Human Factors and Mishap: Fatigue and

Its Effects on The Safety of Flight

Abstract

Fatigue has long been recognized by the NSTB as a high priority item since the inception of their Most Wanted list in 1990.  Several times the NTSB made recommendations to the FAA as well as the NATCA regarding re-evaluation of rest rules and duty time limitations.  Even with new rest rules finally around the corner, fatigue is still an issue and self-evaluation is difficult when impaired with fatigue.  Examining the Colgan flight 3407 accident, parallels can be drawn between the crewmembers inaction and incorrect stall recovery attempt and their level of fatigue.  Countermeasures should include simplification of rest requirement calculations and removal of monetary penalties for crewmembers to remove themselves from duty when sick or fatigued.

Keywords: fatigue, rest rules, duty time limitations, fatigue countermeasures

Human Factors and Mishap: Fatigue and

Its Effects on The Safety of Flight

Of the many human factors and performance topics in existence, fatigue is a top priority for most aviation departments, airlines, flight schools, the Federal Aviation Administration (FAA) and the National Transportation Safety Board (NTSB).  In a 2007 letter to the National Air Traffic Controllers Association (NATCA), the NSTB reiterates the concern relating to fatigue and all transportation industries with more than 80 safety recommendations on the topic since 1989 (Rosenker, 2007).  In a similar letter to the acting FAA administrator, Rosenker, (2008) points out that “The Board has included safety recommendations related to human fatigue in transport operations on its annual Most Wanted List of Transportation Safety Improvements since its inception in 1990.”  While the FAA has since moved forward with new rest and duty time limits, these new regulations are more complicated and confusing than previous ones.  Using the 2009 accident of Colgan flight 3407, it will be shown how primary factors in the accident are actually results of underlying fatigue and improper rest.

Fatigue

The New Oxford American Dictionary (Stevenson, 2010) defines fatigue as “extreme tiredness, typically resulting from mental or physical exertion or illness.”  Various causes for fatigue rang from sleep loss to poor sleep quality, diet deficiency, and even intentional sleep restriction.  According to Reinhart, (2008), fatigue is usually one of two different types: acute and chronic.  Acute fatigue can be associated with current events and activities, once the situation is resolved recovery is attained and restful sleep achieved.  Chronic fatigue is more serious and attributed to a cumulative effect of sleep loss over several months, which can lead the body to become vulnerable to illness, and increased stress.

Negative Effects on the Safety of Flight

Some of the negative effects are stated by Caldwell (1997) “…biological limits imposed by fatigue will impair the performance of even the most highly skilled and motivated individuals.  Thus, the fact that missions are being flown only by the most dedicated ‘high time’ aviators offers no safeguard against the insidious threats posed by sleepiness in the cockpit.  The effects of fatigue cannot be overcome by training or experience.  In addition, the impact of fatigue cannot be negated by monetary or other incentives.  Finally, individual pilots cannot be relied on to accurately judge their own levels of fatigue-induced impairments because judgment capabilities tend to suffer along with performance accuracy in sleepy personnel.”

Additionally, Caldwell (1997) goes on to describe the results of fatigue: “As fatigue levels increase, accuracy and timing degrades, lower standards of performance are unconsciously accepted, the ability to integrate information from individual flight instruments into a meaningful overall pattern is degraded, and a narrowing of attention occurs that leads to forgetting or ignoring important aspects of flight tasks.  In addition, the fatigued pilot tends to decrease physical activity, withdraw from social interactions with others, and lose the ability to effectively divide his mental resources among different tasks.”

Fatigue cannot be mitigated directly with training, and a fatigued pilot cannot sufficiently self-diagnose due to cognitive impairments derived from the fatigue itself.  This makes the issue of fatigue management primarily education and prevention.

Mishaps involving Fatigue

Rarely is fatigue listed as the primary factor attributed to an accident or incident involving aircraft, yet it has been listed as an attributing factor in several.  In a Safety Recommendation letter (Rosenker, 2008), the NTSB stated that “[s]ince 1972, the Board has issued 115 human fatigue-related safety recommendations in all modes of transportation, including 32 recommendations addressing fatigue in the aviation environment and 4 intermodal recommendations.”

