Here’s a companion tutorial to the one on integrity level partitioning. This addresses more general software hazards and how to deal with them. Again you can find a more permanent link on my publications page. Enjoy :)
Archives For Complexity
Complexity, what is, how do we deal with it, and how does it contribute to risk.
How a invention that flew on the SR-71 could help commercial aviation today
In a previous post on unusual attitude I talked about the use of pitch ladders as a means of providing greater attensity to aircraft attitude as well as a better indication of what the aircraft is dong, having entered into it. There are of course still disadvantages with this because such data in a commercial aircraft is usually presented ‘eyes down’, and in high stress, high workload situations it can be difficult to maintain an instrument scan pattern. There is however an alternative, and one that has a number of allied advantages. Continue Reading…
Unreliable airspeed events pose a significant challenge (and safety risk) because such situations throw onto aircrew the most difficult (and error prone) of human cognitive tasks, that of ‘understanding’ a novel situation. This results in a double whammy for unreliable airspeed incidents. That is the likelihood of an error in ‘understanding’ is far greater than any other error type, and having made that sort of error it’s highly likely that it’s going to be a fatal one. Continue Reading…
Stall warning and Alternate law
According to an investigator from Indonesia’s National Transportation Safety Committee (NTSC) several alarms, including the stall warning, could be heard going off on the Cockpit Voice Recorder’s tape.
Now why is that so significant?
The Dreamliner and the Network
Big complicated technologies are rarely (perhaps never) developed by one organisation. Instead they’re a patchwork quilt of individual systems which are developed by domain experts, with the whole being stitched together by a single authority/agency. This practice is nothing new, it’s been around since the earliest days of the cybernetic era, it’s a classic tool that organisations and engineers use to deal with industrial scale design tasks (1). But what is different is that we no longer design systems, and systems of systems, as loose federations of entities. We now think of and design our systems as networks, and thus our system of systems have become a ‘network of networks’ that exhibit much greater degrees of interdependence.
In case anyone missed it the Ebola outbreak in Africa is now into the ‘explosive’ phase of the classic logistics growth curve, see this article from New Scientist for more details.
Here in the west we get all the rhetoric about Islamic State as an existential threat but little to nothing about the big E, even though this epidemic will undoubtedly kill more people than that bunch of crazies ever will. Ebola doesn’t hate us for who we are, but it’ll damn well kill a lot of people regardless.
Another worrying thought is that the more cases, the more generations of the disease clock over and the more chance there is for a much worse variant to emerge that’s got global legs. We’ve been gruesomely lucky to date that Ebola is so nasty, because it tends too burn out before going to far, but that can change ver quickly. This is a small world, and what happens inside a village in West Africa actually matters to people in London, Paris, Sydney or Moscow. Were I PM that’s where I’d be sending our defence force, not back into the cauldron of the Middle East…
Comparing and contrasting
In 2010 NASA was called in by the National Highway Transport Safety Administration to help in figuring out the reason for reported unintended Toyota Camry accelerations. They subsequently published a report including a dedicated software annex. What’s interesting to me is the different outcome and conclusions of the two reports regarding software. Continue Reading…
There’s a very interesting site, run by a couple of Australian lads, called Text is Beautiful that provides some free tools that allow you to visually represent the relationships within a text. No this isn’t the same as Wordle, these guys have gone beyond that to develop what they call a Concept cloud, colours in the Concept Cloud are indicative of distinct themes and themes themselves represent rough groupings of related concepts. What’s a concept? Well a concept is made up of several words, with each concept having it’s own unique thesaurus that is statistically derived from the text.
So without further ado I took the Fundamentals of System Safety course that I teach and dropped it in the hopper, the results as you might guess are above. Very neat to look at and it also gives an interesting insight into how the concepts that the course teaches interrelate. Enjoy. :)
Well I can’t believe I’m saying this but those happy clappers of the software development world, the proponents of Agile, Scrum and the like might (grits teeth), actually, have a point. At least when it comes to the development of novel software systems in circumstances of uncertainty, and possibly even for high assurance systems.
Linguistic security, and the second great crisis of computing
The components that make up distributed systems fundamentally need to talk to each other order to achieve coordinated behaviour. This introduces the need for components to have a common set of expectation of behaviour, including recognising the difference between valid and invalid messages. And fairly obviously this has safety and security implications. Enter the study of linguistic security to address the vulnerabilities introduced by the to date unrecognised expressive power of the languages we communicate with.
