Introduction

According to the National Transportation Safety Board (NTSB), 85% of flight-related accidents in the last 20 years have been due to “pilot error”, despite the aviation culture having the motto of “Safety First.” This is thought to be attributable to the training focused primarily on flight skill and proficiency and less so on risk identification strategies, disclosure, and mitigation of identified risks. The Federal Aviation Administration (FAA) requires all aviators to complete a preflight risk assessment checklist, evaluating the individual risk factors affecting the safety of flight as they relate to the environment, the airframe, mission complexity, external pressures on the crew (mission, supervisor, home, etc) and the pilot. This activity will focus on the human factors relating to flight safety decisions, mitigation strategies, and the GO-NO GO decision.  I-M-S-A-F-E is a common mnemonic to help review these factors.

Issues of Concern

Illness - Piloting aircraft is a task that requires constant focus and attention for prolonged periods to conduct safe flight operations.  All illnesses, even the common cold, can have a detrimental impact on the safety of flight. For instance, during flight nasal and sinus congestion can induce severe acute pain that resolves with tympanic perforation due to the changes in barometric pressure that often accompany flight.  Gastroenteritis and the accompanying dehydration and frequent elimination urgency can make focus on instrument cross-check, in-flight clearance of airspace, and quick response to deconfliction instructions difficult.[1]  Febrile illness can affect wakefulness and job performance, necessary for safe flight.[1]  Before flight, each crew member should do a systems check of their health to determine if they feel well enough to fly.  Designated flight physicians (flight surgeons in the military) are specially trained to assist in the treatment of transient illness and helping the aviators and passengers determine if medications are necessary, which medications are safe to use, or if the illness is a “no go” condition.[2]

Medication - The internal pressure exerted by each member of the aircrew and passenger manifest to complete the flight is also a risk factor. It often makes flyers reluctant to disclose an illness. The awareness that even a minor illness could be a “No Go” event, and the flight physician may ground the affected aircrew member occasionally leads the member to self medicate without medical advice; this is against military regulation and strongly discouraged in civilian aviation by the FAA. According to the official, Air Force Aerospace Medicine Approved Medications list, many over-the-counter medications that are seemingly benign to the patient, can negatively impact performance. Physicians should look for organizational or aircraft, specifically approved medications guidance to ensure no prescription written requires a period of duty, not including flying.  

Stress - While short term stress has been shown to have a positive impact on the performance of mental and physical tasks (for women more so than men), functioning with chronic stress can deteriorate spatial memory and performance in some people according to a 2003 study by Bowman in Hormones & Behavior.[3] Stress can include financial problems, marital issues, family discord, or health concerns. If an aviator is having chronic, un-managed, or new acute stressors, this may impact his/her ability to focus, communicate, and function safely as part of the aircrew. External pressures such as pressure to complete the mission “no matter what,” return home, impress a rater, demonstrate proficiency, or prove a point can induce the flyer to take unnecessary risk and attempt actions that they would not have otherwise, actions that can be injurious or fatal.  Mitigation strategies in those reporting stressors are often to interview aviators and refer to appropriate support staff to help resolve the stressful issue, if severe enough, during a period of non-flying. Open communication between the crew is the first step in mitigation.[4] The other crew members should be aware that their wingman is under increased stress, and if the mission continues, have a lower threshold to verbalize a concern or terminate flying activities in the air, due to that airman’s performance.[5]  

Alcohol - Alcohol consumption impairs the aircrew member’s ability to perform mission-essential duties and is itself a stressor.  Alcohol lowers the threshold of tolerance for hypoxia and increases the risk of spatial disorientation, which can be deadly to everyone on board.[6] FAA requires a minimum of 8 hours between the last effect of alcohol and aircrew responsibilities, and the military requires 12 hours between the last effect of alcohol and aircrew responsibilities- often referred to as time from “bottle to throttle.”  It is imperative that an aircrew self identify if they fall within these parameters, and that all members of the aircrew, medical and technical support staff regard this as a “No-Go” for the safety of flight.[7]

Fatigue - The leading cause of aviation accidents is a human error, with 79% of fatal aviation accidents in the United States cited human error as an attributing cause. With long shifts, frequent time zone transitions, and short periods of rest in-between flight duties, fatigue is the main factor as tracked by the National Transportation Safety Board (NTSB).  Symptoms of fatigue worsen as wakeful time increases, which symptom worsening correlated to time awake – include slower reaction times, decreased ability to concentrate, increased risk tolerance, and degraded ability to make decisions[8]. Within civilian aviation, one study found up to 7% of aviation incidents in civilian aircraft were secondary to aircrew fatigue.  Within military aviation, Air Force statistics note fatigue as a factor in 7.8% of Class A mishaps, the most serious type of aviation accident and Army statistics found fatigue to be a contributing factor in 4% of accidents.[9] A study conducted by the Federal Aviation Administration (FAA) evaluated 55 aviation accidents over 20 years recorded a significant rise in accidents in pilots who had been on duty for 13 hours or more.[10]

In 2011, the FAA established more stringent regulations to decrease pilot fatigue with limits to time on duty flying and mandatory crew rest time.  These changes include widespread application of rest requirements whether the flight is domestic, international, or unscheduled, stricter limits dependent on the number of flight segments and duty day start, a minimum of 24 hours off in a 7-day period, limited flight hours, and a minimum of 10 hour rest period increased from 8 hours between shifts.[11]  Members of the International Civil Aviation Organization (ICAO) all have inscribed shift hour limitations; however, implementation is variable and does not take into account accumulation of sleep debt and circadian rhythm disruption.[12]

