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AF 447 Thread no. 4

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AF 447 Thread no. 4

Old 2nd Jul 2011, 23:11
  #681 (permalink)  
 
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Gee sensing for FBW systems

Indeed the Nz is provided by - state of the art - IR part of ADIRU.

2 separate vertical accelerometers (and Lateral accelerometers) are used for turbulence damping.
But will be used by FCPCs in case of Dual ADIRU (IR part) failure to consolidate the load factor information supplied by the valid ADIRU
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Old 2nd Jul 2011, 23:14
  #682 (permalink)  
 
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Autorim

If trim is manual, why on earth would you trim nose-down and hold the stick hard back?
Good question. I wouldn't. Do we know that the stick was "hard back"? Not yet anyway.

If they had noticed the trim they would have noticed it was doing as asked - they were asking for full nose-up.
Not necessarily. I believe that they forgot, or never really knew, that back stick would trim them up into a stall. I'm not convinced that the PF realized he was pulling back.
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Old 2nd Jul 2011, 23:20
  #683 (permalink)  
 
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Originally Posted by bubbers44 View Post
So the PF with less than a year experience in the Airbus used full nose up SS with this knowledge???? Did he forget? Why did both pilots use full up pitch control if they knew they had no stall protection? All us conventional airline pilots know exactly what would happen. Exactly what their profile did putting them in a deep stall.
I also know exactly what would happen, merely from the perspective of knowing a bit about how stuff that flys (and control systems) is designed and built. I have no answer as to "why" though.

The initial report left all the important stuff out like if they pulled up and with frozen pitot tubes and static pressure dropping did they get an erroneous overspeed warning.
reports are clear that the speeds failed low, not high.

They must have a reason to keep this quiet but eventually they will have to tell us what really happened up there.
I'm curious - from a pilot's perspective, what do you (or any o fthe other real pilots on here) think "really happened" in the colgan crash, where the report says PF pulled hard back through stick shaker and stick pusher ?
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Old 2nd Jul 2011, 23:21
  #684 (permalink)  
 
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Real time information to the crew

RetiredF4
If the speed gets unreliable, i want to be informed about it when the information is available. No need to backtrack it and second guess it from other indications like disconect of autopilot and autothrust.
That´s why i remembered to be technically feasible to have the information even some time (seconds) before System "reconfig".

I´m not convinced that this system is to the best benefit of pilots in abnormal situations.
I hope the advanced planes designers (A, B or ...Z) invest in this issue.
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Old 2nd Jul 2011, 23:26
  #685 (permalink)  
 
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Cool Guys

A human trained in the basic and fundamental technologies of his job can make decisions based on this training without ever having encountered or trained on the scenario in the past
Kind of a misconception. We have only two things going for us when we encounter a new situation - we can sort through past experiences to find ones that might seem relevant (and can do so fairly quickly, especially when the previous experience had a negative consequence, hence "learn from one's mistakes") and less important in the present context b/c a good computer could do so faster, we often can correctly calculate the near-term consequences of a contemplated action. As has been well mentioned, in this case relevant previous experience was lacking, by design.

The point about limiting human tasks to five is no doubt very important, but probably hasn't made it into the design rules. Beastly hard to implement when six very important things go wrong at once, and the flight computers haven't been programmed to boil them down to the root cause.

A few hundred posts ago I suggested that HAL should be tasked with warning the humans that he was starting to "worry" about a situation, and what was bothering him. That would give the humans just one thing to worry about themselves, before the cockpit was filled with stimuli, and with even a second's warning might plant the seed that would let them start the trouble-shooting on the right page.
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Old 2nd Jul 2011, 23:42
  #686 (permalink)  
 
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Originally Posted by OK465 View Post
Exactly.

Then why are some folks claiming it is available when both ADR's are recovered?
Possibly confusion between AOA protections and low/high speed protections.

As I understand it, the latter may come back if the speeds come back, but they are not AOA based, and they are overridable. Low-speed protection may push the nose down if you do nothing, but if you've got the stick back, you win.
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Old 2nd Jul 2011, 23:47
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Originally Posted by Smilin_Ed View Post
Good question. I wouldn't. Do we know that the stick was "hard back"? Not yet anyway.
BEA says "to the left and nose-up stops". For 30s. Is that not "hard back" ?
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Old 2nd Jul 2011, 23:59
  #688 (permalink)  
 
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Possibly confusion between AOA protections and low/high speed protections.
@IFF789:

Read A33Zab's edit (post #663). He has clarified his response to CONF iture and pointed out some ambiguity in terminology.

