HN39
 

Yes, but both schemes are subject to icing, particularly a venturi and thus no great improvement.

Icepack
 

Can you provide any other details? When, where, source, under what circumstances?

In fact, you've got slightly muddled here.

As I understand it, when an Airbus A3(2|3|4|8)0 degrades from Normal to either Alternate, thence to Direct Law you're talking about the FBW flight envelope protections.

When you're talking about an aircraft "handing over" control to the crew you're talking about the FMS, aka the autopilot, which is a completely different beast and one which is not restricted to Airbus - incidents and accidents involving an autopilot reaching its limits and handing a barely-controllable aircraft back to the crew include the China Airlines 747SP over San Francisco, and the American Eagle ATR at Roselawn.

Not sure what you're driving at here... Was this problem specific to the sim or an issue with the actual aircraft?

DozyWannabe

AD 2008-0010R1 07/October/2008

Actual malfunction reproduced in Sim, followed by AD by EASA.

Not necessarily pertaining to Unreliable a/s, but a power supply/controls issue.

Pitot icing
 

RE: AstraMike (#3590)
Quot:
Yes, but both schemes are subject to icing
/unquote

Thank you, I am well aware of that. Any probe needs heating for ice protection. What I don't understand (can anybody help?) that the heating of the Thales pitots does apparently not prevent icing of the drains?

regards,
HN39

No one has responded to Rgbrock1's question (post 3539), which seems very valid to me. Where did this idea that the crew reported experiencing turbulence originate? I cannot find any reference to such an observation in the BEA preliminary report.
Rockhound

In response to Crippen on needing four satellites and the plane's position be degraded without that.

It would be highly unlikely to impossible to not get four satellites in sight from a plane in the middle of the ocean. They only time that tends to happen is in mountainous areas where much of the sky is blocked by the mountains.

TME

Rockhound

Read 3541. "hypotheticals".

Will

HN39:
I think the problem with these pitot probes is not icing of the drainage path but pollution by either corrosion or dust reducing drainage efficiency or perhaps a design which satisfies current certification tests but still cannot drain fast enough the water or melted ice ingested in some high Total Water Content clouds.

DJ

Relative to BEA "independence". All Govt. agencies are interdependent.

What is crucial is NOT independence, but objectivity. Major work is done by AB and others here. Analysis, both engineering and operational, is conducted by interests who have an abiding interest in the outcome of the investigation. This is a given, and not disqualifying; they have the records and the expertise. What is very important is the final product produced by the Agency.

DJ77 re: your last post. Any Pitot system that melted ice at the orifice only to send it to a drain to refreeze would be laughed at, it is as you say.
I don't think the Pitots are framed correctly here, as I have said, to pin all Ua/s on freezing pitots (three at a time), stretches credulity.

Will

Thank you Teachme for your reply about the GPS 'seeing' at least 4 Sats.Would the GPS cope with a very unsteady platform,ie spinning and pitching hence losing sats and gaining others?

GPS reception
 

Yes, if the GPS reception antenna is accelerating relatively to the line of sight of the emitting satellite (being tracked, with others), the demodulation of the GPS spread spectrum signal (hence the SNR) can be further degraded.
Jeff

Pitot issues
 

All,

I fully realize now after reading this board that the pitot issues experienced by AF447 - alluded to by the ACARS messages, statements by the BEA and, if I'm not mistaken, in the BEA prelim. I also realize that pitot issues alone may, or may not have been the initiator of the disaster which obviously befell this flight.

I am not an aviator of any type. I am however a systems engineer by profession so I do have intimate knowledge of various computer systems.
(None to do with aviation though.)

I have seen pitot issues being raised as the cause of some unpleasantness in several other flights, one or two of which have been alluded to on this board.

It seems to me that in this day and age of rapid advances in so many aspects of technology (some of which are astounding) that a more efficient pitot system, or even replacement by new technology, can not be implemented. From my understanding, pitot tube technology dates back to the 19th century and were used on ships? So in two centuries we have not been able to bring this specific technology any further? I find that rather difficult to accept. I understand that to date no commercial airliner has been lost solely due to pitot issues. But taking into account some of the more harrowing reports of these issues isn't it about time some pro-activity be undertaken in perfecting these vital instruments, or even replace them with new technology?????

