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Author Topic: Airbus A330/200 Brazil to Paris flight disappears with 228 on board  (Read 26022 times)
Rattler
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« Reply #20 on: 4 June 2011, 23:16:36 »
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Mid May 2010, Airbus issued a *updated (aka "new)* "generic" stall response as worked out with the FAA at the 17th Performance and Operations Conference .

http://xa.yimg.com/kq/groups/10483604/2002517561/name/Updated%20Stall%20Procedure.pdf

Rattler
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Rattler
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« Reply #21 on: 30 June 2011, 21:10:03 »
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Another UPDATE, this time not factually but from the interpretation POV. For all aviation enthusiasts highly recommended:

http://www.aviationweek.com/aw/generic/story.jsp?channel=comm&id=news/awst/2011/06/06/AW_06_06_2011_p36-330706.xml&headline=null&next=0

The article focusses on the issue that the crew was not able to recover the a/c from the stall, and it concludes that we have a training issue:

Quote
The focus of the investigation into why Air France Flight 447 crashed into the Atlantic a year ago is starting to change now that safety experts have begun evaluating information from the Airbus A330-200’s flight recorders.

Questions surrounding human factors are moving into the spotlight as the investigation further unfolds, with concerns of turbulent weather and pitot-tube icing shifting into the background.


Quote
As far as AF447 crew coordination is concerned, there are at least two indications that there may have been problems. -snip- at the time, the pilot flying (PF), -snip-  continued to pull back his side-stick at Flight Level 380 with thrust set to takeoff/go around, the angle of attack increasing further and speed decreasing. The two pilots also made simultaneous control inputs (pitch up) at around 20,000 ft. and an estimated sink rate of more than 10,000 ft. per minute.


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The sequence of events in the crash that killed all 228 people onboard the flight from Rio de Janeiro to Paris can be segmented into two distinct phases. In the first phase, the pilots were dealing with the failure of speed readings that are almost certain to be linked to iced-over pitot tubes. The second phase began when speed indications returned to normal and the aircraft was at the edge of its flight envelope but under control and not stalled.


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At this stage, the event could have been over, with the aircraft still in alternate law and manual control but stabilized. There appears to be no technical, aerodynamic or meteorological reason that would have kept it from returning to its previously assigned altitude (FL350) by simply applying nose-down stick-forward control inputs.

But then things went terribly wrong. At 2:10:50, the PF continued to provide nose-up inputs, causing the trimmable horizontal stabilizer to go to 13 deg. nose-up from 3 deg. nose-up. The airspeed began decreasing, to 185 kt., and the angle of attack reached 16 deg.


Quote
“We will learn a lot from this accident,” says William R. Voss, president and CEO of the Flight Safety Foundation, who believes that AF447 should have fundamental consequences for the content of pilot training globally. -snip- Voss argues that AF447 would not have crashed if the aircraft had been of an older generation. “Highly automated aircraft have saved many lives, but they fail differently than aircraft of 20 years ago,” he says. He sees it as a “failure of the industry” that pilot training has not kept in step with the latest aircraft technologies. He also argues for improved upset recovery training, as “we are not explicitly training that” and the AF447 A330 “seems to have had pitch-and-roll authority all the way down to the water.”


The article addresses the big questioin FACMan raised as well as the quirms we stick-and-rudder generation guys feel when reading about stuff as the following from a people-in-the-know discussion:

Quote
At the start of accident sequence, two apparently unrelated faults :
PROBE PITOT 1X2/2X3/1X3
WRG:ADIRU1 BUS ADR1-2 TO FCPC2

PROBE FLR is very likely due to icing of probes by high altitude ice crystals.
It triggers a specific 10 seconds ADR (Air Data Reference, R.) checking process by all three PRIMs (primary flight computers, R.).
Starts 02:10:05.

All three PRIMs work in Alternate 2 (Flight Control Law, R.) for 10 seconds.

WRG FLR affects PRIM2 by cutting it from ADR1 data. My take is this happens right at the start of above mentioned 10 seconds ADR checking process.

At the end of these 10 seconds, each PRIM will either confirm and latch Alternate 2 or revert to Normal law, based on differences between ADR values. This is the purpose of this 10 seconds checking. This happens at 02:10:15.

My take is PRIM2 reverted alone to Normal, while PRIM1 & PRIM3 latched Alternate 2. This is because PRIM2's set of ADR data, being different (only ADR2 & ADR3), would have allowed differences into the 50 kts range that triggers reversion to Normal law.

The sentence "the aircraft was in Alternate 2" makes no sense. The PRIMs compute flight laws, not "the aircraft". All three PRIMs are 99.9999% of the time in full agreement. Not this time.

NAV ADR DISAGREE is CMC stamped 02:12 and ACARS ground-received at 02:12:51, which means it happened on board between 02:11:58 and 02:12:43. Aircraft was downwards fast at that time. Therefore, the ADR DISAGREE condition was not in effect to latch Alternate 2 for all three PRIMs at the start of pitch-up sequence at 02:10:16.

At 02:10:16, the pitch-up sequence and "zoom-climb" happened with (according to my research and "flimsy theory") PRIM1 & PRIM3 in Alternate 2 and PRIM2 in Normal.


Lets assume for a second we understand how our PRIMary computers handle their conflicts on different sets of data input, as a pilot with 2.5 minutes left to crash, pitch dark, instruments giving you "unbelievable" values (even if, as usual, they were right in this case), how will you quickly think up something about the conflicts of software and Flight Control Laws (normal vs. alternate) and get a better situational awareness (of your misconception)?

You have to be a true software expert (AND probably a stick-and-rudder guy) to understand instantly that you are following a misconception and hence reacting erroneous, just check out the complexity of the 4 flight laws the a/c in question is providing through its computers (and that partially override human input in order to protect you from errors, in Normal Law) depending on the situation (for a quick overview scroll down to "Control Laws"): http://countjustonce.com/a330/a330-flight-laws.html

Indeed a lot to learn from this accident methinks, not sure though whether industry wants to put in the effort for those 0.000001% probable disasters.

FWIW,

Rattler
« Last Edit: 30 June 2011, 21:24:29 by Rattler » Logged

"War does not determine who is right, war determines who is left...": The Rattler Way Of Life (thanks! to Solideo)... http://www.youtube.com/watch?v=n9v3Vyr5o2Q
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