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AF 447 Thread No. 12

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AF 447 Thread No. 12

Old 8th Dec 2014, 14:12
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@ Lonewolf 50 :


French DGAC has published an 18 page agenda regarding BEA recommendations and for involved airline. It's a slow process.. document is in french, I think that's unpublishable..


May be our friend Winnerhofer could make us some kind of synthesis as he should have it too.
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Old 8th Dec 2014, 22:57
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BEA Recommendations

BEA Final Report:

When airspeeds are below 60 kt, the stall warning is no longer available, even though it may be beneficial for it to be available at all times.
Consequently, the BEA recommends that:
EASA require a review of the conditions for the functioning of the stall warning in flight when speed measurements are very low. [Recommendation FRAN-2012-051]
With BUSS activated the SW complies to this recommendation.
this option is still not installed on AF fleet (except on A380 because it is standard equipment)
The BUSS option was available BEFORE AF447.



It seems that requiring an action from the crew to re-engage this automatic system would, on the one hand, lead to a consistency with the autopilot and the autothrust, and on the other hand stimulate a check on the modes and the consistency of the commands presented at the time of the re-engagement.
Consequently, the BEA recommends that:
EASA require a review of the re-display and reconnection logic of the flight directors after their disappearance, in particular to review the conditions in which an action by the crew would be necessary to re-engage them; [Recommendation FRAN-2012-047]
FD will not re-display without crew intervention.
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Old 9th Dec 2014, 14:51
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Winnerhofer,

You seem to be implying that had AF447 been equipped with BUSS, the accident could have been avoided. An old posting friend of mine jogged my memory regarding the BUSS system which was discussed in previous AF 447 Threads. Having it on AF447 may not have made a difference. First of all, the crew had to recognize the problem was UAS, it seemed that they did recognize the loss of speed, i.e., "We've lost the speeds", but then the AF447 crew never performed the memory UAS/ADR check procedure nor did they recognize what alternate law they were in. The BUSS system simply replaces the pitch and thrust tables which would have been part of the trouble shooting and isolation procedure after UAS recognition and aircraft stabilization, if stabilization corrections were required. The BUSS system becomes active only after all ADRs are shut off. By shutting off all three ADRs with the BUSS, the stall warning protection remains active. Without the BUSS, shutting off 2 ADRs, the stall warning protection remains active. However, if the remaining ADR is affected as in the case with multiple pitot tube icing, the data generated may be inaccurate and flying the pitch and thrust table settings would be the only safe thing to do. In earlier thread discussions regarding the BUSS, my posting friend pointed out that he recalled the BUSS isn't available in altitudes above 25K and once it is enabled, the flight laws can't be change from the direct law it reverts to (a technical discussion item?).

UAS can be a difficult problem to recognize as it can be caused by multiple scenarios which lead to it. IMHO, rapid UAS recognition training is the key ingredient to enhance the crew's ability to quickly detect a UAS situation and then correctly handle it. While the BUSS system is helpful, so were the pitch and thrust tables that were never used…

Last edited by Turbine D; 9th Dec 2014 at 17:05. Reason: Content correction and addition
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Old 9th Dec 2014, 18:45
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@ Turbine D.

You made some wrong assumptions regarding BUSS.

BUSS is more than a replacement of pitch/thrust tables.
BUSS replaces the speed scale and consists of GREEN, AMBER and RED areas based upon AoA and S/F CONFIG, goal is to fly the GREEN.
next to the scale is a pointer which represents the AoA.
The scale range is 10 AoA CLEAN and 20 in any other CONFIG.

BUSS is not inhibited above FL250 but since frozen pitots is only a temporary issue the FL250 restriction is added to the UAS/ADR CHECK procedure.
Initially there was NO FL restriction at all, however switching off 3 ADRs to activate the BUSS comes with increased workload (FMS, Cabin Press and ALTERNATE law).

The law reversion is to ALTERNATE and NOT to DIRECT LAW.

Having it on AF447 may not have made a difference.
You may be right but it could also have made a different outcome.

Last edited by A33Zab; 9th Dec 2014 at 19:08.
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Old 9th Dec 2014, 19:35
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UAS can be a difficult problem to recognize as it can be caused by multiple scenarios which lead to it.

Perhaps .. but this highlights one of the greybeards' concerns in these days of super-automation.

In days past, regardless of widgets, bells and whistles, the flying pilot was always aware of the underlying pitch and thrust settings in relation to what the aeroplane was required to be doing at the time .. ie looking throught the FD to the ball.

If the picture didn't quite gel, there was something awry .. just what that might have been may not have been quite obvious at the time .. but the immediate problem of control was addressed by a constant monitoring of pitch and thrust aligned with comparison between attitude systems to identify what was telling the truth.

If need be the pilot would discount the bells and whistles and go back to DC3 techniques. Not elegant, perhaps, but generally functional.

