INSOMNIA AND FATIGUE IN FLIGHT OPERATIONS
As it is known, one of the most important problems of those working in the aviation industry is insomnia and the excessive fatigue that develops as a result. Sleep is a state of recharging for the human being. According to the results of scientific studies conducted on the sleep needs of an adult, it is found that a normal person needs 7-9 hours of sleep per day, including uninterrupted, deep and REM (Rapid Eye Movements) sleep.
It is known that insomnia or insufficient sleep leads to excessive fatigue, which has a direct effect on flight safety, that excessive fatigue (fatigue) can also be measured thanks to recent developments, and that the effect of excessive fatigue on a person is almost equivalent to consuming certain amounts of alcohol. Despite these facts, unfortunately, many fliers do not fully understand the effects of excessive fatigue. Therefore, tired fliers continue to fly in a “fatigue-exhausted” state without realizing it, causing flight insecurity. In order to better understand the importance of sleep in terms of flight safety, it would be useful to first examine the general structure of sleep.
Stages Of Sleep
Sleep is a physical and mental activity that includes many stages, where the sensory organs work actively and allows the person to refresh. Studies have revealed that sleep consists of 5 stages. Accordingly, there are N1, N2, N3, N4 and REM (Rapid Eye Movements) stages. Since there are no eye movements between N1-N4, they are called Non-REM stages.
If we briefly examine these stages; first of all, a person enters the N1 stage while falling asleep. This stage is the transition stage between wakefulness and sleep. Brain activities slow down, the person becomes unresponsive to sounds and images, and the eyes completely close and begin to make slow and involuntary movements. In addition, sudden muscle movements and contractions can also be encountered during this stage. Since it is the first stage of sleep, if this stage exceeds 10 minutes, what happened a few minutes before sleep can be forgotten, in other words, memory loss occurs.
After this stage, the first stage is N2, where brain waves become irregular and make sudden oscillations. Here, brain waves are irregular, and in the next stage, N3, there is a transition to slow-wave sleep, which occupies 20-50% of brain activity. At this stage, the eyes are still motionless, but the brain waves become more regular. The N4 level is one stage above N3, and the slow-wave movements here occupy more than 50% of brain activity. It is more difficult to wake up a person sleeping at this level than at the N1 level. Especially people awakened at the N3 and N4 levels may take a few minutes to wake up, and they may remain unresponsive and insensitive at this level, so pilots who perform controlled resting sleep in the cockpit during the flight should pay attention to this stage and wake up before passing through this stage. The fifth stage is the REM stage, which is different from the other sleep stages in many ways. Here, the eyes are in constant motion, the brain is in constant activity and is producing random waves, and the muscles are now completely still and have entered a completely resting phase. The REM phase is also called the “dream phase” because dreams often occur during this stage. The immobility of the muscles makes it easier to dream.
Sleep Architecture
During the night, a person completes their sleep with the transitions between the sleep stages mentioned above in a predictable pattern. As shown in the Sleep Architecture Figure, this is called a sleep cycle. The cycle here is generally unbroken and shows a course depending on the hours during sleep. Each cycle takes approximately 90 to 120 minutes. In each sleep cycle, the N1 stage is completed within 5 minutes and the other stages and Non-REM stages are completed and the sleep cycle ends with the REM stage, and sleep activity continues with these sleep cycles throughout the night. In the first half of the night, REM sleep is generally low and sleep activity is continued with Non-REM sleep. This situation covers approximately the first 4 hours of sleep. The recharging REM sleep of a person occurs more commonly after this time period. As shown in Figure 8, the last two cycles of sleep are completed completely with REM between N1 and N2. There may be brief awakenings during sleep from time to time, a person cannot notice most of these awakenings, which can last for a total of 10 minutes during the night and usually occur in adults. Sleep refreshes a person, but this refreshing occurs in a rhythm. Unlike a machine, a person completes his life and activities in a routine that depends on the light conditions of a day, this routine is called Circadian Rhythm, it is useful to examine the Circadian Rhythm to better understand the subject.
