In the aviation industry, human error is consider as a major factor in most aviation accidents. Maintenance tasks that are performed incorrectly or are overlooked by maintenance crew would cause human errors. Examples of human errors in maintenance are installation of incorrect parts, essential checks not being performed and failed to install wanted parts. Among all aviation-related threats, errors made by maintenance crew are more difficult to detect and have the potential to remain dormant, affecting the safe operation of aircraft for longer duration. Although maintenance crews are responsible for their actions, organization problems also contributed to the threat of maintenance errors. Since it is not possible to eliminate all maintenance errors, introducing safety management systems (SMS) to aviation organizations can help identify hazards and control risk.
Human factors issues in aviation maintenance
Maintenance tasks may be carried out in confined spaces, at heights, under burning heat or in freezing cold and worst of all, it is also physically demanding. Good communication, coordination, clerical and focusing skills are needed to perform well in this environment. Fault analysis and rectification have to be solved quickly in order to minimize turnaround time. In addition, there would be latent emotional stress on maintenance personnel whose work has been involved in aviation accidents.
However unlike aircrafts, humans do not come with a set of instructional manuals that helps us to understand their performance and capabilities. Each and every individual varies in many ways, hence one will never know how one maintenance task attributed to errors. Aviation industries become aware of many unpredictable accidents coming from human errors due to different contributing factors (Refer to Figure 1 for a graphical illustration on human error vs contributing factors) (Takahiro S, Terry L, William D, 2008) and have taken steps to implement preventive or control measures. Factors contributing to human errors in maintenance
Statistics have shown that 80% of errors are contributed due to human errors while the remaining percentage is due to mechanical or other failures. (Refer to Figure 2 for a graphical illustration on human error contribution percentile) (“Strategic program plan,” 2007) There is also a breakdown showing which type of maintenance activities having higher rate of human errors. (Refer to Table1, Frequency of Human error vs Type of maintenance activity) (Goldman, 2002)
The Pear Model
Four important human factors of the Pear Model (Refer to Figure 5 for graphical illustration) are: People who do the job, environment in which they work, actions they perform and resources necessary to complete the job.
Human factors program focus on people who perform the work and attend to physical, physiological, psychological and psychosocial factors. Organization must focus on individuals, their physical capabilities, mental state, cognitive size and circumstances that may affect their interaction with others. Factors like each person ‘s size, age, eyesight, strength, endurance, experience, motivation and certification standards must be taken into consideration before each person is tasked to work. Sufficient breaks and rest periods must be catered to ensure each person is not overload. Organization should encourage more teamwork and communications between colleagues so that work accomplished will be safe and efficient. Offering educational programs on health and fitness can help encourage good health and help reduce sick leave. Hence, a good human factors program will consider all the limitations of humans and designs the job accordingly.
Physical workplace in the hanger/shop and organization environment are environments that are focused on human factors program. Conditions like temperature, lighting, noise control, cleanliness, humidity and workplace design are considered physical environment. Cooperation, mutual respect, culture of the organization, communication, leadership, shared goals and shared values are important factors in an excellent organizational environment.
The standard human factors approach to identify skills, knowledge and attitudes to perform each task in a given job is called Job Task Analysis (JTA). It helps to identify what instructions, tools and other resources needed to perform each task. By following exactly to the JTA, each worker will be properly trained and each workplace will also has the necessary equipment and other resources to perform the job.
Resources are viewed from a broad angle, such as anything that is needed to get the job accomplished. Resources that are tangible are test equipment, tools, lifts, computers and technical manuals, and so forth. Amount of time given, level of communication among people of different levels, the number and qualifications of staff to complete a job are considered resources that are less tangible. The most important element under resources is to identify the need for additional resources.
