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AF447 Thread No. 3

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AF447 Thread No. 3

Old 10th Jun 2011, 20:26
  #1761 (permalink)  
 
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The Seattle reference was to post 1747, which has a nice Seattle ring, at least imho.

That said, no argument that anytime one flies, one is exposed to all dimensions of human error, both active and passive. Still, certification is expected to weed out the most sensitive cases, if need be at the expense of efficiency.
Bearfoil makes the case that the pilot had 11 seconds to make the right call once the a/p dropped out. That is in an airplane encountering no extraordinary stresses, at least afwk, in excellent repair, in routine flight and with no serious mechanicals other than the pitot icing. That is scary, at least to me.
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Old 10th Jun 2011, 20:32
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Bear presents the case.

He hasn't made it for unrecoverable in re the 11 or 3 seconds.
Evidentiary shortcomings to confirm causes and effects.

More light won't be shed for a while, and may never be.
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Old 10th Jun 2011, 20:41
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Post Curious!

After I did post the ‘BUSS’ article last week, I realized that when you’ve lost all the speed signals this Back-Up Speed Scale wouldn’t work either.
So went into the books again and found out that modified ADIRU not only send its AOA through IR bus i.s.o. ADR bus (crew needs to switch of ADR part of all ADIRU’s to activate ‘BUSS’) but also the AOAc signal is always present (even if CAS < 60Kts !!!!), only the SSM remain set to NCD if CAS < 60Kts.

Aural Stall Warning:

In Normal Law: Max AOAc = 23 surface degrees.

In Direct Law (think this is a typo error in the docs and should be 'Alternate & Direct'?)

This is the sum of S/F term, a Mach term and a Mach term when Speed brakes are extended. Clean Config base angle is 10.8 and M correction is summed.

There are 4 tables given for all S/F positions and several M numbers. Too complicated to type it over and can’t make copies or duplicate any other way.

Table interpolation in clean config results in:
Mach Corr AOAc
M 0.22 = 0 (10.8)
M 0.28 = 0 (10.8)
M 0.35 = -0.9 (9.9)
M 0.53 = -3.2 (7.6)
M 0.75 = -5.6 (5.2)
M 0.82 = -7 (3.8)
Aural Stall warning is inhibited on ground (except in functional test mode) and above M 0.866.

If all ADR’s are switched off to engage ‘BUSS’ a backup stall warning table is used based on S/F only.
Clean Config value = 8.6 AOAc.

(‘BUSS’ was not installed in this A/C)
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Old 10th Jun 2011, 20:55
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https://docs.google.com/leaf?id=0B0C...thkey=CILGt_QN

That looks a bit like the graph HazelNuts39 posted a few days back.

As I understand his intent, it wasn't BUSS info related. He was mapping Mach and AoA to show the relationship to when stall warning would go off at various Mach numbers.
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Old 10th Jun 2011, 21:01
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Simple question: How is M number computed? As related to the discussion on Stall Warning in the preceding posts.

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Old 10th Jun 2011, 21:08
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"Aural Stall warning is inhibited on ground (except in functional test mode) and above M 0.866."

What caused the STALLSTALL to attenuate at PF's inputs?

Why was it not available at <60 (but airborne?)

Was PF's (initial) reaction to 'overspeed' (as in from bad airdata)? Is there Inertial record of airspeed at >.866M?

Was CL a reaction to O/S? What else could have kept her "flying" to FL380, especially after STALL at "cruise" (a/p) managed parameters? If the STALL was true at a/p drop, how could she have held that much (aero derived) ENERGY?
 
Old 10th Jun 2011, 21:15
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Some peeks at the "code"

Finally getting some engineering stuff versus the basic things I see in the 'bus manuals.

- We may need to define some terms.

- Smilin' Ed may help us ( a squid golden arm), but the mach corrections to Aoa look a bit harsh to me. OTOH, the plane prolly has an efficient subsonic camber and could be more susceptible to mach effects than what he and I and 'bird and Retired flew.

As several of us have observed, if AoA data is available regardless of speed, we could have a case questioning the design. I ain't going that way........ yet.

- Interesting, the use of tables. Of course, original Viper used analog circuits, so everything was "instant" and the outputs were the result of op amps and function definitions mechanized with discrete components. Outputs were basically voltages. Ten years later the system was digitized. Don't know how the digital system handled frame rates and "mixed" the outputs, but control system technology was moving along at a rapid rate.

thanks for the insight, A33
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Old 10th Jun 2011, 21:24
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Was CL a reaction to O/S?
Bear, where does the aircraft get the energy to accelerate from Mach 0.82 to Mach 0.866, particularly when there are indications that they reduced to Mach 0.8 or so before things began to go wrong?
What else could have kept her "flying" to FL380, especially after STALL at "cruise" (a/p) managed parameters?
*smart arsed remark* nose down pitch? (sorry)

Bear, that sequence of events looks to conflict with recorded sequence of events. How do you arrive at "be stalled at A/P managed paramaters" there? The sequence looks more like a/p held parameters -> something -> a/p off -> (we are in alternate law) -> parameter change -> something -> stall. As noted previously, with the momentum of Mass (205 Tons) and V (upwards of Mach 0.8) you don't bleed off the kinetic energy all at once.
If the STALL was true at a/p drop, how could she have held that much (aero derived) ENERGY?
I think you answered your own question. IF "stall at A/P drop," THEN no climb. When you stall, you tend to fall, since you no longer have sufficient lift to defy gravity. Also, it means that "at ap drop" all of that airspeed is already gone, or most of it. That doesn't seem to fit the data provided.

