Friday, May 1, 2009
Fatigue Risk Management in Aircraft Maintenance
On June 10, 1990, British Airways Flight 5390, a BAC1-11, experienced a windscreen blowout shortly after departure from Birmingham Intl Airport (BHX) in the U.K. The left windscreen, which had been replaced prior to the flight, was blown out under effects of the cabin pressure when it overcame the retention of the securing bolts, 84 of which, out of 90 total, were of smaller than specified diameter. The captain was sucked halfway out of the window and was restrained by cabin crew while the copilot flew the aircraft to a safe landing at Southampton Airport (Air Accidents Investigation Branch report, 1992).
While the official accident report illuminated numerous contributing factors that led up to this incident, one of the most insidious factors was the effect of fatigue on the shift maintenance manager (SMM) who conducted the task.
The work was conducted very early in the morning at a time when the human body experiences a natural low, also known as circadian (or time of day) effect. This, combined with lack of sleep before his shift, may have contributed significantly to the SMM’s perceptual judgment error in selecting the wrong size bolts for the job and then justifying that decision by believing that the countersink was too big rather than the bolt was too small, according to the Air Accidents Investigation Branch report.
This error may have been caught if double checking and a pressure check were conducted. However, these procedures were not conducted at the time, and were not required in the maintenance manuals.
Effects of Fatigue
Since the BAC1-11 incident there have been a number of maintenance-related accidents and incidents where mechanic fatigue has been cited as a contributing factor. In this same period there has also been an exponential increase in research conducted on fatigue in aviation maintenance activities. Studies have shown that fatigue can have consequential effects on a person’s cognitive ability. Cognition refers to mental processes such as awareness, perception, reasoning and judgment.
Fatigue has drawn parallels to the effects of alcohol. In 2000, Williamson, Feyer, Friswell, and Finlay-Brown conducted a study on driver fatigue and found that after 17 to 19 hours without sleep, performance on some tests was equivalent or worse than that at 0.05 percent blood alchohol content (BAC). Response speeds were up to 50 percent slower for some tests and accuracy measures were significantly poorer at this level of alcohol. After longer periods without sleep, performance reached levels equivalent to the maximum alcohol dose given to participants (0.1 percent BAC). The findings reinforced empirically that sleep deprivation is likely to compromise decision-making ability and accuracy needed for safety on the road and in other industrial settings.
FAA research has shown that aviation maintenance mechanics routinely get less than the required eight hours of sleep per night. In one study of aviation maintenance mechanics, self-reported data indicated that participants slept an average of six hours and 15 minutes per day. Sleep duration as measured with the Actiwatch sleep measurement device was estimated to be five hours and seven minutes per day on average, according to a 2002 Johnson, Hall, & Watsons study. This data, combined with other findings of the study, posited the following conclusions by the authors:
The assessment of sleep duration showed that the population of aviation maintenance technicians, throughout the industry, is sleep deprived. This is a certain finding and represents a risk to safe work performance. This statement is independent of age, experience, type of company, season of the year, etc., and it is exacerbated by shift work schedules. Based on the data, low and insufficient sleep duration appears to be a cultural characteristic of the aviation maintenance workforce. The questionnaire data strongly support the fact that this general pattern of insufficient sleep is not a result of extended work hours. The combination of the measured data and the questionnaire data indicate that [mechanics] are not cognizant of the fact that they do not get enough rest.
FAA and NTSB Positions
In light of this study, the FAA appears to be resistant to promulgating new regulations for the purpose of decreasing fatigue in the aviation maintenance environment. This has created somewhat of a dichotomy between NTSB and FAA. In fact, a reduction of accidents and incidents caused by human fatigue has been on top of the NTSB Most Wanted list of aviation safety improvements for a number of years. The FAA response to the recommendation has, to date, been unacceptable. The NTSB argument reads as follows:
In 1999, the FAA issued a report, Study of Fatigue Factors Affecting Human Performance in Aviation Maintenance. The FAA expanded this study, completing the first phase of the expanded study and issuing a report in April 2000, titled Evaluation of Aviation Maintenance Working Environments, Fatigue, and Maintenance Errors/Accidents. The expanded study looked at multiple and combined environmental factors of temperature, noise, light, vibration, and sleep, which are known to accelerate fatigue onset, as well as the effects of lifestyle habits on fatigue and human performance. The study was designed to collect data in the aviation maintenance work environment on known factors that affect human fatigue and performance.
The FAA’s findings suggest that fatigue is an issue in this workforce. Data from "mini-logger monitors" that recorded data from the selected parameters of light, noise levels, and temperature; activity monitors that monitored physical activity, sleep, and sleep quality; and answers to background questions that employees were asked, clearly indicate that sleep durations are inadequate to prevent fatigue. For most aviation mechanic specialties, 30 – 40 percent of respondents reported sleep durations of less than six hours, and 25 percent of respondents reported feeling fatigued or exhausted.
The data was intended for use in predicting situations that are conducive to fatigue, accidents, incidents, and errors. Data collection began in August 2000, and the expanded study was planned for completion in December 2003. However, an FAA Aviation Maintenance Human Factors Project report from January 2004 stated that the research had not progressed, nor is any broad research effort or regulatory activity currently being conducted in this area.
The FAA has reported to Congress that, based on several studies completed on the maintenance fatigue issue, it believes that the extreme complexity of the issue of maintenance crew fatigue and duty time do not present appropriate material for regulatory activity, and that education and training in fatigue management are the most appropriate actions for the FAA to sponsor and foster. The agency has consequently conducted education and training activities on fatigue management for aircraft maintenance personnel.