Accidents linked to maintenance
Japan Airlines Flight 123
In August 1985, Japan Airlines flight 123 claimed the lives of 520 people when it crashed into a mountain. It was bound for a short flight from Tokyo to Osaka but at the altitude of 24,000ft, the aircraft suddenly lost control due to the failure of the rear pressure bulkhead and caused the whole cabin to suffer a sudden decompression. The impact of the escaping air caused the separation of the vertical stabilizer, rudder, hydraulic lines and four pressurized hydraulic systems. Investigations revealed that the aircraft had encountered a tail strike incident a few years ago. The repair work done on the aft bulkhead did not comply with the OEM recommended procedure as two doubler plates instead of a single plate were used to do the splice. (Refer to Figure 3 for an illustration of the repair)
Eastern Airlines Flight 855
On May 5, 1983, Eastern Airlines flight 855 was on a flight from Miami, U.S. to Nassau, Bahamas. The plane carried a total of 172 people. While making a descend, the low oil pressure warning indicator on the center engine lighted up. The flight crew shut-off the center engine and decided to return back to Miami with the remaining two engines. On the way back to Miami, the aircraft’s low oil pressure warning indicators for the remaining two engines lighted up followed by flamed out within minutes. Luckily the flight crew managed to re-start the center engine again after the aircraft descended from 13,000ft to 4,000ft without any power. After the aircraft landed safely at Miami airport with one engine, no live loss or injuries were claimed.
The investigation board concluded the cause of the incident was due to all three magnetic chip detectors on the engines had been installed without O-rings (Refer to Figure 4 for an illustration of the Chip) causing oil to leak from the engines during flight. This accident could be avoided if the engineers involved were discipline and carried out the maintenance tasks professionally.
British Airway Flight 5390
On 10 June 1990, British Airlines flight 5390 was on a flight from Birmingham, England to Malaga, Spain. Suddenly at about 17,300ft, the left windscreen on the captain’s side of the cockpit blew out from the cockpit. The captain was sucked out of his seat with half of his body hanging out of the plane and the other half resting on the flight controls. No lives were lost on this flight, but the captain suffered frostbite, bruising, and fractures to his right arm, left thumb and right wrist while flight attendant who aided the captain suffered a dislocated shoulder, frostbitten face and some frostbite damage to his left eye. Investigators found that the maintenance manager who worked on the windscreen had used incorrect bolts during a windscreen repair. Other issues highlighted were failed to check tolerance specification of the bolts, staffing shortage during night shift, parts storage and involvement of supervisors in hands-on maintenance work.
Safety Management Systems
A safety management system (SMS) is a systematic way to managing safety, policies, procedures, accountabilities, and including the necessary organisational structures. The objective of a Safety Management System is to provide a structured management approach to control safety risks in operations. Therefore in order to have an effective safety management, the organisation’s specific structures and processes related to safety of operations must be taken into account. safety management requires planning, organising, communicating and providing direction.
The first step of the SMS progession begins with setting the organisational safety policy. It lay outs the strategy for achieving acceptable levels of safety within the organisation and defines the principles upon which the SMS is built and operated. In order to mitigate and limit risk during operations in the designed processes, safety planning and execution of safety management procedures are needed.
Only with these controls in place, quality management techniques then can be utilised to ensure the intended objectives are met by deployment of safety assurance and if fail, evaluation processes are needed to provide continuous montioring of operations and for identifying areas of safety improvement. Furthermore, SMS also provides the organisational framework to set up and encourage the development of a positive safety culture.
Finally, the implentation of SMS provides the organisation’s management a structured set of tools to meet their respomsibilites for safety defined by the regulator.
Aviation industries have realized that it is not possible to entirely eliminate maintenance errors but to take an approach to identify, correct and minimize the consequences of those errors. And with the implementation of SMS, hazards could be identify and risks could be control. In conclusion, all these human factor studies help aviation industries to make continuous improvement and implementation of solutions to reduce maintenance errors.
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Figure 1. Human error vs Contributing factors. (Takahiro S, Terry L, William D, 2008)
Figure 2. Human error contribution percentile. (“Strategic program plan,” 2007)
Table 1. Frequency of Human error vs Type of maintenance activity. (Goldman, 2002)
Figure 3. Comparison of the correct and incorrect method of the doubler plate repair. (Hobbs, 2008)
Figure 4. Location of O rings on magnetic chip detector. (Hobbs, 2008)
Figure 5. The PEAR Model (FAA, 2012)