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Spatial Disorientation in Aviation

Spatial Orientation

Spatial Orientation is our natural ability to maintain our body orientation and/or posture in relation to the surrounding environment (physical space) at rest and

during motion. Genetically speaking, humans are designed to maintain spatial orientation on the ground. The three-dimensional environment of flight is unfamiliar to the human body, creating sensory conflicts and illusions that make spatial orientation difficult, and sometimes impossible to achieve. Statistics show that between 5 to 10% of all general aviation accidents can be attributed to spatial disorientation, 90% of which are fatal.

Spatial Orientation in Flight

Spatial orientation in flight is difficult to achieve because numerous sensory stimuli (visual, vestibular, and proprioceptive) vary in magnitude, direction, and frequency. Any differences or discrepancies between visual, vestibular, and proprioceptive sensory inputs result in a sensory mismatch that can produce illusions and lead to spatial disorientation. Good spatial orientation relies on the effective perception, integration and interpretation of visual, vestibular (organs of equilibrium located in the inner ear) and proprioceptive (receptors located in the skin, muscles, tendons, and joints) sensory information.

Vestibular Aspects of Spatial Orientation

The inner ear contains the vestibular system, which is also known as the organ of equilibrium. About the size of an pencil eraser, the vestibular system contains two distinct structures: the semicircular canals, which detect changes in angular acceleration, and the otolith organs (the utricule and the saccule), which detect changes in linear acceleration and gravity. Both the semicircular canals and the otolith organs provide information to the brain regarding our body’s position and movement. A connection between the vestibular system and the eyes helps to maintain balance and keep the eyes focused on an object while the head is moving or while the body is rotating.

The Semicircular Canals

The semicircular canals are three half-circular, interconnected tubes located inside each ear that are the equivalent of three gyroscopes located in three planes perpendicular (at right angles) to each other. Each plane corresponds to the rolling, pitching, or yawing motions of an aircraft.

Each canal is filled with a fluid called endolymph and contains a motion sensor with little hairs whose ends are embedded in a gelatinous structure called the cupula. The cupula and the hairs move as the fluid moves inside the canal in response to an angular acceleration.

The movement of the hairs is similar to the movement of seaweed caused by ocean currents or that of wheat fields moved by wind gusts. When the head is still and the airplane is straight and level, the fluid in the canals does not move and the hairs stand straight up, indicating to the brain that there is no rotational acceleration (a turn).

If you turn either your aircraft or your head, the canal moves with your head, but the fluid inside does not move because of its inertia. As the canal moves, the hairs inside also move with it and are bent in the opposite direction of the acceleration by the stationary fluid (A). This hair movement sends a signal to the brain to indicate that the head has turned. The problem starts when you continue turning your aircraft at a constant rate (as in a coordinated turn) for more than 20 seconds.

In this kind of turn, the fluid inside the canal starts moving initially, then friction causes it to catch up with the walls of the rotating canal (B). When this happens, the hairs inside the canal will return to their straight up position, sending an erroneous signal to the brain that the turn has stopped–when, in fact, the turn continues.

If you then start rolling out of the turn to go back to level flight, the fluid inside the canal will continue to move (because of its inertia), and the hairs will now move in the opposite direction (C), sending an erroneous signal to the brain indicating that you are turning in the opposite direction, when in fact, you are actually slowing down from the original turn.

Vestibular Illusions

(Somatogyral – Semicircular Canals)

Illusions involving the semicircular canals of the vestibular system occur primarily under conditions of unreliable or unavailable external visual references and
result in false sensations of rotation. These include the Leans, the Graveyard Spin and Spiral, and the Coriolis Illusion.

The Leans

This 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. The reason a pilot can be unaware of such a gradual turn is that human exposure to a rotational acceleration of 2 degrees per second or lower is below the detection threshold of the semicircular canals. Leveling the wings after such a turn may cause an illusion that the aircraft is banking in the opposite direction. In response to such an illusion, a pilot may lean in the direction of the original turn in a corrective attempt to regain the perception of a correct vertical posture.

The Graveyard Spin

This is an illusion that can occur to a pilot who intentionally or unintentionally enters a spin.

For example, a pilot who enters a spin to the left will initially have a sensation of spinning in the same direction. However, if the left spin continues the pilot will have the sensation that the spin is progressively decreasing. At this point, if the pilot applies right rudder to stop the left spin, the pilot will suddenly sense a spin in the opposite direction (to the right). If the pilot believes that the airplane is spinning to the right, the response will be to apply left rudder to counteract the sensation of a right spin. However, by applying left rudder the pilot will unknowingly re-enter the original left spin. If the pilot cross checks the turn indicator, he/she would see the turn needle indicating a left turn while he/she senses a
right turn. This creates a sensory conflict between what the pilot sees on the instruments and what the pilot feels. If the pilot believes the body sensations instead of trusting the instruments, the left spin will continue. If enough altitude is lost before this illusion is recognized and corrective action is taken, impact with terrain is inevitable.

The Graveyard Spiral

Graveyard Spiral is more common than the Graveyard Spin, and it is associated with a return to level flight following an intentional or unintentional prolonged

bank turn. For example, a pilot who enters a banking turn to the left will initially have a sensation of a turn in the same direction. If the left turn continues (~20 seconds or more), the pilot will experience the sensation that the airplane is no longer turning to the left. At this point, if the pilot attempts to level the wings this action will produce a sensation that the airplane is turning and banking in the opposite direction (to the right). If the pilot believes the illusion of a right turn (which can be very compelling), he/she will reenter the original left turn in an attempt to counteract the sensation of a right turn. Unfortunately, while this is happening, the airplane is still turning to the left and losing altitude. Pulling the control yoke/stick and applying power while turning would not be a good idea–because it would only make the left turn tighter. If the pilot fails to recognize the illusion and does not level the wings, the airplane will continue turning left and losing altitude until it impacts the ground.

