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AF447

Old 23rd Sep 2009, 11:56
  #4441 (permalink)  
 
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Answer to Dagger Dirk

Thanks for disqualifying my questions in that mannor.

Quote: Dagger Dirk
So I'd urge you to disregard this input below as a total red herring (for all the above reasons)

http://www.caa.govt.nz/safety_info/G...g_Handbook.pdf

It states on page 13

Quote:
Generally, the worst continuous icing conditions are found near the freezing level in heavy stratified clouds, or in rain, with icing possible up to 8,000 ft higher. Icing is rare above this higher altitude as the droplets in the clouds are already frozen. In cumuliform clouds with strong updrafts, however large water droplets may be carried to high altitudes and
structural icing is possible up to very high altitudes. Further, in cumuliform cloud the freezing level may distorted upwards in updrafts and downwards in downdrafts, often by many thousands of feet. This leads to the potential for severe icing to occur at almost any level

I didīnt ask those questions without any background, so i think it would be appropriate to allow other readers to make their statements as well.

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Old 23rd Sep 2009, 14:10
  #4442 (permalink)  
 
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Post

people are just starting to realize that the behavior and physical properties of micro sized particulate matter is often extremely different to more commonly sized particles. Especially in the engine icing evaluation. Many of previously established observations (used in certification) have to be re-evaluated.

Like square windows on the De Havilland comet, there are just some things we didnt know, not at all.
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Old 23rd Sep 2009, 14:29
  #4443 (permalink)  
 
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A Re-think Required

Retired F4
Nobody's denying your right to comment but the very valid point is that:
.
a. An experienced crew wouldn't soldier on into heavy icing conditions without diverting off-track.

b. Because cumuliform cloud (and assoc up/downdrafts) is highly localized, I'd very much doubt that a "downed by heavy icing" scenario would be a player at Flt Lvl 350.

c. From that same pdf file you're quoting comes:
.
"1.3.4 High-Level Clouds
High- level clouds, such as cirrus clouds, with their bases above 20,000 ft, are usually composed of ice crystals that will not freeze onto the aeroplane, and so the risk of structural icing is slight when flying at very high levels."
But it's not structural icing that we speak of here. It's a compilation over time of supercooled ice crystals inside pitot tubes - in a continuous layer of cloud dense enough that the pitot heaters' heating capacity is being overcome thermally by the super-cold ice-crystals (not a theory, an admitted fact that's now being belatedly addressed by an AD).

d. Because there's no turbulence or structural icing in dense CirroStratus, there'd be nothing on their Wx Radar and no cause for concern whatsoever for the crew about icing. No instrument tells you that the pitots are ALL icing up and crews normally monitor the Fuel synoptic page, not the Engines page. With those non-moving thrust levers of Airbus and crews relying upon their ECAM for engine-related warnings, they'd just not notice that the thrust was increasing incrementally to offset the "system (but not crew) perceived CAS loss" - and causing them to fly perilously fast.

So it's a really nasty set-up for a nasty surprise just as soon as the split between the two sources of static pressure starts becoming so significant that BARO hold is rejected and the autopilot drops out. Pitch-trim state when the autopilot drops out? Another potential ball-of-wax. Where's the THS taking its auto-trim cue from? The increasingly duff CAS? How much (by way of out-of-trim) pitch force was being HELD by the autopilot. Take that a bit further and you might conclude that when the autopilot dropped out the aircraft was trimmed for the HIGHER speed and the nett result was a strong and instant nose-down BUNT. Just imagine them instant apples!! Straight into Mach Tuck - courtesy of the nose-heavy mis-trim? I'd guess so.

Another question might be: "If the baro hold was being corrupted by a false "computed" static pressure, was the aircraft maintaining a genuine FL350 on 1013Hpa?"

Don't know exactly how the ADIRU calculates its static pressures for baro-hold, so can't really comment upon that. But you can be sure that the static pressure component reported by the pitots' ADM's would be increasingly different to the valid one being reported by the uncorrupted static ports, as the pitots became increasingly blocked.

If you disagree, then dismantle the argument with some sort of well-argued counter-proposition or an indication of where the theory fails.

That crew wasn't a made up of fools, just pro-pilots doing a job and likely getting caught out by a very insidious cascade of cumulative error leading to an instantaneous happenstance. I'd guess that any A330/A340 crew would have lost that battle. We owe it to that lost crew to deduce their predicament by utilizing the best tool that's ever likely to now become available - and that's deduction based upon known precedents.
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Old 23rd Sep 2009, 15:39
  #4444 (permalink)  
 
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Belgique

Belgique

Thank you for your explicit and detailed answer.

It was not my intention, as mentioned in all other posts of myself before (There only had been a few) to blame anything on the aircrew. I dont assume that they flew blindly and willingly in a known ice scenario.

