Pilot's Handbook of Aeronautical Knowledge

Chapter 17: Aeromedical Factors

---

A number of health factors and physiological effects can be linked to flying. These include hypoxia, hyperventilation, middle ear and sinus problems, spatial disorientation, motion sickness, carbon monoxide (CO) poisoning, stress and fatigue, dehydration, and heatstroke. Pilots also should be aware of the effects of alcohol and drugs, anxiety, and excess nitrogen in the blood after scuba diving.

---

Hypoxia

Hypoxia causes a reduction in oxygen available to the brain. Any reduction in mental function while flying can result in life-threatening errors.

Hypoxic hypoxia is a result of insufficient oxygen available to the body as a whole. The reduction in partial pressure of oxygen at high altitude will cause this condition. As an aircraft ascends during flight, the proportion of nitrogen to oxygen in the atmosphere remains the same. However, there are fewer molecules available for the respiratory system.

Transportation of dry ice can cause a specific risk, since dry ice sublimates into large quantities of CO2 gas, which rapidly displaces oxygen-containing air. Without proper ventilation, dry ice can rapidly pressurize. Because of these factors, dry ice is only transported by air under specific safety conditions.

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. In this case, it's not a lack of available oxygen, but instead a lack of blood. The most common form of hypemic hypoxia is CO poisoning. Other causes can be blood loss and anemia. Pilots should refrain from flying for a period of time after donating blood.

Stagnant hypoxia, also called "ischemia," results when the oxygen-rich blood in the lungs is not moving. In this case, oxygen and blood are available, but oxygen is not transported by blood to the brain. A common form of stagnant hypoxia is when a hand, arm, or leg goes "to sleep" due to constricted blood flow. Cold temperatures and shock also can cause stagnant hypoxia. In fight, stagnant hypoxia can result from maneuvers with high G-loads, as the excessive acceleration of gravity may prevent blood from flowing to the brain.

Histotoxic hypoxia refers to inability of the cells to effectively use oxygen. Generally, "toxic" refers to a poison. In this case, it also includes alcohol or drugs. Consumption of alcohol can cause mild to severe histotoxic hypoxia. Drinking one ounce of alcohol can equate to an additional 2,000 feet of physiological altitude.

The first symptoms of hypoxia can include euphoria and a carefree feeling. The effects of hypoxia can cause a pilot to have a false sense of security and be deceived into believing everything is normal. Subsequent symptoms can include:

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

Treatment for hypoxia includes flying at lower altitudes and/ or using supplemental oxygen. The term "time of useful consciousness" describes the maximum time a pilot has to make rational, life-saving decisions and carry them out at a given altitude without supplemental oxygen. Above 10,000 feet, time of useful consciousness rapidly decreases.

---

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, increased breathing rate and anxiety further aggravate the problem.

Pilots should correctly diagnose hypoxia versus hyperventilation, which may seem similar at first. Symptoms include:

• Visual impairment
• Unconsciousness
• Lightheaded or dizzy sensation
• Tingling sensations
• Hot and cold sensations
• Muscle spasms

Abnormal breathing may cause hyperventilation. Breathing normally is the best cure for hyperventilation. In addition to slowing the breathing rate, breathing into a paper bag, talking aloud, or singing helps to overcome hyperventilation.

---

Middle Ear and Sinus Problems

During climbs and descents, gas in various body cavities expands due to a difference between the pressure of the air outside the body and that of the air inside the body. If the gas cannot escape, it can result in ear pain, sinus pain, and temporary loss of hearing.

The middle ear is a small cavity that is closed off from the external ear canal by the eardrum. Pressure differences are equalized by Eustachian tubes, which lead from inside each ear to the back of the throat. The tube open when chewing, yawning, or swallowing.

During a climb, lower external pressure may cause the eardrum to bulge outward. During a descent, higher external pressure can cause the eardrum to bulge inward.

To remedy this often painful condition and restore hearing, pinch the nostrils shut, close the mouth and lips, and blow slowly and gently into the mouth and nose. This will force air through the Eustachian tube into the middle ear.

Flight with a cold, an ear infection, or sore throat can be extremely painful, as well as damaging to the eardrums.

