Archives For Safety

And not quite as simple as you think…

The testimony of Michael Barr, in the recent Oklahoma Toyota court case highlighted problems with the design of Toyota’s watchdog timer for their Camry ETCS-i  throttle control system, amongst other things, which got me thinking about the pervasive role that watchdogs play in safety critical systems.

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Taboo transactions and the safety dilemma Again my thanks goes to Ross Anderson over on the Light Blue Touchpaper blog for the reference, this time to a paper by Alan Fiske  an anthropologist and Philip Tetlock a social psychologist, on what they terms taboo transactions. What they point out is that there are domains of sharing in society which each work on different rules; communal, versus reciprocal obligations for example, or authority versus market. And within each domain we socially ‘transact’ trade-offs between equivalent social goods.

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So what do gambling, thermodynamics and risk all have in common?

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In June of 2011 the Australian Safety Critical Systems Association (ASCSA) published a short discussion paper on what they believed to be the philosophical principles necessary to successfully guide the development of a safety critical system. The paper identified eight management and eight technical principles, but do these principles do justice to the purported purpose of the paper?

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Why something as simple as control stick design can break an aircrew’s situational awareness

One of the less often considered aspects of situational awareness in the cockpit is the element of knowing what the ‘guy in the other seat is doing’. This is a particularly important part of cockpit error management because without a shared understanding of what someone is doing it’s kind of difficult to detect errors.

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Fighter Cockpit Rear View Mirror

What the economic theory of sunk costs tells us about plan continuation bias

Plan continuation bias is a recognised and subtle cognitive bias that tends to force the continuation of an existing plan or course of action even in the face of changing conditions. In the field of aerospace it has been recognised as a significant causal factor in accidents, with a 2004 NASA study finding that in 9 out of the 19 accidents studied aircrew exhibited this behavioural bias. One explanation of this behaviour may be a version of the well known ‘sunk cost‘ economic heuristic.

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One of the tenets of safety engineering is that simple systems are better. Many practical reasons are advanced to justify this assertion, but I’ve always wondered what, if any, theoretical justification was there for such a position.

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In one’s professional life there are certain critical works that open your eyes to how lucidly a technical argument can be stated. Continue Reading…

TCAS Indicator (Image Source: Public Domain)

What TCAS can tell us about AF447 (Updated 27 Sept 09)

The BEA interim report on the AF447 accident confirms that the Traffic Alert and Collision Avoidance System (TCAS) had become inoperative during the early part of the event sequence for an, as yet, un-identified reason. The explanation may actually be fairly straight forward and lie within the fault tolerance requirements of the TCAS specification. Continue Reading…

If the theory of Highly Optimised Tolerance (HOT) theory holds true then we should be able to see a change in the distribution of the severity of adverse events as the design paradigm for a family of systems moves from the, ‘just make it work’ stage to the ‘optimise for robustness’ stage. This is something we can actually test through observation of real world systems.

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The effect of poorly considered originating requirements (the recommendations of the Waterfall accident commisioner) upon system safety requirements for a passenger emergency door release function.

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Buncefield (Image Source Royal Air Support Unit)

The use of integrity levels to achieve ultra high levels of safety has become an ‘accepted wisdom’ in the safety community. Yet I remain unconvinced as to their efficacy, and in this post I argue that integrity levels are not scientific in any real sense of that term.

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