Pitot Static
 

This topic is covered in Techlog, where this question belongs, I believe.

You are correct Greybeard. I'm looking at the pitot system alternative thread now. I should have looked first instead of posting. Mea culpa.
I'm sure the mods will see to it that my posting is appropriately deep-sixed!
Thanks.

GPS Irrelevant
 

GPS reception is not a factor in this accident. Dual or triple GPS are fed into the Fright Management System, along with triple IRU acceleration derived data. Planes crossed the oceans long before GPS with only Inertial Navigation Systems, and can still do it. In fact, the IRU provides a flywheel effect at critical times, as it is based on accelerations, whereas GPS is positionally derived, subtracting where you are from where you were.

Juneau Alaska has a particularly difficult approach and go around requirement. GPS and ground based navigation sensors are supplemented by IRU to provide that flywheel for navigating safely in the go around.

GB

hyperveloce,

Not on any GPS set I worked on. That level of tracking, particularly with an aided GPS, is built into the beasts. An extreme example of aiding performance is in dog fights. The GPS sets lose lock only briefly and bring themselves right back in using the aiding as a clue for likely loop errors.

Military sets do have a slight advantage due to tracking the higher rate P (or Y) code channel. But they need it for jets that can pull 7 G moves. A relatively normal commercial plane's accelerations are not going to give any decent GPS set any particular problem. This is what high order tracking loops are for.

Of course, if the IRU aiding is lost then GPS can become sketchy until the aircraft dynamics settle down. Then it becomes as accurate as before.

Are you, perhaps, referring to a different problem GPS has? It tells you where you were and when you were there. It does not tell you precisely where you are now if you are moving or accelerating. Of course, in usual cases this error is smaller than you need to consider.

JD-EE

Power glitches
 

(Bold mine)

Will, I too saw this record when sifting through the Airworthiness Directives re A330 in 2009 and 2008. It's amazing what remote constellations else actually do happen. E.g. an untight hydraulic line spraying the Avionic bay, leading (during approach) to ECAM warnings due to rotten contacts, and even the risk of fire.

Source: http://www2.lba.de/dokumente/lta/2008/20080091.pdf

This made me to think about why Air France proposed that a lightning strike might have brought down the plane in the first place. Shortly afterwards they even speculated about a general power failure. I still think this was a honest statement originating from their maintenance engineers pondering the ACARS pattern.

The magnetic pulse of a lightning current certainly would have induced spikes and glitches on all sort of electrical cables. But, as it appears, Airbus also thinks about other, yet unexplained possibilities for transients on power lines: "Electrical transients on the 2PP bus bar occur, in particular during engine n.2 failure on A330" (my italics)

The bunch of still unexplained ACARS messages like triple pitot, IR and transient FMGEC1 faults triggered these thoughts: A power down on a specific bus would have triggered specific ECAM/ACARS messages in the first place. Probably not so for spikes and glitches. Due to their HF nature, power spikes do spread, and are also very difficult to track down in the field. NOTE: I'm NOT saying this is what happened. But it could also explain these nose-down events tied to ADIRUs manufactured by a different company -- if you assume the device would have been operated temporarily outside it's electrical specification.

WhyIsThereAir,

When the BEA is claiming transparency, it has to clearly put some basic data on paper :
“The last automatic report was 3 NM left of the airway”
One single line ... but not playing a childish game on the choice of words.

By the way, there is no doubt in the original version, which is in French, that the BEA had no intention whatsoever to bring forward any kind of deviation for that last automatic position report !

GPS and IRU hybridation
 

JD-EE,
You are probably refering to GPS tracking loops aided by an inertial reference (higher resistance to acceleration, jamming, better/faster reacquisition) like for military applications. Is it the case on the Airbus A330 ?
Jeff