While pilots should self-evaluate for stress and emotion during preflight mitigation analysis, stress and emotion do sometimes affect a flight in progress. External pressures from outside sources including supervisors, family, and friends may bias a pilot to make an error in an effort to complete a flight as originally planned. What does the pilot actually think about before making a decision? Does the desire to complete a flight as planned influence or outweigh the need to reduce risk? Only the pilot knows the thought process that leads to a decision, but making safety other than the top priority may cause the pilot to err.

An emotional response could appear spontaneously and lead to an error at any time. After an emotional shock or an important life event, the pilot may not be able to concentrate on the current conditions. On the other hand, individuals may become relaxed during flight and may not be sufficiently alert to react to a threat or error. Occasionally, pilots overfly their destination because they have become completely relaxed. If here today, Aristotle would say that errors become more likely if the pilot is obsessed to the point of exclusion of all else or if the pilot is generally disinterested in the events at hand. Appropriate focus and concentration are the golden mean.

A pilot's erroneous assessment may persist even though it is wrong and despite available evidence to indicate the error. The term for this phenomenon is expectation bias. The NTSB has investigated numerous accidents and incidents that involved pilot errors resulting from expectation bias, particularly in night VMC when fewer cues aid in airport and runway identification. For example, in January 2014, a Boeing 737 landed at the wrong airport in Branson, Missouri, in night VMC. The flight crew expected that the visually identified airport and runway were the intended destination and did not reference flight deck displays to verify the airport and runway. As a result, the airplane landed on Runway 12 at M. Graham Clark Downtown Airport instead of Runway 14 at Branson Airport.

A general aviation pilot routinely flew to a specific airport with parallel runways. The airport had one runway closed by NOTAM for several months, but after some time, the runway closure was reversed. The NOTAM was no longer for 19R/1L, but for 19L/1R. Even after reading the NOTAM and listening to the ATIS broadcast, the pilot perceived it as it had been previously. An error occurred when the pilot initiated an approach to the closed runway.

When presented with conflicting information, some pilots will try to suppress that information if it does not fit in with the expectation rather than triggering an internal “uh-oh.” The phenomenon, not to be confused with expectation bias, has the slightly different name “confirmation bias.” The result of either, if uncorrected, may lead to an error. Either case results in the pilot continuing with a plan despite clues indicating the situation is not as perceived. Fatigue tends to stop pilots from taking extra steps to verify perceived reality and contributes to expectation and confirmation bias susceptibility.

An incident at the San Francisco, California airport (KSFO) is another example involving expectation bias. The NTSB docket for this incident provides extensive information regarding expectation bias and is available [here](http://data.ntsb.gov/Docket?ProjectID=95528).

Expectation bias often occurs on the ground while taxiing. Pilots may expect a particular taxi route and perceive the clearance as expected rather than as given by ATC. Pilots familiar with a particular airport who routinely receive the same taxi clearance may be more susceptible to this error.

Pilots are often thought of as being calm and rational. Like all people, each pilot has a different personality. A normal ability to face reality, handle anxiety, and think rationally under pressure varies over a range. How a particular pilot reacts to a threat may depend on training and experience and may vary considerably. When a threat appears and calls for a decision, two hazardous attitudes may come into play. A pilot might react impulsively without due consideration or with resignation and not respond in a timely manner. Either extreme may increase workload and confusion and may not address a threat or error properly.

Flight crew error creates an undesired aircraft state described as:

When a pilot perceives a flight condition that requires attention, the pilot may know what to do immediately or may need time to process alternatives. The pilot may utilize several different strategies and defenses to manage risk while in the air.

A manufacturer, employer, or a flight school may provide defenses to pilots. Examples include checklists, operating limitations, minimum pilot qualifications, standard operating procedures, and insurance requirements. Regardless of the flight mission, some defenses will always be predetermined.

Like the aircraft, its approved checklists are normally provided. The manufacturer’s approved checklists, placards, and emergency procedures provide a basic defense against threats, errors, or undesired aircraft states. Many flight schools, flying clubs, and larger flight departments may develop checklists and standard operating procedures (SOPs) that enhance the procedures provided by the manufacturer. Many aircraft owners participate in type-specific owner organizations that develop and share best practices. A short video on developing a checklist that includes optional or aftermarket equipment is available [here](http://www.youtube.com/watch?v=6i8l7Nup5Hw&list=PL5vHkqHi51DQdF_PXKQT7uJUPd4UzlxNS&index=10).