet.
Although Breath of Life is designed to be used in an emergency, it meets the FAA guidelines for supplemental oxygen use above 12,500 feet. So if you need to venture above 12,500 feet for more than 30 minutes for traffic or terrain considerations, a few shots of the Breath of Life will keep your blood saturation level high enough to keep you from becoming hypoxic. Each bottle provides an estimated eight- to 12-minute continuous oxygen supply. Used sparingly, as we did in our test, duration will be greatly increased.
Each Breath of Life kit lists for $159.95 plus $12 shipping. Several accessories are available, including a cannula that will stretch the life of each bottle to about 25 minutes of continuous use. A Velcro strap to hold the regulator valve open provides hands-free use. Holsters are available to carry extra bottles, the Onyx pulse oximeter, a cannula, a standard aviation oxygen mask, and an extra Breath of Life nose mask. Many of the above accessories are included in the Aviation kit that lists for $214.95. White Mountain is also working on a computer-controlled flow meter that should be available this summer. It is expected to extend the life of a bottle to 30 minutes by providing on-demand continuous flow. Refill kits containing two or five cylinders are available for $43.95 plus $6 shipping and $89.95 plus $9.50, respectively. The lowest-cost portable oxygen system lists for around $400 and would be more cost-effective for someone who routinely flies higher than 10,000 feet in an unpressurized airplane. Those portable systems can be refilled, unlike the White Mountain bottles.
At just three ounces and small enough to pack away nearly anywhere, the $395 Nonin Onyx pulse oximeter that White Mountain sells makes a practical tool for in-cockpit hypoxia diagnosis. Decreased oxygen saturation levels and elevated heart rate are two sure signs of hypoxia. Forget checking for blue coloration under the fingernails and the other insidious signs; the pulse oximeter gives you a fast, accurate reading that lets you and your passengers know if supplemental oxygen should be used before it’s too late. According to White Mountain, a prescription is not needed for a pulse oximeter if the unit is to be used for nonmedical purposes in conjunction with aviation oxygen—that falls under FAA regulations, not Food and Drug Administration guidelines.
For more information on the Breath of Life and Nonin pulse oximeter, contact White Mountain Products Group, Post Office Box 95, Dyer, Nevada 89010; telephone 888/798-3985 or 775/572-3175; or visit the Web site ( www.wmountain.com). — Peter A. Bedell
Sennheiser recently introduced a new line of headsets for general aviation airplanes and helicopters called the Sound of Silence series. We tested the top-of-the-line $599 HMEC300, which features the company’s NoiseGard active noise canceling.
Typical German understatement leads to a conservative appearance with dark royal blue ear cups and a black leather headband cover. If you are drawn to bold designer colors and starship-type styling, this is not your headset. The set comes with a padded carrying case, cable clip, mic muff, and an adapter to hardwire the unit to the aircraft.
Clamping pressure was enough to provide excellent passive noise canceling. More important, the set was still comfortable three hours into a trip. Part of the comfort equation is the fact that the headset is also very light, weighing only 13.1 ounces, not including the cord.
The microphone is attached to the end of a flexible metal boom and can be positioned exactly as needed. Gain of the mic is adjustable using a very small screwdriver to match radio impedance, if needed. The entire boom rotates for storage and there is a boom friction adjustment on one ear cup. The volume control is on the other ear cup.
A single cord goes from one ear cup to a small switchbox. One slide switch activates the noise-canceling circuitry, and the other allows selection of stereo or monaural input. Sennheiser offers this same headset (the 12.4-ounce, $249 HMEC100) without the ANR circuitry and it is more than adequate, but fire up the electronics in the HMEC300 and the deep rumble of the engine all but disappears. It was so quiet that the volume output on the aircraft radios, set up for another passive headset, had to be lowered significantly. Sennheiser claims that both the 100 and 300 headsets each provide 24 decibels of passive noise reduction. The HMEC300 takes away another 16 dB of racket when its electronics are on. Power for the headset comes from the aircraft’s cigarette lighter or from an optional rechargeable battery pack. We did not test the battery pack.
There are some minor complaints. The cord from the switchbox to the aircraft power source is not of the same high quality as the rest of the unit. It is also a bit short if the cigarette lighter is on the opposite side of the panel. The other cordage appears to be very durable with good strain relief for the plugs. There is no strain relief on the cord going into the ear cup.
Overall, the comfort and performance significantly outweigh the few negatives we observed. The HMEC300 is a high-quality headset and well worth a look if you are contemplating serious quiet on your flight deck. For more information, contact Sennheiser at 860/434-9190 or visit the Web site ( www.sennheiserusa.com). — Bruce Landsberg
For those like me who had great difficulty staying awake in high school or college history classes, the notion of getting excited about a history book seems highly improbable. But now there is an exception. Jeppesen Sanderson has just released Aviation History, a 636-page, large-format textbook by Anne Millbrooke that is guaranteed to satisfy anyone with a passionate appetite for flight.
Aviation History is not a typical history textbook that consists of endless pages of punishing text interrupted only occasionally by a dull black-and-white photograph. It is graphically driven, chock full of colorful photographs (where possible) and beautiful illustrations.
All 10 chapters (from Greek mythology to futuristic designs and concepts) begin with graphical timelines of notable events. They also contain hundreds—if not substantially more than a thousand—colorful sidebars. Some offer bite-sized historical notes that provide insight into certain events, and others provide first-hand accounts of those who were there. More sidebars describe historical events that lend perspective to aeronautical progress, and others contain personal profiles of those who made history. And finally, some boxes contain fascinating bits and pieces of evidence to validate or dispute certain events from a historian’s perspective. Each chapter also includes question-and-answer boxes to help prime you for whatever aviation quizzes you might encounter. (I couldn’t resist that.)
Even the appendices are fascinating and contain, for example, 10 pages dedicated to reproducing the Wright Brothers’ original patent for a flying machine. My favorite appendix is a comprehensive list of aviation firsts. It begins with the first aircraft flight (June 4, 1783) and ends 12 pages later with the first woman to command a space shuttle (Eileen Collins on July 23, 1999).
Millbrooke, a professional historian and fine writer, and the editorial staff at Jeppesen have outdone themselves. Even if you chose not to read the main text and perused only the captions and sidebars, you would still finish the book with a broad and insightful understanding of how aviation got to be where it is today. Simply stated, Aviation History is without peer or competition. Any book that can bring aviation history to life the way this one does deserves to be described with superlatives.
Aviation History lists for $68. For additional information, contact Jeppesen Sanderson at 800/621-5377 or see the Web site ( www.jeppesen.com). — Barry Schiff
Unless otherwise stated, products listed herein have not been evaluated by AOPA Pilot editors. AOPA assumes no responsibility for products or services listed or for claims or actions by manufacturers or vendors. However, members unable to get satisfaction regarding products listed should advise AOPA. To submit products for evaluation, contact: New Products Editor, AOPA Pilot , 421 Aviation Way, Frederick, Maryland 21701; telephone 301/695-2350. Links to all Web sites referenced in this issue can be found on AOPA Online ( www.aopa.org/pilot/links/links0001.shtml).
Safety and Education,
Pilot Health and Medical,
FAA Information and Services,
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