In the aviation industry SHELL model plays a vital role in the identification and rectification of human factors that can affect performance safety and efficiency. It is necessary to analyze the interface between the human operator and the other components of the aviation system. For that purpose, the SHELL model helps to identify and mitigate the risk. and to prevent errors, and improve overall safety in this highly complex and dynamic aviation industry. The ICAO Shell Model in aviation is described in ICAO Doc 9859, Safety Management Manual.
The SHELL Model is a famous framework widely used for Human factors and ergonomics. In general, it is used to study and understand the interaction of various elements, and how they contribute to human factors (safety) in a complex system or environment. This model was conceptualized and introduced by Elwyn Edwards in 1972 and later on, it was modified by Frank Hawkins. The main focus of this model is to analyze, identify, and address those factors that can impact human behavior, performance, and decision-making in the working environment.
Components of the SHELL Model
The shell model is the interaction between the central main Liveware and their surrounding elements (S) Software, (H) hardware, (E) Environment, and (L) liveware. In this model (L) liveware is human or individual. (S) is software that includes manuals instructions, procedures, and other documentation. (H) Hardware means the physical assets equipment and machines that are used in the operations. (E) Environment means the social and physical environment that surrounds the area where the task is performed including noise, climate organizational culture, etc. (L) Liveware to liveware which means the interaction of the individuals with the other individuals that communicate, coordinate, and work as a team in a working environment.
THE SHELL MODEL DIAGRAM
As we see this model visually it looks like a block diagram in which liveware is in the center depicting the human as an operator that is surrounded by the other elements. Each element in this model highlights a specific type of interaction. This allowed them to analyze and examine their potential weakness and opportunities for improvement. That allows us to reduce the chances of human errors and to make countermeasures if any weakness is found.
Shell Model in Aviation
In the Aviation SHELL model is widely used to study human factors in aviation. Due to the sensitive nature of this industry, even a minor mistake can lead to a disaster. Throughout the years starting from the foundation of the aviation industry, most of the incidents and accidents in the aviation industry have taken place due to human errors and mistakes. According to the research by the National Aeronautics and Space Administration found that 70%of all aviation accidents involve human error and some other research indicates that it’s almost 85% that leads to huge financial as well as precious human lives.
To analyze and identify human errors to take appropriate actions for the reduction of such kinds of human error different techniques and frames works are being used. The SHELL model is one of them which is used to understand and analyze the interaction between humans and various other components of the systems. It gave us a structured approach to identifying the potential risks and operational challenges for enhancing safety and efficiency in the complex and sophisticated aviation environment. This model emphasizes humans as having a central role in the operations and the importance of understanding their interaction between people, processes tools, and the environment. Further, each element of the shell model respective to the aviation industry is given under.
1. Liveware
The liveware depicts the human as an operator in the SHELL model. In the aviation industry pilots, air traffic controllers, ground crew, etc. are the liveware because they are at the center of the aviation system. Humans have unique strengths like adaptability, critical thinking to make decisions, etc. But humans do have limitations that reduce their performance like fatigue, stress, etc. That’s why different factors like training, health, experience, and motivation affect their performance.
Nowadays over-reliance on automation can reduce pilot awareness same for the ground crew. Not abundant rest time for personnel can cause fatigue which leads to impairing judgment and reaction time, which is critical especially for aircraft crew and air traffic controllers. Therefore, studying human operator and identifying the factors that impact their performance is necessary especially to make such measures to counter those errors and to optimize personal performance without any risk of those factors that can lead to human error.
Example
In 2013 Asiana Airlines Flight 214 accident. Due to the pilot fatigue factor, confusion about the automation system, and inadequate training. The Pilot mismanaged the aircraft’s descent speed while landing in San Francisco which became the cause of the accident. This highlights the importance of human limitations understanding and the importance of training to optimize human performance.
2. Software
In the SHELL model software means the nonphysical components. like in aviation operation procedures, training manuals, checklists, rules, regulations, etc. That guides the aviation personnel to ensure safe and effective consistency of the operations. For that reason, clear standardized procedures are necessary for safe operations. Any misinterpretation in the procedure can lead to incorrect action which can cause a fatal accident. As the aviation industry is evolving rapidly due to technological advancement, the procedures need to be modified and made more user-friendly for the operators so that they can efficiently implement those procedures.
Example
In 2009 Air France Flight 447, due to the pilot’s lack of clarity regarding procedures of stall recovery became one of the causes of this accident. Here pilot becomes confused when the autopilot is disengaged and conflicting instructions in training become the cause of the improper handling of this situation. This tells us the importance of clear and standardized procedures are necessary for regular updates in training manuals.
3. Hardware
In the SHELL model hardware in the aviation industry means the physical components like aircraft. the cockpit design, ground handling equipment, maintenance tools, ground support vehicles, etc. If the man-machine interface is better it leads to the optimum performance and vice versa. OEM (original equipment manufacturers) must consider ergonomic and usability principles to enhance the man-machine interface. For optimum performance, personal experience and training must be taken for specific hardware or machines that they are operating. Like type rating for the pilot is necessary for a particular aircraft to fly. Regular maintenance and updates are also necessary for the reliability of the physical equipment.
Example
In 1989 United Airlines flight 232 incident told us the importance of the design of the cockpit where during an emergency pilot relied on a combination of throttle adjustments and teamwork to manage that emergency because their hydraulic system failed. The complexity of the cockpit system made it extremely challenging for the pilot to recover.
4. Environment
Aviation noise, weather, air traffic in particular airspace, workload, organizational culture, etc. are some common environmental factors. Like in flight operation weather, visibility, and wind speed directly affect significantly. Internal conditions like workload cockpit noise, and temperature lighting impact the pilot’s performance.
