Updated: Mar 12

Aeromedical Factors Lesson by wifiCFI

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Lesson Contents

Medical Certificates >

Hypoxia >

Hyperventilation >

Middle Ear and Sinus Congestion >

Spatial Disorientation >

Vestibular Illusions >

Visual Illusions >

Motion Sickness >

Carbon Monoxide Poisoning >

Stress >

Fatigue >

Alcohol and Drugs >

DCS and Scuba Diving >

IMSAFE Checklist >

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Medical Certificates (FAR 61.23)

Pilots must have a medical certificate, with few exceptions (gliders), to exercise the privileges of their airmen certificates.

However, once you obtain a medical you still must comply with FAR 61.53 which states “a pilot cannot act as a crewmember on an aircraft if they know, or have reason to know, of any medical condition that would make them unsafe to operate an aircraft.”

Medical certificates are issued after a routine medical exam. The exam is conducted by an FAA designated doctor called an Aviation Medical Examiner (AME).

Where can you find a list of AMEs in your area?

A student pilot must obtain a medical certificate prior to solo flight operations.

1st class medical (FAR 61.23)


Must have a 1st class medical to exercise the privileges of an ATP certificate

Privilege Durations

>40 years old = 6 calendar months

<40 years old = 12 calendar months

2nd class medical (FAR 61.23)


Must have a 2nd class medical to exercise the privileges of a CAX certificate

Privilege Durations

>40 years old = 12 calendar months

<40 years old = 12 calendar months

3rd class medical (FAR 61.23)


Must have a 3rd class medical to perform solo flight as a student, act as PIC with a PPL, or to take a checkride exam for any pilot certificate.

Privilege Durations

>40 years old = 24 calendar months

<40 years old = 60 calendar months

Medical certificate example (FAR 61.23)

Ex. A 42 year old gentleman provides you with a 1st class medical certificate. The certificate is 18 months old. 

Which class is the medical certificate?

Still a 1st class medical. The privileges may change but the class never changes.

Which privileges are still valid?

3rd class privileges are now valid.


This gentleman’s 1st class medical was valid with 1st class privileges for 6 months. It then reverted to a 1st class medical with 2nd class privileges for the next 6 months, and is now a 1st class medical with 3rd class privileges for the final 12 months of its duration.

There are several conditions that would disqualify an individual from obtaining a medical certificate. Whenever you are unsure, contact your local AME.

However, if you provide documentation to the FAA you may be able to obtain a “Special Issuance Authorization.”

A SODA “Statement of Demonstrated Ability” may be available when working through an AME or the local FSDO (Flight Standards District Office). These SODAs will usually contain certain operating limitations.

Aeromedical Factors (PHAK C17)

Overview of topics:



Middle ear and sinus problems

Spatial Disorientation

Motion Sickness

Carbon Monoxide Poisoning

Fatigue and Stress


Hypoxia (PHAK C17)

Hypoxia means “reduced oxygen” or “not enough oxygen.” 

Although any tissue will die if deprived of oxygen long enough, the greatest concern regarding hypoxia during flight is lack of 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 several factors, including an insufficient supply of oxygen, inadequate transportation of oxygen, or the inability of the body tissues to use oxygen. 

There are 4 types of hypoxia that will be covered in the following slides.

Hypoxic Hypoxia (PHAK C17)

Hypoxic hypoxia is a result of insufficient oxygen available to the body as a whole. 

A blocked airway and drowning are obvious examples of how the lungs can be deprived of oxygen, 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 an aircraft ascends during flight, the percentage of each gas in the atmosphere remains the same, but there are fewer molecules available at the pressure required for them to pass between the membranes in the respiratory system. 

This decrease in number of oxygen molecules at sufficient pressure can lead to hypoxic hypoxia.

Not enough oxygen in the environment around you.

Hypemic Hypoxia (PHAK C17)

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.” 

This type of hypoxia is a result of oxygen deficiency in the blood, rather than a lack of inhaled oxygen, and can be caused by a variety of factors. 

It may be due to reduced blood volume (from severe bleeding), or it may result from certain blood diseases, such as anemia. 

