While the U.S. Air Force has taken steps to reduce the rate of physiological events for pilots on Boeing [BA] F-15 fighter aircraft and Beechcraft [TXT] T-6A Texan trainers, including the implementation of 47 recommendations by safety investigators, the reduction in PEs for such aircraft over the last decade has been uneven, according to a recent DoD Inspector General (IG) report.

“The PEs per 100,000 flight hours did not consistently decrease for the aircraft we reviewed,” according to the DoD IG report, Audit of the Department of the Air Force’s Actions to Mitigate Physiological Events. “The four aircraft models we reviewed (the T‑6A Texan II, F‑15C Eagle, F‑15D Eagle, and F‑15E Strike Eagle) reported fewer PEs per 100,000 flight hours in FY 2020 compared to FY 2011. However, the aircraft did not experience a consistent decline in the PE rate each year from FY 2011 through FY 2020.”

PEs per 100,000 flight hours for the F-15E spanned a low of about three in fiscal 2010 to a high of more than 26 in fiscal 2-12, while rates for the T-6A ranged from a low of nearly three in fiscal 2014 to more than 53 in fiscal 2018.

Air Force Physiological Episode Action Team officials told the DoD IG that “because the T‑6A Texan II is the first aircraft flown by Air Force aircrew, the nerves of the aircrew could be a factor in the increase of reported PEs,” per the report, which said that investigators chose the four aircraft in the report because they have had the highest rates of PEs in the Air Force.

Last December, the National Commission on Military Aviation Safety (NCMAS) said that PEs began cropping up in earnest with incidents on the F-22 in 2011 and 2012 and progressed to PE reports on the F-15, F-16, F/A-18, and F-35 fighters and issues on training aircraft with Onboard Oxygen Generating Systems (OBOGS), such as the T-6A, the T-45, and the T-38 (Defense Daily, Dec. 3, 2020)

For the four aircraft in the latest DoD IG study, “the Air Force reported that it has implemented 47 of the 79 safety recommendations proposed by the safety investigation boards or single investigators and is working to implement the remaining 32 recommendations in the areas of guidance, maintenance, training, new design and development, research, and testing,” per the report. “In addition, the 711th Human Performance Wing conducted 67 research studies to investigate human factors, aircraft, and aircrew equipment to better understand and address the causes of PEs. For example, the 711th Human Performance Wing conducted studies related to OBOGS, unexplained PE biomarkers, safety pressure, sampling, hyperoxic oscillation, breathing resistance, and the regulator in the T‑6A Texan II, F‑15C Eagle, F‑15D Eagle, and F‑15E Strike Eagle.”

The DoD IG also said that the Air Force has led an effort to update Military Standard 3050 to allow the development of a non-OBOGS Aircrew Breathing System (ACBS).

“The update is expected to impact ACBS for all future Air Force aircraft platform acquisitions to ensure adequate physiological parameters are incorporated into designs,” per the DoD IG report. “The Air Force modified aircraft maintenance procedures, upgraded and modified aircraft, and improved training on PE recognition for aircrews. The Air Force has modified aircraft maintenance procedures and performed upgrades to reduce PEs. For example, the Air Force is in the process of performing canopy seal bellows replacement, and procuring new canopies for the F‑15C Eagle aircraft. In addition, the Air Force indicated that it will continue to perform the change implemented into the Inspection and Maintenance Requirements Manual and perform additional hypoxia procedures and supplementary steps in its 180‑day maintenance interval.”

The House Armed Services Committee’s (HASC) version of the fiscal 2022 defense authorization bill requires the Pentagon to submit a report on the pilot breathing system for the Lockheed Martin [LMT] F-35 fighter after a National Aeronautics and Space Administration (NASA) report last November pointed to hypoxia-like incidents and cognitive impairments among F-35 pilots (Defense Daily, July 28).

The NASA report last November on pilot breathing systems and physiological episodes encountered by pilots of T-45, T-6, and F/A-18s over the last few years included a brief examination of such incidents on two F-35 aircraft and interviews with five F-35 pilots.

As of July 1, the F-35 Joint Program Office said that it had received reports of 55 in-flight and on-ground PEs.