You are correct regarding this function.

edit:
but if you've got the stick back, you win.
Not necessarily.
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Old 3rd Jul 2011, 00:08
  #689 (permalink)  
 
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Cool Guys

My first post, please be nice to me. I am not a pilot or an aeronautical engineer but I am an electrical engineer who deals in automation that can kill people if it goes wrong, such as transporting 150ton crucibles of molten steel around steel mills. I prefer to read the intelligent and enlightening discussions here than listen to some of our other sources of "entertainment".

There is lots of talk about the man-machine interface. What is the man machine interface? The machine is ideal for multiple repetitive monotonous, tasks. The human works best with minimal tasks at once, 2 or 3 tasks at once is ideal, 4-5 max. A machine can only perform tasks that it has been programmed to do. A human trained in the basic and fundamental technologies of his job can make decisions based on this training without ever having encountered or trained on the scenario in the past. So if the machine encounters a scenario that it is not programmed to deal with, it should naturally pass it over to the human. However the designer and programmers are responsible for passing it over in a format that can be easily handled by the average person. Ie a maximum of 5 tasks. Monitoring the planes speed, AOA, Multiple ECAM messages, A WOOP WOOP STALL, an auto pilot kicking out, a change in handling characteristics, changing trim settings etc. It seems excessive to me.
Of course it would be excessive, so it is not suppose to happen that way. The idea is to prioritize warnings.

A stall is quite high in priority and so is "whoop whoop terrain" hopefully they shouldn't occur at the same time. The other stuff is calling for visual scans to figure out why you were allerted to begin with. If you don't take the propper action something is going to deterioate and alert you furthur.

I suspect that your system designs perform the same way don't they?
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Old 3rd Jul 2011, 00:24
  #690 (permalink)  
 
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Cool

Hi,

RR_NDB

And as you know, it´s easy to put responsibilities in an operator if a Human machine interface (even a poor designed one) is working as designed. Always the management could point to lack of "training", etc. exempting the System.



In fact .. it is the pitot tubes that have been exempted
In fact we know for decades that these Pitot tubes have been certified by not taking into account certain elements or conditions under which they are supposed to work
After some experience .. have realized that they no longer met the requirements expected
What solution do we find?
It was decided to continue to use them despite their lack known
It has continued to let the planes go in places that are not appropriate for these Pitot tubes
At the same time .. asked pilots to cope with procedures (not satisfactory since each time .. reviewed after an event involving the pitot tubes) to counter a bad certification .. or better to counter the fact that they must fly at certain altitudes for economic reasons
Is it normal to give pilots a plane that accessories that are unreliable for their operating domain ? (knowing that Pitot certification does not comply with the the field of employment)
With such principles can be certified tomorrow a plane that has the aerodynamic qualities of a bathtub provide you trow some procedures to the pilots
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Old 3rd Jul 2011, 00:31
  #691 (permalink)  
 
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Immediate a/c feeling to the crew

Hi,

poorjohn
We have only two things going for us when we encounter a new situation
20 years ago i had an incident at night under rain conditions (with no consequences) and made very deep analysis starting next day at 8 AM.

This car had an abnormal position of CG (too ahead) much different to my rear engine car used by me during 500,000 miles +. I had only 1 second (or less) to understand what was going on after i initiated a "test maneuver" to check an abnormal behavior the car showed some 30 minutes before during a 2 hour short trip.

In analyzing the incident (with a friend, air accidents investigator, C130, 707, etc. Captain) i concluded (modeled) we have in our mind "two processors"

1. One "processor", that check if the "scenario" you are facing fits in what you stored in your memory up to this day. It´s put "on line" immediately and first.
2. Another processor that "try" to understand the new situation that seems to be very different from everything you saw before. Both "processors" operate concurrently.

Human beings, has this second capability. Machines has just the first one (they were programmed to deal with a finite number of possible scenarios)

During the "decisive phase" along the incident i had in about 1 second opportunity to select and implement the best solution for a situation i never before imagined as possible to occur. And despite therefore, not being able to find a similar scenario in my "data base".

And during the "high adrenalin" phase i had time to think a lot of things including the surprise with the new intriguing scenario.

I see the pilot as the only one capable to solve new scenarios not imagined by the System designers. And this always will be for an airliner.

To do that he must receive immediately all the BASIC information from a SIMPLE interface. This can be, IMHO the "turning point" when unexpected situations arise.

And if the System for any reason delays his perception, or even worse, present and introduce "new components" the pilot chances reduces accordingly, to timely perform the best and precise actions.

In the described case i was able, despite facing a very rare and highly improbable failure, to feel very fast (in less than one second), the car behavior in order to act decisively and precisely to save my life. In an advanced plane, full of complex "feedback Systems" affected by crew actions "in the loop" the issue is really complex. But it seems to me to be mandatory to allow an immediate understanding of what´s happening, obviously with the help of the System.

