These "physiological episodes occur when a pilot experiences a loss in performance related to insufficient oxygen," Rep. Michael Turner, a Republican from Ohio and chairman of the House Armed Services' Tactical Air and Land Forces Subcommittee, said at a Thursday hearing.
The condition creeps up on the pilot, rendering him dizzy and feeling confused, Navy officials said.
Service leaders sought to assure lawmakers that the service has developed emergency procedures to deal with the problem as an interim fix until a team of experts can find the cause of the problem.
"If we had a confidence problem in the airplane, we would ground the fleet," Rear Admiral Michael Manazir, director of Navy's Air Warfare Division, said. "We don't have that problem; that's why you don't see the commander of NavAir going to that extreme.
But the problem has been difficult to identify, Manazir said.
"We haven't been able to figure that out; we have been chasing ghosts," Manazir said. "You can't figure it out because the monitoring devices that do this are not on the airplane and can't figure out where there was a small oxygen content more than we needed or less than we needed or a carbon monoxide event or poison in the gas."
The problem isn't new to the U.S. military.
Former Defense Secretary Leon Panetta in 2012 restricted flights of the F-22 after two Air National Guard pilots appeared on the CBS news program, "60 Minutes," to say didn't feel safe flying the plane. They complained of dizziness, disorientation, even something called "The Raptor Cough," after the aircraft's name.
The Air Force temporarily grounded the planes in 2011 after more than a dozen pilots reported similar symptoms of oxygen deprivation, a condition known as hypoxia. It did the same in 2010 after pilot Jeff Haney died in a crash in the Alaskan wilderness.
Manazir told lawmakers that he has been flying fighters since 1982 on oxygen and has never experienced a hypoxia event.
The Navy prepares pilots to deal with the problem by exposing them to similar conditions in simulated training.
"What we do with the trainer now is, you get into a simulated cockpit on the ground, you put an oxygen mask on … and they gradually reduce your oxygen content and they train us to recognize the symptoms," Manazir said.
"It is not an instant, you're gone. It's a confusion factor, so when a pilot feels that, he deploys his emergency oxygen, which is 100-percent oxygen bottle like we used to do and he reaches down underneath his left thigh and pulls a handle and goes onto emergency oxygen.
"That backup system immediately gives him emergency oxygen and the symptoms subside enough for him to land the airplane that system has worked 100 percent every time and I am confident it still will."
The Navy has replaced the filtration system and has fielded in about 219 jets so far, according to Rear Admiral Michael Moran, who runs the Navy's Program Executive Officer Tactical Aircraft.
"That really has done a great job of getting rid of the carbon monoxide and improving the breathing of gas for the pilots," he said, explaining that there is still no way to measure it yet. "We are looking at a couple of things that we are testing … that we can put into their emergency gear than can measure the gas."
There is also a new oxygen-monitoring system that will be funded in 2017 once tests are complete, Moran said.
"It is I think an issue that despite all your efforts, assessments and policy and training and everything else, the numbers still don't go down," said Rep. Niki Tsongas, a Democrat Massachusetts, describing how the range of events has been 20 to 30 events per 100,000 flight hours.
"So even as you have made these investments, we are not seeing a lot of progress. What would be a normal or accepted rate of such events for the fleet? What would you look to see … is there such a rate?"
The Navy has not developed a rate for 100,000 flying hours because even one event can result in the loss of an aircraft, Manazir said.
"The rates started to climb in 2010, that's the year where we told everybody, ‘OK we think there is a problem here,'" he said. "So instead of everybody coming back and saying ‘Yeah, I was kind of dizzy, but it's fine. It passed.' I want you to report every single event, so I think the phenomenon you are seeing between 2010 and now is an increase in reporting."
Tsongas also asked Navy officials have they looked at installing an automatic oxygen back-up system.
"We do have the automatic oxygen system as a backup; we are looking increasing the amount of oxygen," Moran said. "Right now, depending on the altitude and really the condition of the pilot, that can last anywhere from 20 minutes and maybe down to five minutes.
The plan is to see of the system can be improved to extend that time "by two to four fold to give that pilot a real back up system," Moran said.
This was not good enough for Tsongas.
"I think we all would be concerned that you are asking a potentially incapacitated pilot to sort of help himself out of this, and it is my understanding that that would only give him 10 minutes were he able to exercise it appropriate," she said.
"You have no idea how far away he might be from the carrier or where he needs to get back to, so as you are looking at creating a budget" an automatic backup might be considered.
Pilots that experience these physiological events are interviewed immediately after the flight but the flight surgeon "to get as much fact as we can to then guide us in a scientific manner toward the cause," Manazir said.
"I'm comfortable that we will get there, but we are not going to stop," he said. "We will look turn over every technical rock that we can to make sure we go after every causal factor."
-- Matthew Cox can be reached at firstname.lastname@example.org.