On April 18, 2006, the safety board informed FAA that it disagrees with the position that regulatory action is not appropriate and that the FAA’s current education and training activities related to this issue can achieve the intent of this safety recommendation. On Feb. 22, 2007, the board informed FAA that it had reviewed Advisory Circular (AC) 120-72, "Maintenance Resource Management (MRM) Training," which seemed to be the primary focus of the FAA’s education and training initiatives related to fatigue among aviation maintenance crews as reported to Congress.
The board found little in AC 120-72 that provides guidance on human fatigue in maintenance crews other than generalized warnings that attention to fatigue is important and should be considered in MRM Training.
The AC contains little guidance as to how an employer should design a program to ensure that maintenance crews are not fatigued. The board asked the FAA whether it has any additional guidance related to fatigue in aviation maintenance crews besides AC 120-72 and whether the FAA will consider establishing duty time limitations for personnel who perform maintenance on air carrier aircraft, as recommended. The FAA has not yet responded.
Addressing the Disparity?
This disparity on how to address fatigue complicates the issue even further. On one hand, the FAA opines that education and training alone will deter mechanics from working while fatigued. While education and training are important components of a total fatigue management program, they are not, in and among themselves, going to create a significant reduction in fatigue-related incidents. Simple exhortations such as "don’t work when you are tired" or "make sure you get plenty of sleep" are not the solution to the problem.
On the other hand, NTSB recommends that work time limitations via regulation should to be established in order to limit the amount of time that an mechanic can work in any given time period. This appears to be a more robust solution, in light of the fact that there are many maintenance organizations pushing their mechanics to work shifts of up to 14 – 16 hours. Elective overtime may also push the mechanic into these hour categories. Empirical research has indicated that people do not perform well in safety-sensitive jobs when a shift is of this duration. The likelihood of committing fatigue-related errors increases significantly.
In order to fully address the ongoing issue of fatigue, a conflation of both the FAA and NTSB positions is warranted. A regulation to address working hours coupled with education and training will be the most effective way that industry can address the ongoing fatigue problem.
Until there is clear guidance on fatigue management, maintenance organizations will be on their own in responding to the issue. Some may understand the severity of the problem and act proactively while others may adopt a look-and-see attitude. Still others might simply ignore the issue altogether. Assuming the proactive position, there are a few steps that organizations can take to at least build a framework for fatigue management. For guidance, however, one may need to look at countries that have consistently been more proactive in safety.
For example, Canada tends to be more proactive in addressing the fatigue issue. In fact, unlike the paucity of information available on the FAA website, Transport Canada (TC) has a rich assortment of information available on fatigue risk management (FRM). Whereas the FAA takes a descriptive approach to fatigue risk management, TC focuses more on a prescriptive approach. The difference being that the FAA puts more emphasis on awareness while TC focuses on palpable countermeasures.
Limitations and Challenges
Assuming an organization implements a fatigue management system by choice or by mandate, there are still a number of limitations and challenges that need to be realized. While this list is far from exhaustive it does highlight a few potential problem areas that should be understood.
First, fatigue is a very subjective phenomenon. There are tests that can accurately determine whether someone is driving under the influence of alcohol. However, there are no scientific tests that can measure whether someone is "working under the influence of fatigue." To compound this issue further, people are not very good at making a self-determination that they are too fatigued to work.
Second, even if there are work hour limits imposed for any given shift, there is still no guarantee that the mechanic will begin the shift with adequate rest. For instance, if there is an eight-hour maximum shift policy but a mechanic arrives at work with only four hours of sleep, then there is a good possibility that he or she will be fatigued, even if the shift is only eight hours long.
Third, tasks that require focused attention such as visual inspections must include sufficient and strategically scheduled breaks. Vigilance decrement is a form of short-term fatigue that can occur very rapidly when a mechanic is conducting a long and tedious task such as a fuselage lap joint inspection (remember Aloha Airlines Flight 243?). Studies indicate that after about 20 minutes, a mechanic is much less likely to detect obvious defects. In general, inspection tasks that involve variety and regular breaks are less likely to suffer from the vigilance decrement.
Fourth, assuming a formal fatigue management program is in place, there may still be some questions about the honesty of mechanics using the program. For example, some organizations use an IFLSC (Individual Fatigue Likelihood Score Card). The IFLSC is used to calculate a fatigue score based on the subjective evaluation by the person filling out the card. If the score exceeds a certain threshold then he or she is to report to their manager that they are too fatigued to work safely. Depending on the severity of the fatigue, that person may have a temporary job reassignment or possibly be sent home for the day. The problem with this method is the potential for misuse. Some mechanics may fill out the card in such a way as to feign fatigue in order to satisfy their own agenda. Or, conversely, and more likely, the mechanic may be dishonest when filling out the card to indicate that they are not suffering from fatigue when in fact they are. This could occur due to personal pride, peer pressure, and fear of retribution, for instance.
The points serve to illuminate some of the complexities and challenges in fatigue management. There is an ongoing disparity between NTSB and FAA in relation to promulgating work time regulations aimed at reducing fatigue.
In the meantime, some organizations have acted proactively and implemented fatigue management programs based on empirical research and best practices. While these programs can be highly effective in mitigating fatigue-related errors, there are certain limitations and challenges that may be encountered and will need to be resolved.
In summary, the FAA will eventually need to promulgate work time rules for the aviation maintenance industry. This, combined with a strong fatigue risk management program to include education and training, will be most effective in reducing fatigue-related errors in the aircraft maintenance domain. Until then, you may just be exhorted to "get plenty of sleep." That is problematic to say the least.