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-   -   AF447 final crew conversation - Thread No. 2 (https://www.pprune.org/tech-log/478681-af447-final-crew-conversation-thread-no-2-a.html)

john_tullamarine 29th Feb 2012 22:28

AF447 final crew conversation - Thread No. 2
 
Link to Thread No. 1

PJ2 29th Feb 2012 23:10

Thanks for the link, John.

HN39;

I won't forget our early exchange on stall AoA and later also with Owain Glyndwr the effects of Mach on AoA and buffet thresholds. The discussion had a profound effect on my understanding of my airplane and of high altitude-high speed flight and AF447 specifically. I would recommend to anyone wanting to know more from those that really do know their stuff, to find this and other exchanges with these two posters.

Re, "...would it help prevent future accidents if sophisticated Flight Guidance and Aircraft Monitoring systems, having rejected three sources of airspeed information as unreliable, and 'knowing' conditions such as configuration, weight and altitude, provide more specific information as to the appropriate response?"

I need to think about it! ;-) Along with weight, altitude & configuration it would use AoA and perhaps also have a running historical window, say the last five or ten minutes, of all relevant indications upon which to build a "safe envelope"? Just thinking out loud.

Initially I think, Yes, it would help, but in the Birgenair and Aeroperu cases more than here. Reason I say this is, most of the Airbus UAS events lost airspeed indication for less than two minutes and from what can be gleaned from the Interim Report 2, those crews affected didn't seem to do anything but wait.

Because pilots are creatures of visual, auditory and tactile habit, a switching to a "novel" presentation may present as much surprise as the event itself and take a moment to get used to...which means it also has to be trained in the sim, which available time these days is heavily-challenged already.

But the Birgenair/Aeroperu cases are completely different and I think such a system/presentation would have saved the aircraft.

Organfreak;

I didn't watch the BBC series, preferring the BEA work plus some discussions on the side. I prefer original sources to anything that will perhaps innocently but most assuredly have a point of view and a theory and must keep an audience entertained to be economically viable. I avoid the "Discovery Channel" kind of stuff for this reason. The needs of television are not those of good investigations because such work is enormously detailed and for most, tedious and certainly would not entertain. "The story" is certainly interesting and I can see where those not familiar with the event would enjoy learning about it though and getting enough from such programming to ask further questions.

Not sure if the BBC was showing Vasquez's work, but it showed up early here and was an enormous help in understanding the weather aircraft transiting the ITCZ deal with on a regular basis.

jcjeant 1st Mar 2012 02:42

Hi,


The needs of television are not those of good investigations because such work is enormously detailed and for most, tedious and certainly would not entertain
Well .. here's yet another has appeared in a few days .. and in which journalists claim to show how the accident really happened :ok:

In this new survey Exhibits reveals what really happened during the last 4 minutes of flight Rio / Paris.
The final report of the BEA about what happened in advance ... :)
Google Traduction

Pices conviction revient en mars sur le crash du Vol AF 447 Rio / Paris - Le zapping du PAF

mm43 1st Mar 2012 07:20


Originally posted by PJ2..

I won't forget our early exchange on stall AoA and later also with Owain Glyndwr the effects of Mach on AoA and buffet thresholds. The discussion had a profound effect on my understanding of my airplane and of high altitude-high speed flight and AF447 specifically.
I must admit I was impressed by Owain Glyndwr's well thought out dissertation on THS v Elevator, AoA and Mach buffet, and some time ago took the liberty of putting a couple of his posts together as a webpage.

THS v Elevator and AoA

roulishollandais 1st Mar 2012 15:38

Thank you..........

roulishollandais 1st Mar 2012 15:45

Tv, Polacko and Otelli storytelling
 

Originally Posted by PJ2
I prefer original sources

That for are we Ppruners !

Lyman 1st Mar 2012 15:50

It might be esoteric, but what I got from Owain was two behaviours. In the long term, the a/c has an all flying tailplane. In the short term, the a/c has a standard PITCH control, one that degrades to "neutral" over time. The aircraft is always seeking cruise, (or attitude: establish), and this conflicts with the need to maneuver, at times.

Which could lead to confusion, unless the configuration (instant) can be sussed visually (screen), or by feel? "What's it seeking?"

Why would this a/c seek to "establish" and hold an attitude that required constant attention from the handling Pilot? An attitude that was intended to be short term, perhaps? PF had the ROLL under control because he knew what was going on, albeit badly. Right, wrong, or sideways, he did NOT get what the PITCH required. This speaks to the a/c's programmimg in ALII. For whatever cause, the handling pilot was unable to 'get'. Is the a/c always correct?

Just a question.

Organfreak 1st Mar 2012 16:45

Lyman:

The aircraft is always seeking cruise...
In ALT2???

