According to Reason (1997), organisational rules and human performance will interact to give rise to six main types of rule-related behaviours that could lead to either a safe or unsafe outcome. Table 1 summarises the three types of rule-related situations interacting with two kinds of performances that gives rise to the various outcomes.
|Good Rule||Bad Rule||No Rule|
|Correct Performance||Correct Compliance||Correct Violation||Correct Improvisation|
|Erroneous Performance||Mistaken Circumvention (Misvention)||Mistaken Compliance (Mispliance)||Mistake|
|Table 1 – Six types of rule-related behaviour, Reason (1997)|
Rules and Performance Types
Organisational rules are written to guide people in the course of their work or return things to normalcy should something unexpected occur (Reason, 1997). Reason (1997) mentions that whilst most organizations, especially those in the aviation and other highly regulated industries, have robust rules or procedures (good rules), it is not possible to cover all the unexpected scenarios (no rules). Reason (1997) further explains that because rules are written by humans, they can sometimes be flawed and not correctly serve the intended purpose (bad rules). From the above table, ‘correct performance’ refers to a behaviour or action that is correctly executed and successful in the outcome whilst ‘erroneous performance’ describes a faulty implementation that leads to an unsuccessful or unintended result.
Erroneous performance or errors deserves a deeper analysis due to their tendency to develop into organisational accidents. These errors can occur at three different performance levels, namely at skill-based (SB), rule-based (RB) and knowledge based (KB) levels (Rasmussen, 1982). Skill-based performances are routine, highly practised tasks that we do in an almost automatic fashion e.g. a pilot flying level at 33000 feet in clear, traffic-less skies. Any human error that occurs at this level is most often due to memory or attentional lapses. Rule-based performances kick in when there is a need to modify our automatic, skill-based performances (Rasmussen, 1982). The pilot who was flying at 33000 feet will have to employ rule-based performance when he notices an approaching traffic. He will then rely on his training or airline procedures to avert a possible collision. An error at this stage is termed as a rule-based mistake. Knowledge-based performance takes effect whenever we are faced with a novel, never-been-trained-for situations (Rasmussen, 1982). Experiencing stall and overspeed warnings at the same time during flight operations, like what happened to Malaysian Airlines Flight 124 on 1 August 2005 enroute to Kuala Lumpur from Perth, is something aircrew are hardly or never trained for and will have to rely on trial and error learning or the modification of past experiences to correct a situation. Errors at this stage are known as knowledge-based mistakes (Rasmussen, 1982). The diagram below gives a pictorial differentiation of errors.
|Diagram 1 - Principal Error Types, (Reason, 1997)|
Characteristics of Rule-Related Behaviours
- Correct Compliance – Correct compliances are proper actions that are carried out through the correct interpretation of good rules. The reason why air travel is considered an extremely safe mode of transportation is due to the fact that highly trained pilots carry out the intended actions in alignment to robust and safe air traffic or aircraft operating procedures. Maintaining proper separation distances and taking a correct landing approach that leads to uneventful flying and landing operations are some example of correct compliance (Reason, 1997).
- Correct Violation – Correct violations refer to actions that are carried out in opposition to improper rules that lead to a safe outcome (Reason, 1997).
- Correct Improvisation – These are actions taken in the absence of any rule or procedure that leads to a safe outcome (Reason, 1997). The most spectacular example of this was the landing of United 232, a DC-10 aircraft that was flying without any controls whatsoever after an engine disintegration of the aircraft’s No. 2 engine severed off all the three hydraulic systems (Reason, 1997). This was said to have a one in a billion chance of occurring and hence there were no emergency procedures written for it. Improvising with just the manipulation of the aircraft engines, they guided the aircraft to Sioux City where it crash landed in a more controlled fashion and saved the lives of more than half of the souls on board (Reason, 1997).
- Misvention – Is the deviation from good safety rules or the committing of errors that leads to unsafe results. Aviation disasters are more often than not a result of misventions (Reason, 1997). One of the classic example of a misvention was the Kegworth air disaster in 1989 involving a new variant of the B737 aircraft. Even though the No. 1 engine of the aircraft had malfunctioned, the crew shut down the perfectly normal No. 2 engine due to unfamiliarity with the new cockpit instrumentation (AAIB, 1990). Their misvention was further fuelled by their preconception that air-conditioning of the aircraft drew its power from the No. 2 engine and since smoke was felt within the cabin, they proceeded to fly on the faulty engine till it crashed way short of the runway (AAIB, 1990).
- Mispliance – Mispliances are effects of wrong actions based on wrong procedures. An episode of a mispliance was none more pronounced than in the American Airlines Flight 587. In a bid to overcome the effects of a wake turbulence, the co-pilot in this flight had given a series of very forceful alternating inputs to his vertical stabilizer through his rudder pedals that snapped off the entire assembly and causing the aircraft to crash into a neighbourhood (NTSB, 2004). What was disturbing about this incident was the finding that American Airlines procedures had in fact encouraged large rudder inputs to counter wake turbulence effects (NTSB, 2004).
- Mistake – Mistakes are wrong actions in the absence of any rule and are also known as knowledge-based errors/mistakes or failures of improvisation (Reason, 1997).
Summarising the Rule Related Behaviours
Given that organisational rules, or sometimes the lack of it, and human performance interact in very complex ways, a useful and simple methodology has been described by Reason (1997) to determine how work-related tasks either go as planned or awry in relation to the rules of the organisation. The method shown in Diagram 2 can be initiated by first querying if a particular task has been covered by rules or training. This is then worked along till the end result of the task is determined as being either a variant of a correct or erroneous action as shown in Table 1. This method can also be a useful tool to initiate proper corrective actions at the appropriate point i.e. either adjusting the human behaviour or the procedures itself that led to an unsafe outcome.
|Diagram 2 - Summary of Rule-Related Behaviours, (Reason, 1997)|
Want to know more?
- This page in Youtube explains more about the British Midland Flight 92 (Kegworth) Air Disaster.
- This page in Youtube explains more about the American Airlines Flight 587.
- This report from the Australian Transport Safety Bureau explains more about the unique problem faced by Malaysian Airlines Flight 124.