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Normalisation of Deviance

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Category: Human Factors Human Factors
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Adherence to standard operating procedures (SOPs) is considered is considered critical to aviation safety. But deviating from SOPs is not unusual. When deviations occur without significant operational or safety consequences, the deviant behaviour can be reinforced. Over time, the deviance becomes normalised.

Sociologist Diane Vaughan, Ph.D., is credited with coining the phrase “normalisation of deviance” in her study of the 1986 space shuttle Challenger disaster. She said, “Social normalization of deviance means that people within the organization become so much accustomed to a deviation that they don’t consider it as deviant, despite the fact that they far exceed their own rules for the elementary safety.”

Normalisation of deviance also has been described as the gradual process by which the unacceptable becomes acceptable in the absence of adverse consequences.

In a 2007 speech, Robert Sumwalt a former airline pilot and then-member of the U.S. National Transportation Safety Board (NTSB), said, “One danger of routinely deviating from standards is that we “normalize” the deviation. This “normalization of deviance,” is problematic because crewmembers can view this new way of doing business as the norm. We get so used to it that the crew can eventually fail to see their actions as being deviations.”

Intentional noncompliance

Data gathered during thousands of line operations safety audit (LOSA) observations shows that flight crews that are intentionally noncompliant with cockpit SOPs are two to three times more like to commit other, unintentional errors to mismanage threats to flight safety. According to the LOSA Collaborative, those observations show that as the number of intentional noncompliance errors increase on a flight, the number of mismanaged threats and errors and the number of instances of undesired aircraft state also increase.

Procedural drift refers to the continuum between strict compliance with a procedure and how that procedure is being performed in the real world or actual operations.

Reasons for procedures not being followed are varied, but can include operational or time pressures, a procedure not being available, or a procedure being judged inadequate.

Accidents & Incidents

As mentioned, the Challenger explosion is often cited in discussions about normalisation of deviance or intentional noncompliance. Another example is the January 2012 capsizing of the Italian cruise ship Costa Concordia in which 32 people died. As the ship approached the coast of Giglio Island, it deviated from its standard course and moved closer to the island to perform a maritime salute, which had been performed several times previously. The ship struck a reef, tearing a hole in the port side. The passengers and crew eventually abandoned the ship.

A more recent aviation accident illustrating normalisation of deviance was the 31 May 2014 runway overrun during rejected takeoff of a Gulfstream GIV at New Bedford, Massachusetts, U.S. (GLF4, Bedford MA USA, 2014) During the engine start process before takeoff the flight crew neglected to disengage the airplane’s gust lock system, which locks the locks the elevator, ailerons, and rudder while the airplane is parked to protect them against wind gust loads. The pilots also neglected to perform a flight control check that would have alerted them to the locked flight controls, NTSB said in its investigative report.

A review of data from the airplane’s quick access recorder revealed that the pilots had neglected to perform complete flight control checks before 98% of their previous 175 takeoffs in the airplane, indicating that this oversight was habitual and not an anomaly.

In the final report, NTSB said: “[T]he probable cause of this accident was the flight crewmembers’ failure to perform the flight control check before takeoff, their attempt to take off with the gust lock system engaged, and their delayed execution of a rejected takeoff after they became aware that the controls were locked.” One of the contributing factors was “the flight crew’s habitual noncompliance with checklists.”


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Further Reading

National Business Aviation Association. “Procedural Non-Compliance: Learning the Markers and Mitigating the Risks.” NBAA Safety Resource.