Errors are a natural part of human performance. Beginners, as well as the most highly skilled experts, are vulnerable to error, and this is perhaps the most important thing to understand about error. To believe people can eliminate errors from their performance is to commit the biggest error of all. Instructors and learners alike should be prepared for occasional errors by learning about common kinds of errors, how errors can be minimized, how to learn from errors, and how to recover from errors when they are made.

Kinds of Errors

There are two kinds of errors: slips and mistakes.


A slip occurs when a person plans to do one thing, but then inadvertently does something else. Slips are errors of action. Slips can take on a variety of different forms. One of the most common forms of slips is to simply neglect to do something. Other forms of slips occur when people confuse two things that are similar. Accidentally using a manual that is similar to the one really needed is an example of this type of slip.

Other forms of slips happen when someone is asked to perform a routine procedure in a slightly different way. For example, Beverly has been assigned runway 30 for many days in a row. This morning she approaches to land and ATC assigns runway 12 instead. As she approaches the traffic pattern, she turns to enter the pattern for runway 30 out of habit.

Time pressure is another common source of slips. Studies of people performing a variety of tasks demonstrated a phenomenon called the speed-accuracy tradeoff. The more hurried one’s work becomes the more slips one is likely to make.


A mistake occurs when a person plans to do the wrong thing and is successful. Mistakes are errors of thought. Mistakes are sometimes the result of gaps or misconceptions in the learner’s understanding. One type of mistake happens when a learner formulates an understanding of a phenomenon and then later encounters a situation that shows how this understanding was incorrect or incomplete. For example, overly simplistic understanding of weather frequently leads inexperienced learners into situations that are unexpected.

Experts are not immune to making mistakes, which sometimes arise from the way an expert draws upon knowledge of familiar problems and responds to them using familiar solutions. [Figure] Mistakes can occur when the expert categorizes a particular case incorrectly. For example, an experienced pilot may become accustomed to ignoring nuisance alerts issued by his traffic alerting system when approaching his home airport, as many aircraft on the ground turn on their transponders prior to takeoff. One night, he ignores an alert that was generated not by an aircraft on the ground, but rather by another aircraft that has turned in front of him on final approach.

Errors, learning process, aviation instructor
Other mistakes arise under pressure. For example, a technician or pilot might perform a cursory inspection of an aircraft to save time, only to have a problem manifest itself later

Reducing Error

Although it is impossible to eliminate errors entirely, there are ways to reduce them, as described in the following paragraphs.

Learning and Practicing

The first line of defense against errors is learning and practice. Higher levels of knowledge and skill are associated with a lower frequency and magnitude of error.

Taking Time

Errors can often be reduced by working deliberately at a comfortable pace. Hurrying does not achieve the same results as faster performance that is gained by increasing one’s skill through continued practice.

Checking for Errors

Another way to help avoid errors is to look actively for evidence of them. Many tasks in aviation offer a means of checking work. Learners should be encouraged to look for new ways of checking their work.

Using Reminders

Errors are reduced when visible reminders are present and actively used. Checklists and other published procedures are examples of reminders. Many aircraft instruments such as heading indicators offer bugs that can be used to remind the pilot about assigned headings and courses and some may also prompt altitudes and airspeeds. Mechanics and pilots alike can use notepads to jot down reminders or information that should otherwise be committed to memory.

Developing Routines

The use of standardized procedures for routine tasks is widely known to help reduce error. Even when a checklist procedure is unavailable or impractical, learners can help reduce the occurrence of error by adopting standardized procedures.

Raising Awareness

Another line of defense against errors is to raise one’s awareness when operating in conditions under which errors are known to happen (e.g., changes in routine, time pressure), or in conditions under which defenses against errors have been compromised (e.g., fatigue, lack of recent practice).

Error Recovery

Given that the occasional error is inevitable, it is a worthwhile exercise to practice recovering from commonly made errors, or those that pose serious consequences. All flight learners need to learn and practice a lost procedure to ensure that they can recover from the situation in which they have lost their way. It is useful to devote the same sort of preparation to other common learner errors.

Learning from Error

Error can be a valuable learning resource. Learners naturally make errors, which instructors can utilize in training to help while being careful not to let the individual practice doing the wrong thing. When a learner makes an error, it is useful to ask them to consider why the error happened, and what could be done differently to prevent the error from happening again in the future. In some cases, errors are slips that simply reveal the need for more practice. In other cases, errors point to aspects of learner methods or habits that might be improved. For example, beginning instrument flight learners commonly make errors when managing two communications radios, each with an active and standby frequency. When the same learners understand each radio’s specific purpose (e.g., ATIS, ground, tower frequencies), error rates often drop quickly.

Instructors and learners should be aware of a natural human tendency to resist learning from errors. That is, there is a tendency to “explain away” errors, dismissing them as one-time events that will likely never happen again. The same phenomenon occurs when observing errors made by others. Reading an accident or incident report, it is easy to spot where a pilot or mechanic made an error and regard the error as something that could never happen to the reader. It is important to note that this type of bias is not necessarily the result of ego or overconfidence; rather, it is something to which we are all susceptible. Psychologist Baruch Fischoff studied hindsight explanations given by people who were presented with descriptions of situations and their ultimate outcomes. When asked to provide explanations for events that had already occurred and for which the outcome was known, people explained that the outcomes were “obvious” and “predictable.” When the same events without the outcomes were presented to a second group, peoples’ prediction of the outcome was no better than chance guessing. The study nicely illustrates the popular adage that “hindsight is 20/20.”

Summary of Instructor Actions

To help learners learn from errors they make and be prepared for them in the future, an instructor should:

  • Explain that pilots and mechanics at all levels of skill and experience make occasional errors.
  • Explain that the magnitude and frequency of errors tend to decrease as skill and experience increases.
  • Explain the difference between slips and mistakes and provide examples of each.
  • Explain ways in which the learner can help minimize errors.
  • Allow the learner to practice recovering from common errors.
  • Point out errors when they occur and ask the learner to explain why they occurred.