More often, hypemic hypoxia occurs because hemoglobin, the actual blood molecule that transports oxygen, is chemically unable to bind oxygen molecules. 

The most common form of hypemic hypoxia is CO poisoning.

CO Blocks O2 From Attaching to Blood Cells.

Stagnant Hypoxia (PHAK C17)

Stagnant means “not flowing,” and stagnant hypoxia or ischemia results when the oxygen-rich blood in the lungs is not moving, for one reason or another, to the tissues. 

An arm or leg “going to sleep” because the blood flow has accidentally been shut off is one form of stagnant hypoxia. 

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).

Blood Not Flowing.

Histotoxic Hypoxia (PHAK C17)

The inability of the cells to effectively use oxygen is defined as histotoxic hypoxia. “Histo” refers to tissues or cells, and “toxic” means poisonous. 

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.

Brain Tissue Rejecting O2.

Hypoxia symptoms (PHAK C17)

Cyanosis (blue fingernails and lips)


Decreased response times

Impaired judgement


Visual impairment


Dizzy sensations


Tingling in fingers and toes

Hypoxia corrective actions (PHAK C17)

Descend to a lower altitude

Stop pulling G’s

Put on an O2 mask

Hyperventilation (PHAK C17)

Hyperventilation is the excessive rate and depth of respiration leading to abnormal loss of carbon dioxide from the blood. 

This condition occurs more often among pilots than is generally recognized

The treatment for hyperventilation involves restoring the proper carbon dioxide level in the body. 

Breathing normally is both the best prevention and the best cure for hyperventilation. 

In addition to slowing the breathing rate, breathing into a paper bag or talking aloud helps to overcome hyperventilation. 

Recovery is usually rapid once the breathing rate is returned to normal.

Middle Ear and Sinus (PHAK C17)

During climbs and descents, the free gas formerly present 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 escape of the expanded gas is impeded, pressure builds up within the cavity and pain is experienced. 

Trapped gas expansion accounts for ear pain and sinus pain, as well as a temporary reduction in the ability to hear. 

Spatial Disorientation (PHAK C17)

Spatial disorientation specifically refers to the lack of orientation with regard to the position, attitude, or movement of the airplane in space.

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 

Visual System—eyes, which sense position based on what is seen

Vestibular Illusions (PHAK C17)

The Leans

A condition called the leans, is the most common illusion during flight and is caused by a sudden return to level flight following a gradual and prolonged turn that went unnoticed by the pilot.

Coriolis Illusion

This 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. 

A movement of the head in a different plane, such as looking at something in a different part of the flight deck, may set the fluid moving, creating the illusion of turning or accelerating on an entirely different axis.

Graveyard Spiral

As in other illusions, a pilot in a prolonged coordinated, constant-rate turn may experience the illusion of not turning. 

During the recovery to level flight, the pilot will then experience the sensation of turning in the opposite direction causing the disoriented pilot to return the aircraft to its original turn. 

Because an aircraft tends to lose altitude in turns unless the pilot compensates for the loss in lift, the pilot may notice a loss of altitude.

Somatogravic Illusion

A rapid acceleration, such as experienced during takeoff, stimulates the otolith organs in the same way as tilting the head backwards. 

This action may create what is known as the “somatogravic illusion” of being in a nose-up attitude, especially in conditions with poor visual references. 

Inversion Illusion

An abrupt change from climb to straight-and-level flight can stimulate the otolith organs enough to create the illusion of tumbling backwards, known as “inversion illusion.” 

Elevator Illusion

An abrupt upward vertical acceleration, as can occur in an updraft, can stimulate the otolith organs to create the illusion of being in a climb. 

This is known as “elevator illusion.” 

An abrupt downward vertical acceleration, usually in a downdraft, has the opposite effect with the disoriented pilot pulling the aircraft into a nose-up attitude.

Visual Illusions (PHAK C17)

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, or “false horizon,” when attempting to align the aircraft with the actual horizon.


When flying in the dark, a stationary light may appear to move if it is stared at for a prolonged period of time.

