the rule of three patrick hudson. normally safe near the limits on the edge
TRANSCRIPT
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The Rule of Three
Patrick Hudson
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•Normally Safe
•Near the limits
•On the edge
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Why didn’t they stop?An Incident
occurs when 2-4
of the signs meet
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What is it?• How did we get into this mess?
– Accidents are made more likely by indirect causes, not just the obvious ones
– We want to minimise regret, which includes not missing opportunities
• Why Three?– British Airways study showed decreasing
resilience with increased number of oranges
• How is it meant to be used? (My ideas)– Move decisions from argument to process– Manage into the Green before it goes wrong– Use as near miss information system
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Empirical support - Why Three?
• AAIB accident re-analysis (David Stephens)
• BA incident study - no accidents was a problem (Herman Jonker)
• New Zealand analysis and experimental study (Koen v d Merwe)
• Experiments found flight performance influenced by knowledge that next sector would be difficult
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Dimensions Used in BA study• Weather• Crew experience• Commercial setting• Short term variation /day-night/ shifts• Equipment• Task• Plan• Destination/ Location• Maintenance/ Checks
• Most of this information is missing in incident reports
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Accident studies for Rule of Three• Stephens found 4.4 oranges in major accidents
with aircraft > 2000 kg, fewer in lighter aircraft• Jonker used British Airways BASIS data for one
year (No accidents)• Four potential categories
– Did the Right Thing 34 0.5– Screwed up but Recovered 8 1.5
– Screwed up but Got Lucky 0 ?– Screwed up and Didn’t Get Lucky 0 ?
• Suggests Got Lucky = 2.5, Didn’t get lucky = 3.5
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Analysis study 100 incidents
• Outcomes Incident Accident• N of of oranges 0 3 1• 1/2 13 7• 3+ 3 10• Transition point between incident and accident at
2.32 oranges (sensitivity 59%)• Transition point for pilot impairment was 3.07
• Evidence suggests that beyond 2.5 pilots are impaired and accidents become much more likely
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Workshop activity
• Small groups n=6 max • Come up with at least one way to use
Rule of Three in your operations– What, who, when, where,how?
• Each ‘call’ is a near miss, how are you going to use the learning information?