The effects of gravity and acceleration on the cardiovascular, visual, vestibular, and other systems are reviewed elsewhere in this text (see Chapter 4). Because +G_z and −G_z forces primarily affect the cardiovascular system, it is extremely important that individuals who fly G-inducing aircraft are assessed for cardiovascular and vestibular disease and know how to use countermeasures effectively.

Whereas civilian aircrew may make due with shirtsleeves and a slender headset for communications, aircrew in military aircraft are protected from head to toe, with gear including a 1- to 2-kg helmet with night vision devices (NVDs) attached, a life-preserver-torso harness unit, Nomex flight suit and gloves, an anti-G suit, and flight boots. Additional heavy and bulky Capstan suits are used for high-altitude missions (1). This life-support and mission-critical gear is physiologically demanding in terms of its bulkiness, heat retention properties, and especially, the weight and forward center of gravity imposed by the
helmet-NVD-mask complex on the cervical spine and soft tissues. High levels of neck muscle activation and cocontraction occur during acceleration and aerial combat maneuvers (2). Back seat occupants are at risk of acute soft tissue neck injury from unexpected acceleration. Numerous authors have addressed aircrew ergonomic issues (3, 4, 5, 6) and their prevention, including neck strengthening exercises, preflight neck warm-up exercises, and eliminating/limiting head movement while pulling Gs.

Most aircraft do not pressurize to sea level pressure while airborne. Whereas healthy crewmembers can tolerate mildly hypoxic environments, the same is not true for individuals with reduced blood oxygen carrying capacity resulting from cardiac or pulmonary disease. Even at normal cabin altitudes of commercial aircraft (6,000-8,000 ft), they may develop hypoxic symptoms and require supplemental oxygen.

Cockpit temperature and humidity are reasonably well controlled in commercial aircraft; however, the same cannot be said for many types of military aircraft. Heat stress is particularly threatening to military crews operating in tropical or desert climates. Long-term engineering solutions include installation of cockpit and cabin air conditioning systems, as well as development of efficient personal cooling garments. The latter may be of particular importance for heavily encumbered aircrew operating in nuclear-biologic-chemical protective gear. Aircrew operating in such environments must also maintain adequate hydration both before and during flight (see also Chapter 7).

Long-haul commercial and military aviators may find sunlight and activity hours drastically altered. It is not unusual for such aviators to traverse eight or ten time zones, which affect their alertness and performance (jet lag). Desynchronization may also occur as a result of working variable shifts (shift lag). With either jet lag or shift lag, operational, family, or social activities during daylight hours hamper recovery sleep. Preventive and mitigating strategies are discussed elsewhere in this volume (see Chapter 23).

Barometric pressure decreases with altitude from a sea level value of 760 mm Hg to the vacuum of space. Without adequate protection, flight crewmembers are not only at risk of becoming hypoxic but also of developing decompression sickness with increasing altitude. Crewmembers at altitude may also experience barotrauma resulting from pressure differentials between body cavities (e.g., sinus, middle ear, diseased teeth, and gastrointestinal tract) and the ambient air. Sinus block and middle ear block are most likely to induce pain, most likely during descent (see Chapter 18). This may distract, or even incapacitate, an affected crewmember. Pressure-equalizing earplugs do not appear to prevent barotrauma on descent from 8,000 ft cabin altitude.

Noise from an aircraft engine, jet, or propeller may affect communication, and may cause acoustic trauma or hearing loss, particularly with prolonged exposure (see also Chapter 5). Noise levels up to 130 dB have been measured in the flight line environment (2). Both aircrew and ground crew working near the flight line are at risk. Hearing conservation programs are therefore used to identify and contain flight line noise where feasible, and to provide hearing protection (earplugs or earmuffs for ground personnel; earplugs, snugly fitting headphone or helmet, and/or noise canceling earphones for aviators) to lower the time-weighted average exposure to permissible levels. Vibration may contribute to back pain among aviators especially in rotary wing aircraft operations.

