Normalization of Deviance

While attending a safety seminar recently, the subject of normalization of deviance came up. The discussion reminded me of the importance of understanding normalization of deviance and how it affects safety in aircraft maintenance.

A basic definition of normalization of deviance is the gradual process by which the unacceptable becomes acceptable in the absence of adverse consequences.

As an example, it is against the law to drive in excess of the speed limit. If the speed limit is 70 mph, you could get a ticket for driving 71 mph. A new driver typically tends to drive the speed limit. Then, as he or she notices almost everyone around them driving over the speed limit, they might tend to speed as well. They might be nervous at first, but soon speeding becomes their normal. They don’t think anything of it unless they are pulled over. Then, they might tend to follow the speed limit again for a brief time, but eventually speeding becomes their normal once again.

So, what are the risks of speeding? The biggest risk is getting a ticket. Depending on your financial status, a $100 speeding ticket might not be a big deal. There is also a risk of increased penalties for repeat offenses, including higher fines and possible revocation of your driver’s license. Another risk is a higher chance of getting in an accident.

People weigh the risks of speeding (getting a ticket and increased risk of getting in an accident) versus the advantages (getting to their destination faster) when they decide how fast they want to drive. 

Then there are speed traps — those roads and highways that police officers patrol heavily. Drivers tend to follow the speed limits strictly in those areas because they know the chances of getting pulled over are extremely high if they are speeding.

Normalization of deviance can have serious consequences. It contributed to the space shuttle Challenger accident in 1986. In the culture of NASA at the time, employees were under pressure and had become accustomed (normalization of deviation) to allowing launches with leaking seals. (Twenty-four previous launches had been successful with known leaks in the seals between rocket stages.) Unfortunately, the leaking seal on Jan. 28, 1986, proved to be anything but successful. 

Take some time to think about how normalization of deviance might exist in an aircraft maintenance environment. Is it choosing not to follow particular maintenance procedures because, “That’s the way we’ve always done it around here?” Are we not paying close enough attention to certain inspection items because we’ve never found anything there before? Do we perform maintenance tasks by memory and then fill out the entire work instruction checklist only after the task is completed? 

It can be easy for normalization of deviance to creep in to our work environment. However, the possible consequences of gradually allowing the unacceptable to become acceptable in aircraft maintenance are much more severe than just getting a speeding ticket!

Thanks for reading, and we appreciate your feedback.



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