Loose_rivets;
Yes, concur, but perhaps you misperceive the intent of the metaphor of a "faraday cage" as used in this discussion. It is useful in conveying an understanding as to why 99.9% of aircraft struck by lightning are not affected. That's all that was intended I think - in lightning strikes, the aircraft is simply part of the path "on the way to electrical ground". That lightning can do the damage described may be true in terms of the energy levels contemplated but the hull losses simply aren't there.

Of far greater concern here, I think you'd agree, is the power of convective columns within the thunderstorm cell(s) and the possibility of low to poor radar returns from same. Like most who do/did this work, I've seen it once or twice and been surprised at the violence of "what wasn't supposed to be there according to the radar"...

poison;
I think looking for cause(s) in the area of electrics/lightning/emergency elect configs etc is looking in the wrong areas; the reasons for saying this have been resident in this thread for about a dozen pages when BOAC first asked the question about the #3 VHF. The ACARS and #3 VHF systems are powered by the AC1 and DC1 buses respectively; the AOM does not list the bus(es) which power the SATCOM but most assuredly SATCOM would not be powered in any abnormal electrical configuration. Only the #1 VHF is powered by the DC ESS bus in either the Emergency Electrical Config or Flight on Batteries Only.

FYI, the ACARS switches automatically from #3VHF to SATCOM when out of VHF range.

If the ACARS sent "maintenance" messages etc then obviously it was working and therefore so was the #3 VHF, ergo the electrical system was working up to the point where, it is rumoured only, flight control/autopilot system maintenance messages, (see previous posts re the possible nature of the messages) were being sent. There is some mention here of "alternate law". Of course, it is impossible to know this at the moment until either the messages are verified and made available publicly, or the DFDR is found.

We don't know what the aircraft was doing or how it was performing after these messages were sent therefore, with present knowledge, even "intelligent" speculation is not possible from that point on and we will have to wait for other sources of facts. The DFDR/CVR will be of immense assistance. Though AF runs a FOQA program, I doubt that the QAR would have survived but we can hope.

4 PW's
You talk about "uninformed drivel" having said in the same post "I read somewhere that Air France 447's wing touched an A320 rudder". Apart from the fact that it was an A321 and happened in Paris this happened in 2006!!!!
I would call this uninformed or not bothering to check your inputs as so many others do or rather do not do.

Curiosity is a part of human nature. There is nothing wrong in speculation. Yes, some posts are repeated over and over again and get boring, but most of readers can filter through it. If you don't like this thread, simply don't read it instead of telling other people what to do. Every regular visitor here knows that crash-related threads contain lots of useless posts.

There is no harm done in speculating here. It does not endanger any hypothetical survivors, it does not hinder the search and recovery efforts, it does not hinder the investigation in any way. If crash-related info and speculation starts getting censored and restricted to the members of the profession, aviation will appear scarier to the general public because they are hiding something. Less people will fly, airlines will make more losses and lots of professional members of this forum will lose jobs. We passengers are paying your wages - and despite often having no clue, we like to be informed.

I do not contribute to PPRuNe (the reason is I have nothing to contribute, being an SLF), but I enjoy reading it, including speculations - I am sure many others do either.

lexxity

Lady Lexxington

Join Date: Jul 2004
Location: The Manor House
Age: 29
Posts: 964


Replying to post #487. Ditching has already been discussed and dismissed due to several factors amongst them the weather, the dark and the sea conditions found on the open sea as opposed to somewhere like the Hudson.

I've never sailed across the South Atlantic, only the North and the swells can be awesome, enough to toss a 70,000grt vessel, designed for those conditions, about so I don't see an airframe standing a chance. I do stand to be corrected though.
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Guess we'll have to rewrite past history and advise people that actually survived ditching in open water in the past that they in fact didn't make it. I've flown with a pilot that survived one. He talked about his ditching being easy, as opposed to the other crew that he knew about that ditched in the North Pacific or Atlantic under adverse conditions and survived.

Swells in the ocean can be awesome. And sometimes the seas are amazingly smooth. U.S. television show covers fishing in the Bering Sea in winter. Sometimes it's amazingly calm, and other times there are terrible sea states. Airframes can, and have, survived water landings(ditchings) so they are survivable.

Unfortunately a debris field has been found so it appears, from the limited information available, that a ditching was not attempted.

Metal fatigue does happen, and has brought down planes in the past. So a bad repair or generally something missed could well be a contributor 3 years later, especially in extreme turbulence no? Not just metal fatigue but there was a case where a tail strike was badly repaired which lead to (correct me if I'm wrong) decompression and an in-flight breakup?

I am uninformed, but I wouldn't dismiss anything in this aircrafts history.

MU3001A

Unfortunately I doubt we will ever know but one thing is for sure that if the comms in that area were little more than non existent the crew would have had an additional source to refer to. As is the case things tend to go wrong when you a farthest away for anywhere & with little or no comms.

cockpitvisit

Good post indeed.


Metal, indeed has a very long memory.

As we all know, bend a piece of metal often enough and long enough and it will break. The trick is to discover where the metal intends to break.

