Skill = Competence + Experience
Understanding weird accidents in commercial aviation
Patrick HudsonTim Hudson
Hudson Global Consulting
1950
Unusual or WEIRD Accidents
• In commercial aviation major accidents are now extremely rare
• Simple risk assessment and analysis models often fail to capture how these accidents are caused
– “That’s weird, how could that happen?”
• We need to understand our risk spaces better
A problem for aviation
• Simple models have difficulty in capturing recent major commercial aviation incidents
• Asiana 214, QF 32, AF 447, BA 38, TK 1951
Capt E.J.Smith, master of R.M.S. Titanic
The wonderful thing about hindsight
Is hindsight’s a wonderful thing
How accidents are caused - Type I
• Linear causes – A causes B causes C
• Deterministic - either it is a cause or it isn’t
• Probably good enough to catch 80% of the accidents we are likely to have
How accidents are caused - Type II
• Non-Linear causes
– Cause and consequence may be disproportionate
– These causes are organizational, not individual
• Deterministic dynamics- either it is a cause or it isn’t
• This is the Organizational Accident Model – James Reason
• Probably good enough to catch 80% of the residual accidents = 96%
How accidents are caused - Type III • Non-Linear causes
• Non-Deterministic dynamics
– Probabilistic rather than specific
• The accidents that remain are WEIRD
– WILDLY
– ERRATIC
– INCIDENT
– RESULTING IN
– DISASTER
• Prior to an event there may be a multitude of possible future outcomes
Types of accidents
• Type I• Simple models may cover 80% of all accidents
• Type II• The next step gets 80% of the remainder = 96%
• Type III• The probabilistic approach may net the next 80% =
99.2%
• Looking backwards everything looks like Type I
Type I
Approach & Landing
CFIT Approach & Landing
Runway incursion
Approac
Type II
CFIT Approach & Landing
Runway incursion
Type II Type II
Type I
Type IIIType III
Scenarios
Scenarios in 3 dimensions
A small number of scenarios are most frequent
Why don’t we?
• There are so many distinct scenarios, many or all are weird;
• We can’t afford the resources to train for all of them;
• We may not even be able to imagine them happening;
• They are extremely infrequent, anyway; so,• We hope, that if we can manage and train for the
inner circles, the rest will generalise for a sufficiently competent pilot.
After mitigation a large number of scenarios are most frequent but with a much lower probability
Type II Type II
Type I
Type IIIType III
Type II Type II
Type I
Type IIIType III
The Rule of Three
• Accidents have many causes (50+)
• There are many (± 7) independent risk dimensions
• A number of these dimensions were marginal
• Marginal conditions score as Orange
• No-Go conditions score as Red
• The Rule of 3 is Three Oranges = Red
Aircraft Operation Dimensions
• Crew Factors Experience, Duty time, CRM
• Aircraft Perf. Category, Aids, Fuel, ADDs
• Weather Cloud base, wind, density alt, icing, wind
• Airfield Nav Aids, ATC, Dimensions, Topography
• Environment Night/day, Traffic, en route situation
• Plan Change, Adequacy, Pressures, Timing
• Platform Design, Stability, Management
Thank you
Patrick HudsonTim Hudson
Hudson Global Consulting