NAVAIR Zeroes In On Causes, Solutions for Physiological Episodes
(Source: US Navy; issued Aril 01, 2019)
PATUXENT RIVER, Md --- Utilizing a rigorous Root Cause Corrective Action (RCCA) analysis process to eliminate contaminated breathing gas as a cause of the physiological episodes being experienced by F/A-18 and T-45 pilots, the two teams tasked with investigating the issue continue to narrow down the list of possible factors.

Each RCCA Core team—one for F/A-18 Hornet and Super Hornet and EA-18G Growler jets, another for the T-45 Goshawk training jet—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.

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

The T-45 team reached its conclusion in September, with the F/A-18 team following in October, after a joint 16-month effort that saw 21,000 samples taken across 11 sites from pilots’ breathing gas, ground sampling and blood analysis. In total, roughly 1,800 compounds were evaluated by an independent panel of toxicologists and multi-disciplinary panel of aeromedical professionals, who determined that none of the compounds played a role in physiological episodes, or 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,” said Capt. Todd St. Laurent, program manager of the Naval Undergraduate Flight Training Systems Program Office.

The RCCA teams include Naval Air Systems Command (NAVAIR) engineers along with instructor pilots, independent doctors and scientists, along with support from dozens of other subject matter experts.

The F/A-18 team is now focused on two potential factors, one being the maintaining of cabin stability by preventing unexpected pressure fluctuations that have been correlated with PE events but not yet shown to be a causal factor, said Don Salamon, deputy assistant program manager for system engineering for the F/A-18 and EA-18G Program Office.

The second focus is on breathing dynamics and factors that can impact gas exchange during respiration, such as hyper/hypocapnia, hypoxic hypoxia, work of breathing, and adsorption/acceleration atelectasis.

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

The T-45 team has closed more than 90 percent of the nearly 350 branches on its RCCA “fault tree,” 50 of which were related to contamination, team lead Ann Dickens said. The team is now focusing on optimal breathing pressure and oxygen concentration as potential factors.

The notion that PEs could be caused by contaminants infiltrating the aircraft’s Onboard Oxygen Generation System (OBOGS) was an early assumption made in the absence of alternative explanations.

“Contamination was an explanation for people getting sick in the aircraft when we couldn’t explain it very well,” Salamon said. “We had people experiencing hypoxia-like symptoms at altitudes below 10,000 feet, and it’s nearly impossible for you to get hypoxic at those altitudes…other than a condition that affects your ability to exchange gases.”

But following seven years of data collection where compounds other than oxygen in OBOGS-generated breathing air were consistently measured in the parts per billion—levels so low as to be functionally nonexistent—the RCCA teams determined contamination could safely be ruled out as a root cause of PEs.

“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,” Salamon said. “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.”

Some other potential factors have also been ruled out—such as electromagnetic exposure—while others have been determined to play a role in F/A-18 PEs, including maintenance-related issues and atelectasis, commonly referred to as collapsed lung.

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Navy Develops and Tests Rapid Pressure Fluctuation Chamber to Study Physiological Events
(Source: US Navy; issued April 01, 2019)
PANAMA CITY, Florida --- A Navy team is developing a solution for detecting symptoms associated with rapid pressure fluctuations in military jets, a phenomenon associated with physiological events (PE) in the E/A-18G and F/A-18 weapon systems.

Naval Surface Warfare Center Panama City Division’s (NSWC PCD) Fluctuating Altitude Simulation Technology (FAST) team recently delivered an aircraft cabin simulator system to the Navy Experimental Diving Unit (NEDU) for their use conducting human subject research.

NSWC PCD engineers designed and fabricated the FAST system to replicate the rapid cockpit pressure fluctuations observed in the Navy’s jet aircraft.

“The purpose of the FAST system is to characterize the symptoms associated with rapid pressure fluctuation, and determine what symptoms may be most closely associated with PE,” said Navy Research Psychologist Lt. Jenna Jewell. “This information allows us to conduct future research that can be more targeted, including focusing on specific symptoms and adding in factors present in the cockpit.”

Aircrews experience PEs when there is both a known or suspected aircraft or aircrew systems malfunction and a loss in performance related to insufficient oxygen delivery, alterations in breathing dynamics, unexpected pressure phenomenon, or other human factors. Research “flights” were conducted at NEDU from November 2018 to January 2019 to simulate the rapid cabin pressure fluctuations aviators experience during flights in a controlled environment. This allowed medical researchers to investigate whether there are physiological or neurocognitive impacts due solely to the pressure fluctuations

The team began with a commercial-off-the-shelf (COTS) Double Occupancy Altitude Chamber (DOAC) to simulate the cockpit environment and modified the features to meet operational objectives, according to Brian Toole, NSWC PCD FAST project manager.

“The NSWC PCD FAST team designed and assembled the FAST system in-house,” said Toole. “NSWC PCD brought the concept to reality by starting with the COTS DOAC and installing our own control system, developing algorithms, and programming the NSWC PCD designed chamber software to meet mission requirements.”

According to NEDU Research Physiologist Lt. Travis Doggett, the FAST study is moving the Navy one step closer to solving critical safety concerns.

“This study is the first-of-its-kind human subject research investigating PEs plaguing Naval Aviators by replicating the cabin pressure fluctuations observed in the Fleet. It is also the first-ever study to investigate and identify the physiological responses and symptomology associated with rapid cabin pressure fluctuations at altitude,” said Doggett.

“The FAST system, coupled with the manned testing, will provide Navy leadership vital information needed to help solve the Chief of Naval Operations number one aviation safety concern – impacting the Navy’s ability to operate safely in the airspace of its choosing, without physiological hindrance,” Doggett added.

How it works

Before simulated flight, participants undergo an initial general medical evaluation to determine inner ear function, retinal tracking, and a neurocognitive exam. Upon completion, participants enter the FAST chamber and fly one of three predetermined flight patterns. During the flight, participants’ vital statistics are tracked constantly and a Doppler ultrasound test is conducted at four different occasions to determine if venous gas bubbles are present in each participant’s heart. In addition, retinal function is tested mid-flight.

Upon completion of the flight, participants undergo the same pre-flight testing to determine if there are any changes in physiological or neurocognitive performance as a result of the rapid pressure fluctuations experienced during simulated flight.

NSWC PCD’s FAST team used their life support expertise to meet this urgent need, rapidly developing the technology by pursuing parallel paths and efficient use of existing assets. The FAST team went from refining conceptual requirements in November 2017 to delivering a fully functional system to NEDU in May 2018.

“Our team at NEDU knew what we wanted to accomplish at the end. We had an idea of the question we wanted to answer, but did not have anything in terms of how to actually make it happen,” said Jewell. “The partnership between NEDU and NSWC PCD is how we got to a solution. For all of this to come to fruition within 14 months of beginning, and now we have a new system that NAVAIR is going to continue relying on to use in the future, is huge for us.”

The FAST cabin is one key step in identifying, mitigating and eliminating environmental factors causing PEs during military aircraft flights. This study is only the first of multiple steps. The next phases include adding additional factors to determine how pressure fluctuations can affect aircrew.

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