Additionally signifying the fatigue as an underlying cause Caldwell (1997) states, “Many of the human errors accounting for well over half of all aviation accidents , are probably the direct result of fatigue-related pilot inattentiveness and failures to respond to critical information in the cockpit.  However, fatigue frequently is not cited as a causal factor in air carrier accidents despite evidence pointing to its role in mishaps.”

Continental Connection flight 3407. In February of 2009 a Colgan Air Bombardier Q400 operating as Continental Connection flight 3407 crashed into a residential neighborhood while on an instrument approach to Buffalo-Niagara airport from Newark, New Jersery.

According to the NTSB (“Loss of control,” 2010) prior to reporting for duty for the accident flight, the captain had completed a two-day trip sequence.  Living in Seattle, Washington, the First Officer began her commute to Newark the day prior to the accident flight, commuting all night from the West to East coast.  Several pilots that saw the first officer during her commute stated she looked responsive and alert.  No person that observed either the First Officer or Captain prior to the accident flight described them as drowsy or fatigued.

What the report does show however is that both the Captain and First Officer had habits of sleeping during commutes, or in the crew lounge prior to flight assignments.  While not directly prior to the accident flight, the Captain had spent the night in the crew room 4 days prior and the First Officer spent 6 hours sleeping in the crew room the day of the accident flight.

Prior to departing Newark the CVR recorded the First Officer stating “I’m ready to be in the hotel room” and “this is one of those times that if I felt like this when I was at home there’s no way I would have come all the way out here.”  Additionally she stated “if I call in sick now I’ve got to put myself in a hotel until I feel better … we’ll see how… it feels flying.  If the pressure’s just too much … I could always call in tomorrow at least I’m in a hotel on the company’s buck but we’ll see.  I’m pretty tough.” (“Loss of control,” 2010).

In addition, during the entire flight, both crewmembers failed to maintain a sterile cockpit, which the NTSB stated as a contributing factor in the accident.  The aircraft departed Newark and flew en-route with no remarkable event other than several sounds of yawning from both the Captain and First Officer recorded on the CVR.

On approach to Buffalo-Niagara, the crew noted that the aircraft was accreting significant amounts of ice on the windshield and wings.  While configuring for the approach with flaps and gear, the Captain slowed the aircraft to 135 knots with the gear down and flaps selected to 15° while the FDR showed them at 10° moving towards 15°.  The Bombardier Q400 AFM indicated that with flaps set to 10°, the approach speed minimum in icing conditions is 144 knots (for the weight that the accident aircraft was at).

Approximately 6 seconds later, the stick shaker activated alerting the crew that a stall was imminent.  Providing aural and tactile cues to the pilot flying, the shaker sends vibrations through the control column and deactivates the autopilot.  When the autopilot disengaged, the FDR showed the airspeed was 131 knots.  The Captain moved the control column aft and advanced the power levers to approximately 10° below the rating detent (not quite full power).  It was noted by the NTSB that this initial pitch-up placed the aircraft approximately at a G load of 1.42, further increasing the stall speed of the aircraft, exacerbating the situation.

Throughout the stall, the aircraft oscillated from 45° of roll, left wing down, to 105° roll, right wing down.  While passing through wings level the first time, the stick pusher (automated nose-down movement of the control yoke to reduce wing angle-of-attack) activated and the First Officer selected flaps 0° (yet another stall exacerbation).  The airspeed was now about 100 knots.  The second time the aircraft was rolling through wings level, the stick pusher activated a second time.

The First Officer stated she had retracted the flaps and now asked if she should retract the gear.  At this point the aircraft was 100° right wing down and 25° airplane nose down, and the stick pusher activated a third time.  Four seconds later the CVR records sounds of impact and the CVR recording ended.

Accident Conclusion

While there were several factors contributing to this specific accident, I believe Caldwell (1997) was correct when he stated “Many of the human errors…are probably the direct result of fatigue-related pilot inattentiveness and failures to respond to critical information in the cockpit.”

At first glance, it’s easy to pinpoint the lack of airmanship from the Captain as the primary causal factor.  Listed in the NTSB report were several training deficiencies, failures, remedial training, and unreported events during the Captain’s training and airline career.  You can even point to the First Officer and her decision to retract the flaps during the stall event as a primary factor for the continued stall and eventual impact.