Progress can have its downside ..
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Old 9th Dec 2014, 20:49
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A33Zab,

Thanks for your clarifications about the BUSS and the law reversion.
BUSS is more than a replacement of pitch/thrust tables.
I just quoted directly from an Airbus safety article and tried to keep it simple. The article statement read:
In order to decrease the crew workload in case of unreliable speed, Airbus has developed the Back-Up Speed Scale (BUSS) that replaces the pitch and thrust tables.
The article was written by Airbus' Flight Operations Engineer and gives some other details such as AOA information being provided through the IRs and not through the ADRs which enables selection of all ADRs off without the loss of stall warning protection. Then, if and when the crew does shut off all 3 ADRs, the Back-Up Speed Scale replaces the PFD speed scale on both PFDs. Also, GPS altitude replaces the Altitude Scale on both PDFs. So then, keeping the pointer in the green (out of the amber or red) is the goal to be achieved by adjusting thrust and pitch thereby keeping above stall speed and below maximum structural speed. The BUSS speed scale was shown with the statement, "Fly the green."
The author concluded with this statement: "In case of any doubt, the pilot should apply the pitch/thrust memory items and then refer to the QRH to safely fly the aircraft and to positively determine the faulty source or sources before eliminating it or them."
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Old 10th Dec 2014, 13:12
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With all ADRs off, the stall warning threshold is not adjusted for Mach. Therefore the green band will not keep the airplane out of natural stall warning (buffet) above FL250. Airbus does not recommend the use of BUSS above FL250.
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Old 12th Dec 2014, 20:48
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Animation of history of flight [AF 447] based on CVR/FDR

Released today by BEA:
Animation of history of flight [AF 447] based on CVR/FDR data, (12/12/2014):

http://www.bea.aero/fr/enquetes/vol....ent.du.vol.mp4

(This is a 204MB MP4 video streaming download that can be played with the VLC player)
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Old 13th Dec 2014, 00:21
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Originally Posted by Winnerhofer
Yes and AF still don't want it on their existing fleet bar A388 because they spend on marketing rather than safety
On what evidence do you base this assertion?

(And how does a decades-old issue regarding throttle control on Audi cars have anything to do with AF447?)

Originally Posted by A33Zab
BUSS is not inhibited above FL250
Right, but as Gysbreght says (and as I'm sure you already know), its use is not recommended above FL250 because the constants used for calculating stall regime become less accurate above that altitude. This is not restricted to the BUSS system, but is likely to be similar on other builders' systems (including Boeing's).

Last edited by DozyWannabe; 13th Dec 2014 at 00:43.
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Old 13th Dec 2014, 10:26
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If someone prefers Youtube version of official BEA animation/simulation released yesterday:

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Old 13th Dec 2014, 17:43
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Winnerhofer,
To do with Thales Pitots...
Glad you clarified that, I would have never guessed.
BEA Vid
Instant replay - See Post #1009 by 4listair
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Old 13th Dec 2014, 22:10
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Thanks for the YouTube presentation.

But why on earth didn't they include :
  1. The live audio for the warnings and cautions ?
  2. The actual transcript of the CVR ?
  3. The THS movement and position ???
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Old 14th Dec 2014, 00:06
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4 - The RUDDER movement and position ?
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Old 15th Dec 2014, 02:28
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As a tactical jet type pilot, the flopping around of the aircraft depicted in the animation instruments is sufficient to identify a stall. I've seen that type of movement before many times.

Too bad none of the guys in AF447's cockpit had ever full stalled and then recovered a jet.

There have to be a number of swept wing former military trainers that could be made available to teach the subject of jet stalls to today's overprotected, computer swaddled, crop of pilots.

I doubt the airlines will fund such training voluntarily. They would have to be directed to by the regulators.
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Old 15th Dec 2014, 12:22
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But you have to remember how the manufacturer had initially pretented to have eliminated the stall ...
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Old 16th Dec 2014, 02:08
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The stall warning system shuts down at slower airspeeds. Each time they did the correct move, adding power and/or decreasing AOA, the airspeed would increase and the stall warnings would commence again. Thus , they believed they were doing something to lead to a stall, and they reversed whatever they had done.

If the stall warning system was designed not to shut off at very low airspeeds when the plane was not in the landing config, they might have clearly recognized that they were in a stall.
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Old 16th Dec 2014, 03:04
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Stall

I don't buy the argument about blaming the accident on the SW system. The crew ignored it more than 50 times in a row. Why would they suddenly start taking heed of it? And any pilot knows that pulling your nose up will only exacerbate a stall.

I doubt anyone envisaged a pilot pulling up so far into a stall that the airspeeds would make the SW system unreliable. The only way in which I can fault the design of the aircraft in this accident is that it didn't force the nose down in response to the repeated attempts by the co-pilot to pull up. That could have possibly prevented the accident. But also opens a whole new can of worms at the same time.
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Old 16th Dec 2014, 05:24
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RobertS975
If the stall warning system was designed not to shut off at very low airspeeds when the plane was not in the landing config, they might have clearly recognized that they were in a stall.
Not sure as Dozy will answer you that for almost 50 second (at the beginning of the event) the stall warning alarm was active and sounding and the pilot continued to pull on the stick with the result of put the aircraft in a stall
You must find better
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Old 16th Dec 2014, 07:45
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If the stall warning system was designed not to shut off at very low airspeeds....they might have clearly recognized that they were in a stall.
It certainly may have helped. If you look at the BEA animation posted earlier, none of the pilots seem to have recognised the Altitude Alert "C - Chord " was sounding continuously. It was only interrupted by "Stall Stall" right up until impact. No one attempted to cancel the noise.

That shows how ineffective a constant aural warning becomes. When work load is high, your brain filters out back ground noises and they get ignored. The stall warning needs to have another stimulus, BEA recommended a visual clue. I wish they had gone further and insisted on a hand vibrator through the side sticks as well.
The sound warning alone was ignored in this case, and was completely ineffective.

Last edited by rudderrudderrat; 16th Dec 2014 at 08:43. Reason: typos
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Old 16th Dec 2014, 09:18
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I wish they had gone further and insisted on a hand vibrator through the side sticks as well.
So the Airbus doesn't have the equivalent of a stick shaker? How did they get away with that?!
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