Example
In 2000 Singapore Airlines flight 006 crashed at Taipei airport due to poor visibility heavy rain and a typhoon. This tells the importance of environmental factors that can significantly impact work performance. So excellent planning according to the environment conditions, and continuous training from time to time are vital for optimum and best output.
5. Liveware-Liveware
The Liveware to Liveware focuses on the interaction between individuals with each other like pilots, air traffic controllers, ground crew, and cabin crew interact with each other. As they need to work with close coordination. That is why in the aviation industry crew resource management (CRM) training is important, to ensure effective collaboration. Even in a stressful environment, they can perform their task without any risk of error.
Culture and linguistics can create barriers so that’s why standard radio telephony language is used in the aviation industry. Especially for critical aviation functions like communication between pilots and ATC. Other than that plan English is set for communication especially in international aviation operations in order to reduce the chance of linguistic-related problems during communication in aviation operations.
Example
In 1977 the deadliest aviation accident in history the “Tenerife Airport Disaster” involving two Boeing 747s occurred due to miscommunication between the KLM pilot, air traffic control and the ground crew caused the collision on the runway. This highlights the importance of effective and positive communication according to protocols set by the regulatory bodies and the importance of up-to-date (CRM) Crew Resource Management training.
Advantages
It helps in the comprehensive analysis of human factors in aviation.
It helps to find mismatches in the interface such as in a liveware-hardware liveware-environment.
This model widely helps in the post-accident investigation to analyze the human factor contribution towards the accident.
This model enhances communication and coordination.
It helps to improve system design to ensure that it aligns with human capabilities and limitations.
It helps to take proactive safety measures before they cause any accident.
It helps to develop training programs. Like CRM which improves decision-making situational awareness and teamwork under high pressure.
Disadvantages
This model only focuses on human-system interaction which can neglect system issues such as financial issues regulatory framework organizational politics etc.
It’s challenging and resource-intensive to analyze all components of the SHELL model comprehensively in real-time complex aviation industry scenarios.
Its effectiveness highly depends upon the experience and skill of the person who is applying it.
It doesn’t directly address the technical or mechanical failure until or unless it interacts with the human factor.
It evaluates the individual interface because of that it might not provide a comprehensive view of how systematic interaction contributes to safety concerns in the aviation industry.
Analyzing Tenerife Accident with SHELL Model
The accident at the Tenerife Airport is considered one of the deadliest accidents in aviation history. In which two Boeing 747s collided on the runway. (Boeing 747s—KLM Flight 4805 and Pan Am Flight 1736) on March 1977 at Tenerife North Airport which took the lives of 583 people. The primary cause of this accident was considered human error, poor visibility, and miscommunication. When we analyze this model with the Shell model. It shows how mismatches in human-system interaction contributed to this disaster.
1. Liveware-hardware
When we talk about human and equipment interaction in this tragedy. At that time Runway was not equipped with ground radar which made it impossible for ATC to identify its location in poor visibility conditions. Also, the taxiway and runway markings were unclear which confused the position of the aircraft, and cockpit instruments at that time also relied on verbal ATC instructions which proves their ineffectiveness of instruments in foggy conditions.
Lesson learned: For better ATC and pilot situational awareness. Installation of ground radar and improvement in runway marking could help a lot.
2. Liveware-Environment
Dense fog caused visibility of less than 500 meters making both aircraft flight crew unable to see each other on the runway. At that time due to a terrorist attack at Gran Canaria Airport, the airport was overcrowded causing a high-stress environment for both crew and ATC.
Lesson learned: Better training and planning regarding such conditions could prevent errors in such kind of high-stress environment.
3. Liveware and software
In this accident, the miscommunication between the air traffic controller and the KLM flight crew member caused the captain’s mistaken interpretation of ATC clearance. As ATC said “Stand by for takeoff” but the captain misinterpreted it as a clearance permission to takeoff. Also, the KLM crew didn’t complete its checklist. They didn’t verify that either runway was clear or not. The use of non-standard phraseology confused them.
Lesson learned: The implementation of checklist discipline and standard phraseology can prevent such kinds of misinterpretation.
4. liveware-liveware
In this case, the KLM, first officer hesitated to challenge their captain’s decision to take off. Also, the ATC and Pan Am crew were confused regarding the location of the KLM aircraft causing a delay in Corrective action. Both flight crews relied on ATC instruction because they didn’t have coordination between both aircraft flight crew.
Lesson learned: Strong CRM training can reduce the chance of miscommunication and poor coordination between crew members. Such as in this case first officer hesitated to challenge their captain’s decision.
Benefits of the SHELL Model
The Tenerife disaster highlights how a mismatch in the L-H, L-S, and L-L Interface led to a catastrophic accident. This shows the importance of the SHELL model in the aviation industry. As a result of this accident and after analyzing errors that led to this accident, Aviation Authorities have taken the following measures.
Standard ICAO phraseology. Such as “takeoff” is only used when clearance is granted.
Mandatory Crew Resource Management training for crew members,
The airport structure is enhanced. Including the installation of ground radar at major airports.
These measures that are taken by the Aviation Authorities show that by applying the application of SHELL model experts become able to identify human system failures and develop critical safety improvements to prevent such kind of catastrophic accidents in the future.
Conclusions
The SHELL model consists of the acronym which is Software, Hardware, Environment, liveware, and Liveware-Liveware which depicts different elements of the systems that interact with the human referred to as the ‘liveware”. We cannot eliminate the risk of human error but by continuous effort and improvements in aviation policies and procedures, we can reduce the risk of accidents caused by humans.
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