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