Expectation and Confirmation Bias: Real Hazards for Pilots, Not Just Textbook Theory

Christina, a student pilot in Florida, asked a columnist whether expectation and confirmation bias are real hazards or just textbook theory. The columnist answered with a personal account from the previous week, admitting he had fallen victim to expectation bias himself.

For years, the airport where he keeps his airplane used magnetic access cards to let hangar tenants through the security gate. After the sole manufacturer of those cards folded, the airport authority installed a lockbox on the fence near the gate holding a single community card, requiring tenants to stop, walk to the box, enter a code on rotary wheels, retrieve the card, and use it to activate the gate reader.

On a recent rainy visit, the columnist went through this entire routine while holding an umbrella, only to find the lockbox empty except for a soggy handwritten note containing the same code, explaining it could now be entered directly into the gate reader, bypassing the card altogether. He had been so locked into his habitual routine that he failed to notice the change and could have entered the code from his car. "I so expected things to be a certain way that I ignored all other inputs," he wrote, calling it "a classic example of expectation bias."

The FAA's Risk Management Handbook discusses expectation bias as especially common during ground operations, such as a pilot following a familiar taxi routing like Alpha, Charlie, and Delta 2 even after the tower issues a different instruction, such as Delta 3. The bias can extend to approach and landing clearances, where a pilot may correctly read back an atypical instruction yet still perform the expected action. Confirmation bias, a related error, is particularly prevalent during preflight planning and weather analysis, where a pilot eager to fly may focus on data supporting the flight while minimizing unfavorable signals — a pattern that in some cases has had deadly consequences.