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Human FactorsLesson 2 of 5

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HUM 002

Human error

What an error is

As a saying, in one line, and in Reason’s definition, with what its last few words rule out.

Errare humanum est

To err is human

Latin saying, often credited to Seneca
  • Human error is simply a deviation from intention
  • We make errors every day
  • Consequences vary

The term error will be applied to all those occasions in which a planned sequence of mental or physical activities fails to achieve its desired goal without the intervention of some chance agency.

Reason, 2013
PlanGoal achievedNot an errorGoal missedAn errorChance agencyNot an error
Only the middle run is an error: the plan failed, and nothing from outside made it fail.

Omission and commission

Error categorisation: something left undone, or something done that should not have been.

Errors of omission

A person fails to carry out a required task.

Errors of commission

A person carries out a task incorrectly, or does something that is not required.

Four error types

Slips and lapses are unintentional, violations intentional. Mistakes are unintentional too, but reached by a dashed line from intentional: the action was intended, but the plan was wrong from the start.

UnintentionalIntentionalSlips and lapsesThe plan is good; the action isnot according to planMistakesThe plan is not correct forreaching the goalViolationsDeliberate: against a rule,procedure or norm
The plan decides it: slips and lapses spoil a good plan, mistakes carry out a bad one faithfully.
SlipUnintentional

An incorrect action.

  • The plan is good; the action is not according to plan.
  • An attentional failure.
  • An error of execution, minor or serious.

ICAO’s example: operating the flap lever instead of the gear lever.

LapseUnintentional

An action forgotten.

  • The plan is good; a step is left out.
  • A memory failure.
  • Distracted, a task is not completed, or a step is omitted while performing it.

ICAO’s example: forgetting a checklist item.

MistakeUnintentional

The plan is not correct for reaching the goal.

  • Deficient, wrong or clumsy plans: the action conforms to an inadequate plan.
  • A failure in the plan of action.
  • Even if the plan were carried out correctly, the intended outcome could not be achieved.
ViolationIntentional

A deliberate violation of a rule, procedure or norm.

  • A deviation from safe procedures, standards or rules.
  • Routine, situational and exceptional: the kinds are below.

Which type is it?

Three questions sort an error into one of the four types, each answered by a definition above.

Three questions at most

1Was a rule, procedure or norm broken on purpose?

2Was the plan correct for reaching the goal?

3Then the action did not go to plan. What happened?

Answer from the top.

Two kinds of mistake

Rule-based and knowledge-based, named after the two upper performance levels in the next block.

Mistakes
Rule-based
Application of bad rules
Misapplication of a good rule
Knowledge-based
Decision-making based on an incomplete evaluation of the situation

Performance levels

Three levels of cognitive functions, after Jens Rasmussen, 1983.

Skill-basedBased on routineRule-basedBased on rulesKnowledge-basedBased on knowledge

Violations

Intentional action, or inaction, against known rules, procedures or norms. Four kinds.

Corner-cuttingor routine violations
Thrill-seekingor optimising violations
Necessaryviolations, also called situational
Exceptionalviolations, under exceptional conditions

The mental economics of violating

Why rules get broken: the costs and benefits of non-compliance, as the one breaking them sees them.

Perceived benefitsImmediatePerceived costsRemote from experience
As the one breaking the rule sees it, the scales tip towards breaking it.
Perceived benefitsImmediate
  • An easier way of working
  • Saves time
  • More exciting
Perceived costsRemote from experience
  • Possible accident
  • Injury to self or others
  • Damage

Costs and benefits of non-compliance: Battmann and Klumb, 1993.

Increasing the benefits of compliance is therefore essentialThe benefits of non-compliance are immediate, and the costs are remote from experience.

Error-prone conditions in ATM

Three conditions in which errors are more likely.

<6First 15 minA controller’s first15 minutes onposition.Light to moderateTraffic conditionsand complexity.Under 6 yearsA controller withless than six yearsof experience.

Mental models

The picture in your head of how things work and what is going on right now. Controllers call theirs “the picture”.

What you see and hearDisplayStripsRadioTraining and experienceThe pictureUsed toUnderstandPredictDecide
What comes in joins what you already know, and every decision is made on the picture that results.
1Built

From training and experience, and from what is in front of you: the display, the strips, the radio.

2Used

To understand what is happening, predict what happens next, and decide what to do.

3Updated

As new information comes in. A picture that is not updated goes out of date.

When the picture is wrong

IncompleteSomething is missing from it: an aircraft, a change, a call not heard.
Out of dateThe traffic has moved on, and the picture has not.
Expected, not seenPeople tend to see and hear what their picture leads them to expect: expectancy, one of the barriers in HUM 003.
A reasonable decision on a wrong picture is still wrongPeople act reasonably on the picture they have: the local rationality principle, HUM 001. The error is often in the picture, not in the reasoning.

Situational awareness and decision making

Why “loss of situational awareness” explains nothing.

  1. Blamed on “loss of situational awareness”Incorrect decision making is often attributed to it.
  2. But there is no cognitive vacuum“Loss of situational awareness” is nonsensical.
  3. People always have a pictureAn idea of what the world around them looks like: a mental model, the block above.
  4. It may be incomplete, or even wrongCompared with what you know in hindsight.
  5. Decisions follow the local rationality principlePeople do reasonable things, given their point of view: HUM 001.
Their picture at the time What hindsight shows
The picture was never empty. It was incomplete.

Information requirement

Information can generally be categorised as either quantitative or qualitative.

QuantitativeOn the display
420 ktSpeed
+1 500 ft/minRate of climb or descent
FL 245Flight level
QualitativeNot usually displayed
ReliabilityValidityTrustworthiness

The quality of the data depends on how the information is sensed and processed, in terms of:

Frequency of updatingAccuracyPrecisionErrorFailureDegradation
The experienced operator learns to recognise and adjust to information of poor qualityThe numbers are on the screen. How far to trust them is not.

Reading material

Human Factors

HUM 002 Human Error PowerPoint / PDF
EPN Group Training Document Human Factors, chapter 2 Reading list, course material
Learn More: Extra Material for Curious Students Reading list, course material
Amalberti, R. (2013). Navigating Safety Reference, paid
Isaac, A. & Ruitenberg, B. (1999). Air Traffic Control: Human Performance Factors Reference, paid
Dekker, S. (2006). The Field Guide to Understanding Human Error Reference, paid
Kern, T. (1998). Flight Discipline Reference, paid
Rasmussen, J. (1983). Skills, rules, and knowledge; signals, signs, and symbols, and other distinctions in human performance models Reference, paid
Reason, J. (2013). A Life in Error Reference, paid
Reason, J. (1990). Human Error Reference, paid
Strauch, B. (2004). Investigating Human Error Reference, paid
Woods, D. et al. (2010). Behind Human Error Reference, paid