Air Force Eyes Fix for Trainer Aircraft Hypoxia Problem

T-6 Texan II aircraft with sun shelter
2nd Lt. Gordon Milne, 47th Student Squadron specialized undergraduate pilot training student, and Lt. Col. Gentry Mobley, 85th Flying Training Squadron commander, prepare for takeoff in a T-6 Texan II at Laughlin Air Force Base, Texas, Nov. 5, 2019. Over the last several years, sun shelters have been constructed to house many aircraft at Laughlin. (Senior Airman Daniel Hambor/U.S. Air Force photo)

The Air Force thinks it's figured out what led to a surge of T-6A Texan II hypoxia incidents in 2018, and soon will be rolling out a new backup oxygen system to make sure pilots can breathe while developing their skills in trainer aircraft.

That year, the service saw a sharp spike in incidents of pilots experiencing hypoxia, a lack of oxygen in the blood, or other related conditions referred to as "unexplained physiological events" while flying aircraft, particularly the T-6. In 2014, there were only five such incidents recorded in the T-6 but, four years later, they shot up to 86.

Insufficient oxygen can lead to pilots becoming dizzy, disoriented, short of breath or even passing out; at worst, it can lead to fatal crashes. The Air Force grew so alarmed that at one point it grounded the entire T-6 fleet for a month and created a team to root out the cause of the problem and put fixes in place.

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The first major finding: With the many flying hours its T-6s were racking up, components in its oxygen systems were beginning to wear out sooner than anticipated.

So the Air Force began replacing oxygen concentrators much earlier than it had been so they don't fail in-flight -- after every 600 flight hours instead of about 4,000. Other components, such as inhalation or exhalation valves in pilots' masks, also were replaced.

Those first steps yielded results. Incidents swiftly fell nearly in half to 44 in 2019, and then to 38 a year later. The service had tallied 19 incidents this year as of July -- continuing the downward trend, though Air Force physician and hypoxia expert Col. William "Doc" Nelson cautioned in a Sept. 24 interview at the Pentagon that a handful of other cases likely would be recorded in August and September.

"We take every [physiological] event seriously," said Maj. Gen. Albert Miller, the Air Force's director of training and readiness who also oversees these issues. Airmen "that fly our aircraft are at the pointy end of the spear for us. So we need to make sure that we give them the systems so that they can perform the mission for the Air Force."

The service is preparing to roll out an upgraded version of the T-6's onboard oxygen generating system, called SureStream, that could begin being installed on the aircraft toward the end of 2022. It will include sensors that measure how much oxygen is being fed to the pilot at any given time, which the T-6 typically hasn't previously had.

And within weeks, the Air Force expects to sign a contract to add an automatic backup oxygen system to the T-6, Miller said. T-6s now do not have such a backup system, which kicks in once the main system starts to fail or isn't producing enough oxygen, and is standard equipment in other airframes. 

The new system will be able to sense whether it is generating enough oxygen, Nelson said. And if not, the backup system will kick in and feed more oxygen from a separate tank into the pilot's mask until the primary system catches up. 

They said that adding sensors to the systems will better allow the Air Force to identify what kind of physiological issue may be happening. Other related conditions include hypocapnia, which is caused by a lack of carbon dioxide in the blood but has similar physical symptoms as hypoxia, making them hard to diagnose definitively.

Those different problems have different remedies, Nelson said. And if the Air Force can better diagnose which condition pilots are experiencing in an aircraft, it can better find the right way to fix that problem.

The service also is looking at adding additional sensors to the pilot's mask itself, that can measure both oxygen and carbon dioxide. This will allow the Air Force to make sure the oxygen being generated is actually making it through the hoses, catching potential problems with the mask.

The timeline for installing the backup system has not been determined, Miller said.

But he cautioned that it will never be possible to entirely eliminate the risk of physiological issues.

As long as people get into airplanes, Miller said, "there will be physiological events. That's why you have a yellow Dixie cup [oxygen mask demonstration] that they brief you on every time you fly [in a commercial airline].

"But we're trying to get after capturing the data, so that we can explain as many of them as we can," he continued. "And by explaining, we can solve the root causes."

-- Stephen Losey can be reached at Follow him on Twitter @StephenLosey.

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