The Coriolis

Coriolis Illusion involves the simultaneous stimulation of two semicircular canals and is associated with a sudden tilting (forward or backwards) of the pilot’s head
while the aircraft is turning. This can occur when you tilt you head down (to look at an approach chart or to write a note on your knee pad), or tilt it up (to look
at an overhead instrument or switch) or tilt it sideways. This produces an almost unbearable sensation that the aircraft is rolling, pitching, and yawing all at the same time, which can be compared with the sensation of rolling down on a hillside. This illusion can make the pilot quickly become disoriented and lose control of the aircraft.

The Otolith Organs

Two otolith organs, the saccule and utricle, are located in each ear and are set at right angles to each other.

The utricle detects changes in linear acceleration in the horizontal plane, while the saccule detects gravity changes in the vertical plane. However, the inertial forces resulting from linear accelerations cannot be distinguished from the force of gravity; therefore, gravity can also produce stimulation of the utricle and saccule. These organs are located at the base (vestibule) of the semicircular canals, and their structure consists of small sacs (maculas) covered by hair cell filaments that project into an overlying gelatinous membrane (cupula) tipped by tiny, chalk-like calcium stones called otoconia.

Change in Gravity

When the head is tilted, the weight of the otoconia of the saccule pulls the cupula, which in turn bends the hairs that send a signal to the brain indicating that the

head has changed position.

A similar response will occur during a vertical take-off in a helicopter or following the sudden opening of a parachute after a free fall.

Change in Linear Acceleration

The inertial forces resulting from a forward linear acceleration (take-off, increased acceleration during level flight, vertical climb) produce a backward displacement of the otoconia of the utricle that pulls the cupula, which in turn bends the haircell filaments that send a signal to the brain, indicating that the head and body have suddenly been moved forward. Exposure to a backward linear acceleration, or to a forward linear decceleration has the opposite effect.

Vestibular Illusions

(Somatogravic – Utricle and Saccule) Illusions

These illusions involving the utricle and the saccule of the vestibular system are most likely under conditions with unreliable or unavailable external visual references. These illusions include: the Inversion Illusion, Head-Up Illusion, and Head-Down Illusion.

The Inversion Illusion

This illusion involves a steep ascent (forward linear acceleration) in a high-performance aircraft, followed by a sudden return to level flight. When the pilot levels off, the aircraft’s speed is relatively higher. This combination of accelerations produces an illusion that the aircraft is in inverted flight. The pilot’s response to this illusion is to lower the nose of the aircraft.

The Head-Up Illusion

The Head-up Illusion involves a sudden forward linear acceleration during level flight where the pilot perceives the illusion that the nose of the aircraft is pitching up.

The pilot’s response to this illusion would be to push the yolk or the stick forward to pitch the nose of the aircraft down. A night take-off from a well-lit airport into a totally dark sky (black hole) or a catapult take-off from an aircraft carrier can also lead to this illusion, and could result in a crash.

The Head-Down Illusion

This illusion  involves a sudden linear deceleration (air braking, lowering flaps, decreasing engine power) during level flight where the pilot perceives the illusion that the nose of the aircraft is pitching down.

The pilot’s response to this illusion would be to pitch the nose of the aircraft up. If this illusion occurs during a low-speed final approach, the pilot could stall the aircraft. The Proprioceptive Receptors The proprioceptive receptors (proprioceptors) are special sensors located in the skin, muscles, tendons, and joints that play a very small role in maintaining spatial orientation in normal individuals. Proprioceptors do give some indication of posture by sensing the relative position of our body parts in relation to each other, and by sensing points of physical contact between body parts and the surrounding environment (floor, wall, seat, arm rest, etc.). For example, proprioceptors make it possible for you to know that you are seated while flying; however, they alone will not let you differentiate between flying straight and level and performing a coordinated turn.

How to Prevent Spatial Disorientation

The following are basic steps that should help prevent spatial disorientation:

  • Take the opportunity to experience spatial disorientation illusions in a Barany chair, a Vertigon, a GYRO, or a Virtual Reality Spatial Disorientation
    Demonstrator.
  • Before flying with less than 3 miles visibility, obtain training and maintain proficiency in airplane control by reference to instruments.
  • When flying at night or in reduced visibility, use the flight instruments.
  • If intending to fly at night, maintain night-flight currency. Include cross-country and local operations at different airports.
  • If only Visual Flight Rules-qualified, do not attempt visual flight when there is a possibility of getting trapped in deteriorating weather.
  • If you experience a vestibular illusion during flight, trust your instruments and disregard your sensory perceptions. Spatial Disorientation and Airsickness. It is important to know the difference between spatial disorientation and airsickness. Airsickness is a normal response of healthy individuals when exposed to a flight environment characterized by unfamiliar motion and orientation clues. Common signs and symptoms of airsickness include: vertigo, loss of appetite, increased salivation and swallowing, burping, stomach awareness, nausea, retching, vomiting, increased need for bowel movements, cold sweating, skin pallor, sensation of fullness of the head, difficulty concentrating, mental confusion, apathy, drowsiness, difficulty focusing, visual flashbacks, eye strain, blurred vision, increased yawning, headache, dizziness, postural instability, and increased fatigue.

