A number of health factors and physiological effects can be linked to flying. Some are minor, while others are important enough to require special attention to ensure safety of flight. Some important medical factors that a pilot should be aware of include hypoxia, hyperventilation, middle ear and sinus problems, spatial disorientation, motion sickness, carbon monoxide (CO) poisoning, stress and fatigue, dehydration, and heatstroke. Other subjects include the effects of alcohol and drugs, anxiety, and excess nitrogen in the blood after scuba diving.

16.2.1 Hypoxia #

Hypoxia means “reduced oxygen” or “not enough oxygen.” Although any tissue will die if deprived of oxygen long enough, usually the most concern is with getting enough oxygen to the brain, since it is particularly vulnerable to oxygen deprivation. Any reduction in mental function while flying can result in life-threatening errors. Hypoxia can be caused by an insufficient supply of oxygen, inadequate transportation of oxygen, or the inability of the body tissues to use oxygen. The forms of hypoxia are based on their causes: hypoxic hypoxia, hypemic hypoxia, stagnant hypoxia, and histotoxic hypoxia.

16.2.2 Hypoxic Hypoxia #

Hypoxic hypoxia is a result of insufficient oxygen available to the body as a whole. A blocked airway and drowning are obvious examples, but the reduction in partial pressure of oxygen at high altitude is an appropriate example for pilots. Although the percentage of oxygen in the atmosphere is constant, its partial pressure decreases proportionately as atmospheric pressure decreases. As the airplane ascends, there are fewer molecules available at the pressure required for them to pass between the membranes in the respiratory system, which can lead to hypoxic hypoxia.

16.2.3 Hypemic Hypoxia #

Hypemic hypoxia occurs when the blood is not able to take up and transport a sufficient amount of oxygen to the cells in the body. Hypemic means “not enough blood.” It may be due to reduced blood volume (severe bleeding) or certain blood diseases such as anemia, but more often occurs because hemoglobin is chemically unable to bind oxygen molecules. The most common form of hypemic hypoxia is CO poisoning. It can also be caused by the loss of blood due to blood donation; blood can require several weeks to return to normal following a donation.

16.2.4 Stagnant Hypoxia #

Stagnant means “not flowing,” and stagnant hypoxia, or ischemia, results when the oxygen-rich blood in the lungs is not moving to the tissues that need it. An arm or leg “going to sleep” because the blood flow has been shut off is one form. This kind of hypoxia can also result from shock, the heart failing to pump blood effectively, or a constricted artery. During flight, stagnant hypoxia can occur with excessive acceleration of gravity (Gs). Cold temperatures also can reduce circulation and decrease the blood supplied to extremities.

16.2.5 Histotoxic Hypoxia #

The inability of the cells to effectively use oxygen is defined as histotoxic hypoxia. In this case, enough oxygen is being transported to the cells that need it, but they are unable to make use of it. This impairment of cellular respiration can be caused by alcohol and other drugs, such as narcotics and poisons. Research has shown that drinking one ounce of alcohol can equate to about an additional 2,000 feet of physiological altitude.

16.2.6 Symptoms of Hypoxia #

High-altitude flying can place a pilot in danger of becoming hypoxic. One noteworthy attribute of the onset of hypoxia is that the first symptoms are euphoria and a carefree feeling. With increased oxygen starvation, the extremities become less responsive and flying becomes less coordinated. Common symptoms include:

• Cyanosis (blue fingernails and lips)
• Headache
• Decreased reaction time
• Impaired judgment
• Euphoria
• Visual impairment
• Drowsiness
• Lightheaded or dizzy sensation
• Tingling in fingers and toes
• Numbness

As hypoxia worsens, the field of vision begins to narrow, and instrument interpretation can become difficult. Even with these symptoms, hypoxia can cause a pilot to have a false sense of security. The treatment for hypoxia includes flying at lower altitudes and/or using supplemental oxygen. The term “time of useful consciousness” describes the maximum time the pilot has to make rational, life-saving decisions and carry them out at a given altitude without supplemental oxygen. As altitude increases above 10,000 feet, the symptoms increase in severity and the time of useful consciousness rapidly decreases. [Figure 16-1] The ability to recognize hypoxia can be greatly improved by experiencing its effects during an altitude chamber “flight,” which the FAA provides through aviation physiology training.

