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AF 447 Thread No. 9

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AF 447 Thread No. 9

Old 6th Jul 2012, 23:42
  #101 (permalink)  
 
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Wrong image in (E) version.

Figure 64 in Final (E) report is different to (F) version.

(F) version:

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Old 7th Jul 2012, 01:57
  #102 (permalink)  
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A33Zab;

Good catch. Figure 64 in the E version is from IR#3, p42.

Likely a transcription error. There are a number of other minor edits in the E version.
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Old 7th Jul 2012, 03:44
  #103 (permalink)  
 
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Meaningful displays in times of need

Thank you Tex.

You have nailed it.

I look at many of the panel displays and some of the military HUD presentations and wonder where the "de-clutter" switch is! When things go south I want to see a few things that are critical and not a lotta B.S. that doesn't contribute to recovering from a bad situation.

I was impressed that the report raised the issue of presenting AoA. That is sure to evoke many comments here. ya think?

Another thing that caught my eye was the reference to control law reversion to "2b". Good grief! 1a, 2c, 3a, and the beat goes on. No matter if you are Chuck Yeager or Sully or Gums, ya need to have a very clear reversion sequence on these FBW systems. Some of the reversion modes on the 'bus are related to max bank/pitch angles and such. But AoA limits ( aka "protections" for the masses) are not all that clear. Sully pointed out in an interview last few days that he would have liked to get another degree or two of pitch just before impact. Couldn't do it.

I am not in favor of a complete "manual" reversion aka "direct" without a clear and determined effort by the crew. I don't think that the AF447 crew would have used such an implementation, but maybe some others might if all their efforts failed to get the jet under control. In our system, we had the limits on AoA and gee to provide optimum energy in severe maneuvering. The AoA limit was not related to stall AoA. Nevertheless, full back stick provided the best normal gee and pitch rate that the jet could provide.

Back to the point that Tex pointed out.... Clear and relevant data on the presentations is essential. When not on Otto-pilot, then basic pitch and roll and such need to be primary. What in the hell was the crew doing with the flight directors in a vertical speed mode, or any other mode? If "x" degrees of pitch are in the boldface procedure, fine. But don't confuse the crew with extraneous flight director B.S.

Lastly, I have been unpleasantly surprised to learn that some jets like the 'bus fly so close to the edges of the envelope at 35 or 37K. I would expect this of some military platforms like the U-2 or SR-71 or the fabled Aurora, but not a commercial jet. Guess I was spoiled by a large margin of speed/mach and such.
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Old 7th Jul 2012, 05:58
  #104 (permalink)  
 
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BEA Webcast Notes

It looks like BEA had a short handout for the press and made frequent admonishments that "all the details are in the full report which you shall receive later". There was also a meeting with the families in the morning. One of the questioners is an experienced Airbus pilot who is working for the families who was not impressed by the report.

There was talk that the FD when present mostly led the crew in the wrong direction. The press questions on FD were all over the map because they don't have much clue what an FD does -- most certainly an FD does not give stall recovery directions. There may have been an indication that stall warning should either shut down the FD or present proper recovery attitude (there's something like an hour or more of dialog and I'm writing from memory).

The flight tests did not go beyond approach to stall. The presenters opined that recovery from the developed stall is out of the envelope and that recovery is highly doubtful, even with proper actions. i.e. certification does NOT require recovery from a developed stall.

There was mention of "lost indicated altitude" that I suspect was because the ADC needs airspeed to present corrected altitude and that there was an apparent initial loss of altitude that PF attempted to correct. Or was the altitude display lost -- perhaps a native French speaker can tell us just what words were used.

The question session I would really like to see is BEA answering questions from qualified pilots who have had time to read the report.
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Old 7th Jul 2012, 06:01
  #105 (permalink)  
 
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Originally Posted by DozyWannabe
Because I have done proofreading before, and I'm good at isolating details.
...
Hopefully this weekend I'll have a chance to give the report more than a skim.
And how do you isolate details as you gave the report only a skim ... ?
But if you know you're good at it, that's probably enough.
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Old 7th Jul 2012, 07:57
  #106 (permalink)  
 
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Originally Posted by RatherBeFlying
There was mention of "lost indicated altitude" that I suspect was because the ADC needs airspeed to present corrected altitude and that there was an apparent initial loss of altitude that PF attempted to correct. Or was the altitude display lost -- perhaps a native French speaker can tell us just what words were used.
The mention made was well for a loss of indicated altitude (under reading) and not a loss of altitude display.

So many questions on the FD during the presentation ...
So little answers ...
And so little in the report too ...

It has been central in the BEA work ... but they won't share the details.

BTW where is the FD/AP Vertical Mode Trace ... ???
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Old 7th Jul 2012, 08:51
  #107 (permalink)  
 
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What did Airbus do in between?

