Managing the Risks of Max Endurance Operations

By LT COL JASON KNAB, AMC FLIGHT SAFETY

With the emerging threat of Great Power Competition, aircrews across all mobility platforms are being pushed to fly longer sorties to achieve more robust capabilities for combatant commanders. This initiative is crucial for operating in the Indo-Pacific area of responsibility and the “tyranny of distance” aircraft must cover to compete with nations like China. As a Major Command (MAJCOM), we have been directed by senior leadership to “Move Faster” and develop capabilities to allow mobility operations to “explode into the theater.” This direction and operational need to deter or defeat Great Power Competition, allowing us to retain the competitive advantage, has led Air Mobility Command (AMC) to start testing Max Endurance Operations (MEO) during exercises and operations across the globe.

MEO has been loosely defined as any planned flight operation extending beyond an augmented flight duty day. Currently, Air Force Manual 11-202V3, Flight Operations, limits the Flight Duty Period (FDP) to approximately 24 hours. MEO exceeds that time, pushing 30–40+ hours of FDP. This length of time may sound ludicrous, but we must examine the rationale behind MEO. It is not being developed for everyday operations for mobility and refueling aircraft but rather as a necessary capability to surge personnel, logistical supplies, and aircraft to sustain initial procedures in contingency operations. We have to move faster and do it safely! The days of dominating with overwhelming airpower are dwindling, and we must be ready.

My team at AMC Flight Safety has been thoroughly engaged in the MEO process. We continue to drive discussions on hazards and threats while fine-tuning new risk mitigation guidance and crafting creative solutions to operate an MEO mission safely. To accomplish this task, we must first understand the hazard we are facing … fatigue!

Sifting through feedback from crews executing MEO missions set in Mobility Guardian ‘23, fatigue was the obvious glaring hazard and concern. Many aircrews expressed concerns that long durations may affect their mental resilience to safely execute longer sorties in complex environments and mission sets. The concerns from the aircrew cited being fatigued during critical phases of flight, including takeoffs, approaches, landings, air-refueling, and other tactical events. Critical phases of flight require increased cognitive and physical abilities, which can be severely degraded when fatigue sets in after long flight durations.

“72 percent of military aviators admitted that they had flown at least once when they were so drowsy, they could have easily fallen asleep. Moreover, a survey of [U.S. Air Force] pilots and navigators found that 94 percent had experienced performance degrading effects of fatigue.”1,2

AMC Safety examined fatigue and the factors that degrade a pilot and crew. Key challenges included sleep loss (chronic/acute), extended wakefulness, circadian rhythm disruptions, workload overload, stress, diet, exercise, and more. For a pilot and crew, these factors are leading causes of poor decision-making, loss of situational awareness, falling asleep (micro-sleep), and communication errors.3,4 Each factor can have deadly consequences, which is why AMC is very determined to find methods to combat and mitigate the risk of fatigue as we fly longer mission sets.

The most glaring reason for fatigue was lack of sleep. “The optimal duration of sleep per night varies among individuals, but 7–8 hours of sleep is recommended for adults.”5 Anything less than that can cause fatigue issues to accumulate. An aviation sleep study reported “that mean sleep duration decreased from 7.8 hours per night to <6 hours over a 7-day duty period, leading to a cumulative sleep loss of 15 hours.”6 “Research has shown that the effects of sleep restriction accumulate, leading to a progressive reduction in performance, which intensifies as sleep restriction per night increases.”7,8 In other words, pre- and post-uninterrupted crew rest during long operations must be a priority. The problem is not only the night before but the nights leading up to an MEO flight. These flights are not local missions, and we must arm ourselves to combat the effects of fatigue.

“My mind clicks on and off … I try letting one eyelid close at a time while I prop the other open with my will. My whole body argues dully that nothing, nothing life can attain, is quite so desirable as sleep. My mind is losing resolution and control.”9 -Charles Lindbergh

As a KC-135 pilot, I have logged many 10+ hour missions and experienced fatigue at varying levels. As an aircrew, we do our best to properly rest, take care of ourselves, and use an appropriate amount of fatigue-fighting caffeinated supplements (coffee, sugar, energy supplements). For MEO missions, an aircrew must continue to apply anti-fatigue measures while AMC develops new guidelines and procedures to combat fatigue during these excessively long sorties.