The principal source of exposure to ionizing radiation in the flight environment is galactic cosmic radiation in the form of neutrons and γ rays. Cosmic ionizing radiation increases with flight altitude and with proximity to the poles. Exposure can damage chromosomes and may increase the risk of cancer and adverse reproductive outcomes. Nuclear cataracts have also been attributed to ionizing radiation exposure. The International Commission on Radiation Protection and Measurement (ICRP-60) limit for occupational exposure is 20 mSv/yr, averaged over 5 yr. The upper limit for unborn children is 22 mSv exposure to the surface of the pregnant woman’s abdomen over the period of gestation. Effective annual doses absorbed by nonpregnant crewmembers are well within these limits, ranging from 2 mSv for the least exposed routes, to 5 mSv for those more exposed. Female crewmembers will need to limit their flight time if they fly during pregnancy. Flight at altitude during increased solar flare activity may expose aircrew to increased doses. The Federal Aviation Administration (FAA) monitors solar activity and is capable of alerting flight crews should abnormal levels exist, and provides a tool to estimate galactic cosmic radiation received in flight (see also Chapter 8).

External sources potentially affecting aviator health include electromagnetic frequency (EMF) radiation emitted by aircraft electrical equipment, light in the ultraviolet (UV) portion of the spectrum, laser beams, and radio frequency sources such as radar. Aircraft window glass and acrylic are opaque to UV radiation at wavelengths less than 320 and 380 nm, respectively. This protects aircrew from all but UV-A (320-400 nm), a significantly less harmful form of UV radiation than the shorter wavelength (290-320 nm) UV-B. Diffey and Roscoe measured UV doses on 18 flights on
Boeing 737s and 767s from the United Kingdom to the Mediterranean. Results verified the assumption that only negligible exposure occurred. Attenuation of radar in the air and the fact that the cockpit itself serves as a “Faraday cage,” a structure made of conducting material that impedes the passage of electromagnetic radiation, both serve to shield aviators from excessive exposure to radar. Cockpit sources of nonionizing radiation (NIR) include the instrument panel and headset/helmet communication system.

Lasers have served the military for years as range finders and target designators. Those in the visible and near infrared range such as the commonly used 10,646 nm Nd:YAG laser may cause retinal damage. Lasers pose a safety hazard for both ground personnel in proximity to the beam and for aviators (ground to air laser illumination). Laser glare may interfere with critical phases of flight, leading to loss of situational awareness, flash blindness, and afterimages similar to those induced by exposure to a high-intensity flash. This may impair aircrew eyesight for a period long enough to cause a mishap. Permanent blindness is a theoretic possibility. Regulations requiring permits for commercial use of lasers in close proximity to airspace have been promulgated to protect aircrew from civilian lasers. In the United States, laser airspace guidelines can be found in FAA Order 7400.2 (Revision “F” as of August 2006), Part 6, Chapter 29 “Outdoor Laser Operations.” Bright light airspace guidelines are in Chapter 30 “High Intensity Light Operations”.

The FAA has established airspace zones around airports: The laser-free zone extends immediately around and above runways. Light irradiance within the zone must be less than 50 nW/cm². The critical flight zone covers 10 nautical miles around the airport; the light limit is 5 μW/cm². The optional sensitive flight zone is designated by the FAA, military or other aviation authorities where light intensity must be less than 100 μW/cm². This might be done for example around a busy flight path or where military operations are taking place.

Military organizations, such as the United States Air Force (USAF), issue aviators laser protective spectacles and visors effective against several wavelengths. The use of tunable multispectrum laser weapons will pose an additional challenge. The International Civil Aviation Organization (ICAO) has published a Manual on Laser Emitters and Flight Safety.

The most obvious difference between cabin and sea level air is the low humidity present in cabin air. This was found to range between 12% and 21% in a 1994 ATA study (5,6). Others have recorded as little as 5% humidity (7). Fluid consumption before and during flight easily compensates for the small increase in evaporative fluid loss. Ozone and carbon dioxide are the principal contaminants of cabin air. Aircraft may cruise through ambient levels of ozone in excess of 1.0 ppmv. Elevated ozone concentrations may cause headaches; eye, nasal, and pharyngeal irritation; as well as impair dark adaptation and visual accommodation. However, catalytic converters in the air intake effectively mitigate this hazard. The FAA limits average concentrations to 0.1 ppmv above 27,000 ft, and peak concentrations to 0.25 ppmv above 32,000 ft (8). Volatile organic compounds and tobacco smoke are of little concern now that smoking is prohibited on all U.S. and most international flights (9). Charcoal filters are in place to remove volatile compounds from the cabin air. Cabin air is exchanged every 3 to 4 minutes (aircraft with recirculation systems typically use 50% outside fresh air, and 50% recirculated air to increase humidity, and thereby passenger comfort. Additional humidification may be added (10). In newer generation aircraft, high-efficiency particulate air (HEPA) filters screen out microorganisms and particles equal or greater than 0.3 μm with 99.99% efficiency. In contrast, offices and homes exchange room air only every 5 and 12 minutes, respectively (11), and often do not employ HEPA filters. Contemporary cabin air studies have proved that cabin air quality is normally well within accepted standards and does not compromise aircrew or passenger health (7,12,24,25).

