Aviation Australia: Types of Error in Maintenance Tasks PDF

Types of Error in Maintenance Tasks (9.8.2) Learning Objectives 9.8.2.1 Describe typical errors that are more prevalent during regular maintenance tasks (Level 2). 9.8.2.2 Describe typical errors that are prevalent during less frequent maintenance tasks (Level 2). 9.8.2.3 Identify...

Types of Error in Maintenance Tasks (9.8.2) Learning Objectives 9.8.2.1 Describe typical errors that are more prevalent during regular maintenance tasks (Level 2). 9.8.2.2 Describe typical errors that are prevalent during less frequent maintenance tasks (Level 2). 9.8.2.3 Identify the main causes of error in aircraft maintenance (Level 2). 9.8.2.4 Explain violations in aircraft maintenance and reasons why violations occur (Level 2). 2023-01-12 B-09 Human Factors Page 281 of 340 CASA Part 66 - Training Materials Only  Types of Errors in Maintenance Tasks Errors During Maintenance Tasks As AMEs are human, errors in the industry are inevitable. Any maintenance task performed on an aircraft is an opportunity for human error to be introduced. Errors in aircraft maintenance engineering tend to take two speci c forms: An error that results in a speci c aircraft problem that was not there before the maintenance task was initiated (e.g., damaging an air duct by stepping on it to gain access when performing a task). An error that results in an unwanted or unsafe condition remaining undetected, i.e., something is missed (a structural crack unnoticed during a visual inspection task). 2023-01-12 B-09 Human Factors Page 282 of 340 CASA Part 66 - Training Materials Only  Errors During Regular Maintenance Tasks A large proportion of maintenance tasks are routine, such as regular, periodic checks of aircraft. Thus, maintenance workers may use a certain set of procedures so frequently that slips and lapses can occur. Sometimes maintenance workers will become so accustomed to doing a regular, often repeated task that they will not use any written guidance. Indeed, it would often be unrealistic and unnecessarily time consuming to expect them to constantly refer to familiar guidance material. However, errors may occur if they do not have a commitment to keep up-to-date with any changes made to these frequently used procedures. These routine tasks are also susceptible to complacency and rule-based errors. © Aviation Australia Routine tasks are susceptible rule-based errors. Errors During Less Frequent Maintenance Tasks When undertaking tasks that are performed less frequently, there is a greater possibility of errors of skill and judgment. If maintenance workers do not familiarise or refamiliarise themselves properly with what needs to be done, they will not work ef ciently and may mistakenly select the wrong procedure or parts. 2023-01-12 B-09 Human Factors Page 283 of 340 CASA Part 66 - Training Materials Only  Errors Due to Individual Practices and Habits Where procedures allow some leeway, aircraft maintenance workers often develop their own strategies or preferred ways of carrying out tasks. Often, a good rule or principle is one that has been used successfully in the past. These good rules become accepted practices that maintenance workers might adopt for day-to-day use. Problems occur when a rule or principle is wrongly applied. For example, aircraft pipe couplings are normally right-hand threads but applying this ‘normally good rule’ to an oxygen pipe (having a different thread) could result in damage to the pipe. Also, there can be dangers in applying rules based on previous experience if, for example, system design differs, as is sometimes the case with Airbus and Boeing. This may have been a factor in an A320 incident, where subtle differences between the operation of the spoilers on the A320 and those of the B757 (with which the engineers were more familiar) meant that actions which would have been appropriate on the B757 were inappropriate in the case of the A320. The assumption that all all threads are right-handed is an example of an error due to habit In addition, young maintenance workers may pick up bad rules, leading to bad habits, by watching others or by being taught incorrectly during their working life. 2023-01-12 B-09 Human Factors Page 284 of 340 CASA Part 66 - Training Materials Only  Violations in Aircraft Maintenance As outlined earlier, a violation differs from an error in that there is an intent to deliberately act against rules, guidelines or accepted practice. It is an unfortunate fact of life that violations occur in aviation maintenance. Most stem from a genuine desire to do a good job, seldom are they acts of vandalism or sabotage. However, they represent a signi cant threat to safety as systems are designed under the assumption that people will follow correct procedures. There are four types of violations: Routine violations Situational violations Optimising violations Exceptional violations. Time pressures and high workloads increase the likelihood of all types of violations occurring. People weigh the perceived risks against the perceived bene ts. Unfortunately, the actual risks can be much higher than the perceived ones. Routine Violations Routine violations are faulty procedures which have become a normal way of operating within