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AF 447 Thread No. 9

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AF 447 Thread No. 9

Old 7th Jul 2012, 17:49
  #121 (permalink)  
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I realise I am rather late at the 'They followed the FD' dining table, but why does this possibility not feature more in the BEA report? Is it not a horrendously poisonous cocktail to present to a confused crew - an apparently 'computer generated so must be right' driven VS demand, totally seductive, when all else has fallen around your ears? Why not a simple 'Select Vertical mode' inhibit?
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Old 7th Jul 2012, 18:00
  #122 (permalink)  
 
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BOAC

The FD on the bus, even on the A300, is just one of many traps.

Fortunately the airline I used to work for put some emphasys during training on that issue.
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Old 7th Jul 2012, 18:08
  #123 (permalink)  
 
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@BOAC

May be because PF was really concerned with "Overspeed"...

2.1.3.3.1 PF’s reactions

On the other hand,
in the absence of airspeed information known to be reliable, it is possible that the
PF thought that the aeroplane was in an overspeed situation, notably due to his
interpretations of several clues:

ˆ The aerodynamic noise,
ˆ The buffeting, that he might have interpreted as being due to high speed,
ˆ The speed trend arrow on the PFD, which at that time indicated acceleration.

He reformulated his impression
a*few seconds later, combined with an attempt to extend the speedbrakes.
Other factors which may have prompted the PF to fear an overspeed situation were:
ˆ The display on the ECAM (max speed 330/.82) combined with the reconfiguration
to alternate law which may have been read;
ˆ The fact that, in cruise, the upper red strip on the speed tape (MMO) is about ten
knots above the current speed, whereas VLS is barely visible at the bottom of the
tape (thirty knots less);
ˆ The dangers associated with overspeed situations embedded in the collective
consciousness of pilots.
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Old 7th Jul 2012, 18:34
  #124 (permalink)  
 
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I realise I am rather late at the 'They followed the FD' dining table, but why does this possibility not feature more in the BEA report? Is it not a horrendously poisonous cocktail to present to a confused crew - an apparently 'computer generated so must be right' driven VS demand, totally seductive, when all else has fallen around your ears? Why not a simple 'Select Vertical mode' inhibit?
Procedure AF for unreliable speed:
Select FD OFF
AF447 crew don't followed the procedure ... sad ...
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Old 7th Jul 2012, 18:41
  #125 (permalink)  
 
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Procedure AF for unreliable speed:
Select FD OFF
AF447 crew don't followed the procedure ... sad ...
YES, but the bars already disapeared when ASI went bust....and the AP kicked off.

A trap!
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Old 7th Jul 2012, 19:01
  #126 (permalink)  
 
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One question I have that I think actually determines my layperson opinion on this is why, given the duration of the incident, there appears to have been no vigorous attempt to acknowledge that the response wasn't having the desired effect and to at least articulate alternative strategies. Odd to persevere with failure and not fight harder.
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Old 7th Jul 2012, 19:16
  #127 (permalink)  
 
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Did the autopilot stall the airplane on bad airdata before it clicked off and handed over to the pilots, or did the PF immediately imply an overspeed, and stall it with the long period of stick back ?

.
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Old 7th Jul 2012, 20:12
  #128 (permalink)  
 
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Originally Posted by PJ2 View Post
When that occurs the V/S or FPA is synchronized with the aircraft parameter, whatever it happens to be at the time of re-engagement. From there, the pilot makes an appropriate selection such as OPEN CLB/DESC, or, for immediate altitude hold, setting the V/S to zero, etc. (Another way to put it...V/S or FPA are simple, selected (ie, not managed), modes - the FDs could not "know" what "1400fpm" or "6000fpm" was for...it just reflected current conditions, from which selections may or may not be made).
Interesting!
Is that behaviour known and clear to an average AB Crew?
Technically I can see the logic behind but on the other hand that could indeed be somewhat misleading if the behaviour is not properly understood by the Crew. And indeed it appears the behaviour was not clear to them because after the intial rapid climb one could conclude they followed the 1400fpm of the FP.
It might at least be a good idea to automatically disconnect the FD in the same way as the AP in case of UAS so that it deliberately has to be reengaged. This might help a crew that failed to properly follow the procedure for whatever reason.