Aircrew infection may result from aerosols and droplets containing respiratory pathogens, contaminated food and water, or exposure to insect-borne diseases such as malaria. Although the risk is low, tuberculosis (TB) transmission during air travel has occurred. Some forms of TB are multidrug resistant tuberculosis (MDR-TB) or extensively drug resistant tuberculosis (XDR-TB) and therefore potential spread in public places such as aircraft is of great public as well as clinical concern (13). Fortunately, aircraft cabin air filtration systems do a good job of filtering out organisms such as influenza, measles, TB, and (severe acute respiratory syndrome) SARS that otherwise would have the potential to become airborne and disseminate in droplet nuclei (14,15). Influenza is more likely to be spread by droplet than by aerosol transmission, which means that it does not travel far (maximum distance about 5 ft) from the source. However, the virus may also be spread by touching recently contaminated surfaces, and by ingesting or having mucous membrane contact with contaminated water or food. For airline travelers, personal protection may be achieved through hand washing, alcohol-based hand sanitizers (which work for influenza, but not for norovirus), avoidance of utensil or food passing, use of respiratory etiquette (e.g., covering mouth to sneeze or cough), and social distancing (3-5 ft). Masks may be an option (a surgical mask on the source to prevent spread, and N95 mask on those potentially exposed to prevent inhalation). Airlines carry surgical masks but generally do not carry N95 masks. The surgical masks are in a first aid kit and in a separate medical kit.

Acute and even incapacitating gastrointestinal illness occurs surprisingly frequently; being reported in up to 33% of international airline pilots at some point in their careers (16). Preventive practices include requiring aircrew to eat different meals at different times, implementing a food handler program with medical surveillance and sanitation training for kitchen staff, using an approved catering source
with periodic (including no-notice) inspections, culturing equipment, surfaces, and finger swabs, ensuring proper holding temperatures, ensuring a safe, potable water supply, and ensuring proper waste removal (personnel engaged in this activity are not to include food handlers).

Finally, mosquito-borne diseases such as malaria may be transmitted to aircrew during layovers in areas infested with infected mosquitoes, or, rarely, by extended waiting in the aircraft while in such areas (17). The risk of infection is contingent upon the presence of endemic malaria in the area, duration of night time exposure, aircraft disinsection, and chemoprophylaxis (18). Aircraft disinsection has been an international practice since the 1920s. Many nations including the United States have discontinued the practice because of reports of insecticide-related illness among cabin crew and passengers, but aircraft disinsection is still sanctioned by international law. Residual application of pyrethroids is probably the most efficacious method (19). AGARD has published a Guide on Aircraft Disinsection for Military and Civilian Air Carriers (26).

Hazardous cargoes may pose potential threats to humans. They may be ignitable, corrosive, reactive, toxic, or radioactive (20). Two 1993 reports by Voge and Tolan evaluated the data in the USAF and Naval Safety Centers’ hazardous cargo incident databases (21,22). Despite regulations prohibiting passenger transport on flights carrying hazardous cargo, infractions did occur. The most common cause was due to improper declaration of the hazardous cargo. Spills and fumes were the most common problems. Physiologic responses ranged from nausea and lightheadedness to loss of consciousness and involved aircrew, passengers, or both. Improperly packaged oxygen-generating canisters aboard ValuJet Flight 592 caused a cockpit fire that resulted in the aircraft crashing into the Everglades, the loss of all aboard (110 lives), and the bankruptcy of the airline (23). When transporting hazardous cargo, thorough planning and declaration, proper storage and well-defined handling procedures, current and comprehensive crew training, provision of protective equipment, implementing emergency procedures as necessary, and verification of proper transfer and full debriefing of errors, incidents, and actual mishaps are essential (see Chapter 9).