Th
e symptoms are usually progressive. First, the desire for food is lost. Then, as saliva collects in the mouth, the person begins to perspire freely, the head aches, and the airsick person may eventually become nauseated and vomit. Severe airsickness may cause a pilot to become completely incapacitated. Although airsickness is uncommon among experienced pilots, it does occur occasionally (especially among student pilots). Some people are more susceptible to airsickness than others. Fatigue, alcohol, drugs, medications, stress, illnesses, anxiety, fear, and insecurity are some factors that can increase individual susceptibility to motion sickness of any type. Women have been shown to be more susceptible to motion sickness than men of any age. In addition, reduced mental activity (low mental workload) during exposure to an unfamiliar motion has been implicated as a predisposing factor for airsickness.

A pilot who concentrates on the mental tasks required to fly an aircraft will be less likely to become airsick because his/ her attention is occupied. This explains why sometimes a student pilot who is at the controls of an aircraft does not get airsick, but the experienced instructor who is only monitoring the student unexpectedly becomes airsick.

A pilot who has been the victim of airsickness knows how uncomfortable and impairing it can be. Most importantly, it jeopardizes the pilot’s flying proficiency and safety, particularly under conditions that require peak piloting skills and performance (equipment malfunctions, instrument flight conditions, bad weather, final approach, and landing). Pilots who are susceptible to airsickness should not take anti-motion sickness medications (prescription or over the- counter). These medications can make one drowsy or affect brain functions in other ways. Research has shown that most anti-motion sickness medications cause a temporary deterioration of navigational skills or other tasks demanding keen judgment.

An effective method to increase pilot resistance to airsickness consists of repetitive exposure to the flying conditions that initially resulted in airsickness. In other words, repeated exposure to the flight environment decreases an individual’s susceptibility to subsequent airsickness. If you become airsick while piloting an aircraft, open the air vents, loosen your clothing, use supplemental oxygen, keep your eyes on a point outside the aircraft, place your head against the seat’s headrest, and avoid unnecessary head movements. Then, cancel the flight, and land as soon as possible.

FAA Aeromedical Training Programs for Civil Aviation Pilots

Physiological Training Course

The Civil Aerospace Medical Institute offers a 1-day training course to familiarize civil aviation pilots and flight crews with the physiological and psychological stressors of flight. Classroom training subjects include spatial disorientation, oxygen equipment, hypoxia, trapped gas, and decompression sickness.

Demonstrations

Spatial disorientation demonstrators provide pilots the experience of vestibular and visual illusions in a safe, ground-based environment–and they teach ways to avoid spatial disorientation while flying. Also, a ground-based altitude chamber flight offers a practical demonstration of rapid decompression and hypoxia. For information and scheduling, call (405) 954-4837, or check the FAA Web site: http://www.faa.gov/pilots/training/airman_education/aerospace_physiology/index.cfm

Medical Facts for Pilots Publication: AM-400-03/1 Written by: Melchor J. Antunano, M.D. Prepared by Federal Aviation Administration Civil Aerospace Medical Institute Aerospace Medical Education Division

Fatigue in Aviation

Fatigue is an expected and ubiquitous aspect of life. For the average individual, fatigue presents a minor inconvenience, resolved with a nap or by stopping whatever activity that brought it on. Typically, there are no significant consequences. However, if that person is involved in safety-related activities such as operating a motor vehicle, piloting an aircraft, performing surgery, or running a nuclear reactor, the consequences of fatigue can be disastrous.

Definition

Defining fatigue in humans is extremely difficult due to the large variability of causes. Causes of fatigue can range from boredom to circadian rhythm disruption to heavy physical exertion. In lay terms, fatigue can simply be defined as weariness. However, from an operational standpoint a more accurate definition might be: “Fatigue is a condition characterized by increased discomfort with lessened capacity for work, reduced efficiency of accomplishment, loss of power or capacity to respond to stimulation, and is usually accompanied by a feeling of weariness and tiredness.”

Two key concepts can be derived from this second definition.

  1. Fatigue can develop from a variety of sources. The important factor is not what causes the fatigue but rather the negative impact fatigue has on a person’s ability to perform tasks. A long day of mental stimulation such as studying for an examination or processing data for a report can be as fatiguing as manual labor. They may feel different—a sore body instead of a headache and bleary eyes—but the end effect is the same, an inability to function normally.
  2. Fatigue leads to a decrease in your ability to carry out tasks. Several studies have demonstrated significant impairment in a person’s ability to carry out tasks that require manual dexterity, concentration, and higher-order intellectual processing. Fatigue may happen acutely, which is to say in a relatively short time (hours) after some significant physical or mental activity. Or, it may occur gradually over several days or weeks. Typically, this situation occurs with someone who does not get sufficient sleep over a prolonged period of time (as with sleep apnea, jet lag, or shift work) or someone who is involved in ongoing physical or mental activity with insufficient rest.

Stressors

General aviation pilots are typically not exposed to the same occupational stresses as commercial pilots (i.e., long duty days, circadian disruptions from night flying or time zone changes, or scheduling changes). Nevertheless, they will still develop fatigue from a variety of other causes. Given the single-pilot operation and relatively higher workload, they would be just as much at risk (possibly even more) to be involved in an accident than a commercial crew. Any fatigued person will exhibit the same problems: sleepiness, difficulty concentrating, apathy, feeling of isolation, annoyance, increased reaction time to stimulus, slowing of higher-level mental functioning, decreased vigilance, memory problems, task fixation, and increased errors while performing tasks. None of these are good things to have happen to a pilot, much less if there is no one else in the aircraft to help out.

In a variety of studies, fatigued individuals consistently under-reported how tired they really were, as measured by physiologic parameters. A tired individual truly does not realize the extent of actual impairment. No degree of experience, motivation, medication, coffee, or will power can overcome fatigue.

