F-35 med surstoffproblemer - Curt Lewis

F-35A Pilots Report Five More Hypoxia-Like Episodes

U.S. Air Force F-35s at Luke AFB, Arizona, are back in the skies after a spate of so-called physiological episodes (PEs) caused the service to ground the aircraft this summer, but the troubling events have continued across the service's F-35 fleet, with pilots reporting tingling fingers and other symptoms that indicate hypoxia five separate times since flights resumed at Luke.

These incidents reflect a significant spike in PEs recorded on the F-35A in the past few months. From 2006-2016 the type saw just 10 PEs; in 2017 so far, the F-35 Joint Program Office has recorded another 10, doubling the overall number reported. Five of those 10 took place between May 2 and June 8 at Luke, and caused the Air Force to temporarily ground the F-35s at that base.

Since Luke F-35s resumed flying, pilots there have reported three additional PEs, according to Col. Ben Bishop, commander of the 56th Operations Group and an F-35 pilot. The symptoms were milder than in the initial five events, and in each instance the pilots were able to safely recover the aircraft, he told Aviation Week in an Oct. 23 interview.

The rate of PEs in the F-35A is significantly higher than in the other F-35 variants. Overall from 2006-2017, the JPO recorded 29 PEs across all variants of the F-35: 20 in the F-35A; four in the U.S. Marine Corps F-35B; and five in the U.S. Navy F-35C.

After months of investigating, the team looking into the F-35A PEs has yet to find one root cause of the problem. The team still is not sure whether the incidents indicate true hypoxia-a lack of oxygen in the blood-or any number of similar physiological states, for instance hypercapnia (high levels of carbon dioxide in the blood, sometimes caused by hyperventilation), histotoxic hypoxia (the presence of a toxin), decompression sickness, or even simply dehydration, lack of sleep, or nervousness.

But although the incidents continue to occur at Luke and elsewhere, the team is at least narrowing down the problem.

The JPO recently briefed the squadron on the test results from the F-35's Onboard Oxygen Generation System (Obogs), which showed no problems with the system, Bishop said. The PE team is looking at ways to refine the algorithm that controls the fluctuations in oxygen concentration levels so the Obogs delivers oxygen at a steadier rate, potentially making breathing easier. But in all cases the Obogs is producing enough oxygen to sustain the pilot, he stressed.

Bishop also is confident the problem is not caused by contamination. There are no indications of carbon monoxide or other toxins on the ramp, or during pilot examinations, he said.

There is one telling aspect of the incidents that may prove key to solving the problem. In each of the three incidents that occurred since June, initiating the backup oxygen system did not immediately ease the pilots' symptoms. This indicates the problem is not true hypoxia, Bishop said.
During pilot training in the Reduced Oxygen Breathing Device (ROBD), which simulates hypoxia, "when you go to 100% oxygen you get relief immediately; that's not happening in a lot of cases here," Bishop said.

Bishop believes pilots could be experiencing hypercapnia-too much carbon dioxide in the blood-due to restricted breathing, potentially caused by the life support system. He does not think the cause is hyperventilation.

"I think there might be something based on how the machine and the human are interacting that's altering the breathing," Bishop said. "So we're obviously very interested in understanding how the valves are working and making sure our pilots can exhale comfortably. If you are having trouble exhaling that can change the way your body normally breathes, which can have unintended consequences."

The team is looking at all pieces of the flight equipment for an indication of something that would restrict pilot breathing and is taking steps to make the life support system as robust as possible, Bishop said. Already, the Air Force has made a number of changes to flight equipment to mitigate the potential for restricted breathing, including reducing the weight of the flight vest to make breathing easier, and making changes to the exhalation valve on the mask to prevent sticking.

The pilots also have the option to wear pulse oximeters to measure their blood oxygen levels during flight. However, these devices are not always reliable as they can slip off, Bishop said.

Initially, there was a lot of concern in the pilot community at Luke over the spike in PEs, Bishop acknowledged.

"I will say, just being very frank and open with you, when we stood down that first day there were some pilots that were not comfortable flying the airplane," said Bishop. He stressed that those pilots were in the minority.

But despite the three additional incidents, pilots have regained confidence both in their leadership and in the F-35 life support system since flights resumed. The squadron took steps to ensure pilots knew they could express their concerns, for instance organizing focus groups for the pilots and town halls for the families. The squadron and the PE team also took steps to educate the pilots on the incidents as well as how to recognize their own unique hypoxia symptoms, for instance by training in the ROBD.

"To be honest, there was some misinformation at first, people were not fully aware of exactly how the systems played out and initially there was some concern in the backup oxygen system," Bishop said. "But by the end of the stand-down, through that education process, the pilots were comfortable."

Today, although the pilots realize the team may never find a single smoking gun, they have "high confidence" that in the event of a PE they will be able to turn on the backup oxygen system and safely recover the aircraft, Bishop stressed. That is the "number one threshold" for continuing flying operations, he said.

"We are not going to make any pilot that's not comfortable flying the aircraft, who doesn't have confidence in the F-35's life support system-we're not going to make them fly," Bishop said. "Up to this point pilot confidence has been high enough that everyone has been able to return to fly."