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AF 447 Thread no. 4

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AF 447 Thread no. 4

Old 29th Jun 2011, 09:20
  #521 (permalink)  
 
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Re: Not seeing the wood for the trees.

PickyPerkins
It might be interesting, and possibly useful, to examine these ten accident reports and compare the situations at the start of each of these events, e.g. how many of them STARTED with a disconnect of the AP?

Would you object to "apparently started with a disconnect of the AP"?
In the period leading up to the AP disconnect the automation might have adjusted trim, throttle etc away from those usual/appropriate for the phase of the flight. Which would complicate the machine -> human takeover.

For example, the problems facing the turkish crew at Schiphol seem to have been greatly compounded by the heavy trim applied before the AP finally disconnected.
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Old 29th Jun 2011, 09:47
  #522 (permalink)  
 
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@GB:

At the weekly Old Bold Pilots breakfast this morning, I asked the guy who was cognizant engineer on the stall warning computers for the DC-9 and MD-80. He was incredulous that the A330 Stall Warning would shut off below 60 knots airspeed. He said the AOA vanes on his planes would measure to about 50 degrees AOA.

I suspect the A330 vane mechanical limit is about 30 degrees, as I don't recall any greater AOA mentioned by BEA. Does anybody know?
85 to -35 degrees.
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Old 29th Jun 2011, 09:49
  #523 (permalink)  
 
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Originally Posted by grity View Post
"AAIB Bulletin No: 6/2001: Consequently, in turbulence the speed scale will probably be oscillating, the aircraft pitch angle could also be oscillating..."

if the bird flow for sume time nearly in a balistic curve, the AoA vane is in a stable normal position... no AoA protection will start working

AoA protection alone seems not very good for stable flight
Not sure I'd call it 'stable', but it is 'flying' below 'stall speed'.

the climb-input is interesting, after the stopp of the autopilot they moved the elevator up to +4 for ten sec. but in the following seconds the G falls to 0.5 and the pitch drops a little down (!) IMO this needs good downwind. then they hold the elevator between 0 and -3 and pushed the 4 engines this must be the climb-input, mayby together with the autotrim
Note 'they' is not pilot input, elevator input may be from Normal law controlling 1g, but is also almost coincident with the second MMO exceed event, so could be "High speed protection" pitch up?

ar you shure AoA reached alpha max? nighter the trim nor the AoA is shown in the diagram. the climb after the startinput could also happen with a lower AoA....
The report states that "the corrected or phase-advanced angle of attack excursion beyond alpha prot caused a change in the pitch flight control law from normal law (NZ law) to angle of attack protection law (AoA law)."

Which suggests it wasn't the real AoA, but it is what the instrumentation reported, and if the signal is noisy you do not want to "phase advance" it by differentiation and extrapolation. If the AoA sensor suffers friction and moves in 'stick-slip' steps this sensor processing would give AoA spikes!

But does that explain the pitch response before the pilot inputs knocked it out of the protection mode? To control to alpha prot with falling airspeed why would it pitch up 10 to 16 degrees? Perhaps that's just what happens when it tries to AoA with very noisy AoA sensor inputs due to the turbulence? As the speed falls does the target alpha prot increase?

Last edited by sensor_validation; 29th Jun 2011 at 10:11.
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Old 29th Jun 2011, 10:08
  #524 (permalink)  
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Originally Posted by fantom #491
has not enjoyed an Airbus type rating course.
- small print noted

It is perhaps pertinent to point out that all the pilots (whose bodies have been recovered from the Med and the Atlantic from the two accidents) had done so, so I'm not too sure what I would have benefited from, apart from the 'enjoyment'?
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Old 29th Jun 2011, 10:14
  #525 (permalink)  
 
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Ridiculous design (AS issue)

RR_NDB:

Before calling this a ridiculous design.....

What are your suggestions how it ought to be?
Maybe AIB (or any other airplane manufacturer) can learn from you?
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Old 29th Jun 2011, 10:43
  #526 (permalink)  
 
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Sensor validation;

Does the report say that airspeed fell below stall speed? IIRC it only stated that airspeed fell below VLS (lowest selectable speed).

The report explicitly states that overspeed protection was not invoked.

But does that explain the pitch response before the pilot inputs knocked it out of the protection mode? To control to alpha prot with falling airspeed why would it pitch up 10 to 16 degrees? Perhaps that's just what happens when it tries to AoA with very noisy AoA sensor inputs due to the turbulence? As the speed falls does the target alpha prot increase?
Capture of alpha-prot means that the FCS maintains an AoA greater than required for level flight, hence loadfactor>1, hence vertical acceleration, increasing v/s and FPA. Since pitch = FPA + AoA, increasing FPA at constant AoA=alphaprot means increasing pitch. Agree that turbulence 'noise' gets into the act too.

EDIT:: I suppose alpha-prot is tied to alpha-max which decreases with increasing Mach. So yes, I would expect that alpha-prot increases with decreasing airspeed, but consider that is a second-order effect. The protection will still keep the airplane a comfortable AoA margin away from the stall, because stall AoA increases also.

