Editor’s Note: This is an issue near to our hearts, as the oxygen system was one of the causal factors which led to the death of a friend of ours in Alaska a little over five years ago, and several of our staff currently fly both the Legacy Hornet and Super Hornet. As most of us are pilots, we can tell you there’s nothing nice about hypoxia and it will kill you the instant you don’t respect it. Let’s hope they come up with a permanent fix to this issue…and soon.

It turns out Navy pilots like to breathe. That’s a potential problem in the Navy’s mainstay fighter, the F/A-18 Hornet, which is suffering failures of its On-Board Oxygen Generation System (OBOGS). While rare, a single case of in-flight oxygen deprivation could potentially kill the pilot, destroy a $30 million to $60 million aircraft, or both — and after five years, the Navy’s still searching for a fix.

“I’m concerned about the high rate of hypoxia — which is caused by a lack of oxygen — and other physiological events apparently being experienced by the crew members of F-18 aircraft over the past five years,” said Rep. Niki Tsongas, a senior Democrat on the House Armed Services subcommittee on tactical air and land forces.

Oxygen deprivation can make a pilot dizzy or confused, both dangerous states of mind when hurtling at hundreds of miles per hour through the air. F-18s carry backup bottles of oxygen as well, but Tsongas noted that emergency supply must be turned on manually — which a sufficiently logy pilot may not be able to do. (After experiencing similar problems, the Air Force F-22 eventually went to an automatic backup). The auxiliary oxygen supply also only lasts about 10 minutes. That’s not necessarily enough to get back to the base or aircraft carrier and land safely.

Navy documents record 297 incidents for all types of F-18 from May 2010 through October 2015. In fact, reports of problems have been increasing, although that may be the result of a full-court press to raise awareness.

“None of the incidents….have resulted in loss or damage of an aircraft,” say the Navy papers, which Breaking Defense obtained. “In all but one instance, the pilot made a full recovery from the episode.” We don’t have information on what happened to that one pilot.

The problem occurs at roughly equal rates both in the aging A/B/C/D models built by the former McDonnell-Douglas and in the newer E/F Super Hornets and EA-18G Growlers being currently built by Boeing. That’s true even though the old and new jets have different oxygen systems. While the baseline Hornets use bulky bottles of liquid oxygen, like most aircraft since the 1940s, the Super Hornets and Growlers use Cobham-built On-Board Oxygen Generation Systems (OBOGS) that purify air from the engine intakes, theoretically giving them an unlimited supply of oxygen — as long as OBOGS works.

“The older F-18s are having problems due, it seems, to the cabin pressure system and possible contamination,” a Hill staffer told me. “The relatively new Super Hornets are having problems as well, at almost the same rate, but the Navy seems to think it is related to the onboard oxygen generation/filtration system.”

Unsurprisingly, subcommittee chairman Rep. Mike Turner singled out “physiological events” as a top issue for today’s hearing with two admirals and the Marine Corps’ deputy commandant for aviation. Similar oxygen problems led to the grounding of the entire Air Force F-22 fleet in 2011. I’ve seen no mention that the two services are cooperating on the current problem, but the Navy’s well aware of the Air Force history.

The Navy documents even note the F-22 and the late-model (E/F/G) Super Hornets use “very similar” on-board oxygen generation systems. But one big factor for the F-22 doesn’t apply here: a faulty g-suit vest, the “Upper Pressure Garment,” that the Navy doesn’t use. In part as a result, grounding the F-18 isn’t on the table.

“If we had a confidence problem in the airplane, we would ground the fleet,” said Rear Adm. Michael Manazir, the director of air warfare on the Navy staff and an F-18 pilot himself. “I’ve never experienced a hypoxic event outside of training,” when pilots are deliberately subjected to partial oxygen deprivation so they learn the warning signs.

“I’m very confident in my Navy team here to go fix the OBOGSs problem,” said Marine Lt. Gen. Jon Davis. (The Navy runs the back office support for many Marine Corps systems). “The Marines love flying the F-18, it’s a workhorse for us, we don’t worry that much about the O-bogs [oxygen system] right now.”

“My youngest son’s a Marine F-18 pilot [who] just got back from deployment,” Davis said. “I think he’s more worried about the numbers of airplanes on the line for him to go train than he is the OBOGS.” Unrelated maintenance issues have grounded almost 20 percent of the Marine Corps’ often-aging aircraft.

Despite five years of watching the F-18 oxygen systems closely, however, the Navy still doesn’t know why the air supply is failing, Manazir admitted. “It’s like chasing a ghost,” he said. “We can’t figure out, because the monitoring devices that do this are not on the airplane,” whether a given incident results from too little oxygen, too much oxygen, excessive carbon monoxide, or some kind of toxin leaking into the air.

Sydney Freedberg’s original article at BreakingDefense can be viewed here.