The Navy this week said it has ruled out contamination as a cause of physiological episodes (PEs) experienced by T-45 Goshawk and F/A-18 Hornet pilots and is continuing to narrow down other potential factors.

The Naval Air Systems Command (NAVAIR) on April 1 said the service used a Root Cause Corrective Action (RCAA) analysis to determine the factors involved. Two separate RCAA core teams–one for F/A-18 Hornets and Super Hornets and EA-18G Growlers as well as a team for the T-45s– “determined last fall that the quality of pilots’ onboard oxygen was unaffected by asphyxiates, carbon monoxide and external or internal contaminants, such as fuel vapor or pyrolysis byproducts, respectively,” NAVAIR said.

A T-45C Goshawk training jet approaches an aircraft carrier. (Photo courtesy of U.S. Navy)

The T-45 team made this determination in September 2018 while the F-18 team reached its conclusion in October. The total RCAA effort took 16 months and included 21,000 samples in 11 sites from pilots’ breathing gas, ground sampling, and blood analysis. An independent panel of toxicologists and aeromedical professionals examined 1,800 compounds and they determined none played a role in the PEs.

“The Naval Aviation Enterprise took this very seriously and went through a rigorous process featuring an independent review by doctors, physiologists and toxicologists that determined definitively that contamination is not the cause of PE,” Capt. Todd St. Laurent, program manager of the Naval Undergraduate Flight Training Systems Program Office, said in a statement.

Early on the Navy assumed contamination of the aircraft’s Onboard Oxygen Generation System (OBOGS) could be causing the PEs, before it had alternative explanations.

Don Salamon, deputy assistant program manager for system engineering for the F/A-18 and EA-18G Program Office, noted the service could not explain why pilots were getting sick with hypoxia-like symptoms at altitudes below 10,000 feet.

“It’s nearly impossible for you to get hypoxic at those altitudes…other than a condition that affects your ability to exchange gases,” Salamon said.

However, the examination has found any non-oxygen compounds found in the OBOGs-generating breathing gas were measured at levels so low they are “functionally nonexistent.”

“We’ve done challenge testing in the labs with aircraft equipment that shows it is nearly impossible to force anything other than oxygen through the OBOGS. Most importantly, the symptomatology of PEs does not match exposure to any type of contaminant. We’ve gotten smarter, and now we understand there are other things that could be happening that manifest as those symptoms, but it’s not exposure to contaminants,” Salamon added.

“We are happy to see that contamination has been ruled out and that all Navy aircraft are delivering clean air to our aviators,” Rear Adm. Fredrick Luchtman, Navy lead for the Physiological Episodes Action Team (PEAT), said.

NAVAIR noted the T-45 team was able to close over 90 percent of the almost 350 branches on its RCAA “fault tree.” Fifty of those branches were related to contamination and now the team is focusing on optimal breating pressure and oxygen concentration as possible factors

Rear Adm. Scott Conn , Director of Air Warfare at the Office of the Chief of Naval Operations, told a House panel today that the Navy has been able to reduce PEs significantly in T-45s.

A Navy F/A-18 Super Hornet. Photo: Boeing.

In FY 2016 there were 35 PE incidents, in FY ’17 there were 31 incidents, in FY ’18 there were six, and “Thus far this fiscal year we’ve had one. So that is progress.”

Conn explained the Navy has been “straighlining” the pipes that come off the engine and go to the OBOGS concentrator to provide a better constant flow.

He also said the Navy has increased flight idle RPM by 1.5 percent “to get better flow to the cockpit and that is what’s driving those numbers down, Conn told the House Armed Services Subcommittee on Tactical and Land Forces.

However, The F-18 issue is not getting resolved so easily or quickly.

“We still have work to do, especially with the Hornets and Growlers—we need to ensure oxygen is being delivered at the right concentration and pressure, and that cockpit pressure stability is continually improving. And just as important, we are working on improving the process of treating aviators who have experienced physiological events so we can make sure they are healthy and can get back in the aircraft,” Luchtman said in a statement.

Conn told the subcommittee the primary driver of PE events in Super Hornets is cabin pressurization and fluctuations. Across F/A-18 E/F and EA-18G Growlers PEs stood at 87 incidents in FY ’16, 73 incidents in FY ’17, 65 incidents in FY ’18, and 41 so far this fiscal year.

“Any progress we’ve made has flattened out. The good news is we know what we need to do, in terms of using data analytics,” Conn said.

He said the Super Hornet PEs are being driven by things like the primary bleed air regulator valve and secondary bleed air regulator valve.

“Some of those are under contract and we’ll start delivering this year. Other gear will start delivering in ’20 and we’re going to install that on the airplane,” Conn said.

Some of the new equipment includes a new digital cabin altimeter that also measures oxygen and can warn the aicrew. “That is being installed this year and will continue being installed out through ’20 until we outfit the fleet.”

Conn said while they have “flatlined on the cabin pressurization,” the service knows what it needs to “and we’re getting at it with respect to getting the items under contract, getting them in the aircraft, and until we do that, and we need the resources that we’re requesting to do so, we’re not going to make any significant change to these cabin pressurization [issues].”

Salamon said in a statement the F/A-18 team is focusing on two main issues: maintaining cabin stability by preventing unexpected pressure fluctuations correlated with PE events and breathing dynamics and factors that can impact gas exchange during respiration.

However, he noted the pressure fluctuations have not yet shown to be a causal factor.

“There is likely no single ‘smoking gun’ that will be found as a result of the investigation. However, we have identified multiple contributors that are being aggressively worked through the [F/A-18 program] with near-term corrective actions,” Salamon said

The RCCA teams are made of NAVAIR engineers, instructor pilots, independent doctors and scientists, and other subject matter experts.