Last edited by HazelNuts39; 29th Jun 2011 at 16:50. Reason: edit of S_V's post
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Old 29th Jun 2011, 11:49
  #527 (permalink)  
 
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Originally Posted by galaxy flyer View Post
Unfortunately, pilots learn to fly on planes that fly like all the planes built since the Wright Flyer, version 1908, not like Airbuses.
The wings still work the same on your airbus and your spamcan.
There have been a disproportionate number of LOC accidents/incidents in Airbus aircraft.
Disproportionately high, or disproportionately low?
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Old 29th Jun 2011, 12:10
  #528 (permalink)  
 
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sensor validation: Note 'they' is not pilot input, elevator input may be from Normal law controlling 1g, but is also almost coincident with the second MMO exceed event, so could be "High speed protection" pitch up?
work the Mr." high speed protector" over the elevator or the trim ???

hope I understand the algebraic sign of the elevatorline right? + =pull , - = push

my little feeling is that all this "MR. protectors" work each beside the many "others", normal they work very good, but they are not team players. there is no "Mr. cross-controller" who says: keep cool wait, first cross- look to bank, altitude, attitude, speed and AoA and after you ask them all what happens, then go slow to a saver place.
no Mr. protector say: "I am out of my range, I stop at this place, over and out!"

and the PF has to wait for this moments and then he need a good portion of adrenaline.....

why did not exist a paralell energie calculation to sort a lot of possible faults out?
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Old 29th Jun 2011, 12:44
  #529 (permalink)  
 
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Originally Posted by grity
my little feeling is that all this "MR. protectors" work each beside the many "others", normal they work very good, but they are not team players.
Maybe so, but high AoA protection has priority over all others.
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Old 29th Jun 2011, 12:51
  #530 (permalink)  
 
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Cognitive Issues

From an earlier post by DozyWannabe
"Quote:
Originally Posted by Lonewolf_50
This takes me to BOAC's question about a crew allowing their aircraft to head into orbit: what airline pilot, flying at altitude, would find a 16 deg nose up attitude something other than abnormal?

Why would either let that nose attitude sustain?

This goes back to what may not be answerable: what did each member of that cockpit crew see in front of him, and what was he paying most attention to?
This is where (and why) I keep going back to Birgenair - where a very experienced pilot stalled and span his 757 despite the fact that the only fault on the aircraft was a single blocked pitot tube. It is impossible to know what was going through his mind, but nevertheless - even with both his F/Os calling "ADI" and "Stall" repeatedly, he apparently did not process the information that the ADI was giving him - that he was excessively nose high for the phase of flight he was supposed to be in. Attempts to remedy the other factors in that accident have been included in pilot training and bulletins from the manufacturers (and indeed a design change to the 757) over the years, but the fact remains that psychological factors in an incident of this nature are possibly not as well understood as they could or should be."

As a little exercise try to recite a nursery rhyme that you know well and at the same time read the text from DozyWannabe above and if you have a friend have them tell you a message that you need to write down.

You will find that you cannot do all these actions. You are overloading your brain's cognitive channel for verbal analysis. This is one of the reasons that using cell phones while driving reduces the ability of the driver - cognitive overload.

I have observed overworked controllers 'not see' aircraft fly past their tower due to overload like this.

Now what happened in the cockpit of AF447 appears to be a cacophony of emergency aural and visual messages from the ECAM. Many of the instruments that the pilots would rely on became invalid and others were showing totally unexpected outputs.
Saying the PF should have seen this or done that is easy when all these messages are teased out on a nice timeline - but when they are all at once nobody's brain can process them all. The response in the human under this pressure can often be 'cognitive or attentional tunneling' where everything except a small portion of the inputs to the brain are just not seen/heard.

Has anyone actually carried out a cognitive assessment of the PF workload when the AF447 series of failures actually occurred?

It seems to me that the aircraft didn't just say - 'You have the aircraft' - every system on the aircraft had to say something plus many of the instruments. The cockpit displays are not analogue gauges which use the spatial analysis cognitive channel, but are textual requiring the same verbal analysis channel as the aural verbal messages and the ECAM text messages.

If there is a design area that needs assessment it is the way the aircraft can rapidly induce cognitive overload. It may be that the lack of discussion on the flight deck was caused by verbal channel overload. To go back to the start of my post: try holding a conversation with someone while carefully reading something different.

Perhaps this is the reason for the repeated 'set power and pitch' effectively saying disregard all those messages they aren't important - fly the aircraft. The implication of this though is perhaps those messages that the designers and systems engineers thought were important are not really important at all. They can actually lead to a worse outcome by overloading a flight crew that tries to listen.
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Old 29th Jun 2011, 13:09
  #531 (permalink)  
 
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Originally Posted by RR_NDB View Post
The use of a "voting scheme" capable to "major a/c reconfig" using identical (sub heated) not adequate Pitot´s is a direct path to PROBLEMS!