16.2.7 Hyperventilation #

Hyperventilation is the excessive rate and depth of respiration leading to abnormal loss of carbon dioxide from the blood. It seldom incapacitates completely, but it causes disturbing symptoms that can alarm the uninformed pilot.

Pilots encountering an unexpected stressful situation may subconsciously increase their breathing rate.

Since many of the symptoms of hyperventilation are similar to those of hypoxia, it is important to correctly diagnose and treat the proper condition; if using supplemental oxygen, check the equipment and flow rate to ensure the symptoms are not hypoxia related. Common symptoms include visual impairment, unconsciousness, a lightheaded or dizzy sensation, tingling sensations, hot and cold sensations, and muscle spasms. The treatment involves restoring the proper carbon dioxide level: breathing normally is both the best prevention and the best cure, and breathing into a paper bag or talking aloud helps. Recovery is usually rapid once the breathing rate is returned to normal.

16.2.8 Middle Ear and Sinus Problems #

During climbs and descents, the free gas present in various body cavities expands due to a difference between the pressure outside and inside the body. If the escape of the expanded gas is impeded, pressure builds up within the cavity and pain is experienced. Normally, pressure differences between the middle ear and the outside world are equalized by the Eustachian tube, which opens during chewing, yawning, or swallowing. [Figure 16-2] During descent, the middle ear is at lower pressure than the external ear canal, and the partial vacuum tends to constrict the walls of the Eustachian tube. To remedy this, pinch the nostrils shut, close the mouth and lips, and blow slowly and gently into the mouth and nose. It may not be possible to equalize the pressure if a pilot has a cold, an ear infection, or sore throat.

In a similar way, air pressure in the sinuses equalizes through small openings that connect the sinuses to the nasal passages; congestion may plug the opening, producing a “sinus block” that occurs most frequently during descent and can cause excruciating pain.

Sinus block can be avoided by not flying with an upper respiratory infection or nasal allergic condition.

16.2.9 Spatial Disorientation and Illusions #

Spatial disorientation specifically refers to the lack of orientation with regard to the position, attitude, or movement of the airplane in space. The body uses three integrated systems: the vestibular system (organs in the inner ear that sense position by balance); the somatosensory system (nerves in the skin, muscles, and joints that sense position based on gravity, feeling, and sound); and the visual system (eyes). During flight in visual meteorological conditions (VMC), the eyes are the major orientation source and usually prevail over false sensations. When these visual cues are removed, as in instrument meteorological conditions (IMC), false sensations can cause a pilot to quickly become disoriented. [Figures 16-3 and 16-4] In both inner ears, three semicircular canals are positioned at right angles to each other, each filled with fluid and fine hairs that deflect with acceleration. The body cannot distinguish between acceleration forces due to gravity and those resulting from maneuvering the aircraft, which can lead to sensory illusions. Prevention is usually the best remedy: unless a pilot has many hours of training in instrument flight, flight should be avoided in reduced visibility or at night when the horizon is not visible.

16.2.10 Vestibular Illusions #

The Leans: can result when a banked attitude is entered too slowly to set the fluid in the “roll” semicircular tubes in motion; an abrupt correction sets the fluid moving, creating the illusion of a bank in the opposite direction. Coriolis Illusion: occurs when a pilot has been in a turn long enough for the fluid to move at the same speed as the canal, and a head movement in a different plane creates the illusion of turning on a different axis—develop a cross-check with minimal head movement. Graveyard Spiral: in a prolonged constant-rate turn the pilot has the illusion of not turning; the absence of any sensation of turning creates the illusion of a level descent, and pulling back on the controls only tightens the spiral. [Figure 16-5] Somatogravic Illusion: a rapid acceleration creates the illusion of a nose-up attitude; the pilot may push into a dive. Inversion Illusion: an abrupt change from climb to level flight can create the illusion of tumbling backwards. Elevator Illusion: an abrupt upward acceleration (updraft) creates the illusion of a climb.

