The blocked pitot explanation certainly makes the possibility look feasible, but surely it would be an umpteen-million to one shot that all of them got blocked at the same time.

How many does an A330 have? A left, a right and a backup?

Four I think, but they all point into the same slush.

Three actually, and that slush could effectively block all of them at the same rate, so as nobody disagree : NO warning NO caution ...

Yes, the spec is a bit broad. I was thinking that for an R/C oscillator entombed in parafin wax within a very solid steel/titanium case, the external temperature would eventually have an effect on its frequency and that a xtal/piezo filter may be in the R/C loop. Thinking in terms of manufacturing to meet the nominal frequency +/- 50Hz, I'd move away from an R/C circuit and use something less affected by temperature and voltage. The stuff I can find just quotes the tolerances without any schematics to back it up.

As there are three timing issues involved, 37.5kHz [output frequency], 1Hz [period] and 375/37500Hz - 10m/s [duration]; simple xtal divider logic would seem more practical.

With regard to the Doppler shift, my feeling is that differentiating that from multi-path would be a nightmare. Perhaps careful reference to the local bathymetry may help sort it out. Best of luck to them!

mm43

And here they all are, on the actual aircraft in question photographed a day or two before it crashed.

http://i49.tinypic.com/zlooht.jpg

mm43

The 2 black thingies inboard and aft of the TAT probes might be “Ice Detection Probes”.

I am only new to this so I may be mistaken !

SPARGO Craic

You are correct - the two items labelled "LOC Antenna" are the ice detection probes. :ok:

Wristwatches typically use 32.768 kHz quartz tuning fork oscillators. They are also very low power and survive modest shocks. I'm not sure they'd survive the shock and vibration specified for the recorders. Going the divider route with a higher frequency crystal uses more power for no practical benefit. The crystal is still vulnerable.

You can, however, find nice stable resistors that hold 0.1% or less over temperature. You can also find nice "NPO" ceramic capacitors that hold within a few dozen ppm/degree C. That's where the temperature variation would come from. Manufacturing tolerances of the capacitors would have to be in the 2.5% range or else trimmed with a parallel resistor for the R in the RC that is calculated and soldered in during manufacture. For reasons of cheap getting it within 1kHz or about 2.5% is "good enough."

After weeks of cold soaking there would be no further temperature inspired variance in the oscillator frequency. And there are oscillator circuits that are remarkably insensitive to battery voltage that could be used. So figuring out that they heard two distinct signals should not be all that difficult.

{^_^}

Again see old thread for more detail discussion last year

Not slush at -40 degC, probably micro-fine ice crystals, which would be harder to melt out, could also insulate the TAT probe, and cause problems with engines...

Icing not expected at cruise altitude, so computer fault? Clearly used to be an issue:-

http://www.iag-inc.com/premium/airbu...ablespeeds.pdf

Subtle Difference in the Blockage Process
 

CONF iture said: Slush? Is not the problem an ingestion of ice crystals over time within Cirro-Stratus/CirroCumulus cloud rather than a "heater OFF" style freezing of moisture at a drain hole (followed by a blockage, partial or complete of the pitot tube itself)? i.e. those high-level cloud types are just composed of ice crystals. That's the important difference.

Concentrate upon the possible difference in the two blockage processes and it may become clearer as to what actual effect it had upon automation.... and why the Thales tubes' heaters were more prone to being overcome. i.e. they were never designed to combat being hit by already frozen ice particles. Think in terms of calories/BTU's in and out - and it's not hard to figure why the pitot heaters finally were overcome. That's the design deficiency.

It would have to be something unusual yet simultaneously common to all three pitot heads (as CONF iture said:"no alarm-raising disagree" to provoke a triple redundancy-based comparative alarm).

........a. a given concentration of ice particles (i.e. fairly thick and continuous cloud at quite a low temperature)
........
........b. a TAT low enough that the accumulation rate of ice particles would ultimately overpower the heating capability of the pitot heaters.
........
........c. If the accumulation/compaction rate was sufficiently subtle (i.e. slow) then the effect would be insidious. Thinking here that the speed loss seen by the system would not be actual but would be acted upon by autothrottle incremental increases, thereby putting the constant airspeed/mach (but actually accelerating) aircraft ever closer to the corner of the coffin corner envelope at that height.
........
When, in turbulence perhaps, the aircraft actually hit that critical mach (that you must avoid), what happened then?
........
Did the autopilot disconnect? Did the pilots assume a coffin corner aerodynamic stall (because they were seeing a low IAS), and then take stall recovery action (lower the nose/cob the throttles?).
........
What would the effect be of doing that? Last time I did "alt and comp" (and had a mach-induced pitch-up), I was intentionally inverted (because I had a very inquiring mind in those days). It was an interesting (and quite aerobatic) ride and I had much greater respect for MCrit after that.
........
Can you ever (and have you ever?) ran this scenario in a simulator? If so, does it faithfully replicate what would happen in the airplane? Or is this subtle and insidious pitot blockage scenario a totally unforeseen circumstance, despite all the prior instances of Thales pitot induced upsets?
I have the gut feeling that to eventually determine with some certainty what happened to cause AF447's loss of control, we must first completely understand the precipitating event.
........

Is it possible for probes to be damaged or removed by hail, has anybody heard of this happening?