[...]
Who can tell me why they implemented this redundancy in respect to AS measurements? I would like to understand the reason.
What other a/c does it any other way ?

The 777 has exactly the same number of identical pitots, also feeding an airdata and FBW system that can go wrong in exactly the same way (pitch-up in cruise - uncommanded in this case - losing speed to point of stall) when fed bad air data.

There's been a lot of discussion about alternatives to pitots, but none of them are ready for production or without engineering problems.

When A and B and every other mfr are doing it exactly the same way, it is probably becuase there is (as yet) no other credible alternative.
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Old 29th Jun 2011, 13:14
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Cognitive Issues

@ Ian W
If there is a design area that needs assessment it is the way the aircraft can rapidly induce cognitive overload. It may be that the lack of discussion on the flight deck was caused by verbal channel overload. To go back to the start of my post: try holding a conversation with someone while carefully reading something different.
Well said.

Back then when flying i would tell my WSO to shut up. Today with my wife continously talking on the right seat in the car (we drive here on the left one) i better don´t tell her to shut up. But lately we missed an highway exit.....
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Old 29th Jun 2011, 13:35
  #533 (permalink)  
 
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Talked with someone at Air France that heard the tape : the aerodynamic noise (due to the stall) was so loud in the cockpit that the pilots thought apparently almost till the end that their speed was incredibly high.

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Old 29th Jun 2011, 13:39
  #534 (permalink)  
 
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Elevator deflection conventions

grity
hope I understand the algebraic sign of the elevatorline right? + =pull , - = push
I don't know what the standard convention is, but in Fig. 6 of this NASA report a + elevator movement results in an increased pitch down moment, i.e. the opposite of your assumption.

The negative slope of the curves in Fig. 6 indicates a stable aircraft, i.e. any disturbance which increases the AoA leads to an increased pitch down moment.
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Old 29th Jun 2011, 13:53
  #535 (permalink)  
 
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Cool

Hi,

Talked with someone at Air France that heard the tape : the aerodynamic noise (due to the stall) was so loud in the cockpit that the pilots thought apparently almost till the end that their speed was incredibly high.
That's what I call "a scoop leak" ...
I don't already read any of this in the press
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Old 29th Jun 2011, 13:54
  #536 (permalink)  
 
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Stall aerodynamic noise

We can imagine how many dB higher for the PAX near the wings. I posted earlier on the feelings of the POB.


Lacking reliable (and clear, direct and simple to immediately) info to understand what was going on and after hearing this noise (typical of high air speed) i ask: This may explain some NU from PF? (probably not questioned by PNF)
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Old 29th Jun 2011, 14:02
  #537 (permalink)  
 
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Excellent post, Ian. Due to the Ecam alerts and warnings, I doubt the PNF was watching what the PF was doing. There was no possible peripheral perception of a yoke moving, unlike non-AB aircraft.

Maybe the A330 shuts off the Stall Warning below 60 kt to reduce the cacophony?

Since the A330 AOA vanes can move to +80 degrees, and the output must indicate actual AOA, why wasn't any AOA greater than +30 degrees (IIRC) enumerated by the BEA?
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Old 29th Jun 2011, 14:27
  #538 (permalink)  
 
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Assertivity

Before calling this a ridiculous design.....
We are here for many reasons. One of the main is for express ASAP our (professional) intuition, feelings, perception, etc. based in what we learned up today. To go direct to the "solutions phase" i prefer (decision making risk taking) first to say "there is a problem". Simply because solutions only can be found AFTER you identify and accept the existence of the problem. Before that, no motivation, no reasons to even think on the issue.

What are your suggestions how it ought to be?
The technical discussion will be made on that. Before going into conceptual and technicalities i suggest before that, to think and answer to the posted question: "Who can tell me why they implemented this redundancy in respect to AS measurements? "

Maybe AIB (or any other airplane manufacturer) can learn from you?
May be (we are technicians here are not with the "tools" to do that) can learn (something) from us, because the Synergy with hundreds of dedicated and good will professionals tend to generate good results by questioning, filtering, "condensing", etc. We are here in a very interesting T.E.A.M. work: Together Everyone Accomplishes More (IIRC M. Favish)
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Old 29th Jun 2011, 14:32
  #539 (permalink)  
 
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Not seeing the wood for the trees

PickyPerkins
It might be interesting, and possibly useful, to examine these ten accident reports and compare the situations at the start of each of these events, e.g. how many of them STARTED with a disconnect of the AP?
Peter H
Would you object to "apparently started with a disconnect of the AP"?
No objection. I agree with you. Human factors and the "startle effect" is exactly what I am getting at.
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Old 29th Jun 2011, 14:36
  #540 (permalink)  
 
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Originally Posted by Graybeard
why wasn't any AOA greater than +30 degrees (IIRC) enumerated by the BEA?
Why don't you spend the few minutes it takes to read the BEA update rather than repeat your incorrect recollections?

There's enough people doing that as it is.
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