Archives For Complexity

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.

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On June 2, 2006, an American Airlines B767-223(ER), N330AA, equipped with General Electric (GE) CF6-80A engines experienced an uncontained failure of the high pressure turbine (HPT) stage 1 disk2 in the No. 1 (left) engine during a high-power ground run for maintenance at Los Angeles International Airport (LAX), Los Angeles, California.

To provide a better appreciation of aircraft level effects I’ve taken the NTBS summary description of the damage sustained by the aircraft and illustrated it with pictures taken of the accident by bystanders and technical staff.

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The Titanic effect

27/09/2010 — 1 Comment

So why did the Titanic sink? The reason highlights the role of implicit design assumptions in complex accidents and the interaction of design with operations of safety critical systems

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Lead Tangara car damage (Source: Commission report)

On the 31st of January 2003 at approx. 7:14 am a four car Tangara passenger train on run C311 from Sydney Central to Port Kembla (G7) oversped on a downhill gradient leading into a curve and left the track. The train driver and six passengers were killed and the remaining passengers suffered various injuries ranging from minor bruising and lacerations to severe disabling injuries. Continue Reading…

A330 Right hand AoA probes (Image source: ATSB)

I’ve just finished reading the ATSB’s second interim report on the the QF 72 in flight upset that resulted in two uncommaned pitch over events (1). In this accident one of the Air Data Inertial Reference Units (ADIRU) provided erroneous data in the form of transient spikes vales of the angle of attack AoA parameter to the flight control computers which then initiated two un-commanded extreme pitch overs.

This post is part of the Airbus aircraft family and system safety thread. Continue Reading…

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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So far as we know flight AF 447 fell out of the sky with its systems performing as their designers had specified, if not how they expected, right up-to the point that it impacted the surface of the ocean.

So how is it possible that incorrect air data could simultaneously cause upsets in aircraft functions as disparate as engine thrust management, flight law protection and traffic avoidance?

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The use of median value voting algorithms as part of fault tolerant design has become an almost ubiquitous design solution, especially for avionics systems. But have we really considered their suitability?

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Pitot sensor (Source: BEA)

The theory of Highly Optimised Tolerance (HOT) predicts that as technological systems evolve to become more robust to common perturbations they still remain vulnerable to rare events (Carlson, Doyle 2002) and this theory may give us an insight into the performance of modern integrated air data systems in the face of in-flight icing incidents. 

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In one’s professional life there are certain critical works that open your eye’s and force you to look at thing’s in a completely new way. For me at least, Richard Feynman’s dissection of the mummery surrounding NASA’s pronouncements on space shuttle reliability is one such work.

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