Antidote to Fatigue

Obtaining adequate sleep is the best way to prevent or resolve fatigue. Sleep provides the body with a period of rest and recuperation. Insufficient sleep will result in significant physical and psychological problems. On average, a healthy adult does best with eight hours of uninterrupted sleep, but significant personal variations occur. For example, increasing sleep difficulties occur as we age, with significant shortening of nighttime sleep. A variety of medical conditions can influence the quality and duration of sleep. To name a few: sleep apnea, restless leg syndrome, certain medications, depression, stress, insomnia, and chronic pain. Some of the more common social or behavioral issues are: late-night activities, excessive alcohol or caffeine use, travel, interpersonal strife, uncomfortable or unfamiliar surroundings, and shift work.

Prevention

No one is immune from fatigue. Yet, in our society, establishing widespread preventive measures to combat fatigue is often a very difficult goal to achieve. Individuals, as well as organizations, often ignore the problem until an accident occurs. Even then, implementing lasting change is not guaranteed. Lifestyle changes are not easy for individuals, particularly if that person isn’t in complete control of the condition. For example, commercial pilots must contend with shift work and circadian rhythm disruption. Often, they also choose to commute long distances to work, so that by the time a work cycle starts they have already traveled for several hours.

While a general aviation pilot may not have to deal with this, a busy lifestyle or other issues may lead to fatigue. Therefore, general aviation pilots must make every effort to modify personal lifestyle factors that cause fatigue.

Lifestyle Recommendations

Don’t…

  • Consume alcohol or caffeine 3-4 hours before going to bed.
  • Eat a heavy meal just before bedtime.
  • Take work to bed.
  • Exercise 2-3 hours before bedtime. While working out promotes a healthy lifestyle, it shouldn’t be done too close to bedtime.
  • Use sleeping pills (prescription or otherwise).

Do…

  • Be mindful of the side effects of certain medications, even over-the-counter medications – drowsiness or impaired alertness is a concern.
  • Consult a physician to diagnose and treat any medical conditions causing sleep problems.
  • Create a comfortable sleep environment at home. Adjust heating and cooling as needed. Get a comfortable mattress.
  • When traveling, select hotels that provide a comfortable environment.
  • Get into the habit of sleeping eight hours per night. When needed, and if possible, nap during the day, but limit the nap to less than 30 minutes. Longer naps produce sleep inertia, which is counterproductive.
  • Try to turn in at the same time each day. This establishes a routine and helps you fall asleep quicker.
  • If you can’t fall asleep within 30 minutes of going to bed, get up and try an activity that helps induce sleep (watch non-violent TV, read, listen to relaxing music, etc).
  • Get plenty of rest and minimize stress before a flight. If problems preclude a good night’s sleep, rethink the flight and postpone it accordingly.

Sport Pilot

DEFINITION OF A LIGHT SPORT AIRCRAFT

14 CFR PART 1.1

Light-sport aircraft means an aircraft, other than a helicopter or powered-lift that, since its original certification, has continued to meet the following: 
(1) A maximum takeoff weight of not more than– (i) 1,320 pounds (600 kilograms) for aircraft not intended for operation on water; or (ii) 1,430 pounds (650 kilograms) for an aircraft intended for operation on water.
(2) A maximum airspeed in level flight with maximum continuous power (VH) of not more than 120 knots CAS under standard atmospheric conditions at sea level.
(3) A maximum never-exceed speed (VNE) of not more than 120 knots CAS for a glider.
(4) A maximum stalling speed or minimum steady flight speed without the use of lift-enhancing devices (VS1) of not more than 45 knots CAS at the aircraft’s maximum certificated takeoff weight and most critical center of gravity.

(5) A maximum seating capacity of no more than two persons, including the pilot.
(6) A single, reciprocating engine, if powered.
(7) A fixed or ground-adjustable propeller if a powered aircraft other than a powered glider.

(8) A fixed or auto-feathering propeller system if a powered glider.
(9) A fixed-pitch, semi-rigid, teetering, two-blade rotor system, if a gyroplane.
(10) A non-pressurized cabin, if equipped with a cabin.
(11) Fixed landing gear, except for an aircraft intended for operation on water or a glider.
(12) Fixed or retractable landing gear, or a hull, for an aircraft intended for operation on water.
(13) Fixed or retractable landing gear for a glider.

MEDICAL REQUIREMENTS FOR SPORT PILOT

(14 CFR part 61.23/53/303)

A Medical or U.S. Driver’s License (Other than Balloon or Glider)

A Student Pilot Seeking Sport Pilot Privileges in a Light-Sport Aircraft
A Pilot Exercising the Privileges of a Sport Pilot Certificate
A Flight Instructor Acting as PIC of a Light-Sport Aircraft

A Person Using a Current and Valid U.S. Driver’s License Must

Comply With Each Restriction and Limitation Imposed on Your Drivers License
Comply With Any Judicial or Administrative Order Applying to the Operation of a Motor Vehicle
Not Have Been Denied Your Most Recent Application for a Medical Certificate (If You Have Applied for Medical Certificate)
Not Have Your Most Recently Issued Medical Certificate Suspended or Revoked (If You Have Been Issued a Medical Certificate)
Not Had Your Most Recent Authorization for a Special Issuance of a Medical Certificate Withdrawn (A Special Issuance Is Not a Denial)

A Person Using a Valid Medical or Current and Valid U.S. Driver’s License Must

Not know or have reason to know of any medical condition that would make that person unable to operate a Light-Sport Aircraft in a safe manner.