Altogether I do not really share the feeling that the report put too little emphasis on the FD. These reports are always very indirect in language and considering that I felt they highlighted the FD rather prominently. To me the report implies most of the committee also had the impression that the FD played an important role especially during the extermely relevant first minute of the incident.
After that things were pear shaped anyway and recovery was getging more and more unlikely. Once they were at 40° AoA things were set firmly for a bad ending. (Anyone trained in doing a 45° Nose dive at 30kFt in a 200t airliner at night in IMC with uncertainty about validity of instrument readings?)
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Old 7th Jul 2012, 20:28
  #129 (permalink)  
 
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Audible Alarms/Noise

What about the affect of the audible alarms. Doesn't the noise make it more difficult to think clearly? Is it really very helpfull to have the alarms keep repeating? I know that when I am in a stressfull situation i just want everyone to shut up for a bit so I can think. Has there been research done on that subject?

Sorry if this has been discussed before. I have read many of the threads, but alas, not all of them.
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Old 7th Jul 2012, 20:41
  #130 (permalink)  
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Is that behaviour known and clear to an average AB Crew?
I would certainly expect so, it's part of knowing one's airplane. But it is one of those transient characteristics that is somewhat "invisible" because normally we're on the way to something else in terms of a selection. On the engine-out on takeoff, we would level off the A320 by selecting "0" on the V/S but when initially rotating the knob it would synch with the current VS, from which an adjustment would be made.

The UAS memorized items require that the AP/AT/FDs are all turned off.

Automatically, (meaning the system does it, not the pilot), turning the FDs off with an abnormality such as an NAV ADR Fault may or may not be a good thing. Solving one specific issue always has a "dozen" other perhaps-unanticipated outcomes so it would have to be studied, just like the THS continued trimming after a stall warning, and the loss of the stall warning (NCD - no computed data) below 60kts. Perhaps it should latch?...but that can't be determined until a full analysis of all possible/knowable outcomes are tested.
After that things were pear shaped anyway and recovery was getging more and more unlikely. Once they were at 40° AoA things were set firmly for a bad ending. (Anyone trained in doing a 45° Nose dive at 30kFt in a 200t airliner at night in IMC with uncertainty about validity of instrument readings?)
Well, there has been input, (by Owain Glyndwr) that recovery may have been possible at various altitudes. Owain indicates that a reasonable "unloading" of the wing/reduction in AoA could be done with a steadily-held 10deg ND and in fact lower down, (thicker air), the recovery would be slightly quicker.

Last edited by Jetdriver; 7th Jul 2012 at 23:21.
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Old 7th Jul 2012, 20:57
  #131 (permalink)  
 
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aircarver

The PF flew a perfectly flyable, reasonably safe and fairly stable plane into a stall.

AF procedures for "unreliable air speed" were not followed at any time.
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Old 7th Jul 2012, 20:57
  #132 (permalink)  
 
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Well, there has been input, (by Owain Glyndwr) that recovery may have been possible at various altitudes.
In the press meeting the BEA had to answer the same question (recovery possible ?)
Their answer was they don't know .. as this was never tested in real life on a A330
But like they stated it .. it's seems that for the BEA that recovery was impossible .. unless a miracle ......

Last edited by jcjeant; 7th Jul 2012 at 21:00.
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Old 7th Jul 2012, 21:17
  #133 (permalink)  
 
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jcjeant;
It seems that for the BEA recovery was impossible .. unless a miracle ......
On reflection, I believe the BEA have developed the Report on the basis that their mandate was to determine the actions and/or events that lead to the aircraft departing the Normal Flight Envelope. The report then covers factual information concerning the LOC through to impact.

