Ergonomic Working Design Model in Reducing Fatigue due to Air Traffic Control (ATC) at Kuala Namu Airport, Indonesia

The design of the systems involving humans and machines traditionally focuses on the hardware or machines only, without considering the human element as an active party. However, in designing machines, it is essential to study human beings as an essential component to determine their limitations. Satisfaction is a person's attitude that can adapt well to work and social relations with workers and others [1].

There are two important interfaces in the human-machine system in which ergonomics plays an important role [2]. The first is a display capable of connecting the engine conditions to humans, while the second interface is a control that tends to adjust to the response obtained from the information displayed earlier. Therefore, between the display and the controls, there need to be interactions.

This research was carried out using the Rapid Upper Limb Assessment (RULA), which is a research method that does not require special equipment in determining the posture of the neck, back, and upper arms. Each movement is given a predefined score [3]. RULA was developed by Mc Atamney and Corlett (1993) as a method used to detect the posture of a risk factor [4]. This method is designed to assess workers and to determine the musculoskeletal burden that is likely to disrupt upper limbs [4].

Work posture analysis of the ATC controller needs to be appropriately carried out to determine the incompatibility between man and machine and the complexity of the work system that continues to provide additional burden.

Several studies have shown that the ATC controller's incorrect work posture causes work-related fatigue, which decreases the productivity of the controller. Therefore, it is necessary to determine a good work posture to minimize the onset of fatigue. This study aims to determine the work postures that lead to the emergence of fatigue, errors, and complaints arising from workers (employees), which causes work-related fatigue. The study also aims to design a strategy capable of minimizing fatigue due to work to create a suitable and comfortable working environment [5] capable of supporting the productivity of workers.

3.1 Work posture assessment from the NBP and RULA questionnaire

Observations on work postures, methods, and interviews were carried out directly with ATC controllers to facilitate the analysis performed when interacting with the work equipment used, as shown in Figure 1.

Data obtained from NBP questionnaires' recapitulation are grouped into several categories of complaints, namely not sore, rather sore, and sore as shown in Table 1 to Table 3. Strata carry out this assessment against each complaint, which is presented by a histogram.

The filling questionnaire results on the NBP indicate that some controllers have disrupted muscle tension. The dominant symptom of skeletal muscle is in the buttocks (67%), waist, upper and lower neck (60%), back (57%), right shoulder (50%), and other limbs (less than 50%).

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Figure 1. Controller interaction with tools

Table 1. Unresolved complaints recapitulation from NBP questionnaire on ATC controller

Table 2. Unresolved score from NBP questionnaire on ATC controller

Table 3. Category of action of RULA

3.2 Working posture resulting in fatigue from work

Various internal and external complex factors influence the relationship between work posture and capacity. For external factors: (i) tasks performed, both physically and mentally, (ii) organizational works, such as rotational jobs, length of working time, rest time, reward and punishment, etc., also (iii) work environment, such as physical, chemical, biological, physiological, and psychological work environment. For internal factors: (i) somatic factors, such as sex, age, body size, health condition, and nutritional status [9], and (ii) psychic factors, such as motivation, perception, trust, etc.

Work postures capable of leading to fatigue are associated with the working controller frequency, which is static and dynamic. A controller working in a static sitting position for a long time finds the job boring and tiring. Faulty seating due to inconsistency with the wearer's anthropometry also adds to the stresses and tends to be the main cause of back problems. Inconsistencies that need attention include the height of the headrests, backrest, seat, and the turning angle of the chair. The mismatch between head and back height with sitting and shoulder height causes skeletal muscle disorders on the neck and shoulders. This pain eventually spreads to the back and waist. Popliteal heights lower than the chair make the foot in a hanging position and causes skeletal muscle disorders in the calf.

Working dynamic muscles occur in the upper and lower parts of the neck. This is worker needs to be upright when reading with the forearm used in typing and holding the mouse. Working dynamic muscles does not negatively affect the controller because the muscles dynamically act as a pump for blood circulation.

3.3 Workplace determination which can cause work post error

In the human-machine system, there are basic elements that interact with each other. These elements include human operators, hardware, software, firmware, and the environment [10]. The elements, such as tools, working strategies, and environment are influential on job performance. Therefore, to achieve high performance, these elements need to be fully harmonized with the abilities, permissibility, and limitations of workers [11]. In this case, the human-machine system in the ATC room, particularly the ACC section, comprises high-tech and complex techniques. Each controller needs to interact with multiple hardware, such as a monitor, display, controller, communication tool, etc. This tends to provide an additional burden both physically and mentally. Figure 2 and Figure 3 displays and controls used by the current ATC controller.

