AF447 wreckage found

[Meccano]

JJFC
If you KNOW an instrument is faulty - are you seriously suggesting we follow it? I hope I'm misunderstanding you here, because any pilot is potentially 100% more reliable than a faulty instrument!
And unfortunately it's not always clear cut. Contradictory indications often occur.
Which instrument to believe then??

Then it is down to the skill and experience of the human at the controls, and he may have to utterly disregard the instrument right in front of him which is screaming for his attention. No easy feat, at the best of times.

[bubbers44]

Trapped frozen pitot tube pressure would give an overspeed zooming to 380 so probably explains the idle power. Once stalled descending at 11,000 ft per minute the ias would rapidly decrease as the static pressure increased. So at 60 knots ias the stall warning quits so the FO's think they have recovered from the stall are in a deep stall. What a system design. It took a lot of their final minutes comforted by false information. Hopefully the BEA will tell us more of what we know they have learned but their brief preliminary report leaving out so much data they have puzzled me. Maybe they have to run it by the French attorneys first.

[pattern_is_full]

Let's try and take this a piece at a time:

Beginning of the incident (first 11 seconds) -

"From 2 h 10 min 05, the autopilot then auto-thrust disengaged and the PF said "I have the controls". The airplane began to roll to the right and the PF made a left nose-up input. The stall warning sounded twice in a row. The recorded parameters show a sharp fall from about 275 kt to 60 kt in the speed displayed on the left primary flight display (PFD), then a few moments later in the speed displayed on the integrated standby instrument system (ISIS)."

- I would expect pitot icing to be a gradual process. Why is there a "sharp fall" of 215 kts in IAS at this point?

I don't doubt the probes were iced, I'm just wondering how that alone would drop the indicated speed so rapidly. If the pitots are blocked, this is not a "real" speed change, correct?

If the pitots are blocked and trapping pressure, a climb should result in an increase in indicated speed as static pressure drops. Correct? (That is not apparently what happened).

If the pitots are blocked, a descent would result in a drop in indicated speed as static pressure increases. Correct?

[Graybeard]

TCAS Fail Unrelated to Other

TCAS computation needs altitude to assess threats and should receive barometric and Radio Altimeter inputs! yes/ no?

TCAS depends on Range, Rate of Closure and Altitude Difference for Collision Avoidance, nothing more.

Range and Rate of Closure are determined by interrogating other aircraft's transponder. TCAS is like ground based ATC radar in that respect. Altitude Difference is found by subtracting other aircraft's reported altitude from own aircraft altitude.

TCAS receives Own Aircraft Altitude from the active ATC transponder, which in turn receives it from its associated Air Data Computer (ADR). This assures that the TCAS is calculating altitude difference from the same altitude that is transmitted to other aircraft TCAS.

Imperfect placement of the static ports on the side of the plane result in skewed static pressure at low airspeeds. The ADR corrects the static pressure based on airspeed when converting it to altitude for relay to the rest of the systems that use altitude.

The OZ A330 that had pitot icing in Aug 2009, indicated a sudden drop of 300 feet in measured altitude along with the airspeed decay to a low number, which is explained by the airspeed correction routine.

Why was the TCAS Fail reported on 447? BEA in their first release explained it was due to logic internal to the TCAS that would not accept the sudden drop in calculated altitude it was receiving.

Do you see the fallacy in that? If you don't want your TCAS working with bogus altitude, you sure don't want your ATC transponder working with it either. If there was such an altitude reasonableness check, it should be in the transponder, not the TCAS.

Maybe the TCAS Fail was like the Wiring Fail reported: the plane could have been getting the crap shaken out of it.

Cancel that last sentence. Found this from 16 April:

PJ2 said WRG means the fault is not correlated by another computer of the FWS.

I don't know why the TCAS reported Fail, but I'm certain it was not due to pitot error.

[philipat]

Using the standard practice of pitch + power to maintain safe flight does not work if the aircraft is ALREADY stalled, which was the case here

.