If You Are a Flight Instructor and You Want to Train Sport Pilots and SP CFIs:

1. Hold a Current and Valid CFI (Valid Pilot Certificate, Meet Currency, Hold Appropriate Endorsements)
2. Appropriate Category and Class Ratings in LSA (5 hours PIC make and model within a “set” Additional Category and Class Privileges Endorsed in Logbook)

3. U.S Drivers License or FAA Medical (If acting as PIC)
4. Comply with all Sport Pilot CFI Privileges and Limits
5. Exercise CFI Privileges

How to Become a Sport Pilot

1. Meet Medical and Eligibility
2. Pass a FAA Sport Pilot Knowledge Test
3. Receive flight instruction in an appropriate aircraft.
4. Pass a FAA Sport Pilot Practical Test
5. Sport Pilot Certificate Issued (All Category and Class Privileges Endorsed in Logbook)

If you are a FAA Certificated Pilot and Want to Exercise Sport Pilot Privileges:

1. Hold at Least a Recreational Pilot Certificate (X-C Training if a Rec Pilot 61.101(c))
2. Hold Category and Class Ratings for the LSA Flying (Additional Category and Class Privileges Endorsed in Logbook)
3. U.S Drivers License or FAA Medical
4. Current Flight Review
5. 3 Takeoffs and Landings within 90 days (if carrying a passenger)
6. Operate only FAA Certificated LSA
7. Comply with all Sport Pilot Privileges and Limits
8. Exercise Sport Pilot Privileges

Circadian Rhythm Disruption and Aviation

It’s All About the Rhythm and Blues

Our body’s biological functions work much like a finely tuned watch: Every part works in unison to keep the body in homeostasis (maintenance of the internal environment within tolerable limits). However, when one working part doesn’t function normally, it tends to disrupt many other vital parts and can upset

homeostasis. Often, we bring disruptions on ourselves with such things as self-imposed stress, and then we must try to get everything back to normal. Managing your circadian rhythm is no different. It must be maintained to operate within normal working parameters, or a variety of negative effects will occur, and some of these could become a safety-of-flight issue.

An Internal Biological Clock

Our circadian rhythm is best described as an internal biological clock that regulates our body functions, based on our wake/sleep cycle. Circadian rhythms are not only important in determining sleep cycles but also in feeding patterns. There are clear patterns of brain wave activity, hormone production, cell regeneration, and other biological activities linked to these daily cycles.

Origin

Circadian rhythms are believed to have originated in the earliest cells, with the purpose of protecting replicating DNA from high ultraviolet radiation during the daytime. As a result, replication was relegated to the dark, and a basic pattern of day/night cycle was engrained within the cell and passed down to subsequent generations. At some time in the distant past, the days may have been longer, because when we are deprived of time clues, we gravitate toward a 25-hour circadian cycle.

The Internal Works of Our Biological Watch

In your brain, there is a type of “pacemaker” located within the suprachiasmatic nuclei. This area regulates the firing of nerve cells that seem to control your circadian rhythm. Scientists can’t explain precisely how this area in your brain “keeps time.” They do know your brain relies on “outside” influences called zeitgebers (German for time givers) to keep it on a normal schedule. The most obvious zeitgeber is daylight. When daylight hits your eyes, cells in the retinas signal your brain. Other zeitgebers are ambient temperature, sleep, social contact, physical activity, and even regular meal times. They all send “timekeeping” clues to your brain, helping keep your circadian rhythm running on schedule.

Circadian Rhythm Disruption

Any time that our normal 25-hour circadian rhythm is altered or interrupted, it will have physiological and behavioral impacts. This is better known as circadian rhythm disruption, or CRD. Normal circadian rhythms are naturally altered as one ages including changes in sleep pattern with respect to earlier onset of sleepiness, early-morning awakenings, and increased need for daytime napping.

Sleep Disorders and CRD

Several chronic sleep disorders can lead or contribute to circadian rhythm disruptions, including:

  • Delayed Sleep Phase Syndrome

    This disorder causes a delay in the normal sleep onset time by two or more hours. People affected by this disorder complain of late-evening insomnia and/or excessive early-morning sleepiness, have difficulties falling asleep before 2:00 a.m., have short sleep periods during weekdays, and prolonged (9-12 hours) sleep periods during the weekends. These individuals tend to experience depression and other psychiatric disorders.

  • Advanced Sleep Phase Syndrome

    This is a disorder where sleepiness occurs well before the desired sleep schedule. The resulting symptoms include evening sleepiness, an early sleep onset, and an morning awakening that is earlier than desired. A person feels the urge to go to sleep between 6:00 and 8:00 p.m. and wakes up between 1:00 and 3:00 a.m. the following morning. This disorder can have a negative impact on an individual’s personal or social life because of the need to leave early-evening social activities to sleep. Evening sleepiness may also represent a driving hazard.

  • Non 24-Hour Sleep-Wake Disorder

    This disorder is the result of an inadvertent delay of the sleep onset time, followed by unsuccessful attempts to sleep at the desired sleep schedule. People affected by this disorder constantly delay sleep onset times that interfere with circadian rhythms. They have a normal sleep duration pattern but live in a free-running “biological clock” of 25 hours instead of the community-accepted 24-hour clock. The sleep cycle is affected by inconsistent insomnia that occurs at different times. Those affected will sometimes fall asleep at a later time and wake up later; or fall asleep at an earlier time and wake up earlier.

