Investigators Find No Root Cause of Physiological Episodes, Identify Physiological Degraders

U.S. Navy photo illustration by Fred Flerlage

Naval Aviation’s Root Cause Corrective Action (RCCA) analysis teams concluded their investigations in December and found no single root cause for Physiological Episodes (PEs) experienced by naval aviators.

They determined, however, that PEs may result from a “stacking of physiological degraders,” according to Rear Adm. Fredrick Luchtman, Commander, Naval Safety Center, and Physiological Episodes Action Team (PEAT) lead.

Each RCCA core team—one for the T-45 Goshawk training jet and another for F/A-18 Hornet and Super Hornet and EA-18G Growler jets—included Naval Air Systems Command (NAVAIR) engineers along with instructor pilots, independent doctors and scientists, along with support from dozens of other subject matter experts.

PEs remain Naval Aviation’s No. 1 priority, Luchtman said.

To mitigate risk, the PEAT and program offices have developed tools and upgraded equipment in the T-45, the F/A-18 and EA-18G.

“The good news is the rate of PEs in the T-45 has gone down 90 percent since the peak rate in March of 2017. For the F-18, the rate has gone down 59 percent since the peak rate in November 2017,” Luchtman said.

He attributes those decreases to new tools and upgrades specific to each aircraft.

His focus now is on air crew awareness, proper equipment fit and educating aviators on how to maximize their physical condition to better withstand the hostile environment in the cockpit.

Physiological Margins

“We have validated that there are some factors—such as hydration, nutrition, sleep, physical conditioning and stress—that enable one to be more resilient in the cockpit,” he said.

“If you can maximize hydration, nutrition and rest, and minimize stress, you make yourself more resilient and able to handle the hostile cockpit environment,” he said.

He compared an aviator’s physiological margin to a suit of armor.

The rate of physiological episodes has gone down 59 percent since its peak in November 2017 for the F/A-18E/F Super Hornet (U.S. Air Force photo by Staff Sgt. Matthew Lotz).

“We call the depth of that armor the physiological margin. It is how well you are prepared to handle an anomaly in the cockpit. Like professional athletes, we need to understand our own physiology and how to maximize our own physiological margin.”

While it is difficult to quantify human performance aspects, the topic of physiological margins and equipment fit have been the focus of the PEAT’s roadshows. The roadshows are designed to keep aviators informed of the PEAT’s findings and aware of upcoming changes before they are published in the Naval Air Training and Operating Procedures Standardization.

Feedback from pilots during the roadshows on the human performance aspects have been mixed, he said.

Rear Adm. Fredrick Luchtman, Physiological Episodes Action Team lead, visited Naval Medical Research Unit Dayton (NAMRU-Dayton) Nov. 4 and experienced the scientific force that is the one-of-a-kind research device called the Kraken. A pilot himself, Luchtman donned his flight suit and strapped into the capsule to experience a profile that addresses pilot spatial disorientation. (U.S. Navy photos)

“There is some level of frustration that there is no single root cause, no smoking gun. But when we walk through the scenario and talk about how one can get to a degraded state in the cockpit based on these physiological aspects adding up, they start nodding their heads,” he said.

Naval Aviation has made it look effortless, he added.

“We have done ourselves a disservice in Naval Aviation by making this look so easy, when in fact this is a hard job in a very demanding and hostile environment where incredible G-forces, temperature variations and an almost overwhelming amount of sensory input are placed upon you. The better physical shape you are in, the better you’ll be able to withstand those demands,” he said.

When physiological degraders add up, they may result in a PE, which applies to either breathing dynamics and hypoxia events, or pressure-related events that result from fluctuating cabin pressure caused by sub performing parts in the Super Hornet’s Environmental Control System (ECS).

“We want to keep parts from failing, but in the event they do fail, aviators can protect themselves even more by making sure they’ve stacked up their physiological margin,” Luchtman said.

Equipment Fit

In April 2018, the RCCA team identified gear fit as a contributing factor to PEs.

If the flight harness is worn too tight or the straps are in the wrong places, it can inhibit the aviator’s ability to take a full, deep breath.

“If you can’t take a deep breath, that becomes a physiological degrader and reduces one’s physiological margin. It adds up with everything else one might be taking into the cockpit, such as dehydration, hypoglycemia, stress or lack of sleep,” Luchtman said.

The proper fit of the mask around the pilot’s face is also critical. As the pilot moves his head around there could be small leaks around the edge of the mask, which can impact the Onboard Oxygen Generating System’s (OBOGS) ability to provide the proper amount of air, he said.