But as I speculated in an earlier post, from the AVAILABLE data, it seems that that is precisely what they did. Would you agree?

[bearfoil]

Graybeard

"Maybe the TCAS Fail was like the Wiring Fail reported: the plane could have been getting the crap shaken out of it."

The autopilot dropped due to A) unreliable airspeed, B) exceeded control limits.

The a/p needn't be commanded to drop by the FMS (AD disagree). It will drop involuntarily all by itself if it cannot control the airplane, (within its limits). If it drops for this reason, Normal Law is retained with Stall protections and overbank protections. If for whatever reason the pitots inhale 30 knot disacrepant airflow, there we have AD disagree, though not ice caused, but turbulence caused. Now it drops to Alternate Law, but ostensibly for other than Unreliable Airspeed. If turbulence induced, one could argue it is not truly unreliable, but for 30 seconds some form of local upset in airflow has discreped the pitot tubes (perhaps both on the same side).

Any turbulence of this description can be sudden in onset. An updraft of 100 knots could be proposed, (Let's give it a radial component just to be mean). An argument could ensue whether its borders would be crisp enough to differentiate long enough between fuselage halves to cause UAS. Either way, there is an in and out (out and back in?) Law exchange that may have occurred. Musical protections? goddamitey, what a handful. (The radial component, from the left, would give it a left wing high result).

An updraft would give it a boost in lift, and a diminution of IAS. Enough of a drop in IAS to cause "UAS"?

IF AoA is AS and Vane reliant, a temporary boost in indicated AoA, reduction of IAS, and rising VS, does this fool the FCS? Was 447 in a transient and turbulence induced Phantom Upset? Something a hand flying pilot may have patiently sat through?

Autoflight into severe Turbulence? VIABLE?

[Modern Elmo]

... If the pitots are blocked, this is not a "real" speed change, correct?

Sorry, not correct. Pitot tube data is reality in regard to relative wind velocity flowing past the lifting surfaces. The pitot tubes provide the only indicated air speed data the flight instrumentation software and the pilots had, aside from seat of the pants feel and intuition.

If the pitots are blocked and trapping pressure, a climb should result in an increase in indicated speed as static pressure drops. Correct? (That is not apparently what happened).

Ice blocking or clogging pitot tubes is not likely to "trap" dynamic pressure, which is (1/2)*air density*(relative wind velocity)^2. Instead, ice clogging the tube will tend to shelter the pressure transducer from dynamic pressure. Less dynamic pressure = slower indicated airspeed.

Pitot-Static (Prandtl) Tube

So NO, a climb will not result in a increase in IAS in the pitot tube scenario you describe.

...

The transcript which has been released is probably incomplete, as a couple of commenters here have already pointed out. I'll bet those three pilots did a lot more talking on their way down.

[bearfoil]

Modern Elmo

"... If the pitots are blocked, this is not a "real" speed change, correct?

"Sorry, not correct. Pitot tube data is reality in regard to relative wind velocity flowing past the lifting surfaces. The pitot tubes provide the only indicated air speed data the flight instrumentation software and the pilots had, aside from seat of the pants feel and intuition. "

Excuse me?

[matthewsjl]

Using the standard practice of pitch + power to maintain safe flight does not work if the aircraft is ALREADY stalled, which was the case here

Actually, I think they did have a chance to use pitch/power. The BEA report states that the aircraft was stalled for the last 3m30s of the flight. The autopilot/throttle kicked out ~4m30 seconds before the recording stopped and that minute between the auto-pilot/throttle leaving and the actual stall appears to be a pilot induced climb with no change in power settings = pilot induced stall.

Of course, once in the stall recovery is a different matter.

[Modern Elmo]

"... If the pitots are blocked, this is not a "real" speed change, correct?

Pitot tubes clogged with ice sure can result in a real change in indicated airspeed.

[Mimpe]

I posted elsewhere, but as you indicate, there will turn out to be a significant degree of unrecognised spatial disorientation in the accident, probably somatogravic with false sensation of pitch down leading to nose up command and stall.

