The aviation world took notice when an apparent case of slow-onset hypoxia caused the September 5, 2014, fatal crash of a Daher TBM 900. A landmark accident if there ever was one, it was all the more significant because it took the life of TBM Owners and Pilots Association Chairman Larry Glazer and his wife, Jane. Glazer was flying from Rochester, New York, to Naples, Florida, when he twice requested a lower altitude from ATC, mentioning an incorrect instrument indication. The airplane continued without any further communications from Glazer, and the airplane crashed off the Jamaican coast. Since then, Glazer’s family raised the wreckage from the ocean, but no official ruling as to probable cause has been published. However, the prevailing belief is that hypoxia was the blame.
The accident prompted Daher-Socata, the French manufacturer of the TBM 900, and Zodiac Aerospace, manufacturer of quick-don oxygen masks, to provide each TBM owner with some unique and inspired hypoxia-awareness training. The company partners with Melbourne, Florida-based Southern AeroMedical Institute (SAMI) to give intensive ground school sessions and high-altitude pressure chamber rides.
SAMI’s pressure chamber—which is also used in bariatric medicine—is unique. There is a Garmin G1000 inside, which lets technicians act as ATC to task-load hypoxic pilots in realistic flying scenarios. The training is also available to others flying any make of airplane.
I recently attended the two-day course, taught by SAMI Medical Director Dr. Paul W. Buza and Senior Aviation Medical Examiner Dr. Ian Blair Fries. It was an eye-opening experience that gave hypoxia the importance it deserves. Most pilot training merely skims the surface of this critical subject. Not this one, which did away with many misconceptions and introduced new concepts. Here are some highlights from my notes:
Forget explosive decompression. Yes, it happens. But the accident record is clear: Slow-onset cabin depressurization causes most fatalities. It begins during the initial climb to altitude, with the autopilot engaged. Think Payne Stewart. There are no cockpit annunciations as the aircraft climbs, so by the time 20 minutes or so have passed—when the airplane has typically reached cruise altitude—the pilot is already impaired. Now, any warnings can be easily overlooked as the pilot fixates on a task, or simply does nothing.
The most common altitude chamber experiences are next to worthless for recognizing slow-onset conditons. The usual drill is for pilots to wear oxygen masks from the moment a pressure chamber is sealed. Once at altitude, the subjects are told to remove their masks, play simple games, and then don their masks so they can recognize the signs of their impairment. That, or subjects breathe an air mixture with a reduced oxygen level.
The problem here is that this doesn’t re-create slow-onset conditions the way the SAMI altitude chamber can. In the SAMI chamber, pilots start at the surface without wearing masks, and then “fly” the G1000 as the cabin is depressurized to approximately 20,000 feet—sometimes higher. By the time the cabin reaches 18,000 feet, most pilots experience hypoxia, whether they realize it or not.
Pilots are mask-averse. Many conventional training programs don’t involve practice donning oxygen masks. An instructor bangs on the side of a simulator, you announce a depressurization, then you point at or touch the oxygen mask while saying “I’d put the mask on now,” and that’s the end of the drill. So most turbine pilots have very little experience actually donning a mask, let alone understanding its features, or the intricacies of the entire oxygen delivery system. Worse, masks frequently are stowed in poorly designed locations and positions, and awkward to access.
Buza and Fries both emphasized that pilots are often reluctant to don a mask—because they don’t want to waste oxygen. So they become conditioned to avoid thinking about mask usage. It takes practice to become proficient in donning a quick-don mask and activating its internal microphone, Buza and Fries said. About five repetitions will do it.
When in doubt, put on the mask! Fries hammered on the idea that putting on the oxygen mask is never an error. He even recommended donning the mask any time there is a crew alert system message or master warning annunciation above 10,000 feet msl. “Think of the messages: bleed air temp; door open; low fuel or oil pressure. All these things imply that a depressurization is possible, so put on the mask, evaluate the situation and decide whether to keep it on,” he said. Of course, once you learn your personal hypoxia symptoms, it’s vital to immediately don your mask whenever you recognize them. Individual symptoms vary, with dizziness; numbness and tingling of the fingers; warm flushing over the chest; and visual changes the most common. In 10 percent of Buza’s subjects, the first symptom was unconsciousness. “Those showing the most resistance to hypoxia are at the most danger,” he said. “Because for them, there’s no warning. It’s just ‘lights out.’” Buza’s research indicates that older pilots recognize hypoxia sooner than younger ones.
Descending alone won’t help. Checklists always mention descending after a cabin depressurization. Good advice? Fries said that opting for a descent instead of donning the oxygen mask is a bad idea. During the descent you’ll be breathing an air mixture that’s 20-percent oxygen, and under partial pressure to boot. “You need to get to a normal, 99-percent blood-oxygen saturation quickly, and the only way to do that is to put on the mask and begin breathing 100-percent oxygen immediately,” he said. “Using oxygen, it takes on average a full minute to go from severe hypoxia—say, a 63-percent blood oxygen saturation—to a normal saturation.”
Time of useful judgment is important, not time of useful consciousness. Time of useful consciousness (TUC) has little meaning when it comes to mental function, Buza and Fries emphasized. Impairment begins long before TUC is reached. “Instead, think of a time of useful judgment, which the FAA calls ‘Effective Performance Time,’ when you’re still able to make relevant decisions,” Fries said. “By the time you reach your time of useful consciousness, it’s way too late. You should have put the mask on long ago.”
