More on AF 447

[VC10]

Why did the THS go to full nose up? Did the computer think it was in Take-off mode? - The THS will automatically try to fair the elevators if the elevators are displaced for a prolonged period

How independant are the inputs to the Hydraulic PFUs - THS & Elevators are normally controlled by Prim 1, if it fails or the associated Hyd system or PCU's fail then Prim 2 takes over, if Prim 2 fails then Sec 2 controls the elevators & Prim 3 controls the THS, if all else fails you have manual control over the THS.

Inbd Ailerons - normally controlled by Prim 1 (LH) & Prim 2 (RH) but both can control both sides in case of failure. Secs 1 & 2 provide back-up in case of Prim 1 AND 2 failure.

Are the PFD & ISIS using the same sensors? - The Capt's Pitot and the Stby ISIS Pitot are next to each other

http://www.airliners.net/photo/Swiss-In ... 1929681/M/

The Capt's Pitot feeds ADIRU 1 via an Air Data Module (ADM) and the Stby Pitot feeds the ISIS ASI directly and via an ADM ADIRU 3

The F/O 's Pitot is in the symmetrical position to the Capt's on the RHS of the fuse.


Major lightening strike could also have played a part..... -I read somewhere that there was no elactrical activity in the storm cell

one knows how easy it is to have a big reaction from a little difference or mistake in the coding! - As the 5 Flt Ctrl computers are self checking each other a glitch would have to be in at least two computers. Considering the number of 330/340's in service for at least 10 years I would have expected a serious glitch would have shown up by now, although I accept it would be possible for one to appear now


I read in the report there was a period when both pilots simultaniously used the side stick. In this case, uless a priority button on the side-stick is used to isolate the other stick the computers will sum both inputs. i.e if both pilots put in a 5 degs nose down demand the a/c will interpret this as a 10 deg nose down demand. If one pilot goes nose up and the other goes nose down the a/c will remain horizontal.

[Chris Trott]

Am I not correct though that all THS automatic functions suspend once Alternate Law is enforced based on the flow charts your showed? According to the report, the THS movement began after "Alternate Law" had been announced.

[Dev One]

VC10, Thanks for your explanations - helps a lot, although my meaning of a glitch meant that there could be an error in the code so that all 5 computers have the same problem. Unless someone has been really clever & produced two different codes by different means!
I must admit that the link to the Airbus Technical notes did confuse me with regards to the operation of the sidestick & their priority buttons - I wonder if the crew were confused likewise - proportional movement of the sidestick in one mode, or computer controlled in the other ( probably badly explained by me here, but I hope you understand what I'm trying to say.)
Keith

[SkippyBing]

although my meaning of a glitch meant that there could be an error in the code so that all 5 computers have the same problem.

I think the glitch was that none of the 5 computers were receiving the correct inputs from the external sensors.

What I'm curious about is whether the black boxes have a GPS feed so that in the even of icing they can say - "Hmmm, the airspeed is reading 0.8M and yet our ground speed is only 60kts, perhaps something's wrong...".

Still nice to read all the comments after the Air Insight article by people who're obviously God's gift to aviation...

[airboatr]

Am I not correct though that all THS automatic functions suspend once Alternate Law is enforced based on the flow charts your showed? .

Trott....
I know people talk to themselves, even - question themselves on occasion, but to type a rhetorical platitudinous question to oneself in public forum is utterly re-damned-diculous.

[VC10]

Am I not correct though that all THS automatic functions suspend once Alternate Law is enforced based on the flow charts your showed? According to the report, the THS movement began after "Alternate Law" had been announced.

Chris, sorry for the slow reply. You are not correct! Auto trim isn't lost until you enter Direct Law. From the FCOM
'ALTERNATE LAW - Flight law is a load factor demand law, similar to normal law, with limited pitch rate feedback and gains, depending on speed and C of G

[Chris Trott]

Thank you for the correction. I guess this is another point where Airbus and I disagree. I've always been taught that a partial failure of a system is to be regarded as a total failure and thus you don't rely on it at all. Airbus seems to think that loss of airspeed information is reason enough to disable autothrust but not automatic trimming. Now, I understand that the computer may use AoA more than IAS information for THS, but first that information isn't available to the crew (thus you can get the "what the hell is it doing?" response which only degrades the ability of the crew to handle the situation) and second that information may also be unreliable as unless the computer can for certain say that the AoA vanes are working properly too, then it should be designed to revert to the most safe condition - give the pilots maximum control.