There is little doubt that cognitive and physical skills deteriorate with age. On the other hand, it is almost equally clear that piloting expertise increases as well. Consequently, determining a cutoff age for retirement that optimizes flight safety is far from a trivial task. The FAA instituted an age-60 mandatory airline transport pilot retirement age in 1959 (the “Age-60 Rule”), and in subsequent years, this was studied by several scientific committees (27) and sustained in multiple court challenges (28). Since 1978, ICAO standards have permitted first officers to fly until their 65th birthday, and in 2006, this was changed to allow pilots to serve as pilot-in-command up to age 65, provided that the other pilot is younger than age 60. The FAA Administrator subsequently commissioned an Aviation Rulemaking Committee (ARC) to study this matter, and a proposal to change the FAA standard. This has passed the senate brought forth by Senator Oberstar on 12-10-2007 and now awaits the President’s signature. Additional longitudinal studies of air carrier and commercial pilots flying larger more complex aircraft are needed (29).

Aircrew fatigue may stem from circadian dysrhythmia, from sleep debt present before flight (induced by the use of coffee or alcohol, psychological stress, indigestion, or clinical sleep disorders), or from several days of trying to sleep at unaccustomed hours in different hotel beds or bases with various environmental stressors such as light, noise, or mosquitoes. Fatigue is common in flights that extend into the 2.00 to 5.00 AM circadian nadir, or that last over 10 hours. Fatigue may occur even on short-haul flights in familiar surroundings when there is a significant sleep debt. Fatigue and countermeasures are further discussed elsewhere in this volume (see Chapter 23).

Inadequate coordination and communication between aircrew has been identified as a source of errors and mishaps since the 1980s. This may be manifest as reticence by first officers, navigators, or cabin crew to question captain/pilot authority due to gender, age, and cultural differences. Communication between military flight leads and other formation members, or between aviators and air traffic controllers, are subject to similar difficulties. Several generations of cockpit or crew resource management (CRM) initiatives have been implemented in both civilian and military arenas with varying degrees of success (30,31). Tailoring training to assure relevance to specific aircraft types (i.e., fighters versus helicopters) and operational-cultural environments has been recommended (32). Relationships with family at home, flight deck and cabin crew during layovers, management, and occasionally even passengers during flight (the most dramatic examples being “air rage” and hostage-taking incidents) are other sources of interpersonal stress.

Menses and pregnancy are two physiologic processes unique to female aircrew. In theory, both could compromise flight performance and possibly safety, both of the flight/mission and of the female crewmember and her fetus. There are special concerns with respect to the effects of the high-G environment and long duration, and/or high-altitude flights, which increase exposure to cosmic ionizing radiation. Circadian dysrhythmia is known to adversely affect menstrual function in cabin crew (33). However, a USAF centrifuge study on female subjects showed no association between the phase of the menstrual cycle and performance during simulated air combat maneuver training up to +7G_z (34).

For pregnant aircrew members, removal from flight duties at or shortly after conception would be most prudent, in order to reduce exposure to radiation and other potential hazards. However, individual responses to pregnancy (e.g., nausea, and vomiting in the first trimester) and individual acceptance of risk (e.g., cosmic radiation exposure) are variable. Many airlines therefore permit female pilots and cabin crew to continue flying until 20 to 27 weeks (coinciding with growth of the pregnant uterus over the protective upper pelvic rim and with onset of mobility restrictions on the part of the crewmember) or later.