But isnīt it a fact, that we tend to look at possible causes in a single-minded way? I mean in a way, where we look at only one thing happening, excluding thereby other possible happenings. Could the chain of events not unfold in several parallel happenings in a quick and as proved deadly mannor? By the way, that is the way most accidents happen. It is called chain of events.

That there was no report of icing at that level or that the crew didnīt observe any icing on radar (which point was discussed highly emotional in this thread) does not neccessarily prove, that it did not develop within an updraft within a short time period. Nature has a lot of surprises at hand, and sometimes they are not yet known to us because nobody cared or nobody expierienced them or nobody reported them.

In accident investigation you look at the familiar, at the unfamiliar, and finally if you dont come to a satisfactory conclusion also at the unthinkable.

The High-Speed-Event does IMHO not fit to the final touchdown in the ocean (Time, location, attitude, speed, sinkrate, found evidence), there must be something else.
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Old 23rd Sep 2009, 16:21
  #4445 (permalink)  
 
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With respect, you make the mistake you describe, F4, in exactly the sequence you relate. You have eliminated here the last relic of your sequence, though it is common. BEA (not unthinkingly, and hence not unthinkable) may be off base. I say this with respect for their mission. No 'conclusion' is at hand, it says that in the report itself. They write what is likely, as they see it. Just because two outcomes seem unlikely, they may coexist in a very logical way. No one wants to believe this a/c lost parts (important ones) at high altitude in overspeed. I don't. I don't want to entertain that the pilots were inattentive rookies, or weren't up to the crisis. Belgique has a possibility that fills in alot of important blanks; I like it because, as a pilot, it makes sense, and as a human, seems least alarming of other possibilities (Plausibility). It too wants scepticism. The problem here is many posters are jumping to conclusions (I have, admittedly) and defending them. The Defense is what is off-putting. As an investigator, it borders on the ridiculous in some cases. Disclosure also requires me to admit that it is almost a perfect explanation of what I think happened here.

Last edited by Will Fraser; 23rd Sep 2009 at 16:31.
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Old 23rd Sep 2009, 17:12
  #4446 (permalink)  
 
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High Speed Incident to Low speed Arrival.....que?

Pages 222/223 and 224 are probably the most important of this thread (for indisputable bottom lines):
.........
However we are getting this "illogical non-sequitur" rejoinder from a number of posters. i.e. Why would a high-speed autopilot disconnect and possible Mach Crit encounter terminate in a high descent rate, nose-up, wings-level, slow-speed arrival at the impact point? Perhaps some extracts from prior posts can clarify "how":

The Conundrum
#4433
....however I am having great difficulty in understanding how an overspeed induced departure will lead to other than a sky full of confetti.or a high speed impact with the water. The fact that AF447 arrived at the surface apparently essentially intact and apparently at low speed and high angle of attack, high sink rate and perhaps in as little as 5 minutes requires an involved process if one assumes an initial overspeed departure from controlled flight.
and
#4461
The High-Speed-Event does IMHO not fit to the final touchdown in the ocean (Time, location, attitude, speed, sinkrate, found evidence), there must be something else.
==> the responses

#4428
Disorientation after a Mach Crit/Mach Tuck encounter inducing a loss-of-control could easily later lead to a nose high/stall entry type ituation. Why? See later (see #4430 et seq - below).

Personally not sure about the plausibility of a double flame-out (from a post-disorientation stall/spin scenario) and failure to relight - culminating in an attempted engines-off ditching (as an explanation for
the assumed wings level water-entry attitude, high RoD and low speed).

The 4 minutes (only) from height could be explained away by the high speed/high RoD required for relight attempts OR that those 4 minutes just represented the time from height to losing all useful electrics (to the ACARS) due to a LOC induced double flame-out.
#4430
Note 1: "Ok, lets follow that line of thought a bit further. The nose starts to tuck (i.e. drop) as trim limits are reached (because of the shifting center of pressure on the wing as you go transonic) and the nose starts to fall, altitude starts to unwind quickly and the crew reacts by reducing power and deploying speed brakes. Assuming they are successful in arresting the plunge, what is the next thing they would encounter? It would be a transonic pitch-up as they decelerate (caused by the center of pressure moving back to its normal subsonic position) as all the nose up trim makes itself felt. Say the aircraft bottomed out at FL 250 while pulling maximum permitted g, and just below M Crit. In an F-4 for example, this type of transition to subsonic could cause a 50% 'g' overshoot because it happens very quickly. Can the Airbus G protection mitigate this 'g' spike quickly enough to keep the wings from breaking (while in alternate law and with an aft cg)?
Would the wings stay on? I don't know since I don't have enough aircraft data, but if the wings did stay on, then you would probably soon find the nose pretty high in the air since the crew would be unlikely to have the presence of mind to drop a wing. Then you could get into a deep stall very quickly. But, can the critical Mach recovery even be made in Alternate Law?

