Pilot Breathing Assessment Volume I: NASA Engineering and Safety Center Technical Assessment Report

Published by NASA Engineering and Safety Center, accessed via The Hill

Lockheed Martin Aeronautics Photo by Liz Kaszynski FP150855 Hehs Beaufort Code One Aerial Photo/Video Mission Location: Beaufort, South Carolina March 19, 2015 VMFAT-501 Warlords Aircraft 10 – Major “RJ” Corkill Aircraft 11 – Major “Stiffler” Fearon Aircraft – Major “Gravy” Rountree

The NASA study focused on why F-15 and F-18 pilots were having physiological episodes related to breathing issues.

But researchers also had the opportunity to “review and analyze a limited amount of F-35 pilot breathing data,” NASA wrote in a post about the study.

Researchers found that the F-35’s breathing system delivered “an unpredictable amount of flow at the beginning, middle and end of each breath and that it changed from breath-to-breath.”

“Such rapid changes in the breath-to-breath supply forces the pilot to continually compensate by adjusting breathing rate, volume, and exhalation/inhalation force,” the study said.

House Armed Services Committee staffers reached out to the Pentagon’s F-35 office to get their perspective on the study, an aide told reporters Wednesday. “They kind of discounted it” because it was based on limited data and wasn’t “formally sanctioned” by the department, the aide said.

As such, the subcommittee’s portion of the National Defense Authorization Act (NDAA) would require the Pentagon, in consultation with NASA, to “investigate, assess and implement corrective actions for the F-35 breathing system initially noted by the National Aeronautics and Space Administration’s Engineering and Safety Center Technical Assessment Report on the F-35 pilot breathing system,” a summary of the bill said.

“Unfortunately it’s taken Congress to get the department to look at those issues and take action,” the aide said, citing past congressional action on physiological episodes related to F-22, F-18, T-45 and T-6 aircraft.

There have been 40 physiological episodes associated with the F-35, the aide said.

“We want to make sure that instead of the pilot having to adapt to the jet, the jet needs to make sure that it complies with the military specifications required for pilot breathing systems,” the aide said. “The pilot shouldn’t have to think about breathing in the airplane. It should just come naturally so that they can focus on the tactical employment.”

Known as the Pentagon’s most expensive weapons system ever, the F-35 program is expected to cost $1.7 trillion over its lifetime.


This report represents the third in a series of studies conducted by the NASA Engineering and Safety Center (NESC) to help shed light on Physiological Episodes (PEs) that pilots have been experiencing while flying high performance aircraft. Building on experiences gained with the USAF’s F-22 in 2012 and the USN’s F/A-18 in 2017, the NESC initiated its Pilot Breathing Assessment (PBA) at NASA Armstrong Flight Research Center in 2018 to gather what was defined in previous studies as the missing element in the PE problem: a robust dataset to quantify how the complex human system interacts with the complex aircraft system operating in the complex flight environment. Before PBA, it was generally accepted that providing adequate oxygen (O2) line pressure and mask flow was sufficient to meet pilot breathing requirements for all high-performance aircraft operations. PBA has shown that the subtleties in parameter stability, timing and sequencing of the pilot-machine interface are critical. An aircraft breathing system begins to deliver air when it senses pilot inhalation and stops when exhalation is sensed. Lags in response make breathing more difficult despite nominal delivery of O2, pressure and flow. In PBA, all such timing and sequencing mismatches, collectively designated as Breathing Sequence Disruptions (BSDs), revealed system/pilot interactions that had not been previously documented. Cabin pressure fluctuations were found to interfere with pilot breathing signals, and mask valves response could become erratic over time; both situations caused regulators to deliver air out of step with pilot demands. Certain flight maneuvers such as high-G turns and rapid altitude changes were found to stress the system’s response to pilots’ immediate air demands. In short, these small, subtle disruptions often go unnoticed but can accumulate to transform simple breathing into complex disrupted patterns, which in turn, forces the pilot to subconsciously adapt or consciously compensate to meet their physiological needs. All PBA flights experienced BSDs, however, disruptions were greater in magnitude and frequency with the use of safety pressure. Cabin pressure fluctuations as small as a few mmHg can cause measurable BSDs. Other features of this report are a Pilot Breathing Almanac which documents the breadth and variety of pilot breathing metrics under various flight conditions. New insights into pilot physiology are presented; for example, pilots may suffer pulmonary decrements during flight that can lower their threshold for developing hypoxia. Specific post-flight results revealed that blood O2 saturation can regularly drop below 95%, the threshold defining mild hypoxia. In separate ground tests, F-35 breathing systems analysis showed BSDs based on unpredictable pressures and flow within breaths, and between adjacent breaths. PBA also designed, developed, and flight-tested a new sensor integrated within the mask that accurately monitors CO2 and water vapor concentrations at high temporal resolution (83 Hz). These new miniaturized sensors produced nearly clinical-quality results, yielding new physiological insights. To support followon work by the military, this report presents a standardized flight test procedure for the services to adapt and use to establish a baseline of aircraft breathing system performance.

Key recommendations for users and manufacturers of high-performance aircraft include:

  1. Measuring pilot breathing, in situ; that should be used in the creation of future hardware and
    system specifications to meet pilot physiological needs, throughout all relevant flight envelopes.
  2. Reconsidering safety pressure’s benefits in light of the problems it introduces to pilot
  3. Trusting subjective pilot reports of breathing as a significant indication of
    breathing system performance and following up in a methodical investigative manner with
    objective data.
  4. Investigating the F-35 Breathing System’s BSDs. 5. Performing standardized
    flight test procedures to establish and evaluate an aircraft’s pilot breathing system performance.