There is incontrovertible evidence that smoking and the use of smokeless tobacco products are deleterious to health (35). Also, each cigarette contributes a “dose” of carbon monoxide equivalent to as much as an additional 5,000 ft of altitude. As early as 1989, the prevalence of smoking was only24% among U.S. Army aircrew, in contrast to 39% among brigade support personnel. Prevalence of smoking among U.S. males at the time was 31% (36). A study of U.S. fighter aircrew in 2000 revealed that none of the 78 survey respondents smoked (37). Unfortunately, in some regions of the globe such as Eastern Europe, aviators have a much higher prevalence of smoking (1). Nicotine-induced withdrawal following smoking cessation is a potential aviation safety concern. Although psychoactive medication such as buproprion is contraindicated because of potential side effects, the use of nicotine replacement therapy is permissible (38). Grossman has reviewed treatment options for aviators who smoke (39). Varenicline for smoking cessation was approved by the U.S. Food and Drug Administration (FDA) in May of 2006, but has not been approved by the FAA at the time of writing. In the United States, smoking has been banned since 1989 in the passenger cabin, (initially for flights <6 hours in duration), and since 2000 smoking has been banned in the cockpit (40). ICAO, at its 19th assembly, in 1992, adopted resolution A29-15, which restricts smoking on international passenger flights (41).

More than 80% of American adults consume alcohol, with per capita consumption of approximately 25 gal/yr (42). Approximately 8% of full-time American workers use illicit drugs (43), and this may be an underestimation (44). The effects of alcohol and drugs on the performance of aircrew has been the subject of many research papers over the last 40 years (45), and violations frequently lead to public scrutiny (46). The number of serious errors committed by pilots rises rapidly when blood alcohol concentrations exceed 0.04%, and some studies have reported performance decrements at levels as low as 0.025% (47,48). Even when the blood alcohol concentration has returned to zero, performance and safety may be impaired for up to 15 hours after alcohol ingestion. This may be due to the effect of hangovers (49), fatigue due to reduced-rapid eye movement (REM) sleep (50). An increased incidence of sleep apnea and hypoxemic episodes also follows alcohol ingestion before bedtime (51) (see also Chapter 9).

A comparison of postmortem specimens from fatal civil aviation accidents between 1994 and 1999 with those occurring between 1989 and 1993 revealed a 25% increase in the number of cases where illicit drugs such as cocaine, amphetamine, marijuana, and barbiturates were found (52). However, the prevalence of such drug use among Class 1 air transport pilots declined from 2.8% to 0.8% during the same period, probably as a result of the drug testing program of the Department of Transportation (DOT). Although controversy exists regarding the short- and long-term effects of many drugs, as well as the social implications of their use, they are unacceptable in any cockpit. Most illicit drugs cause side effects (drowsiness, euphoria, impaired mentation, hallucinations, and flashbacks) that categorically threaten flight safety and performance. The aviation practitioner should be familiar with common illicit drugs and discourage their use among the aviators under his or her care. Health behaviors of military servicemen, including use of tobacco, alcohol, and illicit drugs have been periodically surveyed since 1980, with the latest survey having been completed in 2005 (53, 54, 55).

Potential side effects of prescription and over-the-counter (OTC) medication, including some herbal supplements such as melatonin, valerian, and St. John’s Wort, include drowsiness, hypotension, decreased visual acuity, nausea, dizziness, and subtle impairment of higher neurologic function, only evident with sophisticated testing such as CogScreen Aeromedical Edition (56). With the exception of limited authorized OTC medications, both civilian and military aerospace medical regulations require aircrew to turn to their flight surgeons for treatment or advice on medication use. Following adequate medical review, aviators may be issued waivers to fly, with the proviso that there be reasonably close tracking by the flight surgeon. Despite these safeguards, postmortem studies of mishap pilots have turned up blood levels of various drugs incompatible with safe flight, including sedating antihistamines, antidepressants, and antiseizure medication (52,57).

Most pilots have a sedentary lifestyle that may lead to weight gain, the development of insulin resistance, hyperlipidemia, hypertension, and eventually diabetes and cardiovascular complications including coronary heart disease (CHD) and cerebrovascular disease. CHD is a leading cause of denial or loss of licensure in both civilian and military aviators (58). Although flying consists primarily of light physical activity, physical fitness is a readiness issue for military aircrew. Military pilots are therefore encouraged to exercise regularly, and the provision of fitness programs and facilities on base and the use of periodic physical assessments ensure
compliance (59, 60, 61). Few airlines and commercial flight organizations have adopted health promotion or fitness programs for aircrew, and in general aviation, there is no regulation of lifestyle at all. As the prevalence of obesity and its complications among the general public continues to grow, an increasing number of aircrew will develop and be limited by health problems induced by sedentary lifestyle (62, 63, 64).