Consequently, they are very vague on possible alternative outcomes for which no validated data is available, and it is up to the airframer and regulator to establish procedures that can be used in a LOC situation where the envelope has been "extended".
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Old 7th Jul 2012, 22:17
  #134 (permalink)  
 
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Why no AOA indicators ? The report indicates the data is available buried several pages down, but it isn't an indicator you can fly to.

Seems pitch was being referenced as AOA when they were wildly different.

The airplane was being nervelessly flown in 'coffin corner' by the autopilot with good air data, to save fuel. Once the pitot inputs were lost, the autopilot threw the chore back to the humans, who were even less equipped to do the task without reliable speed data.

Yet the PF kept trying to keep the altitude that it was almost impossible to hand fly at. Why not a procedure requiring dropping down to a less demanding (altitude) in the flight envelope when the autopilot goes on strike. Screw saving fuel until the other problems are sorted out.

.
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Old 7th Jul 2012, 22:59
  #135 (permalink)  
 
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Kinda disappointed by PJ's reference to setting FD modes and such.

Fer chrissakes, attitude and power and an understanding of the aero for your jet should dictate what control inputs you make, and not the flight director or its modes.

Again, I do not advocate the crew reverting via a switch to "direct" law.

The final report makes a case for concern by the crew with overspeed. I can understand that. One thing that happens when the mach gets too high is aileron reversal, and this could have been a concern. Nevertheless, the report clearly mentions over and over the inapropriate application of back stick.

A shameless plug for the primitive FBW system and control laws I flew for 4 years - our AoA was related to the gee command. So at the max allowable AoA we could not command more than one steekeeng gee! The nose could not be commanded for a further rise, and the tail surfaces would be commanding for nose down. So we sat there with full back stick and 27 degrees AoA and one gee until we pushed forward on the stick. Falling like a rock, but we could command less than one gee and gain energy and the fight was still on.

Gotta go....
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Old 7th Jul 2012, 23:07
  #136 (permalink)  
 
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Originally Posted by PJ2 View Post
Well, there has been input, (by Owain Glyndwr) that recovery may have been possible at various altitudes. Owain indicates that a reasonable "unloading" of the wing/reduction in AoA could be done with a steadily-held 10deg ND and in fact lower down, (thicker air), the recovery would be slightly quicker.
Aerodynamically I could well imagine that recovery was possible until quite late in the sequence. Maybe even down to 10 kFt. After all it is a conventional tail airliner and they were not in a spin. So the Tail was in free airflow. With full ND elevator and maybe neutral or at least less extreme NU trim it is liekely that the Nose would have dropped sufficiently to at some point re- attach the airflow over the wing. Might have taken 30s sustained ND or even more but personally I don't share the pesssimism that it wasn't technically possible.

It is more the practical probability which I would consider exteremely low. At no time the crew appeared in a mental constitution to unambiguously diagnose what was going on and to act accordingly and sustain that action until it yields the results (which could have taken rather long and decided action, much much longer and decidedly than they seemed to be willing to pursue a scheme). It appeared they tried something and if it didn't yield within seconds they reverted the action.
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Old 8th Jul 2012, 00:12
  #137 (permalink)  
 
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@gums:

In my mind, PJ2 has always been one of the staunchest and unswerving advocates of attitude & power, flight path stabilization, and 'knowing' your aircraft, both aero & systems-wise.

It appears to me that he is only explaining how the system works & what they were dealing with. But I don't want to speak for someone else.

@ The stall:

I flew 3 T-tail air transport aircraft which did not 'deep stall' and one military conventional tail aircraft that did.

The bottom line on this recovery and associated techniques is that none were ever attempted because there was no recognition that they were ever required.

If the term 'deep stall' is not meaningful enough or does not fit the formal definition, or offensive to anyone, call it a 'pterodactyl' or a 'lemon drop'. That won't change it one bit.