Put another way ... when you are stalled, you don't have the energy to get that other 3000 feet up.


Can someone show me how to make an aircraft climb while it remains in a stall?

Caveat: Hmm, maybe there's a bunch of left over energy if you have an accelerated stall in a high G turn ... I'll need to think about that one ... but there is no evidence that AF 447 was in accel stall nor in a high g turn.

OK, I have an idea. Can I gain altitude after I stall? (Well, one way to do that is to bounce off of the pavement after I hit it. Another is to eject from the stalled jet before it hits the ground ... but none of those apply here ...)

Yes, I probably can, but not much, given the energy I bled off getting to stall in the first place.

Let's see ....

I could be going real fast, pull up on the stick, pitch the nose up, and hold that attitude, and my monemtum carries me up ... before I reach apogee, as energy bleeds like a severed femoral artery ... I stall by reaching critical AoA, and then just past ... a few more feet of "up" are the result of residual momentum from my up vector, rapidly being countered by Mother Earth's gravity.

That does not appear to be what was going on with AF 447, in terms of the altitude increase from FL 350.

Bear, you can't manipulate the data into a stall, then a climb to FL 380. Not until you dig up Bernoulli and make him rewrite that law.

Last edited by Lonewolf_50; 10th Jun 2011 at 21:42.
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Old 10th Jun 2011, 21:52
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A couple of thoughts have occurred to me (I am guilty of two things - much preferring the bus to the boeing, and instantly judging the FO when reading the BEA report):

1 Alternate law was not helpful.

When UAS is detected at high altitude, then maybe direct law would be safer. The stationary stabiliser would help the pilot keep the attitude stable. If he got slow, then he would need constant NU to hold the pitch - and the clue is there for him. Auto-stab is a nice luxury, but is best when combined with Normal Law protections.

2 The "illusion" of turbulence.

I have had nasty mountain wave twice - once in a Boeing and once in an Airbus. The event in the bus was a lift combined with a massive increase in speed. I had to disconnect, pitch up, and then dive when the speed vanished. By the end of the event I was more or less back where I started, save a slight bead of sweat or two.

Having felt that lift, might I (if I felt it again) associate it with a sudden overspeed? It's so easy to imagine UAS in smooth conditions. But what if the PF sees the speed indication go and then feel a huge lift? Pitch up because he has seen this before? Once he has pitched up, he has lost his "feel datum" because the stab is trimming for him. Still with no speed indication the confusion has set in, and there is no escape from the confusion.

It will be very interesting to see the plots. In particular G forces on the a/c and sidestick deflection. So much will be answered when these are available. In the meantime, more high altitude training, including dealing with various serious faults at altitude.

..

Incidentally, I have been shocked at the number of FOs I fly with who have no idea of approximate pitch settings in the bus. They have all gone straight from Piper to Airbus, and have never had to fly by pitch. One of our Boeing FOs was chatting to me about this accident, and he could specify all the pitches for all phases of flight (happy memories!). As others have said, the bus is great but when it all goes wrong it reverts to a basic jet. If you have never flown a basic jet, then this can be a little confusing.
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Old 10th Jun 2011, 21:55
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MACH

@ GY:
How is M number computed?
Not sure if I build the formula correct, but something like this is mentioned. Couldn't find the Root sign

MACH = ROOT(5 * ((Qc/Po+1)^(2/7)-1))

from wiki (thx LoneW 50)
Qc/Po = ratio of impact pressure to static pressure.

@ Bearfoil:

Why was it not available at <60 (but airborne?)
Maybe because pitots (Qc) where clogged with Ice?

Last edited by A33Zab; 10th Jun 2011 at 22:25.
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Old 10th Jun 2011, 21:56
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Newton obtains. Bernoulli was a Swiss plumber.

No, the Stall was bogus, wait, it was in Alternate Law, so Stall was legit. No, she climbed with gusto after Stall, so it was bogus, no, it was below 60 knots, wait, that can't be right, etcetamundo.........

Something told the PF to climb, or not, and he inadvertently climbed to 380. Was it on a hunch?

1. Cavalry Charge

2. Master Caution

3. "I have the controls"

4. Roll left

5. Climb

6. STALLSTALL

7. Time elapses

8. PITCH (Assiette) increases "progressively"

9. After increasing to Ten Degrees, she STARTS to climb...

10. Speeds reacquire

11. PITCH 16

12. AoA 6

13. STALLSTALL

1 through 13 are reported (Observed) by BEA. In this sequence there is the Death of an a/c and 228 souls.