Both military and civil aviation are rapid paced and geographically diverse, resulting in aircrew often not eating at regular times or locations. Obtaining freshly prepared meals containing a variety of healthy foods can also be a challenge. These factors can lead to dietary behaviors that may negatively impact health, flight safety, and/or performance, including risking hypoglycemia and dehydration by skipping meals, eating fat- and salt-laden snacks and meals, and overindulging in caffeine- and sugarrich beverages. Consumption of gas-forming food and drink, such as legumes and carbonated beverages, before and during flight, has traditionally been discouraged. The intent is to avoid discomfort from expanding abdominal gas at altitude, which may be a problem particularly for military aviators. Aircrew should follow dietary guidelines with the goal of a healthy diet (65). The energy needs of piloting aircraft are variable. The maximum energy expenditure in a 70-kg pilot while flying is approximately 150 kcal/hr, twice the 75 kcal/hr energy expenditure of sitting quietly, but less than half the 380 kcal/hr of walking 4.0 mph (66, 67, 68, 69).

In the selected and regularly screened aircrew population, the incidence of serious incapacitating illness is rare, as described later in this chapter. Flight safety and performance are more likely to be affected by acute illnesses such as neck and lower back sprains, and ankle injuries, respiratory tract infections, and gastroenteritis. Ear and sinus barotrauma may result from flying with inflamed respiratory mucosa, while dehydration-related reduced +G_z tolerance and impaired higher cognitive function can result from gastroenteritis. Prudent flight surgeons will both make these hazards known to younger, inexperienced aircrew and work toward primary prevention through staying up to date on standard immunizations, hygienic food preparation, assuring aircrew keep well rested and hydrated, and helping them manage seasonal allergies safely and effectively.

Certain recurrent subacute or chronic illnesses such as migraine headaches are a challenge to diagnose, treat, and therefore address aeromedically (see Chapter 16). Given its 5% to 15% prevalence in the population (70), its subjective nature, and the threat of grounding if diagnosed, it has been assumed that migraine headaches are underreported by aircrew. Until better epidemiologic data and more objective diagnostic techniques are developed, flight surgeons can best approach these issues through relevant aeromedical briefings and by establishing good rapport with crewmembers.

Preston reported 73 disqualifications among 1,000 British airline pilots who had flown between 1954 and 1965, of them 49% for psychiatric and 10% for cardiovascular reasons (77). Twenty-two of 27 pilots who died (81%) did so as a result of a noncommercial aircraft accident. LaVehrne found that among 1,250 Air France pilots, there were 64 permanent groundings, 34% for cardiovascular and 17% for psychiatric reasons (78), while Kidera observed that of 123 medical groundings of United Airlines pilots between 1938 and 1966, 42% were for cardiovascular and 14% for psychiatric reasons (79). In another U.S. airline pilot population (Northwest Airlines), Orford found that cardiac disease accounted for 51%, psychiatric diagnoses for 13%, and neurologic problems for 12% of 103 medical retirements (80). Holt updated the study in 1985, again finding that cardiovascular disease was responsible for 50% of the medical losses in the years since the first study (81).

Band et al. conducted mortality and cancer incidence studies of pilots in two Canadian airlines. Of 913 Canadian airline pilots employed from 1950 through 1988, he found that 71 had died, 23 (32%) in aircraft accidents, 18 (25%) from cardiovascular conditions, 16 (23%) from cancer, and 14 (20%) from other causes (82). For all causes, the standardized mortality rate (SMR) was lower than expected (0.80) consistent with the “healthy worker” effect (healthy workers have lower overall death rates than the general population due to exclusion of the severely ill and disabled). However, SMRs were significantly raised for aircraft accidents (21.29), rectal cancer (4.35), and brain cancer (4.17). There were 57 incident cancer cases ascertained from provincial cancer registries with significantly elevated SMRs being noted for Hodgkin’s disease (4.54), primary brain cancer (3.45), and nonmelanoma skin cancer (1.59).

In a second study, of 2,740 Air Canada pilots employed for at least 1 year between 1980 and 1992, Band again observed a significant reduction in mortality from all causes (SMR 0.63) and an elevated SMR for aircraft accidents (26.57). Among cancers, SMRs for acute myeloid leukemia (4.72) and prostate cancer (1.87) were significantly increased, although the SMR for all cancers (0.61) was significantly decreased. SMRs for malignant melanoma were increased in both studies, but not to the level of statistical significance (83).

