Archives For Air data

QF 72 (Image Source: Terence Ong)

The QF 72 accident illustrates the significant effects that ‘small field’ decisions can have on overall system safety Continue Reading…

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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Reading the 2nd BEA interim report’s analysis of ACARS message timing provides us with a further refinement of a calculation of AF 447’s terminal vertical speed (posted here) based on the cabin vertical speed advisory.

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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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Invalid air data may have triggered the cabin pressure differential safety function on AF 447.

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Recent incidents involving Airbus aircraft have again focused attention on their approach to cockpit automation and it’s interaction with the crew.

Underlying the current debate is perhaps a general view that the automation should somehow be ‘perfect’, and that failure of automation is also a form of moral failing (1). While this weltanschauung undoubtedly serves certain social and psychological needs the debate it engenders doesn’t really further productive discussion on what could or indeed should be done to improve cockpit automation.

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A cross walk of the interim investigation accident reports issued by the ATSB and BEA for the QF72 and AF447 accidents respectively shows that in both accidents the inertial reference units that are part of the onboard air data inertial reference unit (ADIRU) that exhibited anomalous behaviour also declared a failure. Why did this occur?

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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…