Economy of mechanism and fail safe defaults
I’ve just finished reading the testimony of Phil Koopman and Michael Barr given for the Toyota un-commanded acceleration lawsuit. Toyota settled after they were found guilty of acting with reckless disregard, but before the jury came back with their decision on punitive damages, and I’m not surprised.
Or ‘On the breakdown of Bayesian techniques in the presence of knowledge singularities’
One of the abiding problems of safety critical ‘first of’ systems is that you face, as David Collingridge observed, a double bind dilemma:
- Initially an information problem because ‘real’ safety issues (hazards) and their risk cannot be easily identified or quantified until the system is deployed, but
- By the time the system is deployed you now face a power (inertia) problem, that is control or change is difficult once the system is deployed or delivered. Eliminating a hazard is usually very difficult and we can only mitigate them in some fashion.
With apologies to the philosopher George Santayana, I’ll make the point that the BMW Head Up Display technology is in fact not the unalloyed blessing premised by BMW in their marketing material.
No, not the alternative name for this blog. :)
I’ve just given the post Pitch ladders and unusual attitude a solid rewrite adding some new material and looking a little more deeply at some of the underlying safety myths.
Boeing’s Dreamliner program runs into trouble with lithium ion batteries
Lithium batteries performance in providing lightweight, low volume power storage has made them a ubiquitous part of modern consumer life. And high power density also makes them attractive in applications, such as aerospace, where weight and space are at a premium. Unfortunately lithium batteries are also very unforgiving if operated outside their safe operating envelope and can fail in a spectacularly energetic fashion called a thermal runaway (1), as occurred in the recent JAL and ANA 787 incidents.
Why sometimes simpler is better in safety engineering.
I was thinking about how the dubious concept of ‘safety integrity levels’ continues to persist in spite of protracted criticism. in essence if the flaws in the concept of SILs are so obvious why they still persist?
Resilience and common cause considered in the wake of hurricane Sandy
One of the fairly obvious lessons from Hurricane Sandy is the vulnerability of underground infrastructure such as subways, road tunnels and below grade service equipment to flooding events.
The New York City subway system is 108 years old, but it has never faced a disaster as devastating as what we experienced last night”
NYC transport director Joseph Lhota
Yet despite the obviousness of the risk we still insist on placing such services and infrastructure below grade level. Considering actual rises in mean sea level, e.g a 1 foot increase at Battery Park NYC since 1900, and those projected to occur this century perhaps now is the time to recompute the likelihood and risk of storm surges overtopping defensive barriers.
One of the questions that we should ask whenever an accident occurs is whether we could have identified the causes during design? And if we didn’t, is there a flaw in our safety process?
So what do gambling, thermodynamics and risk all have in common?Continue Reading...
I’m currently reading Richard de Crespigny’s book on flight QF 32. In he writes that he felt at one point that he was being over whelmed by the number and complexity of ECAM messages. At that moment he recalled remembering a quote from Gene Kranz, NASA’s flight director, of Apollo 13 fame, “Hold it Gentlemen, Hold it! I don’t care about what went wrong. I need to know what is still working on that space craft.”.
The crew of QF32 are not alone in experiencing the overwhelming flood of data that a modern control system can produce in a crisis situation. Their experience is similar to that of the operators of the Three Mile island nuclear plant who faced a daunting 100+ near simultaneous alarms, or more recently the experiences of QF 72.
The take home point for designers is that, if you’ve carefully constructed a fault monitoring and management system you also need to consider the situation where the damage to the system is so severe that the needs of the operator invert and they need to know ‘what they’ve still got’, rather that what they don’t have.
The term ‘never give up design strategy’ is bandied around in the fault tolerance community, the above lesson should form at least a part of any such strategy.
This post is part of the Airbus aircraft family and system safety thread.
For those of you interested in such things here’s a link to a draft copy of Professor Nancy Leveson’s latest book on system safety Engineering a Safer World, and her STAMP methodology.
Like Safeware it looks to become another classic of the system safety canon.
Here’s a draft of my latest paper to be presented at the Congress of Rail Engineering (CORE 2012) this year in Brisbane. This is more of a mainstream systems engineering paper on the mechanics of writing specifications and some of the conceptual problems in doing so.Continue Reading...
