Definition

Expectation bias can be defined as a cognitive inclination that arises when someone's expectations or beliefs about a situation impact how they perceive and respond to what is happening around them. An article from the U.S. Federal Aviation Administration (FAA) says, "Expectation bias is when we have a strong belief or mindset towards something we expect to see or hear, and act according to those beliefs."

To put it more simply: "What usually takes place, or what I am accustomed to seeing, is what is about to happen."

Description

Expectation bias can appear in any human activity, and it is partly a function of habit and routine.

In aviation, we often associate expectation bias with pilot error. For example, a pilot receives instructions to taxi to a seldom-used runway at a complex airport. Out of habit, the pilot begins taxiing toward a runway more commonly used. Or a pilot sets up for the usual instrument landing system (ILS) approach for a given runway, even though he or she heard the Automatic Terminal Information Service (ATIS) say the ILS was out of service.

Air traffic controllers can make the same kind of human errors. To continue with the example of an ILS out of service, a controller might clear a pilot for an ILS approach out of habit, even though a Notice to Air Missions (NOTAM) said the ILS was inoperative. Similarly, a controller who has worked approaches to Runway 27 for most of a shift might tell a pilot, "Cleared to land, Runway 27," despite knowing winds have shifted to favor another runway.

Case Study

On the morning of Feb. 4, 2023, fog enveloped Austin-Bergstrom International Airport in Texas, United States. A report by the U.S. National Transportation Safety Board (NTSB) says the fog limited visibility for air traffic controllers and flight crews. The report also says the airport did not have surface detection equipment to help controllers monitor aircraft on the ground.

As FedEx flight 1432 approached the airport just after 6:34 a.m., a controller cleared the aircraft to land. Flight 1432 was approximately six minutes from the field. About four minutes later, a Southwest aircraft radioed that it was ready to depart from the same runway the FedEx flight was approaching. At this point, the report said, the FedEx aircraft was about 90 seconds from the runway threshold. The Southwest crew received a clearance to take off.

According to the NTSB, the controller could not see the Southwest 737 and assumed it was already at the hold short line. However, the Southwest aircraft was actually about 550 feet from the hold short line. Another 57 seconds elapsed as the crew taxied to the runway. At this point, according to the NTSB, the FedEx plane was approximately two miles from the runway. Eleven seconds later, the Southwest aircraft was lined up on the runway. Then the Southwest crew ran up the engines in accordance with their company's cold-weather procedures, delaying takeoff for another 19 seconds.

When the FedEx aircraft was on short final approach, its first officer spotted the Southwest 737 rolling down the runway. The FedEx captain began a missed approach. The NTSB report says the two aircraft came within 150 to 170 feet of each other. The report cited a tower controller's expectation bias as a contributory factor.

Defences

The following activities can be undertaken to reduce the likelihood of prolonged expectation bias leading to near misses, incidents and accidents:

• Training that emphasizes when expectation bias is likely to occur (through lessons learned and/or relevant examples).
• Designing software that highlights significant safety information.
• Highlighting where accepted procedures deviate from the normal (e.g. routing practices).
• Self-awareness: Knowing when you are fatigued or stressed, and therefore more susceptible to bias and error.