I don’t think the crew made these decisions because they felt they were the correct decisions, or the best decisions for the situation.  I don’t think the First Officer would have retracted the flaps had she been well rested, healthy and alert.  I don’t think the Captain would have used less than full power or inducing accelerated G forces with an excessive pull-up had he been well rested and alert.  I think the entire accident flight error chain can be traced to fatigue, lack of restful sleep, and poor sleeping environment.

The NSTB noted contributing factors to this accident in “Losing Control” 2010, as “(1) the flight crew’s failure to monitor airspeed in relation to the rising position of the lowspeed cue, (2) the flight crew’s failure to adhere to sterile cockpit procedures, (3) the captain’s failure to effectively manage the flight, and (4) Colgan Air’s inadequate procedures for airspeed selection and management during approaches in icing conditions.”  Subsequently, listed as focus areas were “flight crew monitoring failures, pilot professionalism, fatigue, remedial training, pilot training records, airspeed selection procedures, stall training, Federal Aviation Administration (FAA) oversight, flight operational quality assurance programs, use of personal portable electronic devices on the flight deck, the FAA’s use of safety alerts for operators to transmit safety-critical information, and weather information provided to pilots.”

It is my belief that of the contributing factors that the NSTB listed, three of them are directly related to the fatigue level of the crew.

Fatigue Countermeasures

I think the rest rules the FAA has plans to implement will both improve fatigue mitigation and complicate rest requirement calculations.  Currently there are several different ways to determine rest required, compensatory rest, minimum rest and reduced rest limitations.  New regulations will be based on time “behind the door” of the hotel room instead of aircraft block in (which never accounted for post-flight duties, debrief, nor transportation time to hotel), which is a significant improvement.  Additionally the new rest requirements will take into account the crewmember acclimated time zone, start of duty day, and legs flown.  This will help reduce circadian trough fatigue and will provide more protection than previous regulations allowed.

It will however, significantly complicate the determination of required rest and calculation of maximum duty day.

Author Recommendations

I think the new regulations should be simplified to provide the additional rest and more restrictive duty days with fewer scenarios for variation.  While I agree that duty day should be calculated on acclimated start time and legs flown, I don’t think it should be an algebraic formula to determine.

I believe the accident described in detail could have been avoided if the First Officer had confidence that calling out sick would not have cost her pay or an expensive hotel room.  Currently most airlines provide hotel rooms for cancellations or sick calls only when out of domicile.  They expect you to return home when you call out sick, yet they are fully aware that many pilots commute.  I think providing a hotel room for a commuting pilot when sick or fatigued while in domicile is an inexpensive way to encourage pilots to not fly while sick or fatigued.  This First Officer either could not afford the hotel, or could not afford the loss in pay.  Neither of those consequences are more severe than the resulting accident.

I think flight crews should be disallowed from sleeping in crew rooms overnight.  They are often noisy, uncomfortable, and they fail to provide a quality sleep environment or restful sleep.  This gives the crewmember a false sense of well-being.  They perceive that they acquired restful sleep and are now mentally convinced that they’re no longer fatigued.  We know that a fatigued crewmember cannot self-diagnose signs of fatigue and now there is a false sense of security with rest that wasn’t sufficient.

Conclusion

Fatigue is a monster in disguise.  When it finally rears its ugly head it might be too late to mitigate or even recognize.  Fatigue mitigation must be accomplished through crewmember education and prevention.  Once fatigued, a crewmember is no longer capable of sufficiently recognizing their level of impairment.  While the FAA is moving forward with new rest rules and duty limits, the regulations should be simplified to prevent confusion and to promote sufficient rest.  Monetary penalties should be removed by requiring airlines to provide crewmembers that are either sick or fatigued with hotel accommodations no matter where they call out from work.  In addition, crewmembers should not be allowed to fool themselves into thinking they’ve received restful sleep by spending the night in a crew lounge.

References

Caldwell, J. A. (1997). Fatigue In The Aviation Environment: An Overview Of The Causes And Effects As Well As Recommended Countermeasures. Aviation, Space, and Environmental Medicine, 68(10), 932-938.

National Transportation Safety Board, (2010). Loss Of Control On Approach, Colgan Air, Inc., Operating As Continental Connection Flight 3407, Bombardier Dhc-8-400, N200wq, Clarence Center, New York, February 12, 2009 (NTSB/AAR-10/01)

Reinhart, R. O. (2008). Basic Flight Physiology. (3rd ed.). New York: McGraw-Hill Professional.