Sleep Architecture
Circadian Rhythm
Circadian rhythm is the natural cycle that guides our daily lives. Circadian clock regulates physiological processes such as sleep, wakefulness, body temperature regulation, hormone secretion and physical and cognitive performance within this rhythm. For example, body temperature, which is lower during sleep, is increased to normal temperature approximately 1.5-2 hours before waking up thanks to the circadian clock, and this occurs at the time when a person’s mental and physical competence during the day is adjusted. For example, the circadian clock of a person who normally wakes up at 0700 is activated at 0500-0530, preparing the person for the new day. Accordingly, it is accepted that 
a normal person spends 0200-0600 hours asleep and the circadian clock is activated between 0300-0500. For those who can purify their sleep from environmental conditions such as light and sound, the 24-hour circadian clock can be extended to 25 hours. In fact, the extension or shortening of the cycle here is due to the flexibility of the circadian clock and is the most important part of the issue for us fliers. While people generally have difficulty falling asleep earlier than their normal sleeping hours, they do not have much difficulty falling asleep later, in other words, extending the day. Although the rhythm here is generally programmed over 24 hours, the effect of the distinction between day and night, and therefore the light conditions, is important. However, the problem that concerns us closely is the sudden changes in advancing or regressing this rhythm. These sudden changes have become the lifestyle of pilots flying 24/7 and captains flying ER flights. Despite this lifestyle, human pilots experience problems in adjusting their circadian clocks and, as a result, cases of extreme fatigue (fatigue) are encountered. The main problem here is that the circadian clock cannot adjust itself quickly enough to the sudden changes in time zones, sleep periods, and day/night differences. Physical adaptation to such sudden changes can take days or even weeks, and this is due to the changes in the day/night change that regulates the circadian clock. For example, a pilot who has to go to a 7-hour time difference after an ER (Extended Range) flight or a captain who has to fly at night and sleep during the day as a result of the flights in his monthly schedule falling at night, has his circadian clock order disrupted. However, the problem is that these pilots do not have enough time to adapt to the new order. Accordingly, pilots who cannot adapt to the new circadian clock are forced to fly during the hours they need to perform. In this regard, the physiological capabilities of the pilots are shown in the time zones and performance graph below, as shown in the figure. Accordingly, while pilots show the highest level of performance between 0900-0200, this performance decreases after 0200. A pilot who cannot prepare himself for the new time zone will experience a decrease in performance and feel fatigue, feeling like it is midnight, even though it is normally the middle of the day. The effects of this excessive fatigue will also be similar to the behavior of an alcoholic body.
Cycle Of Daily Pyschomotor Activ›ties
Fatigue
This condition, which usually develops due to sleeplessness and is called Fatigue, is a physical and mental exhaustion or fatigue that exceeds the normal fatigue limits of a person. While it is physically described as the muscles losing their ability to work at the desired level, it is mentally expressed as the inability to perform actions such as comprehension, understanding, interpretation and application in events that require brain skills. Physical fatigue usually occurs due to lack of sleep and not exercising, while mental fatigue is caused by the disruption of the circadian rhythm mentioned above, lack of sleep, stress and intense work tempo.
Pilots are affected by both types of fatigue mentioned here due to their normal working routines. Pilots who are exposed to fatigue, who need to have constant attention and DF, have increased reaction times, decreased attention levels, decreased memory capacity and are forced to adopt an introverted behavior pattern in flight. The most important problem here is that the effects mentioned above are latent, unnoticeable and affect all functions of the person after fatigue caused by sleeplessness. As shown in the table below, sleeping with eyes open, not hearing radio conversations, disruption of communication during the task and partial incapacity-unconsciousness are the events experienced in the cockpit after fatigue.
Especially in the takeoff and descent phases that require intense attention during the flight, making non-standard movements, incorrect SID or STAR, approach practices, unstable approaches, generally decreasing flight competence, fixation on an event, decreased attention or shifting it to one side, disruption of prioritization between tasks, forgetfulness, wrong decision making and their decrease, fixation on an event, decreased attention or shifting it to one side, disruption of prioritization between tasks, forgetfulness, wrong decision making and SA loss as a result of these are the most striking situations experienced after fatigue.
What to do to combat fatigue and sleeplessness; First of all, resting sufficiently during off-duty times, doing sports, taking up hobbies, taking controlled rests during the flight, establishing an effective ECM with the other cockpit member and benefiting from his/her observation skills, ensuring that the cabin crew checks the cockpit at regular intervals and creating awareness about fatigue in the crew planning departments of the companies. It is very important for pilots working at a high flight tempo to combat sleeplessness and fatigue in order to ensure flight safety and to perform their duties effectively. Here, it should be ensured that the pilots who feel tired are rested, kept away from flight activities for a certain period of time, and that all pilots understand the effects of fatigue in refresher training.