Internal sinus pressure equalizes with external pressure through small openings that connect the sinuses to the nasal passages. Congestion can create a painful sinus block, which occurs most frequently during descent. Pilots with an upper respiratory infection or nasal allergic condition should avoid flying.

---

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 that work together to ascertain orientation and movement in space:

• Visual system: Eyes, which sense position based on what is seen.
• Vestibular system: Organs found in the inner ear that sense position by the way we are balanced.
• Somatosensory system: Nerves in the skin, muscles, and joints that, along with hearing, sense position based on gravity, feeling, and sound.

Most of the time, the three streams give a clear idea of where and how the body is moving. However, conflicting information can lead to disorientation.

The visual system is the primary source of information in visual meteorological conditions (VMC), and visual information usually prevails over false sensations. Without the benefit of external vision, false sensations can cause a pilot to quickly become disoriented.

The vestibular system (in the inner ear) features three semicircular canals are positioned at approximate right angles to each other. Each canal is filled with fluid and has a section full of fine hairs. Deflection of these hairs stimulates nerve impulses, sending messages to the brain, which can be used to interpret motion.

The somatosensory 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, but the body cannot distinguish between acceleration forces due to gravity and those resulting from maneuvering the aircraft. This can lead to sensory illusions.

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. Learning to fly with reference only to flight instruments requires training and awareness.

Vestibular Illusions

The leans is caused by a sudden return to level flight following a gradual and prolonged turn that went unnoticed by the pilot. After leveling the wings, the pilot may experience an illusion that the aircraft is banking in the opposite direction. This is the most common illusion during flight. The initial turn often goes unnoticed because a rotational acceleration of two (2) degrees per second or lower is below the detection threshold of the semicircular canals.

Coriolis illusion occurs when a pilot has been in a turn long enough for the fluid in the ear canal to move at the same speed as the canal. Any movement of the head may then disturb the fluid, creating a turning or accelerating illusion.

The graveyard spiral is the the illusion of not turning when the airplane is in a prolonged, coordinated, constant-rate turn. During recovery to level flight, the pilot will experience the sensation of turning in the opposite direction. This illusion may cause the pilot to re-enter the graveyard spiral, eventually with catastrophic results if flying in non-visual conditions. In addition, if pilot instinctively pulls back on the controls in an attempt to climb or stop the descent, this may tighten the spiral and increases the loss of altitude. A loss-of-control accident is possible.

Somatogravic illusion gives the pilot the sensation of being in a nose-up attitude when the aircraft is level. It can be caused by rapid acceleration (such as during takeoff), which stimulates the otolith organs in the same way as tilting the head backwards. The pilot's response may place the aircraft in nose-low or dive attitude. Notably, rapid deceleration can have the opposite effect, causing the pilot to pitch nose-up or stall the aircraft.

Inversion illusion is the sensation of tumbling backwards, which can be caused by an abrupt change from climb to straight-and-level flight.

Elevator illusion conveys a climb or descent sensation, which can be caused by an upward/downward vertical acceleration, such as in an updraft or downdraft. The disoriented pilot may push the aircraft into a nose-low or nose-high attitude.

Visual Illusions

Visual illusions are especially hazardous, since pilots rely on vision for critical information.

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 a false horizon when attempting to align the aircraft with the actual horizon. The disoriented pilots as a result may place the aircraft in a dangerous attitude.

Autokinesis occurs when flying in the dark. A stationary light may appear to move if it is stared at for a prolonged period of time, which may cause the pilot to attempt to align the aircraft with the perceived moving light, potentially causing him/her to lose control of the aircraft.