#4434
For a non T-tail, a sustained deep stall is not really on the cards. A flat spin maybe? Not really. The A330 aerodynamics don't support either proposition. A double flame-out due to a nose-high departure and auto-rotation following a Mach Crit encounter and loss of control? YES, most affirmatively. WHY?
.
Well Airbus test-pilots don't test for any flame-out proclivities during stall or coffin corner auto-rotation, however the A330's engines would be quite vulnerable to that at cruise height (see recent Pinnacle Airline's CRJ example). My guess is that the AF447 crew were burning off height at a great rate attempting relights all the way down and then, logically, were eventually forced to give up on the relight attempts for an engine-off, best configured/best attitude/best speed arrival at ditching station "terra oceana". That's what could have happened to Air Transat's A330 - if the Azores hadn't been in their sights all the way down.
Conclusion: Yes Virginia, a loss of control, stall/incipient autorotation/spin could cause a double flame-out due to intake blanking. The ensuing high-rate/high-speed descent would quickly dump altitude (relights are notoriously unsuccessful at higher altitudes anyway). Eventually the crew would have to give up relight attempts for a controlled engine off arrival at sea-level.

There's a good chance that this would explain the condition of the recovered debris and bodies. Degraded flight controls, nil flap, nil L.E. devices and sea-state would have made any such attempted ditching valiant - but doomed to failure.
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Old 23rd Sep 2009, 17:35
  #4447 (permalink)  
 
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Will, Belgique and F4.

Your three passionate positions and postulations have been argued ad nauseum about 2500 posts ago.

It is actually tough watching the same pig roll arround in the same mud again and again.

It becomes almost irresistable to want to jump in and cite the same sources and references again and again.

But most of us do exactly that.

The answers are in the CVR. I suspect the reolved report will embarass most posters here.
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Old 23rd Sep 2009, 19:51
  #4448 (permalink)  
 
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well, the first article is totally reasonable and really, as obvious as looking down at your shoe and seeing a stream of piss. Dont have to be a rocket scientist to put two and two together.
The disaster of Air France Flight 447 was the result of a preventable mix of human and technical failures
..isnt that what EVERYTHING IS??

To say we have that, is to say we have airplanes, people and air.
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Old 23rd Sep 2009, 21:33
  #4449 (permalink)  
 
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Some more opinion....?
Charles Bremner - Times Online - WBLG: The four reasons why Air France 447 crashed
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Old 23rd Sep 2009, 21:44
  #4450 (permalink)  
 
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As I understand it, the AH is optional on the 330. If fitted, it is top left at LHS panel.
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Old 23rd Sep 2009, 21:55
  #4451 (permalink)  
 
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-- There was a malfunction in the ADIRU, the three air data computers which feed information to the flight system and the pilots.
All 3 of them? And what was the malfunction exactly?
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Old 23rd Sep 2009, 22:39
  #4452 (permalink)  
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I note we have inherited this thread from elsewhere.

Main rule is that the thread stay on tech related matters otherwise it goes to a more appropriate forum.

regards,

JT
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Old 23rd Sep 2009, 22:51
  #4453 (permalink)  
 
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John;

Where would that be?

Jet Blast?


Just askin......
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Old 23rd Sep 2009, 23:06
  #4454 (permalink)  
 
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The four reasons why Air France 447 crashed

-- The aircraft flew into an area of storms which other aircraft avoided by steering around them.
-- The pitot tubes (speed sensors on the front of the plane) suffered faults
-- There was a malfunction in the ADIRU, the three air data computers which feed information to the flight system and the pilots.
-- The pilots may not have had sufficient training to retain control of the malfunctioning aircraft.
Charles Bremner - Times Online - WBLG: The four reasons why Air France 447 crashed

-- The pilots may not have had sufficient training to retain control of the malfunctioning aircraft.
I find that very wrong and feel like complaining, but Ill get sued. That is one of the most upsetting statements Ive ever read, absolute bs, It just points the finger at two people who actually tried to save the lifes of all on board, very very wrong.
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Old 23rd Sep 2009, 23:25
  #4455 (permalink)  
 
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Actually, it points the finger AWAY from the two individuals, who, sadly would not, and should not be blamed as they are not here to defend themselves. The fact they were unable to successfully deal with the situation they found themselves in, would leave open the POSSIBILITY that they had not received adequate training from their company in limited panel flying, recovery from unusual attitudes, and operation in alternate and direct law. And that possibility would form one more hole in the " swiss cheese" , leading to an accident.
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Old 23rd Sep 2009, 23:57
  #4456 (permalink)  
 