Rosenker, M. National Transportation Safety Board, (2007). Safety Recommendation (A-07-30 through -32)

Rosenker, M. National Transportation Safety Board, (2008). Safety Recommendation (A-08-44 and -45)

Stevenson, A. (2010). New Oxford American Dictionary. (3rd ed.). Lindberg, C.A.: Oxford University Press, USA.

 

 

 

Gas Laws and Flight Safety: Dalton’s Law of Partial Pressure

 

Abstract

In February of 2007 an aircraft suffered a windshield fracture at altitude. Due to lack of aircraft systems knowledge and flight physiology awareness, the pilot in command chose to depressurize the aircraft while the oxygen system was turned off. This led both pilots of the accident aircraft to lose consciousness for more than seven minutes while the aircraft descended out of control and suffered structural damage. This paper will outline how Dalton’s law of partial pressure pertains to the accident flight and how proper knowledge of this basic gas law could have prevented the accident.

Keywords: Dalton’s law, partial pressure, hypoxia, time of useful consciousness

 

Gas Laws and Flight Safety: Dalton’s Law of Partial Pressure

Knowledge of the basic gas laws and how they affect pilots and passengers is an essential part of every safe crew member’s awareness. I will first outline Dalton’s Law and how it correlates to altitude induced hypoxia as well as how ignorance for this gas law contributed to an aviation accident. I will then identify the error chain and provide corrective actions to clearly show how this accident could have been prevented.

Dalton’s Law and Hypoxia

The atmosphere that we live and breathe in is a mixture of several gases. The life giving ingredient that is required for almost all life on Earth is oxygen. Oxygen is a colorless, odorless and tasteless gas and is the most abundant element on Earth (Reinhart, 2008). Comprising approximately one fifth of the Earth’s atmosphere, oxygen deprivation can lead to several symptoms ranging from visual acuity impairment, slurred or incoherent speech, to total loss of consciousness.

Dalton’s Law

Dalton’s law states that the total pressure of a gas mixture is the sum of the individual pressure (also called partial pressure) that each gas would exert if it alone occupied the whole volume. This law can also be expressed mathematically: P_T = P₁ + P₂ + P_s + P_n; P_T is the total pressure of the gas mixture and P represents         the partial pressure value of each gas, which is determined by multiplying the percentage of the individual gases time the total pressure (Reinhart, 2008). Simply put, because each gas represents only a portion of the air that we breathe, as we climb in altitude the pressure of each individual gas decreases with the total decrease in pressure.

Partial Pressure

Each gas will exert its own pressure depending on the percentage of that gas in the mixture. As stated by Mortazavi, Eisenberg, Langleben, Ernst and Schiff (2003), “The proportion of atmospheric oxygen remains constant at 21% at altitudes below 100,000 m. Therefore, the partial pressure of oxygen (P_O2 = barometric pressure X 0.21) falls substantially with lower barometric pressure at higher altitude. P_O2 at sea level is 159 and decreases by 50% at 5496 m. For each additional 300 m, P_O2 decreases a further 4–5 mm Hg.”

As the body ascends, even though the percentage of each gas in the atmosphere remains the same the available molecules of oxygen at a pressure required to pass to a blood cell decreases. This decrease in pressure leads to altitude induced hypoxia.

Hypoxia

Hypoxia is defined as an oxygen deficiency in the body and there are several different ways to get hypoxia. Dalton’s law can be used to explain hypoxic hypoxia caused by “high” altitude. As the body climbs in altitude, the partial pressure of oxygen decreases, making diffusion difficult or even impossible in the lungs. This leads to hypoxic symptoms such as euphoria, cyanosis, dizziness, visual impairment, loss of motor control, seizures, and eventually loss of consciousness.

Time Of Useful Consciousness

The time from when an oxygen deficiency begins until a pilot is no longer able to recognize and take action is called time of useful consciousness (or TUC). As altitude increases, TUC decreases, making recognition and action critical.

Accident and Analysis

According to an NTSB report from 2008, in February of 2007 an aircraft accident occurred following an in-flight depressurization. Operated as a 14 CFR part 91 flight, King Air N777AJ was a Raytheon Aircraft Company B200 which required only one pilot. On the accident flight a company employed pilot was the pilot in command and a non-company pilot was also present for the purpose of flight time accumulation. The non-company pilot was not trained nor checked out on the B200 aircraft.