Last edited by Jetdriver; 3rd Jul 2011 at 08:37.
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Old 3rd Jul 2011, 00:50
  #692 (permalink)  
 
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Murphy law specter to complex machines

jcjeant
It was decided to continue to use them despite their lack known
Using this kind of approach you are designing machines that can transition very fast from Normal Law directly to "Murphy Law" conditions, where interfacing issues, etc. could fill the cockpit and crew minds, capable to generate unbelievable situations. Where you may not be able to understand timely what´s going on or even "fly" the aircraft.

We are just "modeling". After receiving reliable pieces of factual information we will be able to "conclude".

Last edited by RR_NDB; 3rd Jul 2011 at 01:00.
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Old 3rd Jul 2011, 01:00
  #693 (permalink)  
 
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infrequentflyer789


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Originally Posted by bubbers44
So the PF with less than a year experience in the Airbus used full nose up SS with this knowledge???? Did he forget? Why did both pilots use full up pitch control if they knew they had no stall protection? All us conventional airline pilots know exactly what would happen. Exactly what their profile did putting them in a deep stall.

I also know exactly what would happen, merely from the perspective of knowing a bit about how stuff that flys (and control systems) is designed and built. I have no answer as to "why" though.


Quote:
The initial report left all the important stuff out like if they pulled up and with frozen pitot tubes and static pressure dropping did they get an erroneous overspeed warning.

reports are clear that the speeds failed low, not high.


Quote:
They must have a reason to keep this quiet but eventually they will have to tell us what really happened up there.

I'm curious - from a pilot's perspective, what do you (or any o fthe other real pilots on here) think "really happened" in the colgan crash, where the report says PF pulled hard back through stick shaker and stick pusher ?


I think the inexperienced Colgan pilots resorted to a previous aircraft the captain had flown that had a tailplane stall recovery procedure that was opposite of wing stall recovery. This wasn't a problem in their aircraft and all pilots are taught to lower the nose in a stall, they raised it causing the crash.

That is why I couldn't understand why on this flight they pulled back on the side stick zooming 2500 ft above their altitude when we all know this would put you in a deep stall which could only be recovered from by lowering the nose a lot and using a lot of power to save the aircraft. Something motivated them to pull back and all I can think of is an overspeed warning that was false. Why else would you pull back? I know the report said they lost their airspeed but if that was the case wouldn't they hold pitch and attitude, not pull back until they went into a full stall?

The fact they are holding all the pertinent information back that they have makes me think we will have some big surprises when they finally have to reveal it to the public.
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Old 3rd Jul 2011, 03:28
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Thanks for you answer A33Zab. The more we talk about the overall system, the more we measure its extreme complexity.

Originally Posted by infrequentflyer789
Nothing. There is no AOA protection outside of normal law.
Incorrect

Originally Posted by rudderrudderrat
The aircraft has been designed to cope with the loss of G & Y Hydraulic systems (hence NO Stab trim). Despite no stabiliser movement, the elevators are powerful enough to control the aircraft from cruising speed to approach and landing.
It depends how was the trim at the time of the malfunction. As reminded earlier by DJ77, if the trim was locked above 8 UP, max speed would be 180kt.
For the 330, it would be B & Y.

Originally Posted by infrequentflyer789
BEA says "to the left and nose-up stops". For 30s. Is that not "hard back" ?
As discussed earlier, IMO, translation is not accurate, and should possibly be as follow :
The PF made an input on the sidestick to the left stop and nose-up, which lasted about 30 seconds.

Originally Posted by A33Zab
That would be hard to prove as is in general.
This one would not have happened for sure, can't say about 5A-ONG (Tripoli). Are there any others? (besides Test flight)
I am still very interested in what Svarin, yourself, and PJ2, wrote on that WRG ACARS message ...
Among the 30 known events of UAS at cruising altitude, AF447 has been the only one to lose control, as I understand it, it has also been the only one to deal with a simultaneous mysterious wiring issue ...
And I don't put too much expectation in the BEA to dig any further in that direction.

But my question to PA 18 151 was more, if the protected aircrafts save many lives, the unprotected ones should logically kill more ... is it the case ?

To me, after 20 years of operation of these FBW Airbus, what the protections did manage to do for sure, is to get bigger incident/accident reports.
But then I don't want to speak too loud as a protection could well save my life one day ... not sure I'll be humble enough to tell that story here tough.
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Old 3rd Jul 2011, 03:42
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Gee sensing deux

Thanks a33Z, shows a variation of design philosophy as well as implementation.

Our FLCS ( flight control system) folks were paranoid about using anything but their own data/sensors. Their data was shared by other systems, but if it came down to "us or them", then "them" had to do their own thing. Although we had the best system flying, autopilot inputs were not even treated with the same respect as pilot stick inputs. Very limited AP capabilities, which surprised many of us.

