February 1, 2011
By Bruce Landsberg
High flight is exhilarating, but the atmosphere up there does not support life as we know it. Every year several accidents are attributed to hypoxia, or lack of oxygen. It’s a small part of the total accident picture but if you operate a turbocharged or turbine-powered aircraft, a solid understanding of the oxygen system, the pressurization system, the associated failure modes, and the design philosophy is more than just a good idea. (See “ Pilot Counsel: Supplemental Oxygen Reviewed,”.)
There have been several high-profile high-altitude mishaps involving hypoxic pilots. The most recent was a Lear 35 carrying pro golfer Payne Stewart. The cabin depressurized, but apparently the crew did not notice. Another well-known sports figure, Louisiana State football coach Bo Rein, was lost in 1979 when the Cessna Conquest II in which he was riding flew halfway across the country and climbed to an altitude of 41,000 feet before running out of fuel and spiraling into the Atlantic Ocean. The aircraft was never recovered.
On March 17, 2006, a Beech Baron 56TC (turbocharged) on an IFR flight plan departed Dawson Community Airport (GDV) in Glendive, Montana, at 6:43 p.m. EST, destined for St. Paul Downtown Airport (STP) in Minnesota.
Earlier that day the pilot had flown from Havre City Airport (HVR) in Havre, Montana, to Glendive. The airplane was fueled before departing Glendive. This was the final leg of a multi-day trip, and the pilot was obviously comfortable at high altitude because ATC records showed prior flights operating at FL270.
All communications were normal until ATC advised the pilot that he was 400 feet higher than his assigned altitude of FL240. The pilot responded, “Lima Lima, roger, I was just trying to look behind me and it’s the first time I’ve ever noticed that I’m making contrails.” The flight was cleared from FL240 for FL270 and leveled at FL270 at 7:03 p.m.
At 7:37 p.m., the pilot called Minneapolis Center to ask if controllers had heard his previous transmissions, stating, “Did you hear me call in a few times?” Multiple attempts to contact the pilot were unsuccessful, and at 7:52 p.m. ATC decided that radio contact had been lost. At 8:11 p.m. ATC expected the Baron to begin its descent for landing at St. Paul in accordance with lost communication procedures. However, by 8:27 p.m., the aircraft had not left cruise altitude nor made any turns to join the arrival course. It continued southeasterly and overflew St. Paul around 8:40 p.m., at which time the North American Aerospace Defense Command (NORAD) was contacted.
At 8:49 p.m., fighters were scrambled to intercept the Baron. In the interim, several airliners attempted both radio and visual contact, but there was no response. The fighters visually acquired the Baron at 9:14 p.m. Position lights, strobes, and rotating beacon were all illuminated, with the interior lights on a “dim setting,” but the pilot could not be seen.
Multiple attempts were made to gain the pilot’s attention by firing flares and conducting an afterburner flyby, but there was no response. At 10:04 p.m. two more fighters relieved the original intercepting flight, which by now was running low on fuel. They also fired flares, but to no avail.
At 10:34 p.m., the airplane began to descend, and at 10:37 p.m. radar contact was lost. The Baron crashed in near-vertical attitude in a sparsely populated area near Winfield, West Virginia, about 10 miles southeast of Charleston. The accident occurred in night visual conditions with no clouds or restrictions to visibility.
The pilot held a private certificate with single- and multiengine land, and instrument airplane ratings. He held a current FAA third class medical certificate; his logbooks showed 2,469 total hours of flight experience, and 757 hours in the accident airplane. The NTSB found the pilot strapped in the left front seat and wearing an oxygen mask.
In addition to the aircraft’s installed oxygen system, a portable oxygen system also was found in the wreckage. A nasal cannula was connected to the airplane’s oxygen system and found on the seat next to the pilot. The pilot’s mask was connected to the portable oxygen system, on the floor of the cabin. The regulator valves of both systems were open approximately halfway, and both were depleted. A pulse oximeter was discovered on the ground six feet outboard of the left wing tip.