Even if you do not have a chronic sleep disorder, there are several measures that can help you get a good night’s sleep. Among these are:

  • Mental or physical relaxation techniques (reading, meditation, yoga).
  • If you don’t fall a sleep within 30 minutes of going to bed, get out of bed and try an activity that helps induce sleep such as reading, listening to relaxing music, watching something boring on TV, etc.
  • Ensure you are in an environment conducive to sleeping (dark, quiet, comfortable temperature and mattress).
  • Exercise regularly, but not too near bedtime.
  • A nutritious, balanced diet.

Shift Work and CRD

Shift work almost always causes a circadian rhythm disruption—the internal body clock is at odds with the shift schedule. Shift-work problems are well documented, ranging from performance issues to accidents and health problems.

Recognizing Circadian Rhythm Disruption

Pilots or passengers who are suffering from CRD may experience one or more of the following symptoms:

  • Difficulty falling and staying asleep, late-night insomnia.
  • Increased daytime sleepiness.
  • A general lack of energy in the morning.
  • An increase of energy in the evening or late at night.
  • Difficulty concentrating, being alert, or accomplishing mental tasks.
  • Oversleeping and trouble getting up.
  • Increased negative moods.

The most debilitating symptom of CRD is, of course, fatigue. Fatigue is typically characterized by:

  • General discomfort.
  • Sleepiness.
  • Irritability.
  • Apathy or loss of interest.
  • Decreased concentration.
  • Loss of appetite.
  • Impaired sensory perceptions.
  • Mood changes.
  • Impaired decision-making.

Fatigue, itself, is a very dangerous condition for any pilot attempting to operate an aircraft. Realizing the cause of the fatigue (in this case, CRD) is the first and most important step in treating it.

Jet Lag is a CRD!

Of all the stressors in aviation, jet lag, or rapid time zone change syndrome, seems to have the biggest impact. This syndrome consists of symptoms that include excessive sleepiness and a lack of daytime alertness in people who travel across time zones. Other Symptoms: Fatigue, insomnia, disorientation, headaches, digestive problems, lightheadedness.

Jet lag is more evident if you fly from west to east because it is more difficult for your body to adjust to “losing time” when you journey east than to “gaining time,” when you fly from east to west.

Tips to Help Minimize Jet Lag

  • Adjust your bedtime by an hour a day a few days before your trip. This will adjust your sleep pattern to match the sleep schedule you will keep at your destination.
  • Reset your watch to the destination time at the beginning of your flight to help you adjust more quickly to the time zone you will be visiting.
  • Drink plenty of water before, during, and after your flight. The air you breathe on airplanes is extremely dry, and some experts believe that dehydration is a predisposing cause of jet lag. Virtually everyone agrees that dehydration can make jet lag worse.
  • Eat lightly but strategically. What you eat can have a direct influence on your wake/sleep cycle. Remember that high protein meals are likely to keep you awake, while foods high in carbohydrates can promote sleep, and fatty foods may make you feel sluggish.
  • Relax on the first day at your destination. If you have the luxury of arriving at your destination a day or two before you have to engage in important activities that require a lot of energy or sharp intellectual focus, give yourself a break and let your body adjust to the time change a little more gradually.
  • As a Passenger:
  • Avoid drinking alcohol or anything with caffeine in it during your flight (includes many soft drinks, coffee, and tea.) Both alcohol and caffeine increase dehydration.
  • Sleep on the plane if it is nighttime at your destination.
  • Use earplugs, headphones, eye masks, or other sleep aids to help block out noise and light, and a travel pillow to make you more comfortable so you can sleep.
  • Stay awake during your flight if it is daytime at your destination. Read, talk with other passengers, watch the movie, or walk the aisles to avoid sleeping at the wrong time.

CRD Affects Your Flying Skills

CRD-induced fatigue that goes untreated or ignored will have both physiological and psychological ramifications that not only can jeopardize your personal health but can also become a safety-of-flight issue. A few of the more well known undesired personal affects are:

  • Increased reaction time
  • Impaired responses in sequential tasks that require time synchronization.
  • Need to increase the magnitude of sensory stimulation to elicit response.
  • Decreased attention
    • Omission or displacement of individual elements in sequential task.
    • Channelized attention to one task at the expense of others.
    • Impaired visual monitoring patterns.
    • Difficulty in self-identifying performance impairment.
  • Impaired memory
    • Difficulty remembering recent events during flight.
    • Tendency to forget secondary tasks.
  • Personal conduct of isolation
    • Tendency to avoid interpersonal interactions.
    • Tendency to avoid tasks that require low workload.
    • Increase distraction due to discomfort.
    • Emotional irritability.
    • Indifference.

    Consequences of CRD on the Flight Environment

    • Increased frequency and severity of piloting errors during aircraft operations.
    • Increased frequency of operational incidents.
    • Increased risk in aviation operations.

    Resetting Your Biological Clock and Recovering

    Once you have fallen victim to CRD, it is imperative to reset your biological clock. Here’s how:

    • Catch Some Rays. Exposing yourself to as much daylight as possible might also be a good idea, because it has been scientifically shown that bright light helps reset circadian rhythms. In addition to resetting the clock, light has a direct and positive affect by increasing brain serotonin levels. At the same time, circadian light therapy has a depressing affect on daytime melatonin, a clear link to depression and sleep disorders.
    • Be Active. When you arrive, taking a nap is the worst thing you can do because it sets your body’s rhythms back to home time. Staying active on arrival will help the body adjust to the new time zone. Eating and sleeping are your body’s time indicators, so it’s important to fit in with what the locals are doing when you arrive. Consequently, if it’s breakfast time, eat breakfast.