I was told my chamber experience was fairly typical. With no mask on, the chamber was slowly raised to an altitude of 20,000 feet. My ears felt the pressure, but I had no other symptoms. SAMI’s “ATC” gave me some turns to a heading, some frequency and course changes, and a flight plan entry. Three minutes after climbing past 20,000 feet, I felt slightly dizzy, my fingertips felt numb, and time seemed to slow as I reached up to the glareshield to change headings. Meanwhile, an oximeter showed my blood-oxygen saturation had dropped to 67 percent—the critical level. And yet, I felt no sense of distress. “Put on the mask,” said Buza. I reached around and had some trouble removing the quick-don mask from its mount—a design requiring you to twist your hand didn’t help, and neither did my hypoxia—and forgot to remove my headset when I tried to don the mask. No way did I don the mask in the five-second time limit. “You would never have made it to 25,000 feet,” Buza said, meaning that I would have passed out.
After the chamber ride all nine participants in the class received training certificates, video recordings of their performance at altitude, a laminated card listing their personal hypoxia symptoms (good for five years, at which time they may change), and printouts of their physiological data—such as oxygen-saturation profiles. For TBM owners the course ranges from $987 (for a group of six trainees) to $1,670 (for a single trainee). Pilots of other types are charged between $1,000 and $1,770 per person. The course is included in the price of new TBMs.
No matter what airplane you fly, the SAMI course is invaluable. And you don’t need to be a turbine pilot. There is evidence to suggest that piston pilots flying long distances at altitudes as low as 8,000 feet can develop hypoxia. For more information, visit SAMI online (www.sami-aeromedical.com).
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The TBM and other general aviation turbine airplanes are sold with Zodiac Aerospace’s Eros quick-donning oxygen masks. After removing the mask from its mount, squeeze the red tabs at its front to inflate the harness, put the mask on, and then release the tabs. Now the mask grips your head to make a tight seal around your mouth and nose.
The mask has three modes: Normal, 100 percent, and Emergency. Normal mode provides a scheduled mix of oxygen to the pilot, based on altitude information from the airplane’s flight management and pressurization systems. The higher you fly, the more oxygen is provided.
The 100-percent mode provides 100-percent oxygen, all the time. Move the rectangular red switch at the front of the mask to select between the normal and 100-percent modes.
The emergency mode provides a continuous flow of oxygen at positive pressure. In other words, the oxygen is force-fed into the mask. Rotate the mask’s central, circular knob to the Emergency position to start the flow. This mode is used to prevent smoke or other fumes from entering the mask. Because oxygen is constantly flowing, you have to force your exhalations in order to breathe correctly, and make radio transmissions. You did remember to turn on the mask’s microphone, yes? —TAH
Aviation Technology Inc.’s AltAlert is a small, portable cabin altitude-sensing unit that clips onto a belt or lapel, or can simply lie on a flat surface. When certain cabin altitude thresholds are reached, AltAlert sounds off with one or more attention-getting red flashing lights, plus audio alarms. Above cabin altitudes of 10,000 feet, the unit flashes red every 15 seconds, and a single, loud “chirp” goes off. The pace steps up with higher altitudes. By the time the cabin passes 15,000 feet the red light is on continuously, and so is the audio alarm. If you missed seeing or hearing any panel-mounted cabin altitude warnings, you certainly couldn’t overlook the AltAlert. The unit is powered by a single, three-volt, CR2032 coin-style lithium battery, which Aviation Technology recommends replacing every 18 months, and immediately after any alarm incident. It’s light, unobtrusive, and only three inches long. —TAH
The AltAlert sells for $395.95 at Aircraft Spruce and Specialty Co. . AOPA members can save 10 percent by using code ALTSAVE, valid until May 30.
Electrical engineer and Icarus Instruments Incorporated’s Steve Silverman, a TBM owner, has developed the Voice Alert System (VAS), a device that works with noise-attenuating headsets, and issues verbal commands whenever an airplane’s cabin altitude exceeds preset values. LEMO jacks, which provide ship’s power to headphones and obviate the need for AA batteries, are required to power the VAS.
One press on the push-button switch, and an automated voice issues the airplane’s current cabin altitude. Holding the switch down lets you select a trigger altitude between 7,000 and 14,900 feet.
When the cabin pressure rises above the preset altitude the automated voice says “Don oxygen mask” twice, through the headset.
An optional, second warning method also is available through the VAS. A second cable is routed to the airplane’s master warning/master caution system. This will cause a “Check Master Warning” alert, directing your attention to the flashing master warning light and its associated cabin altitude annunciator.
The basic VAS is $395 and the master caution alert is $49 (plus installation). It’s a big step toward better hypoxia prevention in pressurized airplanes. A helpful next step would be to make the system compatible with battery-powered headsets. For more information, and to order, visit the website. —TAH
Warning devices are great for alerting you to high cabin altitudes, but they say nothing about something more important: the oxygen level in your bloodstream. Clip an oximeter on your finger, and in a few seconds you’ll see a readout of your pulse rate and blood oxygen saturation. A normal reading is 98 to 99 percent, which is what you should see at the surface, at sea level. Anything below that is cause for concern, and a cue to go on oxygen.
Oximeters used to run hundreds of dollars, but today you can get one for as little as $30 or so. I’ve even seen them given away at trade shows. My oximeter, an Oxi-Go Quick Check Pro, goes for $49.95 at Sporty’s, batteries included. Every pilot should have one, especially turbine pilots.—TAH