In another study, Band found that long-term disability (LTD) rates among Air Canada pilots increased with age, rising from 1.86/1,000 pilots/yr at age 20 to 29, to 9.22/1,000/yr in those aged between 50 and 59 (84). Injuries were most significant among the younger pilots (66% of all causes of LTD under age 30); mental disorders including alcoholism were the most prevalent noninjury conditions among pilots aged 30 to 49 (25.4% of noninjury); while ischemic heart disease was significant in the oldest age-group (27.9% of all noninjury causes between age 50 and 59). Band pointed out that more attention to physical conditioning and other lifestyle modification measures could have prevented many of the injuries and circulatory disorders. He urged pilot associations and airline companies to work together to ensure that preventive programs are implemented.

Irvine and Davies used proportional mortality ratio (PMR) methodology to study mortality and life expectancy in British Airways flight deck crew between 1966 and 1989. Cause of death was ascertained in 411 of 446 cases, and “the predictable excess of aircraft accidents was removed.” Significantly elevated PMRs were observed for malignant melanoma (6.69), cirrhosis (2.88), colon cancer (2.30), and brain/central nervous system (CNS) cancer (2.68) (85). These authors subsequently extended their study to all British Airways pilots and flight engineers employed for at least a year between 1939 and 1992 (86). Standardized mortality ratios for cirrhosis, brain/CNS cancer, and colon cancer were found to be no longer elevated to a level of statistical significance. The SMR for melanoma was significantly raised for pilots, but not for flight engineers. The reason for this difference was not determined. Life expectancy for both groups exceeded that for the general population of England and Wales, even when social class differences were taken into account. Besco et al. similarly found that retired American Airlines pilots had a residual life expectancy after age 60 of greater than 5 years longer than the U.S. population of 60-year-old white males (87).

All of the preceding studies concerned male pilots. The first airline pilot in the United States was not hired until 1973 (by Frontier Airlines). Nicholas published the first epidemiologic study concerning female pilots in 2002 (88), with a follow-up study concerning an observed increase in breast cancer in this population in 2003 (89). Additional studies on disability and mortality among female pilots are needed.

Ballard et al. conducted a meta-analysis of six cohort studies concerning male pilots and female flight attendants reported between 1986 and 1998. For pilots, overall mortality rates were decreased for all causes, lung cancer, all leukemia, ischemic heart disease, and respiratory disease (90). Using a statistic he termed combined socioeconomic status relative risk, he determined that cancer mortality rates were elevated for melanoma (1.97) and brain cancer (1.45), whereas cancer incidence rates were elevated for prostate cancer (1.65) and brain cancer (1.74).

A proportionate mortality study using mortality data from 24 U.S. states from 1984 and 1991 found that cancer of the kidney and renal pelvis was the only cause of death to be significantly increased among male pilots (PMR 1.96) (91). The authors noted that associations between kidney cancer and aviation fuels have been reported in other occupational health studies. However, this finding contrasted with the British Airways and Air Canada studies, both of which
found significantly lower rates than expected for kidney and bladder cancer among pilots (83,86). Finally, a large European study of 28,066 male and 262 female cockpit crewmembers found an increased mortality from malignant melanoma (SMR 1.78) and from aviation accidents, but a reduction in mortality from lung cancer (SMR 0.53) and cardiovascular disease (92).

In summary, contrary to popular belief, airline pilots have an overall lower mortality rate than the general population, and on average live as much as 5 years longer than the general population after age 60. Mortality from noncommercial aircraft accidents is significantly raised. The most common reasons for medical disability are injuries among pilots younger age 30, mental disorders including alcoholism among pilots between 30 and 49, and circulatory disorders among pilots older than 50. Many of these conditions would be preventable by lifestyle modification. With the possible exception of melanoma, no form of cancer is consistently elevated in the pilot populations studied, and overall, the cancer rate for pilots is lower than the general population.

