Each month I receive the NTSB Reporter (firstname.lastname@example.org), which provides an abbreviated version of some of the more interesting NTSB reports that have been issued recently, along with a paragraph or two on a number of recent accidents and other stories of interest. As I read through the weather and other information available to a pilot prior to a flight that resulted in an accident, I often find myself wondering how that pilot could have made a decision to take off based on the available information. The answer may be found in a common quirk of the human mind called confirmation bias.
Confirmation bias describes our tendency to seek out and trust information that confirms what we already think or believe or want to believe, and to avoid or discount information that goes against what we believe or want to believe. This can help to explain the seemingly irrational behavior that pilots often display, especially when they have a strong motivation to depart or continue a flight. Confirmation bias can strike first in the selection of what information to access, or whether to access any outside information at all. A pilot who desperately needs to make a trip may decide that “it doesn’t look that bad” or “it seems like it’s improving” or “it looks like it’s better just east of here,” and then not access any information sources that might negate that opinion. This could explain a pilot who:
• Takes off in miserable conditions without getting weather information from any of the many available sources.
• Fails to check icing reports even though the temperature is such that icing would be possible or even likely.
• Takes off on a short high-elevation runway over gross weight without checking the weight and balance of the airplane or referencing the takeoff performance charts.
Even a pilot who seems to be carefully gathering and assessing all available information in a dispassionate manner may actually be heavily influenced by confirmation bias. The first problem is that, on a difficult weather day, the amount of information available is often more than a pilot can easily process. When this happens, our brains will naturally start looking for something in all that information to help us make sense of what is going on. Research shows that we are more likely to notice information that we agree with or consider positive rather than focusing in on information that is contrary to our beliefs or goals. For example, a pilot preparing to take off in an overloaded airplane on a hot day at a high-elevation airport might notice that the wind is right down the runway, and use that fact as a justification to take off without making the effort to compute weight and balance and takeoff distance.
Confirmation bias can also affect how we gather the information we need. Studies have shown that a person will ask questions so that an affirmative answer supports what they want to do. A pilot who has just gotten a weather report with a forecast for marginal conditions might say, “So, there’s a chance we could make it.” While the answer might be “Yes, there is a chance you could make it,” in reality that chance is miniscule. However, the pilot in the grips of confirmation bias will focus on the positive answer and will not try to define what the odds of making it actually are. To put it simply, we tend not to ask a question if we think we might not like the answer.