Accident

While cruising at 27,000 feet mean sea level the aircraft experienced a windshield fracture. According to the CVR data, the pilot in command was not occupying his duty station but was in the cabin emptying a trash bin, leaving a non-trained pilot at the controls. After the fracture occurred, the pilot returned to his duty station, and made the decision to depressurize the aircraft because he was concerned about the integrity of the windshield. Using non-approved documents, non-approved procedures, and poor judgment, both pilots lost consciousness for more than 7 minutes due to altitude induced hypoxia. During this time the aircraft descended out of control and suffered structural damage and gravity-forces in excess of 4-g’s. Despite the out of control descent, both pilots regained consciousness and were able to successfully land the damaged aircraft.

Error Chain

Like most aviation accidents that occur, a chain of events known as the error chain can be pieced together to determine what eventually led to the accident. Rarely do accidents occur from a single event, but rather a series of errors that lead to a final event. As well as having a clearly defined error chain, this accident flight was also laced with poor decision making, lack of aircraft systems knowledge, failure to utilize manufacturer approved checklists, lack of physiological awareness, and improper pre-flight procedures.

The error chain for this flight began before the flight even started. The checklist found onboard the accident aircraft was not an approved checklist and it did not contain the recommended pre-flight items per the airplane flight manual (AFM). This unapproved checklist didn’t have a procedure for cracked or fractured windshields either. Proving just how inadequate and unprofessional this checklist was, the last item of the Shut Down checklist was “Pajamas…As Req.”

During pre-flight of the oxygen system, the pilot in command stated he successfully tested the oxygen mask and then turned the system off to “save” the oxygen. This was not in accordance with manufacturer recommended pre-flight procedures.

Once the windshield fractured, the error chain continued with the pilot in command’s decision to depressurize the aircraft. The AFM states that following an inflight windshield fracture, cabin pressure should be maintained and safe flight can be continued for up to 25 hours. Post-accident investigation of the windshield showed it to be structurally intact.

These events led to the precipice of the accident when the cabin was intentionally depressurized while the oxygen system was off. When the aircraft was depressurized at 27,000 feet mean sea level, the approximate time of useful consciousness was three to four minutes. Even though post-accident investigations revealed the oxygen system to be fully functional, it was simply never turned on.

Correlation To Dalton’s Law Of Partial Pressure

The pilot in command lacked sufficient awareness and knowledge of Dalton’s law as evidenced by his decision to depart with the oxygen system turned off, and further ignorance by intentionally depressurizing the aircraft. With appropriate working knowledge of flight physiology and the reduction of oxygen’s partial pressure at altitude, the pilot in command would never have decided to turn the oxygen system off prior to departure. Correlation of Dalton’s law with knowledge of decreased time of useful consciousness this accident could have been prevented completely.

Accident Prevention and Conclusion

Although there were several errors in the error chain that eventually led up to this accident, they are all preventable with proper procedures and aircraft systems knowledge. Regarding Dalton’s law, this accident could have been prevented with better knowledge of how altitude affects time of useful consciousness as well as better alertness for potential hypoxia situations. It should have been obvious to the pilot in command that prior to depressurizing the aircraft cabin that the oxygen system should be turned on. This point is over shadowed by the lack of adherence to manufacturer recommendations for aircraft pre-flight and configuration. There should never be a scenario at altitude where the crew would need to first activate the oxygen system prior to donning the oxygen masks.

Utilization of manufacturer recommended checklists, procedures, and operating practices isn’t just a really good idea, it’s required. There is a reason why human performance factors are on just about every pilot check-ride you can attempt, they’re important too. The last frontier of accident prevention that we must endeavor is that of human performance. With nearly every accident occurring because of human error, we must close the gap on preventable accidents like the one I have described.

 

 

 

References

Mortazavi, A., Eisenberg, M. J., Langleben, D., Ernst, P., & Schiff, R. L. (2003). Altitude-Related Hypoxia: Risk Assessment And Management For Passengers On Commercial Aircraft. (Vol. 74-9, pp. 922-927). Alexandria, VA: Aerospace Medical Association.

