U.S. Air Force Col. Jay Flottmann is one of a handful of individuals the service calls “unicorns”—qualified both as a fighter pilot and a physician. As a member of the NASA team charged with studying a troubling surge in hypoxia-like cockpit episodes in the U.S. Navy’s F/A-18 fleet, Flottmann provides critical expertise.
Flottmann, who has extensive experience flying F-15C/Ds, F-22s and T-38s, recently flew several F/A-18 sorties to help the NASA team better understand the vexing problem of why Navy pilots are experiencing so-called “physiological episodes” (PEs)—reporting symptoms like dizziness, finger tingling and impaired judgment commonly associated with a lack of oxygen to the brain—in greater and greater numbers.
The most significant lesson from Flottmann’s report is that the F/A-18 aircraft system, the physical conditions of flight and aircrew flight equipment have a “profound impact” on human physiological systems and human performance, according to the NASA Engineering and Safety Center report, dated Sept. 14 and released Dec. 13. In other words, Flottmann’s assessment supports NASA’s conclusion that it is the complex interaction of the human and aircraft system, not one or the other, that causes the episodes.
Most notably, Flottmann observed troubling tendencies among the pilots themselves, such as not conducting the typical anti-G straining maneuver (AGSM) properly, or at all. These tendencies, coupled with the unforgiving F/A-18 flight environment and certain aspects of the flight equipment, resulted in constricted breathing and a noticeable cough, he concluded.
He noted in a follow-up email to Aviation Week that this was a very small sample size, and it is not accurate to apply this conclusion to all Navy pilots.
Flottmann flew three sorties in the F/A-18 overall—one in the D-model legacy Hornet, equipped with liquid oxygen (LOX), and two in the F-model Super Hornet equipped with an On Board Oxygen Generation System (Obogs). Flottmann, who is used to Air Force procedures, flew with U.S. Navy flight equipment, including the helmet, mask, combination harness, survival vest, anti-G trousers and gloves in addition to standard flight suit and boots.
Flottmann noticed that while the function of the Air Force and Navy masks is similar, the ground “fit test” and custom fit procedures are vastly different. Unlike the Air Force, prior to the flight with the Navy, Flottmann’s mask was not tested for air leaks with equipment that simulates altitude exposure and pressure breathing.
Flottmann also noticed the Navy’s propensity to tighten the chest strap much more than Air Force pilots typically do. In addition, the survival vest equipment (radio, first aid equipment, etc.) is largely located along the lower torso, with much of the weight along the front and side of the abdomen. These two factors contributed to a perception of added weight across the chest that Flottmann described as a “slight ‘squeeze’ while breathing normally.”
During his flights in the Obogs-equipped Navy aircraft, Flottmann also noticed a subtle difference in flow and pressure when breathing off the Obogs system. Whereas in most Air Force breathing regulators (with the exception of the F-22 and F-35) the system provides air as the pilot inhales, the F/A-18F Obogs seemed to provide a constant safety pressure, blowing air into the mask. This “positive pressure” can result in subtle changes in the way a pilot is breathing, Flottmann wrote. Indeed, the front seat pilot of Flottmann’s first F/A-18F mission admitted that on Obogs-equipped aircraft he routinely coughs after nearly any maneuver, particularly high-G ones. Flottmann noticed the pilot coughing after even minor G-loads during the flight.
This cough said to Flottmann that the pilot displayed classic signs of “atelectasis” (both acceleration atelectasis and absorption atelectasis), in which the tiny air sacs called alveoli in the lung bases are partially collapsing due to a combination of high G-loads, 100 percent oxygen and the restrictive anti-G suit.
Flottmann himself experienced familiar sensations following the F/A-18F sorties—a mild chest tightness that reminded him of a sortie he flew in the F-22 during a safety investigation of PEs in the Raptor.
Flottmann also found that neither front seat pilots, though experienced aviators, executed the typical AGSM that Air Force pilots typically perform to help their bodies cope with high G loads.
“Following both missions, I asked each pilot about his AGSM and both admitted that they really did not ‘do that’ very well,” Flottmann wrote. “When I asked about debriefing the AGSM, it was my impression that he did not understand how to evaluate and instruct to the proper techniques shown to enhance G protection and endurance, namely an appropriate breathing pattern.”
In addition, unlike in most Air Force fighter regulators, the F/A-18 does not provide a graduated increase in breathing air through the mask over 4gs to aid inhalation, called “positive pressure breathing for G” (PBG). If pilots are indeed not performing a typical AGSM, this would likely result in acceleration atelectasis, Flottmann wrote.
“I am convinced that the ‘elevated oxygen content’ in the breathing gas (both LOX and OBOGS) coupled with the operation of the CRU-103 breathing regulator negatively affects human performance,” Flottmann wrote, noting that he spent the rest of the day clearing his ears, felt more fatigued than usual, had a mild headache, and noted subtle breathing changes he described as “a propensity to breathe deeply, as if I was trying to inhale deeply out of necessity.”
Though much of the Navy’s investigation of the F/A-18 PEs has focused on cabin pressurization, Flottmann had no such issues, he wrote.
Overall, Flottmann’s observations led him to conclude that the flight equipment, particularly the survival vest and harness, resulted in mild constriction and chest tightness, particularly in the Obogs aircraft.
“Although the sensations were subtle and mild, it is apparent to me that they occurred as a result of the man-machine interface,” he wrote.
Based on his observations, Flottmann recommended the Navy implement PBG in the current CRU-103 regulator, which will improve human performance, especially during high-G flight, and also mitigate what he suspects is absorption compounded by acceleration atelectasis. He also recommended the Navy investigate the potential of allowing the oxygen content of the breathing gas to be scheduled.
Finally, he urged the Navy to conduct centrifuge studies to compare and contrast the wear of the flight gear ensemble and how it affects breathing. The Air Force eventually conducted similar studies during the F-22 investigation and found flight gear configurations and fit contributed to how hard the pilot has to work to breathe.