My thoughts exactly; nicely put. I might add that it's likely the design of these pingers hasn't changed much in decades (maybe replacing mica caps with NPO ceramic?). Once a design is certified, they probably follow the principle: "if it's not broken, don't fix it."

Hi,
The main problem with such scenario is that it just doesn't fit with ACARS reported:
1. Pitot Probes freezing was actually detected by the systems;
2. Auto Pilot and Auto Throttle also disengaged automatically as a consequence of 1 (as designed, and it was not a manual disconnection).

How the pilots reacted is certainly open to speculation but nothing is telling us at this point that an insidious freezing was an issue for the system to change any of the flight parameters. So an upset due to speed issues is very less likely to have happened by itself if it was the only factor in cause.

S~
Olivier

Without regard to 447, I wonder if there hasn't been an overlooked accumulation of ash affecting the bleed holes in pitot probes of planes in the past two months? It would show up as increased speed error. By how much would depend on the design of the probe.

GB

Blockage could have been simultaneous, but unblockage was not ... so appear the ACARS messages, but at this time the overall situation is already highly degraded ...

Hi,
Well, why not if you want it this way... Nonetheless, this sequence is very unlikely: In one hand, simultaneous blockage of 3 probes located at different spot alongside the fuselage when flightpath is notoriously always a bit assymetrical would be a probability seriously close to zero while, on the other hand, unfreezing is due to simultaneous imput of heaters with variations very limited in time. Consequently, all those related "probes" faults would probably not be displayed at all in the first place.
S~
Olivier

Takata and others

The ACARS msg content is that ADIRU:s reported air-speed values disagree. Pitot problem is only one of many possibilities. The error can occur anywhere between the pressure on the pressure transducers (dynamic and static) and the computed speed value produced by the corresponding ADIRU. It has apparently happeded that ADIRUs have malfunctioned (their IR-part) and the error not properly detected/saved by the BIT system (on a Boing, however). Don't look at only one possibility, please.

The Flaps were stowed at impact. (BEA). The spoilers are part of the upper wing surface. The recovered Spoiler shows evidence of collapse in a deployed position.

The spoiler shows evidence of no water impact from underneath, its damage is consistent with overspeed, aerodynamic collapse and removal by the airstream. The Radome, though recovered in pieces, shows much the same sort of failure.

The Vertical Stabilizer (leading edge) shows collapse as though "pushed back". Its damage is symmetrical, intimating that the leading edge was impacted by a force that was distributed while the VS was a part of the airframe. If water impact caused this symmetric failure, the VS would have to have entered the water edge on; though possible, this is highly unlikely. The damage to the vertical take up arm (the missing "end"), cannot have occurred without damage to the Hinge axis, unless it was shaken loose by vibration, something that in itself would not have disrupted the integrity of the Rudder Hinges.

A/P. The auto system uncouples per the following parameters: an inability to keep the a/c from rolling greater than 45 degrees, pitching up more than 15 degrees, pitching down more than nine degrees. If it is assumed that the uncoupling occurred due to one or more of the limits having been attained, it must also be assumed that these rather extensive excursions were abrupt; a pilot would not allow an a/c to slowly degrade its ride to these limits. The ACARS are maintenance hallmarks only, and are sequenced plus or minus one minute? SATCOM has some antenna requirements, so during the cascade of these messages, the a/c must have been in antenna posture aspect that limits conjecture about the end relative to upset.. The Spoiler speaks of a need to slow, other evidence points to overspeed. How fast?

The answer I think is in the debris location. Where were the VS, radome bits, and bodies? This means the first body, laptop and VS establish the first of a series of trajectories (airborne loss of integrity), or, the only one. The Ocean is a mystery to me, so I'll keep reading and staring at the work of others.

bear

Independently, they could have various meaning. But this serie's meaning is quite obvious. Pitot problem is clearly identified with an ACARS telling that each pitot probe is reporting a different value! Then, ADR disagree (unrelated to IR).
You should have another look at BEA's reports as this part is explained in details.

Or, as BEA mentioned also, it possibly separated due to water pressure when wings sank while being (fully/partially) deployed due to (vertical) forces at impact.

... and this aircraft then crashed 5 minutes later, level, with low horizontal and strong vertical acceleration? ... A/P & A/T going off were the first ACARS to be sent and the reason why they disconnected doesn't look obviously documented by the 20+ following ACARS?...

But nobody can find any submerged wreckage around this place!

If there was any measurable evidence of overspeed by studying the wreckage, it should have been reported by investigation in last december's report like they did for other parts showing some clues about what happened. If it was not reported, it means that, either they disagree about it, either that no evidence at all of overspeed was actually found. Otherwise, it would have been a huge conspiration in order to hide something so obvious for you.

Then, look at the daily debris fields recovered during searches (BEA annexes). But as floatting stuff is moving, this is not the best way to draw any conclusion from that, even if the tailfin has been actually recovered in the middle of bodies and other parts of the airframe. Only what is still at the bottom of the ocean would be enlighting, starting with the wreck's location compared to flight plan.
S~
Olivier

takata
Please take a look at the systems schematic. This has been shown multiple times in the old thread. Any signal had to pass a digitizer then to the ADIRU until a speed is computed and the ADR value becomes available.