16.2.11 Visual Illusions #

Visual illusions are especially hazardous because pilots rely on their eyes for correct information. False Horizon: a sloping cloud formation, an obscured horizon, an aurora borealis, a dark scene spread with ground lights and stars, and certain geometric patterns of ground lights can provide inaccurate visual information for aligning the aircraft with the actual horizon. Autokinesis: in the dark, a stationary light will appear to move when stared at for many seconds; the disoriented pilot could lose control attempting to align with the false movement. [Figure 16-6]

16.2.12 Postural Considerations #

The postural system sends signals from the skin, joints, and muscles to the brain that are interpreted in relation to the Earth’s gravitational pull. “Seat of the pants” flying is largely dependent upon these signals. However, because of the forces acting upon the body in certain flight situations, many false sensations can occur due to acceleration forces overpowering gravity. These situations include uncoordinated turns, climbing turns, and turbulence. Skids, slips, and uncoordinated turns feel similar—pilots feel they are being forced sideways in their seat.

16.2.13 Demonstration of Spatial Disorientation #

There are a number of controlled aircraft maneuvers a pilot can perform to experiment with spatial disorientation. These demonstrations teach pilots that judgments of aircraft attitude based on bodily sensations are frequently false, and help instill greater confidence in relying on flight instruments.

A pilot should not attempt any of these maneuvers at low altitudes, or in the absence of an instructor pilot or appropriate safety pilot. Common demonstrations include climbing while accelerating, climbing while turning, diving while turning, tilting to right or left, reversal of motion, and diving or rolling beyond the vertical plane. In each case, opening the eyes and referring to the instruments reveals the aircraft’s true attitude.

16.2.14 Coping with Spatial Disorientation #

To prevent illusions and their potentially disastrous consequences, pilots can: understand the causes of these illusions and remain alert for them; experience spatial disorientation illusions in a device such as a Barany chair; always obtain and understand preflight weather briefings; obtain training and maintain proficiency in airplane control by reference to instruments before flying in marginal visibility or where a visible horizon is not evident; not continue flight into adverse weather or darkness unless proficient with instruments; use reliable, fixed outside visual references; avoid sudden head movement during takeoffs, turns, and approaches; be physically tuned for flight (proper rest and diet, night adaptation); and remember that illness, medication, alcohol, fatigue, sleep loss, and mild hypoxia increase susceptibility. Most importantly, become proficient in the use of flight instruments and rely upon them, disregarding sensory perceptions.

16.2.15 Optical Illusions #

Various terrain features and atmospheric conditions can create optical illusions, primarily associated with landing, since pilots must transition from instruments to visual cues for landing at the end of an instrument approach. The major illusions leading to landing errors are described below. [Figure 16-7]

16.2.16 Runway Width Illusion #

A narrower-than-usual runway can create an illusion the aircraft is at a higher altitude than it actually is, especially when runway length-to-width relationships are comparable. The pilot who does not recognize this illusion will fly a lower approach, with the risk of striking objects along the approach path or landing short. A wider-than-usual runway can have the opposite effect.

16.2.17 Runway and Terrain Slopes Illusion #

An upsloping runway, upsloping terrain, or both, can create an illusion that the aircraft is at a higher altitude than it actually is. The pilot who does not recognize this illusion will fly a lower approach. Downsloping runways and downsloping approach terrain can have the opposite effect.

16.2.18 Featureless Terrain Illusion #

An absence of surrounding ground features, as in an overwater approach, over darkened areas, or terrain made featureless by snow, can create an illusion the aircraft is at a higher altitude than it actually is. This illusion, sometimes referred to as the “black hole approach,” causes pilots to fly a lower approach than is desired.

16.2.19 Water Refraction #

Rain on the windscreen can create an illusion of being at a higher altitude due to the horizon appearing lower than it is. This can result in the pilot flying a lower approach.

