Aeromedical Concerns with Extended Minimum Crew Operations

By Ries Simons, M.D., European Society of Aerospace Medicine Advisory Board; Declan Maher, M.D., Irish Aviation Authority; Roland Vermeiren, M.D., European Society of Aerospace Medicine EC Liaison Officer for the European Union Aviation Safety Agency; and Anthony Sverre Wagstaff, Ph.D., Institute of Health and Society, University of Oslo

Editor’s note: This article is reprinted with permission from Aerospace Medicine and Human Performance Vol. 96, No. 7, July 2025.

The aviation industry is exploring possibilities to operate extended long-haul flights with two pilots on the flight deck during critical flight phases and a single pilot flying during cruise flight while the other pilot is sleeping.

 

This extended minimum crew operations (eMCO) concept raises important aeromedical concerns: 1) a two-pilot flight deck is considered a main safety risk-mitigating factor, and eMCO would therefore necessitate a new aeromedical risk-assessment concept; 2) sensors and algorithms for monitoring physical and/or cognitive incapacitation aren’t available or insufficiently reliable; 3) scientific data of augmented long-haul flights isn’t valid for predicting effects of monotony and boredom or in-flight sleep and sleep inertia on alertness during eMCO cruise flight; and 4) medical conditions regarding urination, defecation, or menstruation may cause an unscheduled visit to the toilet of the single pilot flying during cruise flight, who then has to request the resting pilot to take over the controls.

The European aviation industry is exploring possibilities to certify eMCO, which means two pilots on the flight deck during takeoff, climbout, approach, and landing, while during cruise flight one of the pilots operates the aircraft and the colleague pilot rests/sleeps. Cost-effectiveness and longer onboard sleep duration, facilitating extended flight times, are mentioned as rationale. The paper focuses on the aeromedical safety aspects of eMCO and reflects the aeromedical and human factors concerns based on the results of a scientific literature study and gap analysis performed by the authors in the context of a safety evaluation concerning a potential certification of eMCO.

Incapacitation Risk Assessment

Current aeromedical incapacitation risk-assessment concepts for airline pilots are based on a two-pilot flight deck. The two-pilot flight deck concept is considered a main safety risk-mitigating factor because pilots are trained to monitor and correct each other. Incapacitation training is a mandatory part of commercial airline pilot training, and pilots are trained to manage the flight in case their colleague pilot is incapacitated. This is an important determinant of the current “1 percent rule” risk concept in which a second pilot on the flight deck reduces the risk by a factor of 1,000. Because eMCO is a single-pilot flight during the cruise phase, the European Union Aviation Safety Agency’s operational limitations indicate that pilots with a medical condition, such as operational multipilot limitation (valid only as, or with, a qualified copilot), and pilots beyond the age of 60 can’t be certified for eMCO operations. It’s concluded that a new aeromedical incapacitation risk-assessment concept should be developed before eMCO can be implemented in large-aircraft operations.

In-Flight Incapacitation

Sudden in-flight incapacitation with loss of consciousness of the single pilot flying during cruise flight might be a catastrophic failure condition because the pilot flying might not be able to activate the sleeping pilot in time. Therefore, eMCO can only be implemented if reliable crew monitoring and alerting techniques are developed, along with new automation techniques, to maintain safety of flight before the resting pilot can take over the flight management. Although many physiological monitoring systems are used in clinical settings to monitor clinical patients, algorithms that use these methods to reliably pick up in-flight incapacitation aren’t currently available. Dedicated algorithms will have to be developed and thoroughly tested on reliability and predictive value for pilot incapacitation.

Subtle incapacitation is a reduced state of alertness or a mental preoccupation that may result in impaired judgement and impaired performance. A pilot flying with a reduced state of alertness or a mental preoccupation might deny or be unaware of any dysfunction. Therefore, a second pilot on the flight deck is considered as the main safety instrument to prevent incidents/accidents caused by subtle pilot incapacitation. Behavioral methods developed to replace the monitoring function of a second pilot are still in an experimental stage and would have to be thoroughly tested before they can replace intercollegiate flight deck monitoring.

Sanitary Needs

It’s generally accepted that most healthy pilots will be able to prevent the urge to urinate or defecate over a period of two to three hours by using the bathroom before the start of that period. However, in case of significant caffeine intake, drinking larger volumes of fluids, benign prostatic hyperplasia, overactive bladder, dysuria, uncontrollable bowel action, other gastrointestinal symptoms, or unexpected menstrual problems, unscheduled toilet use may be necessary before the end of a two- to three-hour period. Since withholding urination or defecation may lead to a deterioration of cognitive function and/or abdominal pain, the pilot flying should be able to use the bathroom whenever needed during the eMCO cruise segment. From a medical and human factors point of view, none of the currently evaluated alternative methods for bladder and bowel relief (diapers, urine collectors, relief systems, and diet interventions) seem acceptable or feasible to implement for airline pilots who must remain at the controls in eMCO operations.

It may be possible to schedule toilet breaks and drinking patterns to some extent. However, from the literature it becomes clear that a multitude of mild and common medical conditions regarding urination, defecation, and menstruation can cause an unscheduled urge to use the toilet. In an eMCO operation, with one pilot at the controls, this would mean that the pilot flying might have to declare an incapacitation (i.e., in case of diarrhea, abdominal cramps) and/or request the resting pilot to take over the controls, which means termination of the eMCO segment and consequently less allowable extension of the flight time.

Fatigue, Boredom, Sleep Inertia

The conditions during eMCO are incomparable with the current working conditions on augmented long-haul flights, which are characterized by planned rest periods, ample time to wake up after a rest period, and always a minimum of two pilots on the flight deck. Where in augmented long-haul operations available onboard rest time is divided among three or four pilots, available rest time in long-haul eMCO operations will be divided between two pilots, resulting in longer rest times for each pilot. In this context, it should be considered: 1) whether the in-flight rest is sufficiently recuperative to keep the single pilot flying sufficiently alert, and 2) what the impact of sleep inertia is on performance and alertness of the resting pilot when taking over the controls. Available data from current long-haul flights can’t be used for predicting the effects of monotony and boredom, in-flight sleep and sleep inertia, and scheduling factors on fatigue and alertness levels during eMCO operations. Therefore, there’s a lack of scientific data concerning the effects of circadian sleep pressure between 2:00 to 6:00 at night regarding the alertness of a single pilot flying in a monotonous environment with a lack of stimuli. Before certifying eMCO flights, relevant research is necessary to study the combination of circadian sleep pressure and monotony on performance of the pilot flying. It’s concluded that the lack of scientific data on aeromedical safety aspects of eMCO necessitates tailor-made studies and considerations before eMCO flights might be certified.