Displays or props are needed to convey information to workers in various ways and to make the tasks smooth. Therefore, it is defined as a communication system that connects work facilities and machines with humans as the engine controller. Visual displays generally assist the information received by workers. In certain situations, it can be assisted with display-related hearing. This means that a good display design needs to prioritize functional factors capable of conveying human information in carrying out their job properly without errors. Factors that can lead to work accidents due to poor design of props are read errors, slowness in interpreting data or information, etc.

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Figure 2. Histogram unresolved score from NBP questionnaire on ATC controller

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Figure 3. Controller interaction with tools

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Figure 4. Layout supporting facilities that are unsafe condition and can inhibit movement

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Figure 5. Back (Spine) does not reach the backrest

The color display in ATC Kuala Namu Deli Serdang – Medan Field is monochrome with a black background, red symbol, and white space, which can be changed according to the controller. According to Gavriel Salvendy, hundreds of colors are used more effectively for drawing and solid modeling in computer-aided design. However, for simple code and information, more than 10 colors cause problems. Therefore, the letters' size needs to be adjusted to the distance of view to ensure readings of existing information are more easily and quickly understood. The current font size also does not match the controller's maximum viewing distance, thereby leading to an unnatural (forced) behavior in the reading display. Furthermore, the controller prefers to set the contrast and brightness on the monitor screen to prevent it from glaring.

The observations made by the controller indicate that the ATC needs to accept additional loads due to the complexity of the interaction of the work system, such as incremental loads of hardware incompatibility and unsafe conditions due to the unmanageable wiring arrangements that disturb the clearance legs. In addition, the groundwork used for the placement of control devices, telephones, etc. is too narrow, thereby stacking up some communication devices. In addition, all seats used by the controller have a high armrest that ranges from 66-69 cm from the floor.

The chairs used by the workers seen in Figure 4 and Figure 5, have inadequate backrest height, because when workers want to put their heads to rest in uncomfortable conditions. So that all chairs used by the controller have high armrests ranging from 66-69 cm from the floor, which is declared uncomfortable.

3.4 Conceptual design of working posture

The working posture of ATC controllers that do not rest their back on a special seat leads to complaints on the buttocks (67%), waist, upper and lower neck (60%), back (57%), and right shoulder (50%). This data was obtained from the results of the NBP questionnaire. Therefore, the work posture of the ATC controller needs to be in a sitting position.

The conceptual design of the working posture of the ATC controller with a sitting position minimizes and overcomes the following work-related aches and fatigue complaints: (i) The chair's position needs to be arranged to enable adequate space for free movement of the limbs. (ii) Sitting needs to be carried out with the waist straight, shoulders behind, and buttocks touching the chair's back. (iii) The seat height needs to be set with the foot forming an angle of 90º and pressing the pressure at the thighs' bottom evenly. (iv) The forward and backward on the backrest need to be made as comfortable as possible. The back needs to be on an adjustable chair back. (v) Both legs do not need to hang or cross each other. Furthermore, the footrest needs to be as high as 5-10 cm from the floor. (vi) Working attitude needs to be performed by sitting and standing after each other.

3.5 Complaints analysis and work errors of the operator

The highest level of work posture errors occurred in the older controllers with prolonged tenure. A total of 10 controllers from the 30 ATC were observed as shown in RULA data processing compared to the working period and controller's age.

Controller complaints and errors lead to work-related fatigue and stress, thereby decreasing performance and productivity.

The American Optometric Association called Computer Vision Syndrome (CVS) [12] stated that the eye cannot be permanently damaged due to the computer's continuous use. However, temporary damage is reduced when computer usage is stopped. Furthermore, some symptoms arise when using a computer. Some of the CVS symptoms include (i) Myopia: This is the temporary inability to see distant objects for some minutes to several hours after using the computer. (ii) Tired eyes: This tired eye condition is due to the use of small font size when reading a document on a monitor, which leads to an imbalance of contrast between the text and background, thereby leading to a dry eye. (iii) Blurred vision: This is caused by physiological changes (due to aging or disease). Blurred vision is also caused by seeing a continuous object at a distance of 12 inches and reading with less light. (iv) Dry eyes, irritation, and watery eyes. This situation occurs due to a lack of fluid. The moisture is applied to the eye by blinking. The amount of eye blinks varies according to the activity being performed and decreases due to contracts. Eyes become red and watery when using the computer and tend to reduce the number of flickers. (v) Increased sensitivity to light. (vi) Headache, backache, neck pain, and muscle spasms.

The musculoskeletal disorders caused by the use of a computer or controller include muscle weakness and tendon or neck and back pain up to cumulative trauma. This cumulative trauma is associated with a persistent motion called Repetitive Strain Injury (RSI). The ATC controller's causes of musculoskeletal disorders include unsuitable postures that occur continuously when using the computer, inappropriate back support, sitting in the same position for prolonged periods, and poor ergonomic design.