In an article published in the online magazine Spectrum Eliza Strickland has charted the first 24 hours at Fukushima. A sobering description of the difficulty of the task facing the operators in the wake of the tsunami.
Her article identified a number of specific lessons about nuclear plant design, so in this post I thought I’d look at whether more general lessons for high consequence system design could be inferred in turn from her list.
I’ve recently been reading John Downer on what he terms the Myth of Mechanical Objectivity. To summarise John’s argument he points out that once the risk of an extreme event has been ‘formally’ assessed as being so low as to be acceptable it becomes very hard for society and it’s institutions to justify preparing for it (Downer 2011).
Why We Automate Failure
A recent post on the interface issues surrounding the use of side-stick controllers in current generation passenger aircraft led me to think more generally about the the current pre-eminence of software driven visual displays and why we persist in their use even though there may be a mismatch between what they can provide and what the operator needs.
Airbuses side stick improves crew comfort and control, but is there a hidden cost?
The Airbus FBW side stick flight control has vastly improved the comfort of aircrew flying the Airbus fleet, much as the original Airbus designers predicted (Corps 1988). But the implementation also expresses the Airbus approach to flight control laws and that companies implicit assumption about the way in which humans interact with automation and each other. Here the record is more problematic.
Did the designers of the japanese seawalls consider all the factors?
In an eerie parallel with the Blayais nuclear power plant flooding incident it appears that the designers of tsunami protection for the Japanese coastal cities and infrastructure hit by the 2011 earthquake did not consider all the combinations of environmental factors that go to set the height of a tsunami.
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.
Requirements completeness and the AF447 stall warning
Reading through the BEA’s precis of the data contained on Air France’s AF447 Flight Data Recorder you find that during the final minutes of AF447 the aircrafts stall warning ceased, even though the aircraft was still stalled, thereby removed a significant cue to the aircrew that they had flown the aircraft into a deep stall.
One of the areas of human factors in design is the physical layout of a seated workstation or control console to suit the functional reach capabilities of the user population. Should be simple right? Wrong.Continue Reading...
Good and bad in the design of an Oliver Hazard Perry class frigates ECS propulsion control console HMI.Continue Reading...
A small question for the ATSB
According to the preliminary ATSB report the crew of QF32 took approximately 50 minutes to process all the Electronic Centralised Aircraft Monitor (ECAM) messages. This was despite this normal crew of three being augmented by a check captain in training and a senior check captain.
Back in 1999 I co-authored this paper with Darren Burrowes a colleague of mine on the ADI Minehunter project to capture some of what we’d learned about emergent design attributes and their management on that project. Darren got to present the paper at INCOSE’s International Symposium in Brighton England 1999.Continue Reading...
According to veteran russian cosmonaut Oleg Kotov, quoted in a New Scientist article the soviet Buran shuttle (1) was much safer than the American shuttle due to fundamental design decisions. Kotov’s comments once again underline the importance to safety of architectural decisions in the early phases of a design.
Because they have typically pitch unity ratios (1:1) scales, aircraft primary flight displays provide a pitch display that is limited by the vertical field of view. This display can move very rapidly and be difficult to use in unusual attitude recoveries becoming another adverse performance shaping factor for aircrew in such a scenario. Trials by the USAF have conclusively demonstrated that an articulated style of pitch ladder can reduce disorientation of aircrew in such situations.Continue Reading...
Why more information does not automatically reduce risk
I recently re-read the article Risks and Riddles by Gregory Treverton on the difference between a puzzle and a mystery. Treverton’s thesis, taken up by Malcom Gladwell in Open Secrets, is that there is a significant difference between puzzles, in which the answer hinges on a known missing piece, and mysteries in which the answer is contingent upon information that may be ambiguous or even in conflict. Continue Reading…
Recent work in complexity and robustness theory for engineered systems has highlighted that the architecture with which these systems are designed inherently leads to ‘robust yet fragile’ behavior. This vulnerability has strong implications for the human operator when he or she is expected to intervene in response to the failure of system.Continue Reading...
How the design of the Apollo Command Module Attitude Reference Indicator illustrates the importance of cultural cliches or precedents in coordinating human and software behaviour.Continue Reading...
A UAV and COMAIR near miss over Kabul illustrates the problem of emergent hazards when we integrate systems or operate existing systems in operational contexts not considered by their designers.Continue Reading...