Insufficent trust of remaining instrument indications , and the complexity and foibles of an overly complex avionic system that performs poorly at the edge of the envelope......

[pattern_is_full]

Modern Elmo, by "real" speed change I meant the actual speed of the plane, not what was indicated.

I.E. - did the aircraft actually "sharply" lose 215 kts of TAS (or whatever 215 kts IAS equates to at that altitude, in TAS), or was that indicated "sharp" change an artifact of the icing of the pitot and/or other things - not including the "real" speed.

Sorry if I was unclear.

[jcjeant]

Hi,

A little "OT" but interesting ...

Flight AF 447
Analysis of Air France’s crisis communications

By Hédi Hichri
Account Director
Fleishman-Hillard France, September 2009

http://www.multiupload.com/0G4RRWNBYS

[MountainBear]

I posted elsewhere, but as you indicate, there will turn out to be a significant degree of unrecognised spatial disorientation in the accident, probably somatogravic with false sensation of pitch down leading to nose up command and stall.

What garbage.

I suspect that whatever BEA comes up with will be controversial. We can record what the plane does on the DFDR. We can record what the flight crew says on the CVR. But what we cannot record is WHY they did what they did, unless they say so explicitly, which rarely happens. There is no mind reading device; it doesn't exist. Correlation doesn't equal causation.

Because we cannot read their minds and know their motivations, we are left with being able to only judge the process and the result. The result we already know, and we labor under the burden of hindsight bias. So that just leaves the process. Did they follow their training? Were their actions up to professional standards? If the answer is yes, then the cause of the accident lies elsewhere.

[jcjeant]

Hi,

AF447… What We Now Know « Dark Matter
The Right Attitude « Dark Matter

[Lemain]

- why BEA (and Air France, Airbus and ultimately the French Government) are hiding the whole CVR/FDR transcript? Why only this thin and very filtered information? What they are so affraid off? This is probably the most intriguing air disaster of the latest 50 years!

French was the language being used. Anything in English must have been translated. Translating anything is risky and aviation talk is full of jargon, acronyms, and technical comments....in this case, very probably seasoned with fear. They probably haven't had the CVR for long enough to prepare a certified translation.

[CONF iture]

FDR data do well in French too and original CVR is just perfect ...

[HalloweenJack]

they`ve had the data from both for what? 30 days? and you all want it in the public domain? how about actually investigate first before pampering to the whims of forum hero`s.

we wont see the information for a while yet - this time nexr year most likely.

[shogan1977]

Der Spiegel raises pertinent points

This Der Spiegel article was posted earlier by someone else, but resulted in zero discussion: Doomed Flight AF 447: Questions Raised about Airbus Automated Control System - SPIEGEL ONLINE - News - International

Several of the points raised in this article have not even been touched upon by this group - in particular the potentially detrimental role of the horizontal stabilizer and the questioned culpability (beyond human error) of EASA, Thales (pitot tubes) and potentially Airbus...

But why would co-pilot Bonin pull up instead of pushing the nose down? It wasn't long before the plane's angle became dangerously high.

An explanation for the A330's rising nose, however, could also be provided by a line in the BEA report referring to the trimmable horizontal stabilizer. Situated at the tail of the aircraft next to the flaps controlling the aircraft's pitch, known as the elevator, the horizontal stabilizer likewise helps control the plane's horizontal stability.
According to the BEA's interim report, the horizontal stabilizer moved from three degrees to 13 degrees, almost the maximum. In doing so, it forced the plane into an increasingly steep climb. It "remained in the latter position until the end of the flight," the report notes.

Gerhard Hüttig, a professor at the Institute of Aeronautics and Astronatics at the Technical University in Berlin, considers the high angle of the horizontal stabilizer to be a failure of the Airbus' electronic flight control system. Hüttig, a former Airbus pilot himself, calls it "a programming error with fatal consequences."

"No matter how hard the crew tried to push down the nose of the aircraft, they would have had no chance," Hüttig says.