NTSB. National Transportation Safety Board, (2008). Full Narrative (CHI07LA063). Retrieved from website: http://www.ntsb.gov/aviationquery/brief2.aspx?ev_id=20070208X00156&ntsbno=CHI07LA063&akey=1

Reinhart, R. O. (2008). Basic Flight Physiology. (3rd ed.). New York: McGraw-Hill Professional.

Introduction

Personal physical fitness is a hot topic among pop culture but for many reasons other than the health benefits it yields. Even so, it could be said that next to sex, physical fitness sells second best. It’s the results that everyone likes and desires, never the work that is entails or requires. Having gone through personal transformations from hard work, exercise and strict dieting, everyone always asks, “What’s your secret?” or “What diet did you use?” It’s almost saddening for the asker to hear “Hard work, diet, exercise.” You can see the wind die from their sails and their hopes shatter. As with anything in life: if it were easy, everyone would be doing it.

My personal fitness plan is unique in that my lifestyle is unique. There aren’t very many diets or exercise plans out there that fit into a suitcase. One of the hardest parts of my diet is that I’m often in places with limited choices for healthy eating. This leads to the hard choice of eating unhealthily or not eating at all, not the best options when you’re trying to stay fit. This fitness plan is designed to maintain a healthy aerobic condition and body weight. It is not designed to make anyone (most importantly: me) into an Olympic athlete.

Warm up and Cool Down

To facilitate the slow warm up and cool down of the exercise period, I stretch for 10 minutes before and after the workout. In addition to stretching I begin my run with a short period of speed walking and usually end my run with the same.

Most important to me is the post workout stretching period. Whether scientific or not, I find that a post workout stretch helps prevent injuries and decreases recovery periods in relation to muscle strain.

Type of Exercise

Because it’s universally recognized and generally available anywhere, my primary form of exercise is running (most often on a treadmill). I will run a mile at approximately a 10 minute mile pace and then cool down for one minute. My goal is to reach a target heart rate of 190 beats per minute and sustain that throughout the workout. The cool down period should not bring the heart rate below 150 beats per minute. I run approximately 3 miles which should equate to around 30 minutes on the treadmill or on the trail.

In addition to running I perform resistance training with resistance bands that fit in my suitcase. I started carrying these bands with me everywhere I go when I realized that my excuse for not working out was that no place I stayed had free weight equipment. With the bands I do a variety of resistance training workouts. Bicep curls, tricep extensions, chest press, overhead press, lateral raises, butterfly press, in addition to sit ups and push-ups. I alternate working out my chest and back with legs. Using a combination of the resistance bands and body weight, I work out using: squats, lunges, leg-ups, and calf raises.

Frequency and Time

At a minimum I work out three times per week for just over one hour. This allows ample time for my body to recover from muscle strain while at the same time promoting progression and strengthening.

I schedule 10 minutes at the beginning of the workout for stretching and warm-up. I stretch the same way every time I work out, giving no preference to whether it is chest and back or legs emphasis day. This gives me another chance to help my body recover from previous workouts instead of only focusing on the workout of that day.

My primary method of raising my heart rate to my target is running either on a trail or on the treadmill. I like to walk at a faster than normal pace for 5 minutes and then slowly increase the pace until I’m running at approximately a 10 minute-mile pace.

After running about 3 miles, I will proceed to the resistance training. I schedule 15 minutes of resistance training in order to take advantage of my increased heart rate. I focus on repetitions instead of amount of “weight” or resistance. Counting backwards from 20, I will do 20 repetitions, then the second set I will do 10 repetitions, then finally 5 repetitions. This yields a total of 35 repetitions for each resistance exercise I complete.

Diet

One of the most important aspects of a healthy lifestyle is the diet; consequently it is also one of the harder plans to maintain. There is no fad or instant success story to use, it’s just plain math. I count calories to help prevent my intake exceeding my outtake. I budget myself for 1,800 calories a day and for three days a week I burn about 500-700 of those calories with my workout. Keeping this intake and outtake in balance (or less in than out) ensures that I can keep my weight at a healthy level or even aids in weight loss when desired.

I eat a balanced diet of fats, protein, and carbohydrates. Because my lifestyle tends to dictate what food is available to me (traveling, hotel bars and airports) I try to stick to low fat, high protein, and baked or grilled foods. It’s a funny thing about traveling, you can find almost every vegetable known to man, they’re just deep fried, or coated in butter, or in a crème sauce.

