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AF 447 Thread No. 12

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AF 447 Thread No. 12

Old 16th Dec 2014, 13:50
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Originally Posted by Qantas_A380
Why would they suddenly start taking heed of it?
Because that continuous stall warning period ceased, but unfortunately came back when the left seater applied the most wanted procedure ... which made him quit his stick pushing and confirmed his doubt on the overall FCS integrity.

And any pilot knows that pulling your nose up will only exacerbate a stall.
But the stall warning came back precisely when finally the left seater was pushing the nose down ...

I doubt anyone envisaged a pilot pulling up so far into a stall that the airspeeds would make the SW system unreliable.
The stall warning system behaved as by design but not as by regulation ...

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.
AUTO THS
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Old 16th Dec 2014, 15:29
  #842 (permalink)  
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I wish they had gone further and insisted on a hand vibrator through the side sticks as well.
- I wish they had adopted my boxing glove system....
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Old 17th Dec 2014, 01:48
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In France Regulators, Airlines, Airbus are connected and not independant
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Old 17th Dec 2014, 05:18
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We keep going round and round in this thread but I cannot agree that this could have been prevented by this crew who were dealing with a threat they were ill equipped to handle. When it happened they did not know the unreliable air speed procedure, they did not know stall recognition and recovery procedure at high altitude and there was no way they were going to discover by accident. UAR procedure is conducted with attitude and power and this crew was neither hearing any warnings nor looking at PFD. Their actions were as if they were trying to recover blind folded. Why they were so incompetent is another matter. Their airline training procedure for this situation, their performance assessment during that and recurrent training will have something to say.

Last edited by vilas; 17th Dec 2014 at 05:41.
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Old 17th Dec 2014, 22:09
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There is a lot of cultural baggage behind that reluctance
I take it you are perhaps referring to something along the lines of never ever criticising someone at their place of work....

As an expat living in France I couldn't possibly comment any further.....
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Old 17th Dec 2014, 22:21
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Originally Posted by RobertS975
The stall warning system shuts down at slower airspeeds.
That's an inaccurate statement. The SW system is active at all times - but it can't function without valid data from the AoA vanes, and the AoA vanes are only certified to operate above 60kts IAS. The ADRs treat AoA data as invalid below that IAS, but the knock-on effect on the SW system was likely unforeseen.

As QA380 said:
Originally Posted by Qantas_A380
I doubt anyone envisaged a pilot pulling up so far into a stall that the airspeeds would make the SW system unreliable.
Originally Posted by rudderrudderrat
I wish they had gone further and insisted on a hand vibrator through the side sticks as well.
It might have helped, but the truth is that the tactile shaker has also been ignored or disregarded on a significant number of occasions in the past.

Originally Posted by Winnerhofer
So does the B77W do it better?
Different scenario entirely (failed IR accelerometers in the ADIRU - air data was OK). Indicated airspeed never dropped below 158kts. It's been pointed out repeatedly on earlier threads that other manufacturers have been very quiet on the subject of what invalid AoA data will do to their SW systems, which I suspect indicates that the result (SW cessation) would be similar on other types.

Originally Posted by roulishollandais
In France Regulators, Airlines, Airbus are connected and not independant
Rubbish. The French state currently holds less than a 12% stake in Airbus Group (formerly EADS): Airbus Group - Wikipedia, the free encyclopedia
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Old 17th Dec 2014, 23:12
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I don't know - in what scenario do you mean?
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Old 17th Dec 2014, 23:34
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Right, but it's not really particularly relevant - all it means is that for brief periods, both the AoA and IAS data were effectively NCD. It wouldn't make much difference.
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Old 18th Dec 2014, 00:10
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DozyWannabe Right, but it's not really particularly relevant - all it means is that for brief periods, both the AoA and IAS data were effectively NCD. It wouldn't make much difference.
IIRC it shut off the stall warning horn until the measurements recovered.

Shutting off the stall warning cannot have helped the pilots understanding of the situation.

IIRC the stall warning came back on again just after somebody had tried nose-down, a combination of events which could be considered positively misleading.
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Old 18th Dec 2014, 00:51
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Originally Posted by Winnerhofer
NCD? What is it?
No Computed Data - i.e. the value is invalid and cannot be used for further processing.

Originally Posted by Peter H
IIRC it shut off the stall warning horn until the measurements recovered.
That was a secondary consequence (or "side effect" in engineering-speak) of the systems design as a whole. The SW ceased because it was no longer receiving valid data from upstream - there was no design intent to "shut off" the SW directly.

Shutting off the stall warning cannot have helped the pilots understanding of the situation.
Undoubtedly.

IIRC the stall warning came back on again just after somebody had tried nose-down, a combination of events which could be considered positively misleading.
Yes - but we've got to remember that what we're talking about with AF447 is a scenario which would have previously been considered a massive outlier on the probability curve. Namely that the crew would deliberately put the aircraft into a stall condition, hold it there through almost a minute of stall warning and continue to pull up until the airflow over the sensors rendered the information nonsensical.

We've been over this many times in earlier threads, and the fact is that if you latch stall warning for one scenario, it runs the risk of giving false information in several other scenarios. It's a very difficult system to make completely failsafe across the board - and as I repeated above, the silence from other airframers does tend to suggest that their systems would have behaved in a similar manner.