    Coping With CRD While On Duty

    • Sleep well at home before any flight.
    • Try to get at least as much sleep per 24 hours as you would normally at home.
    • If you are sleepy, try to sleep. Employ strategic (combat) napping techniques.
    • Whenever possible, take a 30-minute nap prior to a long flight.
    • Avoid naps of more than 30 minutes, as they involve deep sleep.
    • Taking a nap is better than not sleeping at all.
  • Avoid pilot adaptation to a local circadian rhythm following transmeridian flights with short layovers.
  • Try to maintain the circadian rhythm from your place of origin, and at the same, time try to sleep longer.
  • Use caffeine strategically during the flight to counteract circadian rhythm sleepiness.
  • While in the cockpit seat, converse with others, stretch your legs, and take regular breaks.
  • Try to avoid night flights following a transmeridian flight.
  • Transmeridian flights should be alternated with intrameridian flights, enabling you to return to your normal circadian rhythm.
  • Remember, circadian rhythm disruption can lead to acute or even chronic fatigue. Fatigue in the cockpit has shown to be just as debilitating as drugs and alcohol. Do not let CRD-induced fatigue become a hindrance to aviation safety.

    MEDICAL FACTS FOR PILOTS Publication No. AM-400-09/3 Written by  J.R. Brown Melchor J. Antuñano, M.D Federal Aviation Administration Civil Aerospace Medical Institute

    Maneuvering Speed or Structural Cruising Speed?

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    VA – known as maneuvering speed is the maximum speed at which you can safely stall an airplane. During

    certification of the aircraft the forces are measured on the elevator (see image) and a maximum speed, i.e. maneuvering speed is established. At any speed above VA you would exceed structural limits before reaching a stall. And the goal is to let the airplane stall and recover and not disintegrate in the “bumpy” weather.

    VNO is maximum structural cruising speed. This is related to wind gusts measured on the wings. This has to do with the wings bending and twisting. Not structural limits on the elevator.

    Some instructors teach students that VA is turbulent penetration speed which is really not completely accurate and may confuse things.

    Effects of lightning strike on an aircraft

    Pilot or a passenger, we all have wondered what would happen if the airplane that I’m flying in is hit by lightning?

    We know that friction causes drag.  What we may not realize is that this same friction also creates static electricity.  As an airplane flies through the air it continuously creates a static charge, especially on the aircraft control surfaces.  This situation is only made worse when flying through any kind of precipitation or even worse, volcanic ash.   Static wicks which are attached to the trailing edges of control surfaces are designed to help dissipate this charge to the surrounding air.  Static wicks protect not only our flight instruments and radios but also the flight surfaces themselves.  Without the static wicks attached, the static charge on the surface would try to “jump” the un-conductive control hinges to the rest of the aircraft.  This “jump” or arc could cause permanent damage to the surface itself if the static charge had the opportunity to build sufficiently.  To further protect against this damaging “jump”, manufacturers also attach conductive bonding strips to keep the static build-up to a minimum.

    The airplanes are primarily made of aluminum which is an excellent conductor of electricity.  This conductive property of aluminum creates a “Faraday cage” around the airplane protecting its’ contents. This “cage” shields the contents inside from the current that might be present on the surface of the Faraday cage.   Although there is a lot of static electricity on the outside skin of an aircraft, the aluminum conducts the electricity away from the interior and towards those static wicks.

    Now some aircraft are not manufactured with traditional aluminum but with a high-strength composite material; like the Beechcraft Premier or Cessna Columbia.  Fortunately, engineers have designed strike protection into the composite material by making one of the layers a graphite cloth and aluminum ply.  This ply, which is highly conductive, also serves to create the same “Faraday cage” affect that is found on traditionally manufactured airplanes.  Some composite airplanes also have an additional layer of protection against lightning strikes by installing Metal Oxide Varistors (MOV) throughout the circuitry.  MOVs are designed for failure.  If an MOV senses a sudden surge of current (from say a lightning strike) than it is designed to break and protect the rest of the aircraft’s delicate electronic systems.

    So obviously with all these various lightning strike/static electricity protection systems, engineers are designing aircraft with the assumption that aircraft stand a reasonable good chance of being struck by lightning.  In fact, it is believed that most commercial aircraft are struck up to twice a year. Most of the time, a lightning strike is a minor event (thanks to those protective systems).  The only evidence left behind in most strikes is a small lightning entry and exit point.   In the photo below, you can see where lightning made a small entry point on the top part of the aircraft’s radome (nose) and you can see the exit point about 6 inches lower.

    Sometimes aircraft damage from a lightning strike is more severe.  Lightning has been known to pop circuit breakers (which fails aircraft systems), magnetize control surfaces, punch large holes through aluminum (although this is extremely rare) and flicker or even cause the failure of some glass cockpit displays. This leads us to the next question, has an airplane ever crashed as a direct result of lightning?

    I wish I could say no, but accident investigation evidence says otherwise.  The Flight Safety Foundation (FSF) through the Aviation Safety Network lists several airplane accidents where lightning was a direct contributing factor in the accident.  You can see the list for yourself.  The most recent listing is a Dornier 228 that on December 04, 2003 took a direct lightning strike that the crew immediately reported.  The lightning apparently damaged the rudder and made aircraft control very difficult.  Fortunately, there were no fatalities although but the aircraft was considered a total loss.  There are older accidents listed as well by the Aviation Safety Network and some of these, although very tragic, have benefited travel safety today in the form of better design and engineering in aircraft systems.

    Pilot Certificates (or licenses)

    Private pilot certificate, private pilot license, PPL, CPL, commercial pilot ….? What are all these terms? This article will briefly discuss these and similar terms so you can better understand what all these things mean.

    The following article is for basic understanding of the pilot certificates and licenses, and is not written for the professional educational purposes. Many advanced areas of knowledge have been omitted to keep this simple and easily understandable. Professional aviation knowledge articles are available in a different area of this site.