I focus less on what I specifically eat and more on the caloric content overall. Micromanaging my diet to the point of specific foods creates more headache than results I’ve found.

Conclusion

This diet and exercise plan has helped me maintain a healthy weight and a healthy lifestyle. It has changed the way I choose food while eating out at restaurants and when I go shopping. The workout regime has helped me find time in my busy schedule to spend time on myself and my well-being. Overall it has improved my quality of life as well as long term health outlook.

Anatomically considered an extension of the brain, the eye is the biological camera for the human body. Focusing light energy and translating it into electrical energy then transmitting that data to the brain via the optic nerve is the complex process known more commonly as eye-sight.

Light first passes through the outer layer of the eyeball called the cornea. Working as a “lens cap” for the eyeball it also has refractive (bending) properties that help focus the light entering the eye. Next, light rays entering the eye are refracted by the lens and focused onto the retina. The retina is comparable to the film in a camera. Focus can be changed by ciliary muscles that surround the lens and with contraction or relaxation can change the shape of the lens which affects focus.

The colored membrane that determines eye color is the iris and the center portion of the iris is the pupil. By modulating the size of the pupil the eye can control how much light is allowed to enter and changes the depth of field. Allowing more light into the eye by increasing the size of the pupil, such as in low light situations, the depth of field is decreased. This means the nearest and farthest distances within which everything is in focus is shortened. This modulation is used primarily to make vision easier in high or low light situations.

Once allowed to enter the eye and focused, the light energy meets the retina, or the “film” of the eye. The retina contains cells that translate light energy into electrical energy. Using cone cells to sense bright lights and colors and rod cells for low light or night vision, this data is transmitted to the brain via the optic nerve. Rods are used primarily as peripheral vision and are considered to be 10,000 times more sensitive to light than the cones (which is the reason peripheral vision, or off-set viewing, is recommended for night time traffic scanning). Where the optic nerve is formed on the retina is devoid of cones and rods which results in a blind spot. Each eye compensates for the other eye’s blind spot.

There are several visual impairments that can either develop or be genetically inherited. Most common is myopia, or nearsightedness. This is caused by the focal point of the lens being in front of the retina. Conversely, presbyopia is a form of farsightedness caused by the stiffening of the lens makes accommodation (the ability to change the focal point) difficult.  This requires objects to be farther away from the eye to be in focus which could result in poor vision up close yet still yield good distant vision. Correction for this involves reading glasses which magnifies close up objects allowing them to be focused.

An additional impairment to visual acuity is called astigmatism, or an unequal and variable curvature of the lens and the cornea that prevents an equal focus at varying distances. This causes light rays to refract unequally through the lens creating varying levels of focus in either eye. This condition can be mediated or completely rectified with glasses, contact lenses or a vision correction procedure.

Along with refraction and focus irregularities, vision can be impaired by lens clarity. In some cases the lens can become opaque resulting in a cataract. Cataracts may form by age alone or extended exposure to ultra-violet rays absorbed while flying at high altitudes for long periods of time. In addition, less light may pass through the lens due to age-related yellowing which interferes with the depth of field. Prevention is the best method by wearing UV filtering sunglasses that block the full ultraviolet range. Once developed cataracts can be removed and replaced with surgery.

Finally, the eye can even be affected temporarily by factors that are known to affect the brain in the same manner. Hypoxia, fatigue, carbon monoxide, or toxins can severely impair the eyes ability to see clearly. Hypoxia increases time required for adaptation to night vision and can occur at altitudes as low as 5,000 feet. Carbon monoxide build up in the blood affects the pilot in the same way hypoxia does because carbon monoxide blocks the hemoglobin’s ability to attach to and carry oxygen. Fatigue can affect mental alertness and visual recognition, which could impair a pilot’s ability to scan, maintain focus, or even impair judgment. Toxins, such as alcohol, create a state of histotoxic hypoxia that can reduce visual acuity well past when the last drink was consumed.

These various components that work together, mostly unconsciously, allow us to operate visually in the cockpit and on a day-to-day basis. Maintaining a healthy lifestyle as well as taking precautions to protect and preserve your vision will ensure a long and safe career in the cockpit.