Expectation Bias


Years ago when I moved into a new neighborhood, I was exploring different routes to drive to my new house. After only a short while, perhaps even just a few days, a stop sign showed up at an intersection with another residential street on one of the routes I was beginning to favor. I believed it was new, but with so much new to me at the time, I wasn’t sure. Of course, as I continued to drive that route, I got accustomed to stopping at that intersection.

A few months later, I witnessed a minor traffic accident there. I hung around to offer my statement to the investigating police officer. I overheard one of the drivers explain with sincerity but also with incredulity, “Where did that stop sign come from? I’ve driven by this corner every day for years and it was never here before.” After conferring with the officer, I learned that indeed the stop sign had been installed during my first week in the area. This driver was so accustomed to that route with no stop sign, that even months later he failed to recognize that it was there.

Expectation bias is a powerful force. As pilots we must strive to avoid falling victim to its insidious dangers. I am certainly susceptible to expectation bias and work hard to overcome that tendency … not always successfully. Recently a gentleman sent in an OTA that we published. In the write up, he mentions his husband in the other seat. While I recognize and support these men’s rights, I am a product of a time when one’s spouse universally meant a person of the opposite sex.

So, fueled by that expectation bias and lack of further thought while under time pressures, when I encountered this item, I merely assumed that something had gotten bollixed up in the multiple transcriptions from original e-mail to final layout. So I changed “husband” to “wife.” It was quite disconcerting to have my error—and the insult it caused—pointed out to me; Messrs. Fernandez and Sternbergh have since graciously accepted my apologies.

Expectation bias hits us from all sides. It might be as innocent as insisting a product isn’t on the shelf after
its labeling changed. Or it could be as costly as missing a new stop sign on a familiar street. Of course, in the cockpit it can have potentially disastrous consequences, such as turning base from the same point on downwind so habitually that you do so even after Tower tells you to extend, and you find yourself cutting off final traffic and needing an avoidance maneuver—and a phone call.

I like to think I do pretty well recognizing and avoiding expectation bias in the cockpit. However, this little life lesson shows just how pervasive it can be. We’re just human. So, I’m going to double down my efforts to recognize and avoid expectation bias in every endeavor. Surely, if I’m successful outside of flying, I’ll be better equipped to ward off most any danger from expectation bias when I fly. So, hopefully, I’ll be a better, safer pilot for it. Plus, there’s the bonus of avoiding little fender benders at new stop signs.


  1. Very well said and thank you for the reminder that in every situation flight we in counter we should be prepared to be more professional Pilots as we all are because we are not perfect and mistakes will happen but we learned from them to not let it happen again. IFR or VFR

  2. I ran afoul of expectation bias recently at my home ‘drome. Unknown to me (and I don’t recall ever seeing a NOTAM on this) the Tower frequency was changed from what it had been for the past 14 years I have been at this airport. I taxied to the hold short line and couldn’t figure out why Tower frequency was totally quiet, and no one was answering my calls. A quick check of the Airports tab on Foreflight revealed that Tower frequency had indeed changed. Expectation bias is real.

  3. One of the most tragic examples of expectation bias that I have heard of was back in November of 1979. An Air New Zealand DC-10 scenic flight over Antarctica crashed into the flanks of Mount Erebus, all 257 souls perished. The operational people in Auckland had made a change to the INS coordinates for the route just hours before the fateful flight but had not told the flight crew, who had never been to “the ice” before but had been shown videos taken by other flight crews on prior flights.
    The final but by far the major link in the accident chain was the weather. There was a broken layer, and once under that layer it was “clear and a million”, so the flight crew adopted VFR minimums approved by the airline and the regulatory agency. But the angle of the sun (which never set in November at that latitude), the cloud base above and the flat ice ahead and below gave way to “white-out”, with no depth perception, and multiple reflections and refractions provided mirages. The flight crew saw what they expected to see from the videos, but film recovered at the crash site from passengers showed a very different picture. Ironically, Mount Erebus was in plain site ahead of the flight crew but became invisible because they didn’t expect it to be there, and it was only the TAWS system that too late prompted the captain to order “Go Around power please”, the last words recorded of the flight.
    This is a bit off-topic as it’s not GA and/or Part 91 that many of us fly, but it’s personal to me- I’m from New Zealand originally and like every “Kiwi” was touched in some way by that accident. Also, my brother-in-law was a policemen in New Zealand and was on a team sent down to the crash site for body retrieval. Some of his photos of victims are indescribable.

  4. I’m not at all interested in your comment about gender/spouses, since it brings out undesirable concepts that stand against nature and God. Please stick to other examples.

  5. Unlike BP, who seems afraid or ashamed to leave his name, I am interested in your comments about gender. I’m not sure how far his suppositions about God and nature’s stances extend, though, so it’s pretty hard to take a firm stand . . .
    I was talking to a young couple and mistakenly thought that the young man was the pilot and the young woman the passenger. It was politely pointed out to me that the opposite was the case. I was quickly forced to confront my bias, change my thinking, and remind me that it’s better to be quiet and be thought a fool, than speak up and remove all doubt.
    I would understand and agree that you should probably take these two posts down, they add little to the conversation.


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