During the squadron roadshows, a team of experts from the Aircrew Systems Program Office spot checks aviators’ flight gear and suggests how to get a better fit.

(U.S. Navy photos)

F/A-18E/F Mitigations

There are several efforts underway in the Super Hornet community: updates to the PE reporting guidance implemented in Fall 2019; introduction of the Hornet Health Assessment and Readiness Tool (HhART) to the fleet last year; and the ongoing installation of a digital pressure gauge, which will increase air crew awareness.

“We are in the process of replacing the analog pressure gauge with a digital pressure gauge that will record data and provide a digital readout of cabin altitude for the pilot. It will indicate whether or not the cabin altitude is on or off schedule or is too high or too low,” he said.

Modifications are underway and are expected to take 10 days to two weeks per aircraft.

One of the most effective mitigations to date is HhART, he said.

To reduce fluctuations within the aircraft’s Environmental Control System, the program office has developed a tool to identify sub performing parts before they fail.

The tool uses data collected via Slam Sticks worn by pilots during flight and evaluates how well parts are functioning. (For more on HhART, see article on page 17.)

“Since we instituted HhART, along with a couple of other changes, we’ve driven the rate down in F-18s significantly,” he said.

T-45 Goshawk Mitigations

All of the Navy’s T-45 Goshawks have been upgraded with the CRU-123 oxygen monitoring system, which checks the quality of air as it comes out the OBOGS concentrator to make sure it’s delivering the appropriate oxygen concentration. (U.S. Navy Photo by Liz Wolter)

Early in its investigation, the T-45 RCCA identified a primary contributing factor to oxygen-related PEs: low inlet pressure to the OBOGS concentrator, Luchtman said.

Program office engineers straightened the 90-degree bend in the inlet pipe and increased idle RPM on the engine.

“With the engine moving faster, it provides more air on the inlet side of the OBOGS concentrator. Those two things really eliminated the air-flow pressure issues with the OBOGS concentrator,” he said.

Another upgrade to the T-45 was the installation of the CRU-123 solid-state oxygen monitor in summer 2017.

“As the air comes out of the OBOGS concentrator, it passes through the monitor first. It’s a check on the quality of the air to make sure we’re delivering the appropriate oxygen concentration. If it’s incorrect, it gives the pilot a warning,” he said.

All T-45s have the CRU-123 and it’s working well, he added.

Physiological Monitors

“While the formal investigation has concluded, we are continuing to explore how we can optimize the human in the cockpit,” Luchtman said.

He is pushing for the development of physiological monitors that will show how the human is performing in real time, under temperature variances, under Gs, under pressure.

But he has learned that it is not as easy as it sounds.

“I’ve had to temper my enthusiasm because it takes a new approach to design sensors that will fit within the confines of the cockpit, survive the hostile environment and provide useable data,” he said.

Anything new must also be verified and validated before introduction to the fleet.

Despite the challenges, the Aircrew Systems Program Office is currently exploring five monitoring devices, which are in various stages of test, he said. 

The Navy is also working closely with the Air Force to identify a sensor for tactical aircraft that will not only provide useful data but will warn of an impending condition.

“We are depending on industry to help us develop and integrate the sensors into the cockpit, onto our flight gear and into our existing aircraft systems,” he said.

Way Forward

With the conclusion of the RCCA investigation, the functions of the PEAT will roll under the auspices of the Naval Safety Center at the end of April.

At that time, Luchtman is slated to take command of the Naval Safety Center to ensure continued flag oversight of physiological episodes.

“We are very thankful, not only to Naval Aviation leadership, but naval leadership as a whole and Congress for their support. There’s never been a question about resources when it comes to anything related to PE, and I do not see that changing.

“This remains Naval Aviation’s No. 1 safety priority and will continue to be until we’ve driven this rate down as low as we can.”

Andrea Watters is editor in chief of Naval Aviation News.  

Onboard Oxygen Generating System

Location of the T-6 Texan aircraft on-board oxygen generating system. U. S. Air Force photo by Lt. Col. Kyle

The Onboard Oxygen Generating System (OBOGS) was the first target of the root cause corrective action (RCCA) analysis process to understand physiological episodes (PEs).

“There was a lot of theory and discussion of contamination early on,” said Rear Adm. Fredrick Luchtman, Navy lead for the Physiological Episodes Action Team (PEAT).

“We took our OBOGS concentrators apart and put them through rigorous testing. We collected more than 21,000 samples of air and determined that the OBOGS air is extremely clean and not prone to contamination,” he said.