The Baron, manufactured in 1968, had a factory-installed onboard oxygen system. The most recent annual inspection was completed on March 27, 2005, and at that time the aircraft had accumulated 2,670.9 total hours of operation. There was no evidence of preimpact malfunction of engines or airframe, and the combustion heater revealed no evidence of leakage (which could have been a source of carbon monoxide poisoning). Both the installed and portable oxygen systems were functional. The service ceiling was 32,200 feet, which is at the upper limits for piston aircraft.
The pilot kept an electronic journal where he wrote, according to the NTSB, “He would attempt to fly high in an effort to get more efficiency from the engines, and would use the oximeter to monitor his blood oxygen levels. He stated that below 80-percent oxygen saturation, ‘I notice a degradation of my cognitive ability.’
“The pilot described using a nasal cannula at altitudes exceeding 18,000 feet, and in one entry at 23,000 feet, he added that his blood oxygen level stayed ‘in the 90s.’ He stated that the oxygen mask was ‘more effective at getting oxygen into my lungs and blood but less comfortable and needs to be briefly pulled away for drinking or eating.’
“According to the pilot’s logbook, he had also flown up to 31,000 feet using mask and cannula. During another flight his oxygen mask hose became disconnected, so he stuck the hose in his mouth, and continued the flight.”
There are often subtleties in flight-critical systems that pilots must understand. The factory-installed system guidance noted that it was “absolutely necessary” to close the console control valve or the remaining supply could be depleted. Rather important guidance.
The portable oxygen system appeared to be something of the pilot’s own design. The tank was manufactured in October 2001 for industrial use and modified with an aviation-oxygen-system-compatible fitting. The attached nonaltitude-compensating regulator was manufactured in 1971, and the flow rate was not adjustable. It wasn’t approved for aviation use, but rather intended for medical application, presumably at ground level.
The system allowed the use of either a cannula or a mask. (Cannulas are only allowed up to FL180; masks are required above that altitude.) The pilot’s mask had been derated by the manufacturer to 25,000 feet.
Investigators found two tanks, one aircraft and one industrial, plumbed together and strapped to a two-wheeled dolly in the pilot’s hangar. Although the airplane had operated at high altitude during the multiple-day trip, there was no evidence that either of the oxygen systems had been serviced at any of the intermediate airports.
Unfortunately, some pilots don’t worry about oxygen until it’s gone. Don’t become a statistic: Protect yourself on your next flight by taking this quiz to learn more about the causes and effects of hypoxia >>
The NTSB stated the probable cause as “The pilot’s inadequate preflight preparation to ensure an adequate supply of supplemental oxygen, and his inadequate in-flight planning and decision making, which resulted in exhaustion of his oxygen supply, and incapacitation from hypoxia during cruise flight.”
Just as engines need fuel, we need an adequate supply of oxygen. This pilot appears to have been too casual regarding the complexities and nuances of high-altitude operation. He ran out of oxygen.
Was he not fully functioning as a result of an unapproved system? We’ll never know. But why did he run out? One hypothesis is that in a quest for efficiency, and perhaps cost effectiveness, the pilot stretched his oxygen supply too far. Nobody likes to waste money—but how much is your life worth?
Saving a few thousand dollars on hardware and oxygen refills doesn’t seem like a fair trade for a human life.
Hypoxia is a killer, and a subtle one because it can take us out gradually. Many pilots never realize that they’ve been robbed of an essential life component. The regulations regarding oxygen use and equipment may seem overly conservative. A patched-together system usually works perfectly, or nearly so, until the last flight. This one apparently was working, but was it adequate—and did it warn that there were only a few minutes of life left?
A pilot apparently runs out of oxygen at FL270 and his airplane continues flying on autopilot until it runs out of fuel and crashes. The oxygen system was “modified” but that doesn’t appear to have been a factor.
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