Some of America’s F/A-18 pilots say they are being asked to take greater risks than ever before because aging equipment on the fighter jets, particularly ones that help them breathe, is failing.

It appears the life support systems on all versions of the F/A-18 – one of the most important combat aircraft in service – are increasingly failing to supply pilots with safe, breathable air.

When there is a breakdown of life support systems, like the so-called “On-board Oxygen Generating System” (OBOGS), or cabin pressurization systems, pilots often experience what the Navy and Marine Corps call “physiological episodes.”

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That means pilots experience hypoxia, an oxygen deficiency, and decompression sickness. They can experience dizziness, tingling in the fingers or toes and confusion – some have even lost consciousness.

PACIFIC OCEAN (May 3, 2017) An F/A-18E Super Hornet from the “Kestrels” of Strike Fighter Squadron (VFA) 137 lands on the flight deck of the Nimitz-class aircraft carrier USS Carl Vinson. (U.S. Navy photo by Mass Communication Specialist 2nd Class Z.A. Landers/Released)

And that puts everyone on the fighter jet in serious danger. The Navy told Fox News this week that hypoxia, or a loss of oxygen, was a “possible contributing factor” in at least three fatal F/A-18 crashes.

During a congressional hearing in March, Rear Adm. DeWolfe Miller, director of the Air Warfare Division for the U.S. Navy, confirmed that from 2015 to 2016 some models of the F/A-18 experienced as much as a 90 percent increase in potentially deadly physiological events.

Three active-duty F/A-18 pilots, who spoke to Fox News under the condition that their name not be used, said they are putting their lives in danger just by getting behind the controls of an aging fighter jet.

“When I go flying in combat, what’s more likely to kill me is not getting shot down by enemy fire,” said one of the F/A-18 pilots. “It’s a failure in my most basic life support system.”

He added that his feelings were shared by many F/A-18 pilots.

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“If you ask 10 aircrew: ‘What are you most scared of?’” he said, "nine out of 10 would probably say, 'OBOGS failure or decompression.'”

Two of these three pilots said they have experienced hypoxia-like episodes in the cockpit. One saw an indication of pressurization problems and pulled the “green apple,” a green-colored ring that has about 10 minutes of emergency oxygen stored in the ejection seat.

ARABIAN GULF (April 11, 2017) An F/A-18C Hornet attached to the "Ragin' Bulls" of Strike Fighter Squadron (VFA) 37 lands on the flight deck of the aircraft carrier USS George H.W. Bush (CVN 77). (U.S. Navy photo by Mass Communication Specialist 3rd Class Christopher Gaines/Released)

The other pilot had pressurization problems but was already hypoxic by the time he realized it. He said he basically felt like he was “intoxicated.”

“I remember having trouble thinking. I obviously had trouble performing procedures, and I definitely did not have awareness of how much trouble we were in,” he said.

In fact, he said, his mental state was so impaired by hypoxia that he didn’t pull the “green apple” because he became was more concerned about burdening the maintenance crew with the task of refilling the oxygen – than his own life.

He landed safely, but that was “just luck,” he said.

The military is aware of the problem. According to a memo Fox News obtained from the House Armed Service Committee, the Navy has noticed a rise in hypoxia among pilots operating F/A-18s. In fact, since 2009, there’s been a steady climb in such episodes.

To deal with the situation, the Navy has installed decompression chambers on two of its deployed aircraft carriers—the USS Carl Vinson and the USS George H. W. Bush. The USS Ronald Reagan will deploy soon with one onboard. But this only helps pilots who make it back to the ship.

The real issue is how to prevent the oxygen problems before they cause trouble. As a Marine pilot noted, his job “is an inherently risky business.”

“But,” he added,” the Navy and Marine Corps should give you a better than average chance.”

This issue isn’t limited to frontline combat aircraft. As first reported by Fox Business Network and Fox News, in April the T-45 aircraft used to train pilots was grounded after instructor pilots refused to fly because of an alarming occurrence of physiological episodes. According to one T-45 pilot, the decision to strike was made in part because they felt the risk was not worth the gain when they were only training and not flying vital combat missions.

PACIFIC OCEAN (April 17, 2017) A Marine inspects the flight controls of an F/A-18 Hornet, assigned to the Checkerboards of Marine Strike Fighter Attack Squadron (VMFA) 312, on the flight deck aboard the aircraft carrier USS Theodore Roosevelt. (U.S. Navy Photo by Mass Communication Specialist 3rd Class Spencer Roberts/Released)

But that same aviator notes F/A-18 pilots need to stay combat ready and, as a result, need to keep flying despite the added risk.

Following this pilot protest, Vice Chief of Naval Operations, Admiral Bill Moran, ordered a “30-day Review” of the episodes involving the T-45 and F/A-18, including how the issues were addressed. Moran promised to “provide a full and open accounting to our aviation community, their families, and the public.”

Vice Adm. Mike Shoemaker, Commander in the Naval Air Forces, said the issue was his “No. 1 safety priority.”

“We will not be limited by money or manpower as we diligently work toward solutions," he said.

One of the Navy pilots who spoke to Fox News acknowledges the Navy is doing the best it could to address the problem. One thing the pilots and their leadership agree on, he said, is that it’s “a complex problem.”

A Marine Corps Aviation public affairs officer told Fox News that Marine Corps Aviation has seen fewer incidents than Navy pilots, but said its leaders are taking “this matter very seriously. Physiological events remain a top safety concern until we fully understand all causal factors.”

Boeing, the aircrafts manufacturer, said it was looking into the matter.

“We are working closely with the Navy to help identify root causes of physiological episodes and their solutions,” the company told Fox News. “Crew safety is a top priority for us, and we’ll continue to be a proactive partner on the way forward.”

The Navy has also been training pilots in simulators with a device that induces hypoxia so it can recognize the symptoms and learn how to deal with them. And the Navy is also providing pilots with portable hypobaric recording watches that may alert them if cabin pressurization fails, as well as devices that measure and record cabin pressure changes for post-flight review. The Navy has also increased the frequency of aircraft inspections.

But the precise cause of the growing incidents of hypoxia and other physiological episodes is still not known. On top of that, there is nothing currently in a jet that will detect if pilots aren’t getting the right amount of oxygen and then automatically switch over to an emergency supply.

So, for now, the issue is identified but unresolved.

“The heat needs to come, and I think it needs to come at the highest levels,” a Marine pilot told Fox News. “The guys at the lowest levels are working their butts off, and we don’t see any change.”