16.2.20 Haze #

Atmospheric haze can create an illusion of being at a greater distance and height from the runway, so the pilot tends to be low on the approach. Conversely, extremely clear air can give the illusion of being closer than actual, resulting in a high approach.

Flying into fog can create an illusion of pitching up; pilots who do not recognize this illusion will often steepen the approach quite abruptly.

16.2.21 Ground Lighting Illusions #

Lights along a straight path, such as a road or lights on moving trains, can be mistaken for runway and approach lights. Bright runway and approach lighting systems, especially where few lights illuminate the surrounding terrain, may create the illusion of less distance to the runway; the pilot who does not recognize this illusion will often fly a higher approach.

16.2.22 How To Prevent Landing Errors Due to Optical Illusions #

To prevent these illusions, pilots can: anticipate the possibility of visual illusions during approaches to unfamiliar airports, particularly at night or in adverse weather; consult airport diagrams and the Airport/Facility Directory (A/FD) for information on runway slope, terrain, and lighting; make frequent reference to the altimeter; conduct an aerial visual inspection of unfamiliar airports before landing if possible; use VASI or PAPI systems or an electronic glideslope whenever available; utilize the visual descent point (VDP) found on many nonprecision instrument approach charts; recognize that the chances of an approach accident increase when an emergency or other activity distracts from usual procedures; and maintain optimum proficiency in landing procedures.

16.2.23 Motion Sickness #

Motion sickness, or airsickness, is caused by the brain receiving conflicting messages about the state of the body. A pilot may experience it during initial flights, but it generally goes away within the first few lessons. Symptoms include general discomfort, nausea, dizziness, paleness, sweating, and vomiting. If prone to motion sickness, let the flight instructor know. If symptoms are experienced during a lesson, opening fresh air vents, focusing on objects outside the airplane, and avoiding unnecessary head movements may help. Although medications like Dramamine can prevent airsickness in passengers, they are not recommended while flying since they can cause drowsiness.

16.2.24 Carbon Monoxide (CO) Poisoning #

CO is a colorless and odorless gas produced by all internal combustion engines. Attaching itself to the hemoglobin about 200 times more easily than oxygen, CO prevents the hemoglobin from carrying oxygen to the cells, resulting in hypemic hypoxia. Aircraft heater vents and defrost vents may provide CO a passageway into the cabin, particularly if the engine exhaust system has a leak. If a strong odor of exhaust gases is detected, assume CO is present; however, CO may be present in dangerous amounts even with no exhaust odor. Some effects are headache, blurred vision, dizziness, drowsiness, and/or loss of muscle power. Immediate corrective actions include turning off the heater, opening fresh air vents and windows, and using supplemental oxygen if available.

Tobacco smoke also causes CO poisoning.

16.2.25 Stress #

Stress is the body’s response to physical and psychological demands placed upon it. Examples of stressors include physical stress (noise or vibration), physiological stress (fatigue), and psychological stress (difficult work or personal situations).

Stress falls into two broad categories: acute (short term) and chronic (long term). Acute stress triggers a “fight or flight” response and a healthy person can normally cope with it. Chronic stress presents an intolerable burden, exceeds the ability to cope, and causes performance to fall sharply. Pilots experiencing this level of stress are not safe and should consult a physician.

16.2.26 Fatigue #

Fatigue is frequently associated with pilot error. Effects include degradation of attention and concentration, impaired coordination, and decreased ability to communicate. Acute fatigue is short term and is normally cured by rest and 8 hours of sound sleep. A special type is skill fatigue, which causes timing disruption and disruption of the perceptual field.

Chronic fatigue, extending over a long period, usually has psychological roots, is not relieved by rest, and usually requires treatment by a physician. If suffering from fatigue, stay on the ground—if fatigue occurs in the flight deck, no amount of training or experience can overcome its detrimental effects.

16.2.27 Dehydration and Heatstroke #

Dehydration is a critical loss of water from the body. Causes include hot flight decks, wind, humidity, and diuretic drinks (coffee, tea, alcohol, and caffeinated soft drinks). Common signs are headache, fatigue, cramps, sleepiness, and dizziness; the first noticeable effect is fatigue.