3.6 Posture analysis of ATC

The most of the time, air traffic controllers work in a seated position. The wrong work posture analysis on the ATC controller is caused by machine, human, method, environment, and equipment factors. (i) Machine: This factor is less ergonomic because the machine or monitor is too close to the controller, thereby making the equipment layout narrow and less good for the eyes. (ii) Man: The controller's difficulty to work due to the narrow working platform creates an additional load for the controller, thereby decreasing its productivity. Complaints due to wrong sitting position, prolonged working hours with the same position (fixed), and static muscles in certain parts of the spine and upper arms cause discomfort to the musculoskeletal system. (iii) Method: PT. Angkasa Pura II has a proper Standard Operation Procedure (SOP). However, the controller is not concerned about the SOP that has been determined, therefore, it is not properly realized. (iv) Environment: Noisy environments arise from existing speaker sounds, conversations between controllers, and talks between aircraft pilots and controllers on the ATC [13]. This noise tends to complicate the reception of the controller-provided information to the pilot or vice versa. This leads to the occurrence of something that is not desirable because an error in the receipt of information tends to cause an accident.

There are several things to note in addition to environmental noise factors, there are also the lack of fresh air, such as smoking in an air-conditioned room, also leads to illness. This results in non-smoking controllers becoming passive cigarette smokers because, in most cases, the room is not properly facilitated with an adequate exhaust fan to filter the cigarette smoke. A monotonous and unattractive room also makes the controller cramped while inside. In addition, poorly maintained cleanliness causes equipment to become dusty. This affects the state of the machine, such as its age. (v) Equipment: The existing seats are adjustable, therefore, the problems that arise come from people that lack discipline, thereby leading to a wrong work posture.

3.7 Workplace analysis in ATC section

Another factor to consider when choosing an optimum workplace is the environment. In the human-machine system in the ATC room, work involves high and complex technology. Each operator needs to interact with multiple hardware, such as a monitor, display, controller, communication tool, etc. Observation showed that the controller needs to get a load of hardware incompatibility.

The interviews conducted with ATC controllers showed that the current disadvantages of displays and controls are found from the incompatibility between the controller and the engine as: (i) the controllers find it difficult to receive voice information from aircraft pilots due to spelling errors. The controller's noise conditions cause this because the ATC's work environment includes control centered area (ACC), and provision of approach control (APP) in one room, thereby adding additional load to the controller. (ii) The cold air temperature makes the controller feel cold and stiff, especially at night, because they need to adjust the machine's condition, and (iii) the controllers are often disturbed by ATC machines, which makes them panic while on duty, especially when the traffic is solid.

The weakness of the controller's work other than those due to hardware incompatibility, microclimate factors, such as air temperature, humidity, velocity, and intensity of lighting, also need to be within comfortable limits. This is to ensure the microclimate condition does not provide an additional burden to the controller.

3.8 Proposed (model) conceptual design posture in ATC section

Currently, the ATC controller's work posture with a sitting position is still not good because they sit with the position of the spine, which is not on the back of the chair, especially at the waist. Therefore, the design on work posture ATC controller with a sitting position is conducted to overcome this error and minimize work-related aches and fatigues are as (i) the chair's position needs to be arranged to ensure there is adequate space to move the limbs freely. The controller can lie down when the traffic is not crowded, using a chair equipped with headrests. (ii) The controllers need to sit with the waist straight, shoulders behind the buttocks, and touch the chair's back. This is carried out to ensure the controllers avoid sitting in a wrong posture to avoid pain in the lower back. (iii) The seat height needs to be set to ensure that the foot forms an angle of 90º and the pressure at the bottom of the thigh is evenly distributed. This is carried out to ensure the fatigue on the thigh has a sitting position that can be spared, to ensure the controller works comfortably and safely. The uneven pressure on the thighs causes pain and numbness in the controller's foot due to improper blood circulation. (iv) Allows for comfortable forward and backward movement. The back needs to be on an adjustable chair. Working posture with the best attitude is obtained by adjusting forward and backward on the seat for the controller to ensure the muscles feel good. (v) Both legs do not need to hang or cross each other. Therefore, the controllers need a footrest as high as 5-10 cm from the floor. This is carried out to prevent sores' occurrence in the legs because the work posture in the right sitting position does not lead to the emergence of fatigue. Furthermore, the legs do not hang due to the incorporation of a fixed Table 4. (vi) Perform working attitude by sitting and standing after each other. Work posture with a prolonged sitting position causes sore in the waist, back, buttocks, upper neck, and arms. This situation is overcome with a working attitude and the possibility of sitting, interspersed with standing, thereby ensuring that the muscles that contract continuously can relax, leading to a decrease in fatigue and work-related stiff complaints.

Table 4. Recommended of proper sitting posture