the person’s work group (e.g., a maintenance team). They can become routine for a number of reasons. For example, maintenance workers may believe that correct procedures are over-prescriptive and violate them to simplify a task (cutting corners), to save time and effort. Examples of routine violations are not performing an engine run after a borescope inspection (“It never leaks”), or not changing the ‘O’ ring seals on the engine gearbox drive pad after a borescope inspection (“They are never damaged”). Routine violations are committed to avoid unnecessary effort or to circumvent clumsy or inappropriate procedures. Example: Cutting corners A 747 was about to make a rst ight after servicing in which oil lines on one engine had been changed. After nding oil leaks on the engine run, technicians tightened the suspect oil lines. A further engine run was not carried out because a tug had arrived to tow the aircraft to the ight line. Technicians followed the aircraft to the terminal, where they performed an engine dry motor, but did not fully start the engine. No oil leaks were found. The aircraft departed, but then an oil leak from the engine caused an in- ight shut down (IFSD) and diversion. 2023-01-12 B-09 Human Factors Page 285 of 340 CASA Part 66 - Training Materials Only  Situational Violations Situational violations occur due to the particular factors that exist at the time, such as time pressure, high workload, unworkable procedures, inadequate tooling or poor working conditions. These occur often when, in order to get the job done, maintenance workers consider that a procedure cannot be followed because it will take too long or be unsafe to do so. Example: Inadequate Resources An example of a situational violation is an incident which occurred where the door of a B747 opened in- ight. An engineer with a tight deadline discovered that he needed a special jig to drill some holes in a new door torque tube. The jig was not available, so the engineer decided to drill the holes by hand. If he had complied with the maintenance manual, he could not have done the job and the aircraft's next ight would have been cancelled. Situational violations to get the job done occur in circumstances when it is impossible to complete the job by sticking to the rules. 2023-01-12 B-09 Human Factors Page 286 of 340 CASA Part 66 - Training Materials Only  Optimising Violations Optimising violations involve breaking the rules for ‘kicks’. These are often quite unrelated to the actual task. The person just uses the opportunity to satisfy a personal need. Example: Speeding An example of an optimising violation is a maintenance worker who is late to meet an arriving aircraft. They have to drive across the airport, and they do so faster than the speed limit allows. Thrill-seeking or optimising violations are committed for fun or to avoid boredom but can also be done in a misguided effort to do a good job. Other examples of thrill-seeking violations The most obvious examples are found in the handling of vehicles: speeding, cutting in, tail- gating, ‘road rage’, etc. Sometimes working at heights or con ned space entry procedures are violated because people are thrill-seeking; Some towing incidents and accidents involving ground support equipment contacting aircraft are due to thrill-seeking. Towing incidents are typically a result of Optimising Violations Exceptional Violations Exceptional violations are typi ed by particular tasks or operating circumstances that make violations inevitable, no matter how well-intentioned the maintenance worker might be. For example, an error in a document speci es an incorrect torque value, or the wrong type of oil. 2023-01-12 B-09 Human Factors Page 287 of 340 CASA Part 66 - Training Materials Only  Why People Violate Rules ‘I can handle it’ or ‘I can get away with it.’ Some people prefer to rely on their own skills and experience, especially more experienced and more skilled people. ‘I can’t help it.’ Procedures are confusing or ambiguous. ‘Everyone does it.’ Peer pressure or other norms. “It’s what they want” or ‘They’ll turn a blind eye.’ Cutting corners thinking that doing so will bene t everyone. ‘It's easier this way.’ If the instructions were followed to the letter, the job wouldn’t get done. ‘I didn’t know there was a procedure’ or ‘I know what is in the procedure’ (when they don’t). © Aviation Australia Why people violate rules These are some of the beliefs that lead people to violate. Any attempt at improving compliance must address these issues. Several of them relate to the widely held attitude that violating is okay when done by a skilled person. They believe their skill shows them how to bend the rules and get away with it. Some of these beliefs have to do with the fact that violations may be going on all over the maintenance organisation. Consequently, people feel powerless to avoid them. Indeed, they might feel that violations are expected of them. They may also be aware that managers turn a blind eye to violations that get the job done and so meet tight deadlines. 