Posted before but to refresh the memory:

(not all related to AF447)

All Thales probes have been replaced per AD 2009-0195

Besides the probe replacement program, several hardware and software changes have been introduced:
  • BUSS (SW always available) - already available before AF447!
  • FMGEC: AP/FD not available at UAS condition. AD 2011-0199R1
  • FCPC: F/CTL ALT LAW (PROT LOST) ECAM MSG accompanied with reason.
  • FCDC: More rigid 'USE MAN PITCH TRIM' PFD message when autotrim not available.
  • FWC: **NAV IAS DISCREPANCY MSG When 2/more IAS are detected to be different.
  • Added AoA data filtering to improve SW detection in turbulent conditions.
  • AoA: Conical shaped ground base to prevent water ingression.
** Don't know if F-GZCP was equipped with this mod but the mod was available at that time. (BEA doesn't mention the presence of this message, suspect it was NOT available in F-GZCP)
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Old 7th Jul 2012, 09:56
  #108 (permalink)  
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My apologies if this has been covered in the previous 8 threads/thousands of posts, but can an AB person explain the two reported VS vertical modes in the report, 'VS+6000fpm+' and 'VS+1400fpm'?

My experience of FDs/A/Ps is that if the selected ALT is 350 and I am climbing above that I would expect a -ve VS demand to regain. Where did these two UP 'settings' come from? To what 'target' were the FD controllers working? Were these figures software/system induced or crew selected?

It seems as if the FDs, when 'valid', were reacting to the existing rates which is not the way I expect - ie 'Flight Followers' rather than 'Flight Directors'.
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Old 7th Jul 2012, 10:11
  #109 (permalink)  
 
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Hi BOAC,

It seems as if the FDs, when 'valid', were reacting to the existing rates which is not the way I expect - ie 'Flight Followers' rather than 'Flight Directors'.
Correct. This is probably the most confusing part about the FD logic. The FDs are withdrawn automatically during unreliable airspeeds and the FMA modes are lost. If two airspeeds erroneously agree, then the FDs will reappear with present HDG and instantaneous VS. In the confusion of the moment, it appears to me that this crew then followed these new FD modes.

See EASA Airworthiness Directives Publishing Tool and download easa_ad_2011_0199_R1.pdf (21 kb) for a full explanation.
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Old 7th Jul 2012, 10:12
  #110 (permalink)  
 
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A33Zab,

Two comments:
Originally Posted by EASA AD No : 2011-0199R1
Since that AD was issued, new FCPC software standards have been developed that will inhibit autopilot engagement under unreliable airspeed conditions.
Does it also inhibit reappearance of the FD?

The BUSS, if fitted, must not be used above FL250. The main reason for that is that the back-up stall warning threshold does not change with Mach number and the selected value of 8.6 degrees is too high above FL250.

Last edited by HazelNuts39; 7th Jul 2012 at 10:35. Reason: 8.6 value added
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Old 7th Jul 2012, 10:24
  #111 (permalink)  
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Thanks rrat - apart, then, from the obvious lack of flying ability of the crew and absent cockpit management skills, this system function may well be a major contributory cause of the accident.

Even that AD does not 'cut the mustard' for me - it refers primarily to A/P engagement and only a fleeting mention of the FDs.

"Further analyses have shown that, after such an event, if two airspeed
sources become similar while still erroneous, the flight guidance computers
will display the FD bars again, and enable the re-engagement of AP and
A/THR. However, in some cases, the AP orders may be inappropriate, such
as possible abrupt pitch command."

What about the FD 'orders'? Does the software mod direct the FMC to target selected altitude rather than any other convenient number?

Last edited by BOAC; 7th Jul 2012 at 10:30.
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Old 7th Jul 2012, 10:46
  #112 (permalink)  
 
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@HN39:

Does it also inhibit reappearance of the FD?
According company info it does:
---
The Flight Control Primary Computer (FCPC) has been modified by installing a new software standard; P11AM20A 2K2.
The only improvement introduced with this software update concerns the autopilot inhibition under unreliable airspeed condition.
When there are significant differences between all airspeed sources,
the flight controls revert to alternate law, the autopilot (AP) and AutoThrust (A/THR) automatically disconnect and the Flight Director (FD) bars are automatically removed


---

The BUSS, if fitted, must not be used above FL250. The reason for that is that the back-up stall warning threshold does not change with Mach number and the selected value is too high above FL250.
The FL250 threshold is explained in FCOM as:
---
Cases of unreliable speed situation caused by temporary contamination of the pitots with water or ice (typically above FL250), usually disappear after a few minutes.
The flight crew flies pitch/thrust and activates the BUSS only if the unreliable speed situation appears or remains below FL250.
This distinction (FL 250) ensures a good balance between crew workload and safety
(continued flight using the BUSS or temporary use of pitch/thrust tables).