They had degraded flight controls, no autopilot and no flight instruments.

Partial control
 

Is it true to say that on Alternate Law, the A/C can be manually controlled thru the stabilizer and the rudder?

SLF, non-journo question. If all the controls, autopilot etc., are knocked out, how long does it take for them to reboot under 'normal' conditions?

PJ2 -
I submit that if the radar in use today isn't capable of "seeing" this kind of convective activity, that you avoid these areas completely. Using the C-Band radar we had, I don't recall an active cell failing to show up on the scope.....providing the operator knew how to use it.

I find it very frustrating that with the availability of sat. internet access in the back, with the resultant access to excellent real-time wx data including radar, the SLF have better weather information than we do up front at times. How long will it take to incorporate a useful, current data stream to the cockpit. I guess only the bean counters know the answer to that one.

My understanding is that the "AP Disconnect/alternate law" message preceded the later string of system failures. If correct then the indication is some sort of "upset" or turbulence induced unusual attitude prior to other issues...or am I misreading the information available. Based on the early comments by AF it seems in line with the picture of an upset followed by various system failures indicating some type of catastrophic failure.

If a sudden unexpected extreme turbulence event caught the pilots by surprise and forced the plane into a position of unusual attitude severe enough to disconnect the AP would the switch to alternate law create problems in recovering the aircraft?

I didn't really want to comment on this, so I won't speculate on the reasons why AF447 crashed.
However, what worries me is that it seems some professionals are really dismissive of the potential of lighning damage on modern aircraft.

I've read through all of the posts and it seems strange that no one has mentioned positive lightning, which account for less than 5% of all strikes.
Positve strikes are at least 6, and often up to 10 times more powerful than standard strikes. Modern passenger aircraft are not built to withstand positive strikes as the technology is not available: the discovery of positive lightning is pretty recent.
Positive lighning occurs when a positively charged leader forms at the cloud, and a negatively charged streamer issues from the ground.

Positive strikes can occur far away from CB (of course, originating in CB), due to their immense energy which can reach up to 300KA and would therefore far exceed the 20nm cordon recommended for CB avoidance for shear/turblence/strikes etc. Compare this to standard negative strikes of up to 30 KA and it is easy to see why these strikes are very dangerous.
For pilots who dismiss lightning strikes as almost harmless, well, you'd be right. Up to 95% of the time. It is unlikely to happen, but it can and has bought down aircraft, Pan Am 214 is an example.

Regarding the flight control law questions:

No entirely true. In normal law the flight contol computers provide various protections which keep the aircraft within operating and structural limitation. The first level of degradation is alternate law in which some of those protections are lost, but the aircraft still flies normally. The next level of degradation is direct law, at this point, the aircraft does not have any protections but still flies like any normal aircraft with full control authority. The last level of degradation is manual back-up where the pilot has only rudder and manual pitch trim to control the aircraft while computers are reset. Manual reversion is not designed to be used to control the aircraft in other than straight and level flight as a temporary siutation. I have landed the 332 in the sim in manual reversion and it can be done, but the chances of being in that situation are exceedingly slim.

Regarding the PRIM and SEC question, the loss of PRIM 1 and SEC 1 would probably leave the aircraft in alternate law which is not an emergency situation in itself but would be another distraction if more failures were occuring. With any 1 of the 3 prims, and 1 of the 2 secs the aircraft is in normal law. The degredation logic is somewhat complex, but with any 1 of either type of the flight computers you could at least have direct law.

The flight computers are all independently designed and built by different companies to ensure that a design or manufacturing flaws could not affect all of the computers.

Hi Coyote44, Alternate Law is no big issue - some of the magic protections will be lost depending on the failure (bank angle, g, overspeed, alpha etc). The aircraft effectively becomes a traditional airplane. Then comes Direct Law, which is still fully functional control of flight, before it eventually degrades to rudder, trim and thrust control only.

A330 Flight Controls
 

PRIM 1 and SEC 1 refer to the FLIGHT CONTROL PRIMARY COMPUTER (FCPC)

ISIS Integrated Standby Instrument System

ADIRU Air Data Inertial Reference Unit

I suggest an excellent article on A330/340 Flight Controls

http://www.davi.ws/avionics/TheAvion...ook_Cap_12.pdf

Snaproll & Sika
 

Thanks for the input. I was merely trying to enquire if their systems could've degraded to backup mode, which in severe turbulance would've been impossible to control, IMHO.

I am a SLF and I have been bashed many times for my comments but there are two posts on this thread that I must criticize.

Metal fatigue occurs over the time, a strike (i.e. with another object) will not have any significant impact on the metal fatigue failure. CI611 went down 20 over years after being poorly repaired...

Faraday cage...it is an ideal conductor therefore does not need to be grounded (actually is otherwise)...one of its function is to protect from lightening strikes... Wikipedia has a quite good description of it...

edit: deSitter gave a accurate description of a Faraday cage

FSLF

Coyote, the short answer is yes. If all the computers were lost and they were in manual reversion and they were in severe turbulence, then the plane would be almost impossible to control.