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Fatigue and Flying
2010-03-18

Fatigue and Flying

Acute fatigue occurs when a long period passes with a lack of sleep. Chronic fatigue occurs when several acute fatigue periods occur without adequate recovery time between. While some fatigue is related to lack of sleep, not all is. Fatigue can result from inadequate nutrition and over exertion. More information needs to be obtained on fatigue distinguished from sleep as a factor in accidents.

Some factors of physical condition are controllable and some are not. Acute fatigue occurs when a long period passes with a lack of sleep. Chronic fatigue occurs when several acute fatigue periods occur without adequate recovery time between. Stress is the result of events causing preoccupation, reducing external awareness, and making activities subject to distraction. Stress causes the taking of risks that would otherwise be unacceptable. The mental/physical condition resulting from fatigue and stress may cause the pilot to make unwise decisions.

There are many causes of fatigue: lack of sleep, hypoxia, noise, time zone factors, temperature extremes, dehydration, stress and more. When you are fatigued you are more irritable and easily annoyed, you will suffer for lapses in short term memory, your attention will fixate to the exclusion of all else, your performance skills will decrease and you will be unaware of any impairment.

The causes of fatigue are primarily lack of recent sleep or a chronic sleep deficiency. Additional fatigue arises from our physiological reaction to noise and vibration, illness, hunger, caffeine "down time", unresolved stress, hypoxia, dehydration, errors in judgment and extended mental/physical demands.

What to Expect from Fatigue
Reduced vigilance
Increased temper excursions
Reduced ability to concentrate
Reduce awareness of deviations
Increased rationalization of errors
Increase in ‘know-better’ mistakes
Fatigue increases if you are "doing nothing"
Reduced comprehension of ATC instructions

Subtle Fatigue

This problem often begins with a distraction that causes fixation on an instrument or occurrence. Complex flight operations are the first skills to deteriorate.

Silence prevails
Seat posture relaxes
Bad judgment prevails
Instruments are ignored
Attention and vision fixates
Eye/hand skills begin to fail
Writing becomes less linear
Heading excursions take place
Movements decrease and slow
Clearances cannot be copied in total
Knowing where you are becomes a problem
Pilot accepts what exists as O.K. without checking
External references begin to fade from consciousness

Sleep

The most common cause of diminished alertness and proficiency is lack of sleep. This condition is said to affect 30% of the U.S. population. This may be due to an actual loss of sleep or a change in a sleep pattern called the circadian rhythm. Pilots tend to neglect their need for sleep. The need for sleep is a defining limit to pilot mental capability. You must have sleep or your mind will fail. Once beyond the limit pilot performance deteriorates and can become irrational. Sleep is a restorative and can be both stored and deprived within limits set by the biological clock of the individual. As you grow older you will need less sleep. Jet lag sleep patterns are worse when flying from west to east. Accident rates climb precipitously when your body begins demanding sleep. The average American gets about one hour too little sleep each night.

Accident rates rise in the afternoon and become significant at night. Postponing sleep causes a sleep deficit that as it increases an accident becomes more likely. Jet lag is a type of sleep deficit. A sleep deficit can best be resolved by going to bed early, not by sleeping late. A large deficit cannot be made up in one night. 21% of aircraft accidents cite sleep deficiency as a factor.

When drowsiness occurs you cease to monitor the instruments. You will tend to fixate and drift off mentally. We go into a mental autopilot not thinking of what we are doing. This is the lowest level of alertness. The next level of alertness is one in which you are in constant search-and-scan, seeing what you are looking at, hearing what is said and asking question. This is the flying" mode from pre-flight to shutdown. This gradual deterioration of alertness is best observed in watching others. It can creep up on you and influence your flying without your even noticing. Your alertness rises again when you have located a problem. You focus on it and prepare to execute a solution. This might occur when required to make a crosswind landing. The highest level of alertness is when adrenaline begins to flow and survival becomes a factor.

Medicine

Any over-the-counter medication whose name ends in "ine" should be checked in a flight medical examiner for use before flying. Beware of any medicine that is supposed to make you feel better. At altitude the effects may be damaging to flight safety.

Medicine taken is just as likely, even more likely, to be the basis for grounding a pilot than is the ailment itself. Medicinal side effects are both variable and unpredictable. Virtually all medications have side effects. Never take a medication for the first time and then fly. Make the safe decision if you are sick.

Carbon Monoxide

Is poisoning due to the exhaust fumes resulting from carbon burning with insufficient oxygen to produce complete oxidation. The resulting gas has one atom of carbon and one atom of oxygen. CO is odorless, colorless and cannot be tasted. CO poisoning may not be distinguished from fatigue or hypoxia except that the occurrence can occur at any altitude. Engine exhaust in an aircraft has 7% CO. Very small amounts of CO over a period of time will reduce a pilot’s ability to fly safely. It is the length of exposure as well as the amount that makes the critical difference. Susceptibility to CO poisoning increases with altitude due to the propensity of CO to enter blood. CO is 200 times more attracted to the blood hemoglobin as is oxygen. As little as one part CO to 20,000 (.005%) parts of air is enough to begin the death process of the brain.

Above 10% CO poisoning you will suffer from a headache. Above 20% you will be sleepy and sick to your stomach, HEADACHE, vision and speech problems. You will be incapacitated above 40% and dead at 70%. If you get a headache while flying, open the window and shut off heater.

CO reduces ability of blood to carry oxygen. Symptoms are similar to hypoxia. Headache, drowsiness, dizziness should initially be corrected by opening outside air vents. CO has a half-life in your body of about five hours. It will take a full day to recover. 70% of exhaust system failures result in CO poisoning. CO prevents the hemoglobin from both carrying and releasing oxygen. Antihistamines, alcohol, lack of sleep, or blood deficiency will exacerbate CO poisoning. Prevention of CO poisoning is directly preventable by proper aircraft maintenance. Club aircraft require extra alertness. You might suspect CO exists in your cabin air as soon as you smell some engine exhaust fumes.

Descend
Land ASAP
Use any oxygen
Shut off the heater
Get medical treatment
When in doubt, get on the ground.

Cold Weather

Hot or cold temperatures affect the quality of the preflight. In the winter, as your body cools you tend to mentally and physically slow down. Flying in an unheated aircraft in the winter will drastically decrease your flying efficiency and effectiveness.

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