(And as an aside - a pilot with any basic knowledge of aerodynamics should be able to work out that a SW triggered by a nose-down input means something hinky is going on...)
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Old 18th Dec 2014, 15:58
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Dozy
(And as an aside - a pilot with any basic knowledge of aerodynamics should be able to work out that a SW triggered by a nose-down input means something hinky is going on...)
No basic knowledge of aerodynamics ?
So what the hell does these 3 pilots in the pointy end of a A330 ?
Who (allow) permit that ?
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Old 18th Dec 2014, 19:01
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Hello. Question from a layperson following the discussion: The BEA report states that 61 sec after the AP disconnect all three pitot probes were working again. Would it have been possible for the pilots at this point to return to Normal Law and possibly activate the AP again? Or would have the stall (near stall?) situation prevented that?
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Old 18th Dec 2014, 19:47
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@jcj - I didn't say the crew had no basic knowledge of aerodynamics, I just stated that a pilot with a basic knowledge of aerodynamics should (given sufficient time to think) be able to work out that something was wrong if the SW sounded in response to putting the nose down (and consequently *reducing* AoA).

What we've discussed several times in these threads and many others is that while all pilots must have a grounding in the basics of aerodynamics (principles of flight, thrust, lift, AoA, stall etc.) in order to get their PPL - it seems that once in the ATPL world, recurrent training does not seem to refresh any of that knowledge periodically.

Originally Posted by Winnerhofer
Once the plane is in ALT, it remains in ALT until overseen by maintenance.
Not exactly - Alternate Law is only "latched" (as in cannot revert to Normal) if the divergent conditions last for more than 10 seconds. A transient condition of less than 10 seconds will allow for a return to Normal Law in flight.

In this case the pitot tubes were blocked for too long and Alt2B was latched.
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Old 18th Dec 2014, 20:45
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SW

I must say I agree with Dozy in regards to the stall warning shutting off without valid data. Allowing it to operate with invalid data may indeed see more false stall warning alarms and pilots may begin to distrust the system.

It was unfortunate that the SW activated in response to ND input but basic airmanship must come into play here and identify that a nose down input cannot exacerbate a stall.

Does anyone know how SW systems operate on other aircraft without valid data?
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Old 18th Dec 2014, 23:30
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There are no "land phases" to "bar".

Alternate Law transitions to Direct when landing gear is selected down - the only significant difference (other than minor changes in handling characteristics) between that and normal operation is the possible need for manual pitch trim correction. And as such the "USE MAN PITCH TRIM" message is displayed on the PFD.

All in all it should be fairly transparent with no "gotchas".

Last edited by DozyWannabe; 19th Dec 2014 at 00:05.
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Old 19th Dec 2014, 05:31
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Originally Posted by Dozy
Alternate Law transitions to Direct when landing gear is selected down - the only significant difference (other than minor changes in handling characteristics) between that and normal operation is the possible need for manual pitch trim correction. And as such the "USE MAN PITCH TRIM" message is displayed on the PFD.
Rubbish too.
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Old 19th Dec 2014, 07:01
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Alternate Law Landing A330

Alternate law transitioning to Direct at gear down is an A320 not A330

Alternate law pitch control is similar to normal law. Alternate law has maneuver protection, automatic pitch trim, and ground and landing modes identical to normal law. Therefore, at 100 ft RA pitch control enters landing mode, which is close to direct law - but not exactly.

Flare mode affects only pitch and provides a direct stick-to-elevator relationship. Automatic pitch trim is disabled, but manual pitch trim is available if needed. Therefore the airplane exhibits its natural aerodynamic positive speed stability (that is, it tends to pitch down if slowed below the trimmed airspeed).
The Flare mode is blended in from Flight mode over a period of two seconds when descending below 100 feet radio altitude.
At 50 feet, a slight pitch down elevator order is applied. The purpose is to generate a more natural feel in the flare where the pilot has to move the sidestick aft to achieve a progressive flare and allow the nose to derotate after touchdown.
In contrast, if the flight-mode pitch law were to remain in effect, the sidestick would have to be neutralized once the flare attitude was reached and then after touchdown moved forward to lower the nose before the tail became aerodynamically ineffective.
Airbus has described Flare mode as “a smoother Direct law” as it has some damping provided by load factor and pitch rate feedbacks. High angle of attack protection and bank angle protection are both provided in the flare mode, though neither component is available in the actual Direct law. Pitch attitude, load factor, and high speed protection, however, are not provided.
In cases where both radio altimeters are inoperative, the normal trigger point for the Flare mode to engage cannot be determined, so Flare mode engages when both the autopilot is off and the landing gear is down. In that event, alpha floor (an autothrust function) also remains available, though it is normally disabled at 100 feet RA.
Upon touchdown, Ground mode blends in over a two second period for pitch, and the roll mode is blended in within two seconds of being on the ground and the pitch attitude decreasing below 2.5°.
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Old 19th Dec 2014, 13:45
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Originally Posted by Bpalmer
Alternate law transitioning to Direct at gear down is an A320 not A330
Correct - I was having trouble finding hard data on the A330/340, so went with this A320 document: http://www.737ng.co.uk/a320training.pdf

in the interim.

(Page 15 of the PDF, Page 13 : "Normal Procedures") of the document.
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Old 19th Dec 2014, 16:27
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quoting Herr Winnerhofer, post 999

Yes and AF still don't want it on their existing fleet bar A388 because they spend on marketing rather than safety so you see that the BEA's recommendation to make BUSS standard is not implemented just as their long list which has invisibly fallen by the wayside.
Incredibly, none of AF's pilots even whispered the issue of BUSS so it really takes two to tango.



Definitely not about AF A380 BUSS option..you should learn better tango.


Just from insider old chap, A 380 driver: AF 380 have been BUSS equiped and from the beginning of deliveries.


PS: ah nos bons vieux MD avec leurs sièges en cuir. Cheers.

Last edited by VNAV PATH; 19th Dec 2014 at 16:33. Reason: better orthograph
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Old 19th Dec 2014, 18:14
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@VNAV:

A380(& A350) comes with BUSS standard, there is NO option to leave it out.
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