Exactly what orders [Captain Marc Dubois] issued [after re-entering the cockpit] are not part of last Friday's report. But sources close to the investigation are saying that he said: "This is a stall. Reduce power and nose down!"

This order would have been the correct one were the situation not already hopeless. By that time, the jet, which was pointing steeply upwards, was already losing vertical altitude at a rate of 200 kilometers per hour.

Indeed, the BEA report documents efforts undertaken following the captain's return to bring the plane's nose down. Forty-one seconds before impact, both co-pilots were pushing on the controls. Then Bonin cried desperately: "Go ahead, you have the controls." There were just 30 seconds left before the end.

But why were all the crew's efforts in the cockpit in vain? Did the plane no longer react to the cockpit commands as it fell? Or did the horizontal stabilizer, which was still almost fully deflected at 13 degrees, continue to force the nose of the plane up?

Hüttig, who also advises the victims' families regarding technical issues, is concerned about the description of the horizontal stabilizer as being at 13 degrees. That is consistent with behavior he observed in an Air France A330 simulator in Paris a few months ago, when he replicated the situation together with other pilots. "The phenomenon is startlingly similar," he says.

Was it really the stabilizer that doomed the pilots? In theory, they could still have adjusted it -- its position can be manually altered using a wheel near the thrust levers. But as Hüttig notes, one would first have to know that the stabilizer is deflected.

Huttig pointed out that Airbus published a detailed explanation of the correct behavior in the event of a stall in the January issue of its internal safety magazine. "And there, all of a sudden, they mention manually trimming the stabilizers," he says.

It remains an open question who will be proved right at the end of the investigations. But it is already clear that no one individual will bear the burden of responsibility alone. The pilots could have stabilized the aircraft if they had reacted differently. But the airline had also probably not prepared them properly for such a situation. Similarly, Airbus' recommendations were insufficient. That much is spelled out in the files of the French authorities which investigated the crash of the A330. "To date," the experts say, the deficiencies have "not been rectified."

The Pitot Tubes and culpability of EASA?
As stated in the report (2h 10min 05sec) the autopilot and auto-thrust disengaged due to icing of the pitot tubes (manufactured by Thales - see below) which resulted in loss of speed readings.

If the speed sensors fail, it has a "particularly confusing" effect in Airbus models, the experts say, pointing to the high degree of automation in the cockpit. "If the control computers, which are actually supposed to provide more safety, fail, then the automatic systems can become a danger at that moment," says William Voss, president of the Flight Safety Foundation.

The manufacturer Thales was well aware of the catastrophic consequences of a failure of the speed sensors as early as 2005. At the time, the French company concluded that such a failure could "cause plane crashes."

A total of 32 cases are known in which A330 crews got into difficulties because the speed sensors failed. In all the cases, the planes had pitot sensors from Thales, which were significantly more prone to failure than a rival model from an American manufacturer.

But none of the responsible parties intervened. In 2007, Airbus merely "recommended" that the sensors be replaced. Air France took that as a reason not to carry out the costly work -- and it even got official blessing for doing so. The European Aviation Safety Agency wrote that it currently saw "no unsafe condition that warrants a mandatory modification of the Thales pitot tubes."

Several comments have been made here claiming that the passengers wouldn't have noticed anything...(I wish it were true)

The passengers, who had just a short time before been pressed into the backs of their seats, were now being held into their seats only by their seatbelts. "At this moment, I would have feared for my life even if I was sitting in the passenger cabin," said one A330 pilot after reading the BEA report. That the plane was in freefall would have been clear to all on board. The nose of the plane pointed skyward at an angle of 16 degrees. "That's more than immediately following takeoff," the pilot said.

[YorkshireTyke]

...........I'll bet those three pilots did a lot more talking on their way down.

I bet there were a few " merde's" being thrown around !

shogan1977

Nice, I agree. I know nothing about the Airbus, is there any indicator readily available to the pilots to show what angle the stabiliser is at ? Is there any way of trimming the stabiliser really "manually" ?