---

But you are correct: the Backup Stall Warning values are fixed values for S/F config.
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Old 7th Jul 2012, 11:13
  #113 (permalink)  
 
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A33Zab,

IMHO the FCOM explains the reasoning behind the selection of 8.6 degrees. Once chosen, this value limits the usability of the BUSS to below FL250. Higher altitudes require lower values of the S/W threshold, which would have impaired the usefulness of the system at low altitude.

Last edited by HazelNuts39; 7th Jul 2012 at 11:48. Reason: clarification
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Old 7th Jul 2012, 11:23
  #114 (permalink)  
 
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@BOAC:

but can an AB person explain the two reported VS vertical modes in the report, 'VS+6000fpm+' and 'VS+1400fpm'?
I'll return later for more FD/FMGEC info. [job is calling]

For now:

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Old 7th Jul 2012, 11:32
  #115 (permalink)  
 
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Hi BOAC,
Does the software mod direct the FMC to target selected altitude rather than any other convenient number?
As far as I'm aware - No. It would have been necessary to reprogram the FDs with Open Descent etc. to reacquire the FL they had departed from.

The first line of the Memory items of the "Unreliable speed Indication / ADR Check Proc"
AP/FD .... Off
was never accomplished. It doesn't help to solve the problem when the FDs keep reappearing with erroneous guidance.
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Old 7th Jul 2012, 12:16
  #116 (permalink)  
 
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From the Final Report

At 2 h 10 min 05, the autopilot then the auto-thrust disconnected and the PF said
“I have the controls”. The aeroplane began to roll to the right and the PF made
a nose-up and left input. The stall warning triggered briefly twice in a row. The
recorded parameters showed a sharp fall from about 275 kt to 60 kt in the speed
displayed on the left primary flight display (PFD), then a few moments later in the
speed displayed on the integrated standby instrument system (ISIS). The flight
control law reconfigured from normal to alternate. The Flight Directors (FD) were
not disconnected by the crew, but the crossbars disappeared.
When the ASI came back, the bars reappeared and the AP would have been be available again.
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Old 7th Jul 2012, 13:55
  #117 (permalink)  
 
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I noted (from the report) a GPS altitude was available. Is there a procedure for using it in the face of erroneous airdata altitude ?

.
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Old 7th Jul 2012, 15:38
  #118 (permalink)  
 
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In the confusion of the moment, it appears to me that this crew then followed these new FD modes.
This one sentence sums up everything I dislike about the final report.

It seems to me that there are two areas of wide-spread agreement.

(1) The pilots were confused about what was happening to them.
(2) Despite this confusion they acted.

There is no widespread agreement as to why they acted the way they did.

Instead, the report describes an olio of pet agendas including confusing technology, psychological error, training issues, etc. To mix a metaphor, in response to this cloud of unknown gnats BEA loads its formidable cannon of recommendations with grapeshot, praying that somehow one of those little lead balls will hit the little gnat actually responsible.

Complex systems fail in complex ways but that's no excuse for making hash.
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Old 7th Jul 2012, 15:49
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There is no widespread agreement as to why they acted the way they did.
Probably never will be...

But if "turning over all the rocks" results in finding something that can be potentially problematical the 'next time', whether or not it was only a 'possible' factor in this case, it deserves attention.

One gnat at a time...

Last edited by OK465; 7th Jul 2012 at 15:51. Reason: complex sentence structure
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Old 7th Jul 2012, 15:58
  #120 (permalink)  
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BOAC, OK465, RRR, A33Zab;

I believe the reason for ensuring the disengagment of the FDs during the UAS drill is based upon the default longitudinal AP/FD engagement mode of V/S or FPA. The removal and reappearance of the FDs would logically be the same as pushing the FD switch OFF then back ON again. 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).

The essential aspect of the UAS drill is flight path stabilization via pitch & power. The FDs could non-intuitively counter that response depending upon conditions at re-engagement.

Mountain Bear;
Complex systems fail in complex ways but that's no excuse for making hash.
Ensuring a stable flight path would have avoided the accident.

While the slavishly-following-the-FD theory makes sense, as posited by some even before the report was issued, it makes no sense to many who have flown bread-and-butter transports that could actually be stalled any time and who now fly this or any aircraft with complex automation; it's a tool in the kit and nothing more - still is. "Looking through" the directors to the raw data on the instruments and combining that with one's understanding of the energy and stability of the machine was always a valued approach but not anymore.

The ability to understand and even have some depth of intuition about flight in heavy transports in the operational environment is the larger story here.

Last edited by PJ2; 7th Jul 2012 at 16:55.
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