Originally Posted by Lookleft
xetroV- The 777 does indeed only have one ADIRU unit but that unit consists of multiple accelerometers and l@ser gyros. This redundancy within the unit didn't prevent an incident to an MAS 777 doing something very similar to the Qf incident-also off the coast of WA. I don't think its a problem unique to one manufacturer or another but an indication of the lack of understanding of how software interacts.
Thanks for that information, makes sense! Interesting to know that an "ADIRU" in one aircraft may be much more elaborate than an "ADIRU" in another. Apart from the obvious difference with the A330, it should be noted that Boeing itself uses dual (or optionally triple) ADIRUs with less built-in redundancy in their own B737 NGs. Strange that nobody at Boeing thought of a more sexy acronym for the B777. AADIRU, anyone?
I agree with your statement about software interaction. This is becoming increasingly important as more and more aircraft systems are being integrated and interconnected, while at the same time the required navigation performance and vertical separation are continuously being reduced, as the skies get busier. At the very least, accurate and quick internal error detection algorithms should provide smooth systems degradation that is immediately obvious and totally transparent to the flight crew. Sudden uncommanded autopilot upsets are not what I call "fail passive" (let alone "fail safe").