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Beyond that, partial panel, unusual attitude recovery are 'recoverable' because they are trained in a setting where the pilot will know if his inputs have corrected the upset. Here, if it happened due to Unreliable airspeed, AP chasing crap IAS and trimming as if it was part of a fairy tale, there is no reason to think the pilots could have recovered from an unknown and uncued 'status'; when would they know they had succeeded? Without cues to rely on (demonstrably absent if UAS is the culprit), where is straight and level? what is our position? where is up? Unreliable airspeed recoveries as reported in other instances have proven resistant to a checklist; it is perhaps possible to train UAS in conditions similar to what we imagine existed for 447, but why? Who will determine what 'Recovery' looks like on the panel? Repetitive loss of airspeed is demonstrated in this type involving thousands of feet lost in altitude, and visual extra cockpit cues for reference.

More important to me would be an a/p that annunciates its actions, with visual cues on the glass, so the pilot can 'get' the a/c by panel when the pitots go astray, knowing that what he has is flying, and what is required is constant duplication by manual handling after disconnect, which itself would be announced prior to, not after its occurrence, and that by surprise.

Oh, and an Artificial Horizon.

Let me ask a quick question. If the pilot had been hand flying the a/c in Normal Law, what's the probability of losing it to Alt Law2 after loss of pitot probes? This flight went to AltLaw2 because the a/p quit. If the a/p isn't in the mix, would the outcome have been substantially different?

Last edited by Will Fraser; 24th Sep 2009 at 00:08.
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Old 24th Sep 2009, 06:13
  #4457 (permalink)  
 
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Indeed, Will. And despite lawyers and cultural norms, sometimes <censored> happens.

I suspect that describes the situation better than a lot of commentary here. The burr under my saddle is a desire to find the contributing causes, not a apportion any sort of blame. With the data I want engineers can work to prevent it happening again. And I am just techie enough that I would enjoy hearing outlines of ideas for improvement of equipment such as people have had.

One such idea is new pitots. An even better idea is being adopted, probably for the wrong reason, with two new probes and one old Thales probe on the same plane. Different probes give different failure mechanisms, even if only slightly different. That would give computers something to chew on.

One idea I've entertained is phase tracking GPS as a means of detecting attitude using three or better four antennas, wing-tips, aft, and optionally forward. The GPS pretty much has to be tracking carrier phase to derive meaningful attitude data. The nice thing about phase tracking GPS is that you don't need to know precisely where you are to determine relative differences in position of nearby locations to surprising degrees of precision. The breaking point for this is that this does not account for up or down drafts that are not perfectly up and down. At some altitudes flying over mountain ranges can give winds at rather odd angles, I've observed on the ground. I don't know if that holds at altitude.

What I don't know is whether floating such technical ideas in the group to see what actual pilots salute and what they kiss off is within this group's purview.

JD-EE
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Old 24th Sep 2009, 10:28
  #4458 (permalink)  
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I'll allow for journalistic mis-quoting, but where is the evidence that

-- The aircraft flew into an area of storms which other aircraft avoided by steering around them.
- I was not aware that the precise track of 447 was known?
-- There was a malfunction in the ADIRU, the three air data computers which feed information to the flight system and the pilots?
I was under the impression that the ADIRUs were thought to have behaved exactly as designed, rejecting supposedly conflicting information - ie intially a detected IAS change of at least 30kts in one second?

It would be of significant interest to AB operators to know what particular 'malfunctions' were fed into the simulator in these tests, what sequence of warnings were generated (eg did you receive a cascading failure of ADIRUs?), and what instrumentation was then left available to the crew - eg did the standby attitude still function correctly?

I think we are all pretty much on the same track generally, John, but to state categorically 4 primary individual causes of the accident is indeed a bold step.
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Old 24th Sep 2009, 12:42
  #4459 (permalink)  
 
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GPS / Attitude Tracking

If I recall correctly, this has been used for a long time as part of fighter jet stabilization technology, and I wonder why it hasn't been brought into commercial aviation. Gee, it first came over my horizon in the early 1990s... Hardly rocket science by today's standards.... ?? / CP
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Old 24th Sep 2009, 20:57
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BOAC

To my memory, the ship had deviated left, the buzz about 'lightning', company 'pirep' for 'fortes turbulence' and Msr. Gourgeon's claim that 447's aircrew had been 'unlucky' in reading the Radar were red herrings.

Been awhile, but is GPS to Mil standard nowadays? Used to be purposely degraded to prevent folks like google earth to have the capability of Uncle's satellites.

GPS in hyper accurate mode x4 would very nearly provide sufficient data to turn a wide body into a 'drone'. Oh-Oh, incoming.
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