He attributes some of the early confusion to the fact that the OBOGS does not technically generate oxygen.

Ambient air is pulled into the system and passes through two sieve beds. The filters hold the oxygen and purge the nitrogen, then the system allows the concentrated oxygen to pass to the pilot.

“There’s no chemical process in which chemicals or contaminants could be introduced. The system doesn’t work in reverse and it cannot deliver anything less than 21 percent concentrated oxygen because that’s what’s in ambient air,” Luchtman said.

All Navy tactical aircraft, including the T-6 Texan, T-45 Goshawk, F/A-18E/F Super Hornet, EA-18G Growler and F-35C Lightning II, use OBOGS concentrators, and several replacement systems are in the works, he said.

The T-6 currently is flying with the 105 model and has begun taking delivery of the 106A Concentrator, which allows for some data recording, Luchtman said.

The T-45 currently flies with the GGU-7 and will upgrade to the GGU-25 concentrator beginning in second quarter fiscal 2022. The F-18 currently flies with the GGU-12, which will be upgraded in 2023 to a Life Support Systems Integration, which will provide scheduled delivery of a graduated amount of oxygen that increases as altitude increases. — Andrea Watters

Fleet Finds Unique F/A-18 Diagnostics Invaluable

The ultimate goal is to integrate the Hornet Health Assessment and Readiness Tool into the aircraft’s numerous complex systems to help improve supply, maintenance and readiness postures for F/A-18s and EA-18Gs. (U.S. Air Force photo by Staff Sgt. Matthew Lotz)

One year after first hitting the fleet, a unique F/A-18 analytical tool, Hornet Health Assessment and Readiness Tool (HhART), continues to benefit the warfighter and demonstrate how a mix of data analytics and engineering can serve as an accelerator for naval aircraft readiness.

“This cutting-edge technology will reduce unscheduled maintenance and make diagnostics and maintenance planning easier for the warfighter,” said Don Salamon, an engineer for the Physiological Episodes (PE) Integrated Product Team within the F/A-18 and EA-18G Program Office.

“While the inception of HhART stemmed from PE investigations, the resulting tool puts data to use in a practical, proactive way, directly supporting the ability to maintain increased aircraft readiness as well as maintenance and supply postures,” Salamon said.

HhART leverages aircraft and sensor data, maintenance information and advanced data analytics to create a health and performance dashboard display of the aircraft’s critical Environmental Control System (ECS). 

This information provides the fleet with enhanced prognostic and predictive capabilities to facilitate better troubleshooting and more efficient maintenance of this complex system of aircraft components. 

Naval Air Systems Command (NAVAIR) employed the tool and began surveilling the fleet in March 2019, providing squadrons with direct, proactive feedback and maintenance recommendations on flagged aircraft.

HhART became the top corrective action taken to combat PEs and after great initial success, the program rapidly expanded, leveraging data correlations and unique features identifying underperforming or failing systems ahead of the onboard aircraft prognostics, Salamon said.

He attributes its success to program office and NAVAIR leadership empowering and providing resource support to the multifaceted HhART Team, led by the PE IPT and comprised of data scientists and technical experts from NAVAIR, Naval Air Warfare Center Training Systems Division, Naval Sea Systems Command, the Carderock Division of the Naval Surface Warfare Center, the Center for Naval Analyses and The Boeing Company. 

“This cross-functional and collaborative effort between Industry and government highlights the Navy’s organic capabilities to execute true applications of ‘big data’ and produce actionable results and outcomes,” said Capt. Jason Denney, F/A-18 and EA-18G Program manager.

After a successful year in the fleet, the HhART team is transitioning this same methodology to other aircraft systems that are primed to benefit from similar data analysis, such as fuel systems, flight controls, propulsion systems and generator control units—the current number one degrader for both the F/A-18E/F Super Hornet and EA-18G  Growler.

The tool provides operators and maintainers with an indication of issues or degradation of systems in near real-time, enabling a more proactive approach and quicker identification of trends that often inform supply chain management decisions.

The ultimate goal for HhART is integration directly into the aircraft’s numerous complex systems, further supporting improved supply, maintenance and readiness postures for F/A-18s and EA-18Gs. The team behind it is currently digging into the data analysis and engineering challenges to bring that plan to fruition.

“The HhART Team has done an amazing job in creating this program and we expect, with its continued development and expansion to other aircraft systems, that it will become an indispensable tool for maintaining increased readiness for our aircraft platforms,” Denney said.

Written by Erin Mangum with the  F/A-18 and EA-18G Program Office.