Demonstration of Spatial Disorientation

False sensations in maneuvers are an effective demonstration of disorientation. In teaching this, pilots can understand the susceptibility of the human system to spatial disorientation, and that bodily sensations are frequently false. Students also will have fewer instances of disorientation, and they will transition to relying on flight instruments for assessing true aircraft attitude. All maneuvers are done with the pilot's eyes closed:

• Climbing while accelerating: With the pilot's eyes closed, the instructor accelerates while maintaining straight-and­ level attitude. The illusion, without visual references, is that the aircraft is climbing.
• Climbing while turning: A coordinated turn of about 1.5 positive G (approximately 50° bank) is entered for 90°. While in the turn, slight positive Gs cause the illusion of climb. Upon sensing the climb, the pilot should immediately open the eyes to see that a slowly established, coordinated turn produces the same sensation as a climb.
• Diving while turning: Repeating the previous procedure, but with the pilot's eyes should be kept closed until recovery from the turn is approximately one-half completed, causing the illusion of diving while turning.
• Tilting to right or left: While in a straight-and-level attitude, the instructor executes a moderate or slight skid to the left with wings level, causing the illusion of the body being tilted to the right.
• Reversal of motion: This illusion can be demonstrated in any of the three planes of motion. While straight and level, the instructor rolls the aircraft to approximately 45° bank attitude while maintaining heading and pitch attitude. This creates the illusion of a strong sense of rotation in the opposite direction. After this illusion is noted, the pilot should open his or her eyes and observe that the aircraft is in a banked attitude.
• Diving or rolling beyond the vertical plane: This maneuver may produce extreme disorientation. While in straight-and-level flight, the pilot should sit normally, either with eyes closed or gaze lowered to the floor. The instructor pilot starts a positive, coordinated roll toward a 30° or 40° angle of bank. As this is in progress, the pilot tilts his or her head forward, looks to the right or left, then immediately returns his/her head to an upright position. The instructor pilot should time the maneuver so the roll is stopped as the pilot returns his/her head upright. An intense disorientation is usually produced by this maneuver, and the pilot experiences the sensation of falling downward into the direction of the roll.

Pilots should understand the causes of vestibular and visual illusions and remain constantly alert for them. Training and proficiency are essential when flying in marginal visibility or where a visible horizon is not evident (such as flight over open water at night). Adverse weather conditions and dusk/darkness also require instrument proficiency. Sudden head movements should be avoided, and the IMSAFE checklist should be conducted before each flight.

Optical Illusions

Vision is the most important of the five senses for safe flight. Terrain features and atmospheric conditions can create optical illusions, most often when landing.

• Runway width illusion occurs when a narrower-than-usual runway can create an illusion that the aircraft is at a higher altitude than it actually is. Pilots who do not recognize this illusion may fly a lower approach, which can result in striking objects or landing short.
• Runway and terrain slopes illusion is caused by an upsloping runway, upsloping terrain, or both. The result is an illusion that the aircraft is at a higher altitude than it actually is, risking a low approach. Downsloping runways and terrain can have the opposite effect.
• Featureless terrain illusion can occur in overwater approach over darkened areas, or in terrain blanketed by snow. In such cases, without surrounding ground features, the aircraft may seem at a higher altitude than it actually is.
• Rain on the windscreen can create the illusion of water refraction — the perception of being at a higher altitude due to the horizon appearing lower than it is. This can result in a low approach.
• Atmospheric haze can create the illusion of being at a greater distance and height from the runway, which may cause a low approach.
• Flying into fog can create an illusion of pitching up. Pilots may steepen the approach abruptly.
• Lights along a straight path, such as a road or lights on moving trains, can cause ground lighting illusions, as they can be mistaken for runway/approach lights. Also, bright runway/approach lighting systems (especially in dark surroundings), may create the illusion of less distance to the runway, leading to a high approach.

Pilots should anticipate the possibility of visual illusions during approaches to unfamiliar airports, particularly at night or in adverse weather conditions. The altimeter and VASI should be used on approach, as well as the Visual Descent Point (VDP) found on many non-precision instrument approach charts.

---

Additional Risk Factors

Motion sickness is caused by the brain receiving conflicting messages about the state of the body. Opening fresh air vents, focusing on objects outside the airplane, and avoiding unnecessary head movements may help alleviate some of the discomfort. Medications are not recommended, as they may cause drowsiness.

Carbon Monoxide (CO) is a colorless and odorless gas produced by all internal combustion engines. When pilots are exposed, CO prevents the hemoglobin from carrying oxygen to the cells, resulting in hypemic hypoxia. Symptoms of CO poisoning include headache, blurred vision, dizziness, drowsiness, and/or loss of muscle power. Prolonged exposure can be fatal.

