Archives For Safety

The practice of safety engineering in various high consequence industries.

Midlands hotel

A quick report from sunny Manchester, where I’m attending the IET’s annual combined conference on system safety and cyber security. Day one of the conference proper and I got to be lead off with the first keynote. I was thinking about getting everyone to do some Tai Chii to limber up (maybe next year). Thanks once again to Dr Carl Sandom for inviting me over, it was a pleasure. I just hope the audience felt the same way. :) Continue Reading…

Tenerife disaster moments after the impact

TCAS, emergent properties and risk trade-offs

There’s been some comment from various regulator’s regarding the use of Traffic Collision Avoidance System (TCAS) on the ground, experience shows that TCAS is sometimes turned on and off at the same time as the Mode S transponder. Eurocontrol doesn’t like it and is quite explicit about their dislike, ‘do not use it while taxiing’ they say, likewise the FAA also states that you should ‘minimise use on ground’. There are legitimate reasons for this dislike, having too many TCAS transponders operating within a specific area can degrade system performance as well as potentially interfering with airport ground radars. And as the FAA point out operating with the AD-B transponder on will also ensure that the aircraft is visible to ATC and other ADS-B (in) equipped aircraft (1). Which leaves us with the question, why are aircrew using TCAS on the ground? Is it because it’s just easy enough to turn on at the push back? Or is there another reason?

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Interesting article on old school rail safety and lessons for the modern nuclear industry. As a somewhat ironic addendum the early nuclear industry safety studies also overlooked the risks posed by large inventories of fuel rods on site, the then assumption being that they’d be shipped off to a reprocessing facility as soon as possible, it’s hard to predict the future. :)

Right hand AoA probes (Image source: ATSB)

When good voting algorithms go bad

Thinking about the QF72 incident, it struck me that average value based voting methods are based on the calculation of a population statistic. Now population statistics work well when the population is normally distributed, or otherwise clustered around some value. But if the distribution has heavy tails, we can expect that extreme values will occur fairly regularly and therefor the ‘average’ value means much less. In fact for some distributions we may not be able to put a cap on the upper value that an ‘average’ could be, e.g. it could have an infinite value and the idea of an average is therefore meaningless.

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An interesting post by Mike Thicke over at Cloud Chamber on the potential use of prediction markets to predict the location of MH370. Prediction markets integrate ‘diffused’ knowledge using a market mechanism to derive a predicted likelihood, essentially market prices are assigned to various outcomes and are treated as analogs of their likelihood. Market trading then established what the market ‘thinks’ is the value of each outcome. The technique has a long and colourful history, but it does seem to work. As an aside prediction markets are still predicting a No vote in the upcoming referendum on Scottish Independence despite recent polls to the contrary.

Returning to the MH370 saga, if the ATSB is not intending to use a Bayesian search plan then one could in principle crowd source the effort through such a prediction market. One could run the market in a dynamic fashion with the market prices updating as new information comes in from the ongoing search. Any investors out there?

MH370 underwater search area map (Image source- Australian Govt)

Just saw a sound bite of our Prime Minister reiterating that we’ll spare no expense to find MH370. Throwing money is one thing, but I’m kind of hoping that the ATSB will pull it’s finger out of it’s bureaucratic ass and actually apply the best search methods to the search. Unkind? Perhaps, but then maybe the families of the lost deserve the best that we can do…

Enshrined in Australia’s current workplace health and safety legislation is the principle of ‘So Far As Is Reasonably Practical’. In essence SFAIRP requires you to eliminate or to reduce risk to a negligible level as is (surprise) reasonably practical. While there’s been a lot of commentary on the increased requirements for diligence (read industry moaning and groaning) there’s been little or no consideration of what is the ‘theory of risk’ that backs this legislative principle and how it shapes the current legislation, let alone whether for good or ill. So I thought I’d take a stab at it. :) Continue Reading…