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Aviation Medical Factors

in Human Factors

A “go/no-go” decision based on a pilot’s medical factors is made before each flight. The pilot should not only preflight check the aircraft, but also himself or herself before every flight. A pilot should ask, “Can I pass my medical examination right now?” If the answer is not an absolute “yes,” do not fly. This is especially true for pilots embarking on flights in IMC. Instrument flying is much more demanding than flying in VMC, and peak performance is critical for the safety of flight.

Pilot performance can be seriously degraded by both prescribed and over-the-counter medications, as well as by the medical conditions for which they are taken. Many medications, such as tranquilizers, sedatives, strong pain relievers, and cough suppressants, have primary effects that impair judgment, memory, alertness, coordination, vision, and the ability to make calculations. Others, such as antihistamines, blood pressure drugs, muscle relaxants, and agents to control diarrhea and motion sickness, have side effects that impair the same critical functions. Any medication that depresses the nervous system, such as a sedative, tranquilizer, or antihistamine, makes a pilot much more susceptible to hypoxia.

Title 14 of the Code of Federal Regulations (14 CFR) prohibits pilots from performing crewmember duties while using any medication that affects the faculties in any way contrary to safety. The safest rule is not to fly as a crewmember while taking any medication, unless approved to do so by the Federal Aviation Administration (FAA). If there is any doubt regarding the effects of any medication, consult an Aviation Medical Examiner (AME) before flying.


14 CFR part 91 prohibits pilots from performing crewmember duties within 8 hours after drinking any alcoholic beverage or while under the influence. Extensive research has provided a number of facts about the hazards of alcohol consumption and flying. As little as one ounce of liquor, one bottle of beer, or four ounces of wine can impair flying skills and render a pilot much more susceptible to disorientation and hypoxia. Even after the body completely metabolizes a moderate amount of alcohol, a pilot can still be impaired for many hours. There is simply no way of increasing the metabolism of alcohol or alleviating a hangover.


Fatigue is one of the most treacherous hazards to flight safety, as it may not be apparent to a pilot until serious errors are made. Fatigue can be either acute (short-term) or chronic (long-term).

Acute Fatigue

A normal occurrence of everyday living, acute fatigue is the tiredness felt after long periods of physical and mental strain, including strenuous muscular effort, immobility, heavy mental workload, strong emotional pressure, monotony, and lack of sleep. Adequate rest, regular exercise, and proper nutrition prevent acute fatigue.

Indications of fatigue are generally subtle and hard to recognize because the individual being assessed is generally the person making the assessment, as in single pilot operations. Therefore, the pilot must look at small errors that occur to provide an indication of becoming fatigued.

These include:

  • Misplacing items during the preflight;
  • Leaving material (pencils, charts) in the planning area;
  • Missing radio calls;
  • Answering calls improperly (read-backs); and
  • Improper tuning of frequencies.
Chronic Fatigue

Chronic fatigue occurs when there is not enough time for a full recovery from repeated episodes of acute fatigue. Chronic fatigue’s underlying cause is generally not “rest-related” and may have deeper points of origin. Therefore, rest alone may not resolve chronic fatigue.

Chronic fatigue is a combination of both physiological problems and psychological issues. Psychological problems such as financial, home life, or job related stresses cause a lack of qualified rest that is only resolved by mitigating the underpinning problems. Without resolution, performance continues to fall off, judgment becomes impaired, and unwarranted risks are taken. Recovery from chronic fatigue requires a prolonged and deliberate solution. In either case, unless adequate precautions are taken, personal performance could be impaired and adversely affect pilot judgment and decision-making.

IMSAFE Checklist

The following checklist, IMSAFE, is intended for a pilot’s personal preflight use. A quick check of the items on this list will help a pilot make a good self-evaluation prior to any flight. If the answer to any of the checklist questions is yes, then the pilot should consider not flying.


Do I have any symptoms?


Have I been taking prescription or over-the-counter drugs?


Am I under psychological pressure from the job? Do I have money, health, or family problems?


Have I been drinking within 8 hours? Within 24 hours?


Am I tired and not adequately rested?


Have I eaten enough of the proper foods to keep adequately nourished during the entire flight?


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