Episodes of in-flight incapacitation are frequently experienced by airline pilots [27%-29% of International Federation of Airline Pilots’ Associations (IFALPA) pilots surveyed in 1968 and 1998 reported having experienced at least one such occurrence] (16,93). The most frequent reason is gastrointestinal disturbances (uncontrolled diarrhea, nausea, vomiting, or severe indigestion). However, very few pilots report these events spontaneously and few, if any, commercial airline accidents have been attributed to pilot incapacitation or for medical causes (94). This contrasts with general aviation, where several accidents caused by in-flight incapacitation occur each year as a result of cardiovascular/cerebrovascular events, alcohol or drug use, carbon monoxide poisoning, or seizures (95). Human factors specific to aviation may also cause or contribute to in-flight incapacitation, including hypoxia, spatial disorientation, and improper G-protection maneuvers, as described elsewhere in this text (see Chapters 2, 4, and 6). Most cardiovascular deaths in pilots younger than 35 years are due to hypertrophic cardiomyopathy (based on the sports medicine literature), whereas in men older than 35 years, nearly all are due to CAD. Autopsy studies have shown the prevalence of significant CAD in pilots to be similar to that in the general population (96). In addition, although the mortality rate for cardiovascular disease among younger pilots is lower than the general population, cardiovascular mortality among older pilots approaches that found in the Framingham study (Table 11-2) (97). DeJohn has reviewed in-flight incapacitation studies conducted between 1968 and 2000 (98). Mitchell and Evans examined the use of the “1% rule” by governments to set limits for aircrew incapacitation, and concluded that it may be too restrictive. They recommended instead that the maximum acceptable sudden incapacitation limit should be set at 2% per year (99).

The mortality and incidence rates for cancer among 1,577 female and 187 male cabin attendants were studied by Pukkala and Auvinen (73). He observed statistically significant increases in SIR for breast cancer (1.87) and bone cancer (15.10), with the breast cancer risk being most prominent 15 years after recruitment. Significant increases for leukemia (3.57) and melanoma (2.11) were also seen. Lynge similarly reported an increased risk for breast cancer among Danish cabin attendants (SIR 1.61), although because of small numbers it was not statistically significant (101). Wartenberg found an increased risk of breast cancer (SIR 2.0) among retired U.S. female cabin attendants (102). Linnersjo found an SIR of 1.01 for cancer overall, and 1.3 for breast cancer (a nonsignificant increase), among Swedish cabin crews, although both men and women had increased rates of melanoma and nonmelanoma skin cancers (103). Similarly, Haldorsen failed to find an increase in breast cancer incidence among Norwegian airline cabin attendants (SIR = 1.1), but he reported an increased incidence of melanoma and nonmelanoma skin cancers (104). Elevated SMRs for acquired immunodeficiency syndrome (AIDS) and aircraft accidents have been reported among male cabin crew (105).

A number of studies have examined the risk for spontaneous abortion and menstruation irregularities among female cabin attendants. Cone and Vaughan reported a 15% rate of spontaneous abortions among 9,392 flight attendants who were pregnant at any time between 1990 and 1991 (106). This is comparable to the 10% to 20% rate reported for the general U.S. population. Aspholm reported in a retrospective Finnish study of 1,751 pregnancies among female cabin crew aged between 24 and 39, with the onset of pregnancy between 1973 and 1994, a spontaneous abortion rate of 12.1% (107). Again, this rate is similar to that for all Finnish women. Both studies showed a slightly increased spontaneous abortion rate among those who worked during the first trimester of pregnancy, but pointed out that any employment during the
first trimester may be a risk factor for spontaneous abortion. Pregnancy outcome among cabin attendants (and pilots) is similar to that of the general population (108).

The U.S. National Institute for Occupational Safety and Health (NIOSH) has published several papers to characterize radiation and other exposures in the aircraft cabin environment and to assess health effects among flight attendants and pilots as part of the “Flight Crew Research Program.”

Agredans has reported that accessibility to air travel correlates strongly with melanoma incidence, and attributes it to increased UV radiation exposure and sunburn among travelers to sunny leisure destinations (109). However, Rafnsson found no difference in the prevalence of risk factors for malignant melanoma between a random sample of the population and aircrew, and concludes that the increased incidence of malignant melanoma found in previous studies of pilots and cabin attendants cannot solely be explained by excessive sun exposure (110).