To help prevent dehydration, drink two to four quarts of water every 24 hours. The thirst mechanism arrives too late and is turned off too easily, so pilots should stay ahead and not rely on thirst, and limit caffeine and alcohol. Heatstroke is caused by an inability of the body to control its temperature; carry an ample supply of water and use it at frequent intervals on any long flight. Wearing light-colored, porous clothing and a hat, and keeping the flight deck well ventilated, aids in dissipating excess heat.

16.2.28 Alcohol #

Alcohol impairs the efficiency of the human body. [Figure 16-8] Even in small amounts, alcohol can impair judgment, decrease sense of responsibility, affect coordination, constrict visual field, diminish memory, reduce reasoning power, and lower attention span. The body requires about 3 hours to rid itself of all the alcohol contained in one mixed drink or one beer.

While experiencing a hangover, a pilot is still under the influence of alcohol. Altitude multiplies the effects: when combined with altitude, the alcohol from two drinks may have the same effect as three or four, because alcohol interferes with the brain’s ability to utilize oxygen, producing a form of histotoxic hypoxia. 14 CFR part 91 requires that blood alcohol level be less than .04 percent and that 8 hours pass between drinking alcohol and piloting an airplane. It is a good idea to be more conservative than the regulations.

16.2.29 Drugs #

Pilot performance can be seriously degraded by both prescription and over-the-counter medications, as well as by the medical conditions for which they are taken. Many medications have primary effects that may impair judgment, memory, alertness, coordination, vision, and the ability to make calculations; others have side effects that may impair the same functions. [Figure 16-9] Any medication that depresses the nervous system can make a pilot more susceptible to hypoxia. Over-the-counter analgesics such as aspirin, acetaminophen, and ibuprofen have few side effects in the correct dosage; however, flying is almost always precluded while using prescription analgesics such as those containing propoxyphene, oxycodone, meperidine, and codeine. Stimulants can produce anxiety and mood swings; depressants lower blood pressure and slow reaction responses. Some antibiotics can produce dangerous side effects. Unless specifically prescribed by a physician, do not take more than one drug at a time, and never mix drugs with alcohol.

14 CFR prohibits pilots from performing crewmember duties while using any medication that affects the body in any way contrary to safety; if in doubt, consult an AME before flying.

16.2.30 Altitude-Induced Decompression Sickness (DCS) #

Decompression sickness (DCS) describes a condition resulting from exposure to low barometric pressures that cause inert gases (mainly nitrogen), normally dissolved in body fluids and tissues, to come out of solution and form bubbles. The most common symptom is joint pain, known as “the bends.” [Figure 16-10] What to do when altitude-induced DCS occurs: put on the oxygen mask immediately and switch the regulator to 100 percent oxygen; begin an emergency descent and land as soon as possible (even if symptoms disappear during descent, land and seek medical evaluation while continuing to breathe oxygen); if a symptom is joint pain, keep the affected area still; and upon landing, seek medical assistance from an FAA medical officer, AME, military flight surgeon, or hyperbaric medicine specialist. Delayed signs and symptoms can occur after return to ground level.

16.2.31 DCS After Scuba Diving #

Scuba diving subjects the body to increased pressure, which allows more nitrogen to dissolve in body tissues and fluids. The reduction of atmospheric pressure that accompanies flying can produce physical problems for scuba divers. A pilot or passenger who intends to fly after scuba diving should allow the body sufficient time to rid itself of excess nitrogen.

The recommended waiting time before going to flight altitudes of up to 8,000 feet is at least 12 hours after diving that does not require controlled ascent (nondecompression stop diving), and at least 24 hours after diving that does require controlled ascent (decompression stop diving). The waiting time before going to flight altitudes above 8,000 feet should be at least 24 hours after any scuba dive. These recommended altitudes are actual flight altitudes above mean sea level and not pressurized cabin altitudes. [Figure 16-11]