    CERTIFICATE OR LICENSE:

    First of all, let us clarify the issue of certificate or a license. In the United States, any individual who needs or wants to fly any aircraft, is required by the Federal Law to apply for and obtain a relevant pilot certificate. Pilot certificates once issued, are valid for the life time of the holder (certain exceptions are there, but for the sake of this discussion they are not relevant, and we will address them in a

    different article). In other words, in the US, the pilot certificate is more like an educational credential. Like your high school diploma, or a college degree, and so forth. Once you achieve the requirements, and are issued the certificate, it is yours forever.

    In some, or I would say, in most other countries, the same privilege, i.e. the credentials to fly an aircraft, are issued in the form of a license. This license, just like your car driver’s license, or a business license, has an expiration date. And, the holder needs to pay the fee to renew the license at the time of the expiration or upgrade etc. And of course, there is a frequent expiration date for the license.

    US pilot certificate is issued free of charge, and never expires, whereas, a pilot license usually comes

    with an application fee, issuance fee, renewal fee, upgrade fee, etc. I guess you got the point. A pilot license is a source of revenue for those governments. And of course, as it is a license, it can be revoked any time with or without any cause!

    COMMON PILOT CERTIFICATES AND LICENSES:

    STUDENT PILOT CERTIFICATE:

    A student pilot certificate (or a license in most countries) a.k.a SPL, is required to fly SOLO in an aircraft. In simple words, when you are in the process of learning how to fly, at some point your flight instructor (known as CFI in the US) would let you go fly around on your own. To be able to do this, i.e. fly on your own (sole

    occupant of the aircraft, thereby called SOLO), you need to have a student pilot certificate or an SPL. When you are with a flight instructor in an aircraft, you do not need to have any certificate or license. In the US, this is the only pilot certificate that has an expiration date on it. If the student pilot certificate is issued before the 40th birthday of the applicant, the expiration date is set at 3 years, otherwise it is 2 years. The certificate is issued free of charge, however, there is usually a fee involved for the medical certificate (upon completion of the medical examination by the approved Aviation Medical Examiner – AME).

    PRIVATE PILOT CERTIFICATE:

    A private pilot certificate (or a license in most countries) a.k.a. PPL, is the minimum required to fly around for pleasure or personal transportation (like your class c driver’s license) and take your family and friends with you without any restrictions (for the most part). There are certain restrictions on licenses, but as far as the US private pilot certificate is concerned, you are allowed to fly an aircraft that you own, or a rental, day or night time, and with the required additional credentials, even in the clouds (Instrument Rating). In simple words, you can fly as long as you are not flying as a professional pilot, i.e. getting paid to fly. For that, you would need a commercial pilot certificate (or a commercial pilot license – CPL).

    COMMERCIAL PILOT CERTIFICATE:

    A commercial pilot certificate (or a license in most countries) a.k.a. CPL, is the minimum required to fly professionally as a job. A holder of a commercial pilot certificate or a license is eligible to fly an aircraft as a professional pilot. Of course there are more additional qualifications, credentials, or ratings as we call them in aviation lingo or terminology, but the idea is that the commercial pilot is the bare minimum requirement for a job as a pilot.

    OTHER PILOT CERTIFICATES:

    In the US, there are a few other pilot certificates which are available for the public. There is a recreational pilot certificate, a sport pilot certificate, an airline transport pilot certificate, and then there are some additional ratings like instrument rating, type specific type ratings etc. We have discussed all these certificates and ratings in a different article in detail.

    Flying Club vs Flight School

    If you spend long enough time in general aviation, especially in teaching environment, you are definitely going to hear these two terms above. And if you are thinking about learning how to fly, then you are probably wondering what is the diference between a flying club and a flight school anyways. Well, we will nail this issue here in this post once and for all!

    Flying Club: A flying club, just like the name itself, is in fact a club. A flying club could be a private non-profit organization, a for-profit organization, a government or semi-government run organization, or many other unique setups. Typically, a flying club will have members consisting of the following:

    • Aircraft owners
    • Aircaft users/renters
    • Pilots – student pilots, private pilots, commercial pilots, and above
    • Flight Instructors

    A flying club also has it’s management, i.e. general manager, president, mechanics, accounting people etc. The basics of a flying club setup is that aircraft owners lease their aircraft to the club, and then rent from the club itself whenever they need to use the aircraft. They can not only rent their own aircraft, but any other aircraft that is available to the members of the club. This increases their selection of the aircraft available to them. The cost of aircraft ownership/operation is subsidized by letting other nn-owner member pilots to rent and fly the club aircraft. The non-owner members pay for the aircraft rental, and most of the times, some sort of membership fee as well. The club aircraft get better rates for insurance, fuel etc as now they are a bulk customer and not individual aircraft. I hope you get the idea of this cost savings, not only for the aircraft owners but also for other renters as well.

    Now, there are flight instructor members as well in the club. They make their services available to club members, of course for a fee. If a new member wants to join the club, he or she will definitely need some training. Whether it is training to get a pilot certificate, or just an insurance checkout, the flight instructors (CFI) do the job. And this is how they mak their living, or in most cases, get paid to enjoy and share the love of aviation.

    Flight School: A flight school is a business involved in training people how to fly. This is what they do, and this is their expertise. They are usually owned by someone, has a chief flight instructor, and employed flight instructors and other professionals. The flight schools also rent aircraft (in most cases) to renters. Flight schools are usually designed and operated as any other school – i.e. imagine your high school. From the school principal all the way down to the housekeeping staff.