Runway Width Illusion

A narrower-than-usual runway can create an illusion that the aircraft is at a higher altitude than it actually is, especially when runway length-to-width relationships are comparable.

A wider-than usual runway can have the opposite effect with the risk of the pilot leveling out the aircraft high and landing hard or overshooting the runway.

Runway Slope 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.

Featureless Terrain

An absence of surrounding ground features, as in an overwater approach over darkened areas or terrain made featureless by snow, can create an illusion that 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.

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.


Atmospheric haze can create an illusion of being at a greater distance and height from the runway.


Flying into fog can create an illusion of pitching up.

Ground Lighting

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. 

Motion Sickness (PHAK C17)

Motion sickness, or airsickness, is caused by the brain receiving conflicting messages about the state of the body. A pilot may experience motion sickness during initial flights, but it generally goes away within the first few lessons. 

Combating Motion Sickness:

Fly straight and level

Increase cool airflow

Have brown bags at the ready

Let student lightly place hands on the controls

Carbon Monoxide Poisoning (PHAK C17)

CO (Carbon Monoxide) is a colorless and odorless gas produced by all internal combustion engines. 

Attaching itself to the hemoglobin in the blood about 200 times more easily than oxygen, CO prevents the hemoglobin from carrying oxygen to the cells, resulting in hypemic hypoxia.

Where does it come from?

Typically from the aircraft heater.

How to combat CO poisoning?

Turn off heater and open windows. Find a close, suitable place to land.

Symptoms of Carbon Monoxide Poisoning:


Blurred Vision



Loss of muscle power

Stress (PHAK C17)

Stress is the body’s response to physical and psychological demands placed upon it.

Stress falls into two broad categories: acute (short term) and chronic (long term).


Involves an immediate threat that is perceived as danger. This is the type of stress that triggers a “fight or flight” response in an individual, whether the threat is real or imagined.


Chronic stress can be defined as a level of stress that presents an intolerable burden, exceeds the ability of an individual to cope, and causes individual performance to fall sharply. 

Fatigue (PHAK C17)

Fatigue is frequently associated with pilot error. Some of the effects of fatigue include degradation of attention and concentration, impaired coordination, and decreased ability to communicate. These factors seriously influence the ability to make effective decisions. 


Acute fatigue is short term and is a normal occurrence in everyday living. It is the kind of tiredness people feel after a period of strenuous effort, excitement, or lack of sleep.


Chronic fatigue, extending over a long period of time, usually has psychological roots, although an underlying disease is sometimes responsible. Continuous high-stress levels produce chronic fatigue.

Alcohol (PHAK C17)

Alcohol impairs the efficiency of the human body. 

Studies have shown that consuming alcohol is closely linked to performance deterioration. 

Pilots must make hundreds of decisions, some of them time-critical, during the course of a flight. 

The safe outcome of any flight depends on the ability to make the correct decisions and take the appropriate actions during routine occurrences, as well as abnormal situations.

Rules: (FAR 91.17)

8 hours from bottle to throttle

.04% BAC max

No flying while hungover (under the influence)

Drugs (PHAK C17)

14 CFR part 91, section 91.17 prohibits the use of any drug that affects the person’s faculties in any way contrary to safety.

DCS and Scuba Diving (PHAK C17)


Decompression sickness (DCS) describes a condition characterized by a variety of symptoms resulting from exposure to low barometric pressures that cause inert gases (mainly nitrogen), normally dissolved in body fluids and tissues, to come out of physical solution and form bubbles.

Scuba Diving

Scuba diving subjects the body to increased pressure, which allows more nitrogen to dissolve in body tissues and fluids. 

Scuba Diving Wait Times (AIM 8-1-4)


Always perform the IMSAFE checklist prior to each flight.

I- Illness

M- Medication

S- Stress

A- Alcohol

F- Fatigue

E- Eating/Emotion

FAA Sources Used for this Lesson

14 CFR Part 61

14 CFR Part 91

Pilot’s Handbook of Aeronautical Knowledge (PHAK) Chapter 17

Aeronautical Information Manual (AIM)

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