Some of the suggested fatigue mitigation steps AMC is looking at may include changing operational risk management practices, deliberate MEO scheduling requirements, wearable health monitoring devices, increased pre- and post-crew rest times, crew complement changes, multiple crews instead of augmented, A-code swapping, hypnotics, increased inflight crew rest cycles, and stimulants. A combination of mitigation techniques and procedures will be needed to keep aircrews safe while maximizing our capabilities to protect our national interests across the globe.

Through feedback, we are aware of the concern about stimulants and will be leaning heavily on medical professionals for advice when using them to combat fatigue.

“Stimulants only temporarily diminish the effects of fatigue but do not alleviate these effects, making them a transient fix. Stimulants should, therefore, be considered a last-resort countermeasure when preventive strategies and other countermeasures have failed to mitigate fatigue.”10,11

AMC is committed to developing risk-mitigating procedures and operational rules to protect our aircrew as they complete MEO sorties and achieve mission objectives. In the research and test phase of MEO, some crews may try different mitigation techniques to better our understanding and craft future procedures. These crews will be monitored, and appropriate safety personnel will be actively involved to avoid possible mistakes and errors while exploring the capabilities of MEO.

AMC has launched a Max Endurance planning team to gain traction on MEO. The highly experienced team has been working to develop operational guidance for aircrews while also allowing commanders to maximize capabilities, minimizing the risks of fatigue and other issues associated with endurance operations. To assist AMC in developing an MEO concept of operations, the safety team continues to hold crosstalk between industry partners, Global Strike, and healthcare professionals. They are also using data and feedback from Mobility Guardian ’23 and other MEO test operations to better develop the future MEO concept of operations. Our mission is to provide commanders and crews with a solid plan to execute the MEO mission successfully and safely. This capability is necessary to maintain the competitive edge when dealing with near-peer threats that Great Power Competition presents.

Long-endurance operations are associated with many risks, and the crew’s health, welfare, and mission success will be top priorities. We encourage crews to use ASAPs (Airman Safety Action Program submissions) and their local safety flight offices to provide feedback from MEO sorties. All feedback helps our team advise and craft new innovative strategies to Minimize Risk and Maximize Capabilities. In addition, we are working on the modification of the AMC Operational Risk Management form to propose new attributes for MEO sorties. These features should allow crews and commanders to measure operational risk while directing them to the appropriate level of risk approval authority. Risk management is our mission, and we will work diligently to increase safety on all MEO missions. LET’S GO!


  1. Caldwell J.A., Gilreath S.R. 2002. A survey of aircrew fatigue in a sample of U.S. Army aviation personnel. Aviat. Space Environ. Med. 73, 472–480. ↩︎
  2. Miller J.C., Melfi, M. 2006. Causes and Effects of Fatigue in Experienced Military Aircrew. (Brooks City-Base, U.S.A.: Air Force Research Laboratory). ↩︎
  3. 3 Wingelaar-Jagt, Y.Q., Wingelaar, T.T., Riedel, W.J., and Ramaekers, J.G. 2021. “Fatigue in Aviation: Safety Risks, Preventive Strategies and Pharmacological Interventions.” Frontiers in Physiology, 12, 712628. https://doi.org/10.3389/fphys.2021.712628 ↩︎
  4. https://skybrary.aero/articles/fatigue ↩︎
  5. Hirshkowitz M., Whiton K., Albert S.M., Alessi C., Bruni O., DonCarlos L., et al. 2015. National Sleep Foundation’s updated sleep duration recommendations: final report. Sleep Health 1, 233–243. ↩︎
  6. Samel A., Vejvoda M., Maass H. 2004. “Sleep deficit and stress hormones in helicopter pilots on 7-day duty for emergency medical services.” Aviat. Space Environ. Med. 75, 935–940. ↩︎
  7. Ibid. ↩︎
  8. International Civil Aviation Organization (ICAO). 2020. “Manual for the Oversight of Fatigue Management Approaches (Doc 9966).” (Montreal, Canada: International Civil Aviation Organization). ↩︎
  9. Lindbergh C.A. (1953). The Spirit of St. Louis. New York: Scribner. ↩︎
  10. Russo M.B. 2007. “Recommendations for the ethical use of pharmacologic fatigue countermeasures in the U.S. military.” Aviat. Space Environ. Med. 78:8. ↩︎
  11. Caldwell J.A., Mallis M.M., Caldwell J.L., Paul M.A., Miller J.C., Neri D.F. 2009. Fatigue countermeasures in aviation. Aviat. Space Environ. Med. 80, 29–59. ↩︎