Aircraft heater vents and defrost vents may provide CO a passageway into the cabin, particularly if the engine exhaust system has a leak or is damaged. An exhaust gas odor should suggest that CO is present. It also can present a risk in smaller amounts. Disposable, inexpensive CO detectors are widely available.

Stress causes an increase in adrenaline, metabolism, blood sugar, heart rate, respiration, blood pressure, and perspiration. Acute stress involves an immediate threat that is perceived as danger. Chronic stress, due to psychological pressures, causes individual performance to fall sharply.

Fatigue causes lowered attention and concentration, impaired coordination, and decreased ability to communicate. Acute fatigue is short term and normal, requiring only rest for recovery.

Skill fatigue is a type of acute fatigue that results in workflow timing disruptions, as well as disruption of the perceptual field.

Chronic fatigue is caused by continuously high levels of stress. It usually requires treatment by a physician.

Pilots should avoid exposure to chemicals commonly found in aircraft fluids. Hydraulic fluid, engine oil, and fuel have specific risks associated with eye and/or skin contact, as well as inhalation and ingestion.

Dehydration is a critical loss of water from the body, commonly caused by hot airplanes, wind, humidity, and diuretic drinks (coffee, tea, alcohol, and caffeinated soft drinks). The first noticeable effect of dehydration is fatigue. Additional signs include headache, fatigue, cramps, sleepiness, and dizziness. High temperatures and altitudes increase the risk of dehydration. Pilots should drink two to four quarts of water every 24 hours.

Heatstroke is caused by the inability of the body to control its temperature. Water should be carried and used at frequent intervals on any long flight, whether the pilot is thirsty or not.

The influence of alcohol drastically reduces the chances of completing a flight without incident. Impairments in vision and hearing can occur from consuming one drink. When combined with altitude, the alcohol from two drinks may have the same effect as three or four drinks. Title 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 aircraft.

Title 14 CFR part 91, section 91.17 prohibits the use of any medication that affects a pilot in any way contrary to safety. The safest rule is not to fly as a crew-member while taking any medication, unless approved to do so by the FAA.

Title 14 CFR part 61, section 61.53 prohibits acting as pilot-in-command or in any other capacity as a required pilot flight crew-member, while that person is aware of a medical condition that would invalidate their medical certificate, or is taking medication or receiving other treatment that would invalidate their medical certificate.

---

Altitude-Induced Decompression Sickness (DCS)

Nitrogen is an inert gas normally stored throughout the human body (tissues and fluids) in physical solution. Exposure to decreased barometric pressures — such as when flying in an unpressurized aircraft — can cause nitrogen and other inert gasses to come out of physical solution and form bubbles. Decompression Sickness (DCS) is characterized by a variety of symptoms, most commonly joint pain, also known as as "the bends."

Altitude-induced DCS requires immediate attention, starting with supplemental oxygen and emergency descent to the first suitable airport. A physician specialized in aviation or hyperbaric medicine may be necessary, and a a hyperbaric chamber may be used for recovery.

Note that symptoms of DCS can occur after return to ground level, and may not be present during flight.

Scuba diving subjects the body to increased pressure, which allows more nitrogen to dissolve in body tissues and fluids. A pilot or passenger who intends to fly after scuba diving should allow the body sufficient time to rid itself of excess nitrogen absorbed during diving.

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 (non-decompression 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. Divers should use these figures as actual flight altitudes and not cabin-pressure altitudes, since unexpected decompression could lead to a medical emergency.

---

Vision in Flight

The human eye includes an aperture, a lens, a mechanism for focusing, and a surface for registering images. The retina contains light sensitive cells that convert light energy into electrical impulses that travel through nerves to the brain.

The two kinds of light-sensitive cells in the eyes are rods and cones.

Cones are are concentrated toward the center of the field of vision at the back of the retina, and they are responsible for all color vision.

Rods detect movement and provide vision in dim light. They are unable to discern color. Large amounts of light overwhelm rods, and they require time to "reset" and adapt to the dark again.

Vision Types

Photopic vision provides the capability for seeing color and resolving fine detail. It is experienced during daylight or under brightly illuminated lights.

