By National FAA Safety Team
Notice Number: NOTC5112
An Aviation Maintenance Technician (AMT) hears their radio crackle. Maintenance Control wants them to evaluate damage to an aileron the crew of a departing aircraft detected. After reporting the extent of the damage to Maintenance Control they conclude the aileron damage is allowable, and the AMT defers it according to the company’s procedures. The aircraft departs on time. Later the AMT takes a second look at the structural repair manual, and learns the focus had only been on the allowable damage table. The team had not noticed the damage was, in fact, in a critical area that required them to consult the aircraft manufacturer. The AMT then realized they had inadvertently released the aircraft to fly with a potentially dangerous flaw. This was a team of very responsible, experienced, people. How can professionals make such a mistake?
Well, when the plan is to get an airplane out on time human beings will use every tool at their disposal, including mental shortcuts. Mental shortcuts are not bad. They lead to success nearly all the time, the key word here being “nearly”. In this case the people making the decision relied on good judgment, but did not consider a mental bias called Confirmation Bias.
Confirmation Bias refers to a type of mental shortcut whereby an AMT, or any human, may tend to notice facts supporting their decision rather than information contradicting it. People are less likely to accept facts not lining up nicely with what is already “known” or “believed”. As the strength of our mental model increases, we tend to ignore, or undervalue the relevance of facts contradicting our established beliefs.
A mental bias can lead to unconscious behavior, and it is difficult to prevent what you don’t intend to do. So, work as a team. Two heads are better than one, and many better than two. Try to disprove the decision. No one likes a contrary person, but they are happy to have someone keep them from making a big mistake. Listen to the new guy. They have not had the opportunity to become familiar with the operation “Norms”, and might be able to point out problems more experienced people won’t notice. Adhere to a plan to strictly follow procedures. This will help you avoid cherry picking data to support a risky plan.