:suspect: :sad: := :( :hmm:

Owain Glyndwr 1st Mar 2012 17:38

Lyman

Quote:
[what I got from Owain was two behaviours]
unquote

Wherever you got that, it wasn't from me!

Even in Alt2 the C* law is a manoeuvre command system for goodness sake. The control laws don't 'seek' anything. They hold what's there until told by the pilot to change it. There is no conflict except in your mind.

Lyman 1st Mar 2012 18:21

Owain.

If from the initial PITCH up command, the THS had been trimming the command, the a/c would have STALLED well before the top of climb, where there was no energy left, and the STALL was unfelt, unobserved (per your comment).

Had it not remained at -3.4, then, the a/c would have fallen out, buffeted, and the two man crew would be left with inescapable evidence that STALL recovery was a necessity. Point of fact, the a/c would have recovered on her own had she been allowed to STALL. Instead, the a/c drained energy until at full power, when it mushed into an attitude that was to remain until water contact.

After the loss of energy, the THS then started to trim in NU, and remained at 13.2 (-) until water contact. It stands to reason A) you are not wrong, and B), the lack of SA, CUES, and CRM prevented the crew from sussing the STALL.

No judgment, no accusation. It remains that had the a/c STALLED earlier, the cues would have been present and the outcome may have been different. No?

RR_NDB 1st Mar 2012 18:47

Transient in Feedback Systems
 
A33Zab


@RRR:
Don't know what you mean with 'sub'heated, its self temp. controlled.
The heat applied is inversely proportional to the temperature of the probe.
Will post on the subject applied to:

1) Sub heated Pitot's
2) RH not recorded

I am elaborating and will post ASAP.

Owain Glyndwr 1st Mar 2012 21:54

AF447
 
Lyman,

I'll give it one go then I'm back into hibernation.

[quote] If from the initial PITCH up command, the THS had been trimming the command, the a/c would have STALLED well before the top of climb, where there was no energy left, and the STALL was unfelt, unobserved (per your comment). [unquote]

You keep writing as if the THS has a life of its own. It hasn't. It is slaved to the elevator through an integral term (see the block diagram PJ2 posted a while back). It WAS trimming in the initial phase of the second stall approach - it moved from around 2.5 deg to around 3.4.

It matters not one jot whether the pitching moment comes from elevator, THS or some combination thereof. The aircraft responds to the total pitching moment commanded by the pilot and there is absolutely no evidence to the contrary. That being so, the THS movement would have no effect on the point at which the aircraft stalled - it was merely sharing out the commanded pitching moment to minimise elevator movement.The time at which stall occurred was driven purely by pilot input as a commanded 'g' history.

I did NOT say the stall was unfelt or unobserved. I said that it was difficult to distinguish between turbulence buffet and stall buffet and that there were no pitching moment breaks. As a nonpilot writing in a professional pilot's forum I try to avoid sticking my neck out where it can get chopped off, so I was careful to say that the other clues indicating stall (high attitude, inability to arrest rate of descent) were best left to pilots to evaluate.

I did not add of course that there was this little matter of a voice calling STALL STALL every five seconds or so.

All in all I cannot accept that the stalled condition was unrecognisable.

[quote] Had it not remained at -3.4, then, the a/c would have fallen out, buffeted, and the two man crew would be left with inescapable evidence that STALL recovery was a necessity. Point of fact, the a/c would have recovered on her own had she been allowed to STALL. Instead, the a/c drained energy until at full power, when it mushed into an attitude that was to remain until water contact.[unquote]

Since stall AoA is independent of THS setting, your argument won't hold. The aircraft WAS allowed to stall and it did buffet. Just allowing the aircraft to stall won't get you out of it unless you remove the pitching moment that is holding you in there. This didn't happen.

[quote] It stands to reason A) you are not wrong, [unquote]

True ;)

[quote] and B), the lack of SA, CUES, and CRM prevented the crew from sussing the STALL. [unquote]

Also truehttp://images.ibsrv.net/ibsrv/res/sr...y_dog_eyes.gif

[quote]No judgment, no accusation. It remains that had the a/c STALLED earlier, the cues would have been present and the outcome may have been different. No?[unquote]

No

RR_NDB 2nd Mar 2012 12:13

THS
 
Hi,

Owain Glyndwr,

In your opinion what kind of improvement(s)* could and should be made to the aircraft Systems in order to effectively "help" the crew in similar situations in respect to THS operation.

Kudos for your analysis.

Rgds

(*) Algorithms, indications, etc.

fizz57 2nd Mar 2012 12:30

"DON'T PULL" flashing on the PFD in time with the stall warning?

RR_NDB 2nd Mar 2012 12:39

Transient in Feedback Systems (I)
 
Hi,

Feedback loops are designed (and potentially capable) to improve a System.

