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Old 3rd Jun 2009, 23:22
  #777 (permalink)  
Join Date: Jul 2007
Location: Europe
Posts: 92
Red Paddy:
To me there is only one thing that could cause a shutdown that would leave non essential items operating while essential items such as the ADIRU's and ISIS shut down and that would be a fire in the avionics bay knocking out essential systems in an erratic manner and not shutting down non essientials first.
Paddy, my absolute sympathies to your neighbours, I understand that search for "the truth" is priority to them. There are multiple scenarios possible for that sequence of ACARS messages. I did not have the time to clearly verify how the mentioned systems are interconnected, but it is clear that PRIM1 and SEC1 are both at DC ESS as well as HOT BAT. So a massive failure at those could possibly lead to the picture we have and strike the aircraft at its very heart.

The computer systems are placed in a way in the e-bay that a local physical damage (bomb blast / fire) would not render e. g. all PRIM unservicable. This has been taken care for by design.

On the other hand, this alone does not render the plane uncontrollable. In essence, even only one backup ISIS could provide enough navigational aid to bring it back to earth in one piece (providing PFD or ND on its front), albeit I imagine the workload would be quite massive. If it were only the computers that were mentioned in the ACARS messages, it could possibly even still execute an automated ILS approach, if I'm not mistaken.

If the timing of the ACARS message correspond to the occurrence of failures over time is not sure at the moment. It could well be that the Maintenance Computer System, which collects these data, waits for several occurences of failure reports before relaying them to the home base. So for me it is not sure that really the AP disconnected at first, then the PRIM1 etc. It was not designed as a real-time DFDR backup, just for maintenance information and action, eliminating false alarms.

In an Airbus, you can go to 'Direct Law' (I think!). But, also as far as I know, that means that you won't have elevators or ailerons to fly with, just the rudder and the trim controls.......
Direct Law delivers full authority. But other than Normal Law, the Sidestick commands real rudder movements without limits, as opposed to protected roll rates / g-loads etc. (Saw it afterwards, was already answered by khorton and GlidingAerobats.)

As an add-on, if ADIRU and ISIS are completely non-functional, and you have no external horizon reference - is that even recoverable?
There is a gyroscopic horizon in the cockpit, if that's what you mean...
There is even 3 ADIRU (one would be enough), 2 ISIS (which can in a way replace the 3 ADIRUs), 3 PRIM (one would be enough), 2 SEC (which can provide backup to PRIMs) and so on... As said above, the ACARS messages alone do not indicate a helpless bird.

Lost in Saigon:
One very important piece of information is missing though. Was the cabin vertical speed indicating a climb or a descent?
I would very much argue this to be a climb, i. e. pressure loss. If it would be a descent, there had two independent computers to be failed *and* a source of overpressure to be present (aircraft descent, increased bleed air pressure), because the outflow valves would have to be stuck in their present position or being closed. But still to be verified, agreed.

Q. Which part of your aircraft is most likely to be struck?
A. The nose.
No, lightning bolts do not come from upfront like birds.

We only hear (but have no evidence or confirmation that it is "A330" wreckage) of "pieces" found and a 20km "oil slick".
As press has it, I think Brazil authorities confirmed that these were of AF447. But then, no information about where they derived this from...

If one where to judge by that, they flew right through the worst CB activity in the region.
To me, Spiegel is not exactly known as a sound aeronautics treasure of wisdom, so I would not bet my money on their published charts.

If anyone could provide me with the MSN number of the cited Qantas A332 (AF447 being MSN660), then I could check the make and model of the ADIRU of these two.
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