Just don't call me late for dinner.
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Old 8th Jul 2012, 00:17
  #138 (permalink)  
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gums;

Well, if true, and the Report does spend some time on this, yes, it is disappointing that the pilots in this case actually "obeyed" the FDs, but quite frankly I have never heard of any pilot I know actually blindly following the flight directors and ignoring the instruments.

Guys I flew with, regularly turned the FDs off if they weren't following them - it's just something one does on the Airbus without even thinking about it, so drilled into Airbus pilots is this requirement.

Ever since the A320 accident at Madras, Airbus pilots have been made VERY aware that if the flight directors aren't going to be followed, turn them off, (the original problem concerning IDLE-OPEN DESCENT with one FD on has long since been fixed).

Now if you're following them, you're not going to turn them off, but if you're going to follow them you had better be damn certain in your own aviator's mind where these bars are taking YOUR airplane.

When a few first suggested that the PF might actually have followed the FD I dismissed it - no transport pilot, esp. an Airbus one, would blindly follow FDs without always questioning what the FD is leading one towards - the computers are high-speed idiots, nothing more. We regularly talked of "looking through" the FDs during momentary changes in flight dynamics and we'd wait for the FDs to catch up to the airplane while temporarily ignoring them. That just comes from a lot of hand-flying but you'll never get it from turning the knobs.

OK465 - thank you - you're quite correct - I'm just explaining the system.

It's an ordinary, very good FD that deserves the same respect and treatment any computer system does - "check six", "trust, but verify", hand-fly raw data - it works because it's an airplane and a beautiful one at that; it is not a computer platform or an iPlane.

Henra - we're on the same page - yes, it could have been recovered. No, I wouldn't have expected this crew to try given how cockpit discipline was conducted.

Last edited by Jetdriver; 8th Jul 2012 at 01:05.
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Old 8th Jul 2012, 00:44
  #139 (permalink)  
 
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Thanks, PJ, it's what I thot, but some newbies may not realize the fine points. Blindly following the FD's is not always recommended when the steam gauges are telling you that something is awry.

For OK, the jet was not in a "deep stall", but rather "deeply stalled". A nose down stick and maybe even power could have recovered the thing, given 35,000 friggin' feet to do so.

It comes down to realizing what the jet is doing and what you can do about it with the tools you are given.

The complicated reversion laws and pilots thinking they have this and that "protections" is not healthy, IMHO. Ya gotta have a baseline that you can count on without a manual switch to "direct" law, which I do not recommend unless you are Chuck Yeager. And then we have the THS that follows the pilot back stick to achieve the commanded gee, NOT THE AOA!!! So to recover, the pilot had to roll the THS trim down and also push forward on the stick in order to provide the nose down moment required. I was surprised that BEA discussed the longitudinal static stability. Considering that the jet control laws disregard AoA other than warnings and some limits in "normal law", would seem to me that we could look at that aspect a bit more.
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Old 8th Jul 2012, 01:04
  #140 (permalink)  
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gums;

What "de-confuses" the airplane is flying it like any other airplane. I don't think I was unusual in the way I thought about the A320/A330/A340...I was never "aware" that there were "protections"...it was flown like a DC8, or a Lockheed or a B767 - just never took anything for granted. It is astonishing that this should be permitted to change as it is so fundamental to staying alive and keeping others who are with you alive.

Demonstrating one's knowledge of the autoflight should be one of many exercises instead of the way the entire sim exercise is conducted. These days I suspect one risks drawing criticism if one insists on hand-flying some exercises. But the instructors have to sign the sheets saying such stuff was covered, so the sheets have to change.

Raw data, non-FD, manually-flown (including autothrust OFF), ILS and non-precision approaches ought to be regular exercises in recurrent sims.

The beancounters and even ops managers may resist that thinking but indications are, here in the Report and in the US particularly after Colgan, (as mentioned in the Report) that it is time to re-prioritize skills, teaching/training, standards and checking.

Last edited by Jetdriver; 8th Jul 2012 at 11:24.
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