The primary recommended strategies for circadian rhythm dysrhythmia or jet lag include gradual adjustment of bedtime and rise times in anticipation of the time zone change, light therapy, and appropriate sleep hygiene techniques, which include avoidance of caffeine, alcohol, exercise, and eating heavy meals immediately before bedtime.[13]  To manage circadian rhythm dysfunction in anticipation for crossing time zones, eastward travel recommendations include moving back both sleep and wake times 30 minutes per day starting three days before departure and for westward travel,  30 minutes forward.  Another helpful suggestion for eastward travel is to increase bright light within the first 2 to 3 hours of waking and bright light avoidance close to bedtime. This approach may require the use of sunglasses while driving and using heavy window treatments to sufficiently block sunlight.  The opposite is recommended for westward travel, with the recommendation for increased exposure to light in the evening and bright light avoidance when first waking up for several hours.[14]

If first-line non-pharmacologic management is not sufficient, caffeine may be used to aid fatigue and improve alertness. While not allowed for civilian aircrew, in the military, use of stimulants, colloquially known as “go pills” such as dextroamphetamine and modafinil are prescribed to mitigate drowsiness during flight.[15] Sedatives, also called “no-go pills,” such as zolpidem, temazepam, and zaleplon, are prescribed to manage circadian rhythm mismatch. Due to differing half-lives between medications and possible side effects, use is closely regulated and limited.[16]

When non-pharmacologic means are not sufficient to manage circadian rhythm dysfunction, sedatives may be an option. Of note, the FAA does not approve the regular use of sleep aids. For example, prescription of zolpidem is allowed by the FAA; however, use is limited to no more than twice a week.  Additionally, FAA regulations require that pilots ground themselves at minimum for five times the amount of the specific drug's half-life. For example, while diphenhydramine is over the counter, due to its long half-life, a pilot could not take it any sooner than 60 hours prior to flying duties. For “no-go pill” used in the military, over the counter medications like diphenhydramine or melatonin are not approved for military aviation use. In civilian aircrew use, zolpidem and melatonin are permitted no later than 24 hours prior to taking off.  Zolpidem is typically the sedative of choice for military operations with a moderate length do not fly timeframe of 6 hours. Temazepam is the longest acting sedative allowed in military operations with a 12-hour restriction on subsequent flight duty. Temazepam in civilian aviation use requires 72 hours before the next flight duty. Zaleplon has the shortest half-life of all the sedatives allowed in military aviation with a 4-hour restriction before flight duty. Zaleplon use requires 6 hours prior to flight duty in civilian aviation.  The other sedatives allowed by the FAA for civilian aircrew use but not in the military include eszopiclone with a 30-hour minimum wait time before flight duty and ramelteon with a 24-hour minimum wait time prior to flight duty. 

Caffeine is the most commonly utilized psychoactive drug to promote wakefulness. Prescribed stimulating medications or “go pills” such as modafinil and dextroamphetamine are not approved for use in commercial pilots by the FAA. In the military, these two medications are used to promote wakefulness. However, stimulant use is under tight regulations. They may be prescribed specifically for operational scenarios where unavoidable long sorties are required in the military, yet, the medications must have previous ground testing to determine if the pilot has any unacceptable side effects. Side effects of stimulants include insomnia (the intended side effect), decreased appetite, weight loss, hypertension, tachycardia, lightheartedness, headaches, irritability, overconfidence, aggression, and gastrointestinal effects such as diarrhea, constipation and abdominal pain. There is also limited evidence of increased tics, so caution is advisable for patients with tic disorders such as Tourette syndrome. Technically, modafinil does not classify as a stimulant, but it does have stimulant-like effects. Like stimulants, modafinil does improve alertness and wakefulness. Modafinil has a slower gradual onset with a half-life of 15 hours, so it tends to have fewer side effects than dextroamphetamine.[17] Dextroamphetamine has a shorter half-life of 12 hours with a quicker onset, so it tends to have more noticeable side effects and requires more frequent re-dosing. Overall, non-pharmacologic management of fatigue is considered the first line.[18]

Emotion and Energy - The FAA also requires the aircrew to consider if they are emotionally upset or have any acute physiologic needs, such as hunger. These immediate needs can impact the ability airman to focus on the less existential needs like airspeed, altitude, and other matters of flight safety. Hunger is usually fairly easy to correct in the preflight period.  Identification of emotional state and discussion before take-off can help to mitigate negative emotions. Still, occasionally, self-awareness should appropriately lead an airman to seek guidance and support to deal with emotional stress. Flight physicians may elect to give the airman time to focus on personal recovery during a period of no flight to ensure that no aviation-related mishaps occur as a result of impaired focus. 

Clinical Significance

The safety of flight begins on the ground in the preparation and planning stages of the mission. Just as the aircraft gets inspected during preflight for wear and tear and anticipated maintenance is conducted before the mission, the aircrew conducts a mandatory risk assessment of themselves individually and as a crew, to ensure the risk of the human factor does not outweigh the necessity of the mission. Human error is the number one factor in the majority of aviation accidents and becomes worse with illness, inappropriate medication use, stress, alcohol, fatigue, immediate physiological or emotional need. Providers should be aware of the IMSAFE (Illness, Medication, Stress, Alcohol, Fatigue, Emotion/Energy) preflight check of the crew.  As a medical provider, it is essential to be aware of the known risks contributing to the human factor in-flight safety decisions to “Go or No-Go” and how to counsel aircrew on ways to mitigate the risks through the therapeutic alliance, behavioral guidance, and pharmacologic means if necessary.