For example, the AS probes in auto mode receives just the required electric power.

Feedback loops are designed with "time constants" and eventually with techniques like hysteresis. The engineering takes into account essential aspects like stability, etc.

I posted some comments assertively saying the AS probes the industry is still using, are "subheated".

I am based in several facts and i can discuss each one when necessary.

I have some questions to the Pilots (daily facing UAS threaths) and to the Technicians here:

1) Is the power being applied to the AS probes enough in order to their proper operation?
2) The delay between a sudden atmospheric temperature drop and the "reheating" of the probes could explain the "failures" leading to UAS?
3) The differences between US and FR probes may be explained by "different" time constants?
4) Is the max power sufficient to provide a safe operation in most environments?


Is there "recording capability" in current Systems in order to analyze the UAS incidents more precisely?

Could be better to enter WX using MAX instead of AUTO? (Operating "open loop")?

lomapaseo 2nd Mar 2012 14:43

RR NDB


1) Is the power being applied to the AS probes enough in order to their proper operation?
2) The delay between a sudden atmospheric temperature drop and the "reheating" of the probes could explain the "failures" leading to UAS?
3) The differences between US and FR probes may be explained by "different" time constants?
4) Is the max power sufficient to provide a safe operation in most environments?


good start but to better understand what questions are applicable first search on High altitude "ice crystals" in aviation

I suspect that you may better understand the time differentials between sensing and applying enough heat.

Note that you car windscreen will still ice up and then shed while the defroster is on high, as the sleet density vs your speed changes rapidly.

RR_NDB 2nd Mar 2012 15:08

Time constant
 
lomapaseo,

i suspect US probe is "faster" to adapt to a "new environment".

The max power is the same to both probes.

Anyway i will go deep in this subject as you suggested.

IMHO the System should be STABLE under "brief failures". Like AS probes anomalies.

RR_NDB 2nd Mar 2012 15:25

K.I.S.S.
 
Hi,


I suspect that you may better understand the time differentials between sensing and applying enough heat.


In AUTO mode you will have a delay from "sensing" to "correct" to the required probe temperature.

if you apply maximum available power, ("open loop condition") no delay at all :)

At which cost? Roughly 1 KW being used, i estimate.

And the environment is frequent, i understand.

Are you saying is difficult to decide (System or crew) when apply max power?

HazelNuts39 2nd Mar 2012 16:22


Originally Posted by RR NDB
1) Is the power being applied to the AS probes enough in order to their proper operation?

Not sure that I understand the question. If the amount of heat is the problem, then it was obviously not enough to prevent blockage of the pitots in the particular conditions encountered by AF447. However, as stated by PJ2's #1420 in thread no.1:

The problem of momentarily blocked pitot tubes is extremely rare. Appendix 7 of the BEA Second Interim Report, which see, lists the events which occurred to Airbus. (...) but given the millions of ice-crystal-cloud-penetrations that occur each year without result, "avoiding all cloud" isn't realistic.

2) The delay between a sudden atmospheric temperature drop and the "reheating" of the probes could explain the "failures" leading to UAS?
The recorded data show the opposite of a temperature drop. At 02:09:30 the temperature was ISA +10.6C, trending downwards (Interim #3, p.48), and at 02:10:00 it was ISA +15.6C (p.86).

RR_NDB 2nd Mar 2012 17:19

1st question
 
Hi,

HazelNuts39,


Not sure that I understand the question.


Is the power being applied to the AS probes enough in order to their proper operation?

The power UNDER STEADY STATE CONDITIONS (operating at MAX POWER) is enough?

Operating at MAX power there is no delay, i.e. you are in a "open loop" mode wasting energy and stressing materials when not necessary.

I guess the max available power is enough. (Just guessing).

And i suspect the amount of heat are not being sufficient when encountering ice. This "encountering" was mentioned to be heard on CVR.

I took into account PJ2 post when formulating all 6 questions,


The problem of momentarily blocked pitot tubes is extremely rare. Appendix 7 of the BEA Second Interim Report, which see, lists the events which occurred to Airbus. (...) but given the millions of ice-crystal-cloud-penetrations that occur each year without result, "avoiding all cloud" isn't realistic.

The recorded data show the opposite of a temperature drop. At 02:09:30 the temperature was ISA +10.6C, trending downwards (Interim #3, p.48), and at 02:10:00 it was ISA +15.6C (p.86).
I am talking in the transient, just after noise increased in CVR due ice crystals "collisions" to windshield an nose cone surfaces.

I also took into account the recorded temperature, (higher than expected and imposing a FL375 REC MAX) not relevant to my rationale. I am looking to the transient, the so called t0+, just after encountering ice crystals when the heat MUST BE PRESENT immediately to assure proper AS sensors operation.


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