Our attitude display came from the nav inertial system, and we could fly without the inertial even turned on. HAL didn't care, as he had Nz and body rates of his own.

The deal with rate and accel sensing for the FLCS is you want the displayed attitude and such in the cockpit to be independent of the FLCS system. It is very easy and more redundant/reliable to have gee/rate sensors for each FLCS conmputer, and let the ADIRU equivalent be displayed and used for the autopilot inputs. In our case, we had four confusers - one in "standby", and the middle value of the other three for commanding the servo-actuators. If it got down to two, then the most benign value was used.

Not all sensor inputs were quad reduntant. AoA was supplied by two cones and an aero probe with all kindsa holes in it ( hemispherical probe). Q and static pressure was also dual, but FLCS had priority and other stuff got the leftovers. However, the system had the "standby gains" feature in case the air data was deemed unreliable or simply went to lala land. IMHO, this feature should have been incorporated in the 'bus FLCS. Easy and very safe. Stick might be more sensitive if at a very high "q", but would also be less sensitive below the chosen "stby gain" value. Wioth gear down, values were reduced to typical approach "q" values.

sorry for design philosophy, but the final report may get into this aspect of the Airbus implementation.
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Old 3rd Jul 2011, 04:01
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Chronology of events @ 5 sec interval.

Here an updated chronology:

Thx to HN39 which pointed me on the fact I used the first released BEA update which did contain some errors, e.g. switched AOA angle with Pitch angle.

I used all available resources (as known today) and contributions in the forum about this subject.
Bolt printing is data provided from BEA report.

A33Zab.

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Old 3rd Jul 2011, 05:19
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Stall Warning-Communication

Going back to a post by Ian_W http://www.pprune.org/6542805-post525.html, and a discussion of cognitive overload.
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.
I imagine most of us have experienced this effect where you effectively 'turn off your ears so you can get some room to think.'

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.
Underlining by me for emphasis. One of the AF447 issues may be that the aural stall warnings leading up to the actual stall were ignored because of "verbal analysis channel overload".

The stall warning is one of the highest priority warnings in any aircraft. It deserves its own mode of communication.

The F-4 had a very nice stall warning consisting of an excentric weight mounted on an electric motor attached to the left rudder pedal. When warning AOA was reached on our single AOA sensor, you received a brisk foot massage. Unfortunately on a transport aircraft where it is completely realistic to be flying with your feet off the pedals, rudder pedal shakers cannot be depended upon to convey the message.
The DC-10 had a stick shaker of similar principle. Unfortunately the Airbus A320/330/340/380 have a dinky little stick that can be highly sensitive to motion, so stick shakers are out as a means of conveying a stall warning.
There is another part of aircrew anatomy that is available for receiving the message of a vibrating stall warning effector, the part that they sit on.
By vibrating the seat bottom, the crew could receive a stall warning message through a tactile mode of sensing and not add to the cockpit uproar.

Of course, it is important that AOA warnings are available while weight is off wheels, no matter what the airspeed indication.
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Old 3rd Jul 2011, 08:14
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Originally Posted by Machinbird
Unfortunately on a transport aircraft where it is completely realistic to be flying with your feet off the pedals, rudder pedal shakers cannot be depended upon to convey the message. (...)Unfortunately the Airbus A320/330/340/380 have a dinky little stick that can be highly sensitive to motion, so stick shakers are out as a means of conveying a stall warning.
Like feet-on-pedals, the sidestick is not normally held in the hand in cruise.
By vibrating the seat bottom, the crew could receive a stall warning message through a tactile mode of sensing and not add to the cockpit uproar.
Excellent idea! I wonder if it was ever considered in the design.

Last edited by HazelNuts39; 3rd Jul 2011 at 08:49.
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Old 3rd Jul 2011, 08:29
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Originally Posted by infrequentflyer789
BEA says "to the left and nose-up stops". For 30s. Is that not "hard back" ?

Originally Posted by CONF iture
As discussed earlier, IMO, translation is not accurate, and should possibly be as follow :
The PF made an input on the sidestick to the left stop and nose-up, which lasted about 30 seconds.
The original French reads: "Le PF exerce une action sur le manche en butée à gauche et à cabrer, qui dure environ 30 secondes."
Perhaps this can be read either way, but if the BEA meant what you suggest, this would be very sloppy writing. In addition, IMHO it doesn't really matter whether the nose-up command was to the stop. The AoA was beyond 40 degrees, and only a prolonged command to the nose-down stop would have made any difference.
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Old 3rd Jul 2011, 08:34
  #700 (permalink)  
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Yes, the sidestick shaker concept has previously been tested in an Airbus sim.

I'am guessing the results were non favourable to warrant production.
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