2023-01-12 B-09 Human Factors Page 288 of 340 CASA Part 66 - Training Materials Only  Situational Factors that Promote Violations Time pressure High workload Unworkable procedures Inadequate equipment Bad working conditions Supervisors who turn a blind eye. Removing or moderating these local factors that produce errors and violations is a major part of managing unsafe acts. © Aviation Australia Situational Factors that Promote Violations 2023-01-12 B-09 Human Factors Page 289 of 340 CASA Part 66 - Training Materials Only  Use of Unapproved and Informal Procedures (‘Black Books’) In many highly- regulated industries, especially those with confusing or highly technical instructions, it is common for the workforce to write their own procedures. These can be jealously guarded and passed on to new members of the workgroup. They are sometimes known as ‘black books’. Studies show that, in some workplaces, around 56% of workers and 51% of managers keep unapproved and informal procedures. While ‘black books’ can be convenient and save time, in aircraft maintenance there is a danger that contains incorrect information. This may be because the information was transcribed incorrectly, or because the source of the information, such as an approved maintenance manual, may have undergone changes since the black book was written. Image by Glenn Carstens-Peters on Unsplash Information in 'Black books' can have transcription errors or be outdated 2023-01-12 B-09 Human Factors Page 290 of 340 CASA Part 66 - Training Materials Only  Bad Procedures Many violations are due to bad procedures. As we have already seen, situational violations arise because: People want to get the job done. The tools or the situation make it impossible to do the job when following the procedures to the letter. In the nuclear industry, for example, nearly 70% of all human performance problems have been traced to bad procedures. That is, procedures gave the wrong information, or were inappropriate or unworkable for the present situation. Sometimes the procedures were not known, did not exist, were out of date, could not be found or could not be understood. As any aircraft maintenance worker knows, poor procedure or documentation is not just a feature of the nuclear power industry. 2023-01-12 B-09 Human Factors Page 291 of 340 CASA Part 66 - Training Materials Only  How Violations Differ from Errors Errors are unintended whereas violations are deliberate (the act, not the occasional bad consequences). Another major difference is that errors arise from information problems, whereas violations are shaped mainly by attitudes, beliefs, group norms and safety culture. The distinction between errors and violations depends upon: Intentionality Information versus motivation Demographics. Intentionality We do not generally intend to make slips, lapses or mistakes, but people do generally intend to deviate from procedures. Most people do not intend for any bad consequences to arise from their actions. Only saboteurs intend both the act and its bad consequences. Information versus Motivation Errors commonly arise as the result of information problems, either in the head or in the world. In short, errors are generally corrected by improving the information available. Violations, on the other hand, arise largely from motivational factors, from beliefs, attitudes, norms and the organisational culture at large. These are harder to correct. Demographics Men violate more than women and the young violate more than the old. The same does not apply to errors. 2023-01-12 B-09 Human Factors Page 292 of 340 CASA Part 66 - Training Materials Only  Main Causes of Error in Aircraft Maintenance When Professor James Reason analysed the reports of 122 maintenance incidents occurring within a major airline over a 3-year period, he identi ed the main causes as: Omissions (56%) Incorrect installation (30%) Wrong parts (8%) Other (6%). These ndings have been duplicated and con rmed in other organisations and in wider studies. It is likely that the ndings are representative for the aircraft maintenance industry as a whole. © Aviation Australia Main Causes of Error in Aircraft Maintenance Omissions Omissions can occur for a variety of reasons, such as forgetting, deviating from a procedure (accidental or deliberate), or becoming distracted. The B737 double engine oil loss incident, in which the HP rotor drive covers were not re tted is an example of omission. 2023-01-12 B-09 Human Factors Page 293 of 340 CASA Part 66 - Training Materials Only  Incorrect Installation Incorrect installation is unsurprising, as there is usually only one way in which something can be taken apart but many possible ways in which it can be reassembled, especially for complex components. Reason illustrates this with a simple example of a bolt and several nuts (see gure below), asking the questions: How many ways can this be disassembled? (the answer being 1) and How many ways can it be reassembled and still look the same? (the answer being about 40 000, excluding errors of omission!). Source: CASA (2013) Reason’s Bolt and Nuts Example Wrong Parts In the British Airways BAC1-11 windscreen blowout accident in 1990, the error was tting the wrong part number bolts to the windscreen. This is an example of ‘wrong parts’. A less speci c example is a maintenance worker servicing an engine with the incorrect grade of oil. 2023-01-12 B-09 Human Factors Page 294 of 340 CASA Part 66 - Training Materials Only