Mesopic vision is achieved by a combination of rods and cones and is experienced at dawn, dusk, and during full moonlight. Visual acuity decreases and color perception changes.

Scotopic vision is experienced under low-light levels and the cones become ineffective, resulting in poor resolution of detail. Visual acuity decreases dramatically, color perception is lost, and a night blind spot in the central field of view appears.

The area where the optic nerve connects to the retina in the back of each eye is known as the optic disk. There is a total absence of cones and rods in this area, and thus a central blind spot. This typically is not a problem, since an object cannot be in the blind spot of both eyes at the same time. However, if the field of vision of one eye is obstructed, an object can fall in the blind spot.

While looking at the above image:

• Completely cover your left eye (without closing or pressing on it) using your hand or other flat object.
• With your right eye, stare directly at the airplane on the left side of the picture. In your periphery, you will notice the black X on the right side of the picture.
• Slowly move the screen closer to you while continuing to stare at the airplane (or move closer to the screen).
• When the page is about 16-18 inches from you, the black X should disappear completely because it has been imaged onto the blind spot of your right eye. (Resist the temptation to move your right eye while the black X is gone or else it reappears. Keep staring at the airplane.)
• As you continue to look at the airplane, keep moving the page closer to you a few more inches, and the black X will come back into view.

You can try this with your right eye covered by staring at the black X with your left eye. As you move closer, the airplane will disappear.

Empty-field myopia occurs when flying above the clouds or in a haze layer. Without external points of focus, the eyes seek a comfortable focal distance (10-30 feet). This can mean "looking without seeing." Focusing on distant light sources helps prevent the onset of empty-field myopia.

Pilots trained in night-flying techniques can become comfortable and proficient. Dark-adapted rods are the primary receptors for night vision, while also responsible for most peripheral vision. Because of the central location of cones in the eye, a night blind spot in the center of the field of vision can develop. To see an object clearly at night, pilots should looking 5° to 10° off center of the object.

Dark adaptation is the adjustment of the human eye to a dark environment, which requires time. Dark adaptation will take longer if moving from a bright area to a dark area, compared to moving from a dim area to a dark area. Cones adapt rapidly in changes to light, whereas rods can take approximately 30 minutes to fully adapt to darkness. Bright light undermines night adaptation, requiring the adaptation process to be repeated.

Scanning techniques enable the identification of objects at night. Pilots should look right-left or left-right, scanning at the greatest distance an object can be perceived (top) and move inward toward the position of the aircraft (bottom). For each stop, an area approximately 30° wide should be scanned. The duration of each stop is based on the degree of detail that is required, but no stop should last longer than 2 to 3 seconds. When moving from one viewing point to the next, pilots should overlap the previous field of view by 10°.

Off-center viewing requires an object be viewed by looking 10° above, below, or to either side of the object, so that the peripheral vision can maintain contact with an object. With off-center viewing, the images of an object viewed longer than two to three seconds will disappear. Avoid viewing an object for longer than two or three seconds. The peripheral field of vision will continue to pick up the object when the eyes are shifted from one off-center point to another.

Night Vision Protection

If a night flight is scheduled, pilots and crew members should wear sunglasses when exposed to bright sunlight. This increases the rate of dark adaptation at night and improves night visual sensitivity.

Lack of oxygen to the rods (hypoxia) significantly reduces their sensitivity. Clear vision requires significant oxygen, especially at night. Without supplemental oxygen, the pilot's night vision declines at pressure altitudes above 4,000 feet. For the pilot suffering the effects of hypoxic hypoxia, a simple descent to a lower altitude may not be sufficient to reestablish vision, and visual acuity may not be regained for over an hour.

If a high-intensity lighting area is encountered during flight, turn the aircraft away and fly in the periphery of the lighted area. When possible, plan a night route to avoid direct flight over built-up, brightly lit areas.

Flight deck lighting should be kept as low as possible. During an adjustment period after departure, night vision should continue to improve until optimum night adaptation is achieved. When it is necessary to read maps, charts, and checklists, use a dim white (or red) flashlight and avoid shining it in your or any other crew-member's eyes.

