Aviation maintenance technicians often work long hours under pressure, including working through the night. This often results in not just extreme fatigue but errors, some of which may potentially be life threatening to pilots and passengers as well as to the AMT themselves.
It is no secret that fatigue can come in different forms, physical, mental, and emotional. Physical fatigue brings about muscle soreness, oxygen debt, or extreme tiredness caused by sleep deprivation, illness, or poor nutrition.
Many AMTs may experience the weariness of emotional fatigue resulting from performing undesirable tasks which may additionally be performed under trying conditions. High levels of focus and concentration associated with complex tasks create mental fatigue, which combined with the physical or emotional, leads to increased errors and risks in safety sensitive arenas.
There are a countless number of documented errors and accidents attributed to tiredness and fatigue in the maintenance workplace. 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 alcohol content. 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 blood alcohol content).
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.
Further FAA studies and self-reporting by aviation maintenance mechanics indicate the average sleep for aviation maintenance mechanics routinely to be five to six hours per night, two to three hours short of the required eight hours per night. Additional studies reveal data that sleep deprivation is a cultural norm in the aviation maintenance workplace, although mechanics as a group are not generally cognizant of the fact that they do not get enough rest.
One of the most notable aviation maintenance fatigue-related accidents occurred in 1990 when British Airways Flight 5390 experienced a windscreen blowout shortly after departure from Birmingham International Airport in the United Kingdom. The left windscreen, which had been replaced prior to the flight, was blown out under the effects of the cabin pressure when it overcame the retention of the securing bolts. Eighty four of the 90 total bolts were of smaller than specified diameter.
The captain was sucked halfway out of the window at 18,000 feet and was miraculously restrained by the 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 cited numerous contributing factors that led up to this incident, one of the most insidious was the effect of fatigue on the aircraft mechanic 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 effect. This, combined with lack of sleep before his shift, may have contributed significantly to the aircraft mechanic’s perceptual judgmental 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.