BEA would have us believe that the procuring cause of this accident was the Pilot's initial Climb (NU) input. If not, then they owe some more data.

Old Chinese saying: "Half the Truth is a Whole LIE...."

Quote:
Why was it not available at <60 (but airborne?)
Maybe because pitots (Qp) where clogged with Ice?



I meant the STALLSTALL. It is computed by AoA not a/s. What hath the AoA have to do with Pitots? Frozen AoA vanes? Quite the coincidence, No? Wait, there's this: The AoA vanes could not have frozen in STALL angle, not without at least a chirp. And they "Started" @ angle< STALL, so they froze at the very moment of Vane excursion into STALL angle?

Last edited by bearfoil; 10th Jun 2011 at 22:08.
 
Old 10th Jun 2011, 22:16
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Stallstall

@ Bear

I meant the STALLSTALL. It is computed by AoA not a/s. What hath the AoA have to do with Pitots? Frozen AoA vanes? Quite the coincidence, No?
I see, was focused on Qc, if M = 0 = no correction = STALLSTALL trigger @ 10.8 AOA.
But if probes open up again AOA STALLSTALL could be @ 3.8 AOA to trigger = intermittent STALLSTALL between AOA 10.8 and 3.8.

Didn't check the report if AOA was in this range.

Last edited by A33Zab; 10th Jun 2011 at 22:34.
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Old 10th Jun 2011, 22:16
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hundredpercentplease

Be interesting to see if the g trace predicted by HazelNuts39 fits what comes out in the report, if reported ...

Bear: Step 14 includes gravity at work, and a variety of things attempted (I presume) that didn't work. That too would be of interest to learn from the good folks at BEA. Sometimes learning what doesn't work helps identify what does.

Garage Years:

This wiki article has an easy to understand calculation of Mach numbers in air:

Speed of sound - Wikipedia, the free encyclopedia

Start at "Practical formula for dry air" and work your way down.
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Old 10th Jun 2011, 22:42
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Lonewolf

".....Bear: Step 14 includes gravity at work, and a variety of things attempted (I presume) that didn't work. That too would be of interest to learn from the good folks at BEA. Sometimes learning what doesn't work helps identify what does..."

Indeedy. Thusly: From the git, the authority had far more data than any civilian. Then they found stuff, and they had that much more. Then they had a powwow with the Brasiliens, and had Medical and even more stuff. Then the wreck, the boxes, ad pano.

They will always have more than anyone, that is the game. The longer this continues, the less they will have to give up. That too, is the game. Safety is less important than Control, in the game. On the Flight Deck, Safety is everything. The twain shall not meet, and that is the endgame.

A33Zab Thanks. For everything.
 
Old 10th Jun 2011, 22:46
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Valid Indications?

Just a reminder that sometime between 02:11:51 and 02:11:59 both PFD's had the FPV page selected. Reference to the ACARS messages will show these two sequential FPV messages timestamped 0211. They had precedence over the FLR message which was received at 02:11:55, and there would appear to have been a queue/link glitch which delayed their transmission.
At 2 h 12 min 02, the PF said "I don’t have any more indications", and the PNF said "we have no valid indications".
My point is the comments that both pilots made could be directly related to the FPV pages having no valid data, or in more general terms there was nothing on their PFDs which seemed valid.
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Old 10th Jun 2011, 22:53
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The question should be - how is Mach computed in the A 330 ADC?
Note how temperature is in the theoretical calculations: – TAT in the ADC?
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Old 10th Jun 2011, 22:57
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mm43

Hiya.

Quote:
At 2 h 12 min 02, the PF said "I don’t have any more indications", and the PNF said "we have no valid indications".

At this point in the recording, the pilots have known for two minutes that they are in Stink. I see the PNF's use of the word "valid" as a courteous correction to the record. (CVR) IE, "Nothing is making sense"."Je ne comprends riens."

IOW: We have indications, none of which make sense.

Possible?
 
Old 10th Jun 2011, 23:08
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Hi Bear;

Possibly the Captain asked to see the FPV page, and the PNF/PF comments confirmed no FPV and or any other valid data. I don't think their selecting the FPV pages just prior to 0212 was a coincidence - more likely related to what they said.
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Old 10th Jun 2011, 23:11
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Yep I remember now the FPV was N/A. Thanks.
 
Old 10th Jun 2011, 23:18
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TAT Calculation

ADR internal calculations:

Just as I mentioned before:



TAT calculation is back to Elementary School:




The Calender-Van Dusen equation for a 500ohm platinum sensing element is used.
  • RT/RO = TAT + α[TAT - δ(TAT/100-1)(TAT/100) - β(TAT/100 –1)(TAT/100) 3]
where
  • TAT = temperature in °C
  • RT = resistance at temperature "T"
  • RO = resistance at 0 °C (500 ohms)
  • α = .003832
  • δ = 1.81
  • β = 0.0 for T > 0.0° C and 0.1 for T<0.0 °C

Last edited by A33Zab; 11th Jun 2011 at 03:13.
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