When an airport has pilot-controlled lighting, the airfield lighting should be reduced to the lowest usable intensity. Position the aircraft at a part of the airfield where the least amount of lighting exists. Select approach and departure routes that avoid bright illumination.

Night Flying and Stress

Drugs, exhaustion, poor physical conditioning, alcohol, and tobacco are all risk factors during any phase of flight, especially at night. Missing or postponing meals can cause low blood sugar, which impairs night flight performance. A lack of vitamin A impairs night vision (although high quantities of vitamin A do not increase night vision).

Distance Estimation and Depth Perception

Motion parallax refers to the apparent motion of stationary objects. When looking perpendicular from the flight path, near objects can appear to move backward, past, or opposite the path of motion, while far objects can seem to move in the direction of motion or remain fixed. The rate of apparent movement depends on the distance the observer is from the object.

An object may appear to have a different geometric perspective when viewed at varying distances and from different angles. In the linear perspective, parallel lines, such as runway lights, power lines and railroad tracks, tend to converge as distance from the observer increases. In apparent foreshortening, the true shape of an object or a terrain feature appears elliptical when viewed from a distance. With vertical position in the field, objects or terrain features farther away from the observer appear higher on the horizon than those closer to the observer.

As distance increases, the clarity of an object, its detail, its texture, and the shadow cast by are visual cues for its distance. However, at night these distinctions in the aerial perspective may become blurry. Additionally, shadows depend on the position of light sources. If a shadow of an object is cast toward the observer, the object is closer than the light source is to the observer.

Binocular cues depend upon the slightly different viewing angle of each eye toward an object. In the flight environment, most distances are so great that binocular cues are of little or no value. In addition, binocular cues operate on a more subconscious level than monocular cues and are performed automatically.

Night Vision Illusions

Autokinesis is caused by staring at a single point of light against a dark background for more than a few seconds. The light will appear to move on its own in about 8 to 10 seconds. This illusion can be eliminated or reduced by visual scanning, by increasing the number of lights, or by varying the light intensity.

A false horizon can occur when the natural horizon is obscured or not readily apparent. It can be generated by confusing bright stars and city lights. It can also occur while flying toward the shore of an ocean or a large lake. Because of the relative darkness of the water, the lights along the shoreline can be mistaken for stars in the sky.

A reversible perspective illusion may make an aircraft appear to be moving away from a second aircraft when it is, in fact, approaching a second aircraft. This illusion often occurs when an aircraft is flying parallel to another's course. To determine the direction of flight, pilots should observe aircraft lights and their relative position to the horizon. If the intensity of the lights increases, the aircraft is approaching. If the lights dim, the aircraft is moving away.

A size-distance illusion results from viewing a source of light that is increasing or decreasing in brightness (luminance). Pilots may interpret the light as approaching or retreating.

Fascination, also called "fixation," occurs when pilots ignore orientation cues and fix their attention on a goal or an object, such as when they are concentrating on aircraft instruments, or when attempting to land. This can be especially dangerous at night because aircraft ground-closure rates are difficult to determine.

Flicker vertigo is caused by a light flickering at a rate between 4 and 20 cycles per second, which can produce nausea, vomiting, and vertigo. Convulsions and unconsciousness are possible. Proper scanning techniques at night can prevent flicker vertigo.

Night Landing Illusions

Above featureless terrain at night, there is a natural tendency to fly a lower`than-normal approach. Rain, haze, or a dark runway environment can also cause low approaches. Regularly spaced lights along a road or highway can appear to be runway lights

Have a plan for night flight before departure. Study the area, and know how to navigate your way through areas that may pose a problem at night. Always consider safer alternatives rather than hope things will work out by taking a chance.

Enhanced Night Vision Systems

A Synthetic Vision System (SVS) is an electronic means to display a synthetic vision image of the external scene topography, which enhances pilot awareness of spatial position relative to important features in all visibility conditions.

Enhanced Vision (EV) or Enhanced Flight Vision System (EFVS) is an electronic means to provide a display of the external scene by use of an imaging sensor, such as a Forward-Looking InfraRed (FLIR) or millimeter wave radar (MMWR).

---

Commercial Pilot & Flight Instructor Test Questions