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AF 447 Thread no. 4

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AF 447 Thread no. 4

Old 24th Jun 2011, 23:55
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Originally Posted by Old Carthusian
I realise that some of us don't really want to go in this direction (I am a pilot too but not on big jets) but to understand this accident I would suggest it is necessary to leave no stone unturned no matter how painful it is. Some have already shown this aversion to commenting on the pilots and I have to regretfully submit that this is not the right approach.
I can't speak for others. I have, for myself, figured that the pilots did some things which appear to be disastrously wrong. Now, they either both had a really bad hangover or other form of really bad day or something led them to commit errors all the while thinking they were the correct thing to do.

The former case is unprovable. We can look at other issues to resolve the situation. Can we answer the "why" questions for "entering the storm", "pulling up on the stick in response to disconnects", "continuing the same errors after the second stall warning", and others?

It looks to me like a training error led to the pull ups, especially after the plane spuriously (with perhaps no accurate remedy possible) dropped the stall warnings when the measurable air speeds dropped to or below 60 knots. With that revised AirBus stall training syllabus I'm inclined to look to the training issue as the most serious one other than the pitot probes, of course.

But, that's just my hypothesis. There could be a real wiring problem, as unlikely as I see it, involved to compound the problems. There could be other problems that could have lead to the stall and led to it not being diagnosed in time. So that's what we're all discussing.
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Old 25th Jun 2011, 00:58
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No pilot I know would pull full up at altitude because of loss of airspeed. We fly pitch and power for altitude and weight. Never would we pull up in a steep climb at that altitude. We have a checklist for that. Too bad the captain went back for rest when it happened. He could have handled it properly in my opinion. I only did one of those long flights to Sao Paulo and back and I didn't like leaving the cockpit to two FO's even though I trusted them. I never did it again. All of our junior FO's had at least 3 times the experience of the PF in Air France. Probably 100 times more hands on no autopilot flying.
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Old 25th Jun 2011, 03:22
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I hope this Wall Street Journal article is not old news. Seems like AF447 may have been one of the motivating reasons.
Major Changes Building in Commercial-Pilot Training - WSJ.com (a truncated teaser)
They are talking about actual flying training! Not that simulator stuff. The kind of training where improper performance will create an immediate and visible impression on the psyche.
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Old 25th Jun 2011, 04:28
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Not seeing the wood for the trees.

A major part of this thread has been and still is (very appropriately and usefully) along the lines of looking at the bark of one tree using a variety of microscopes. I would like to step back for a moment and try to look at the wood. Bear with me for a moment.

A good deal of the credit for eventually finding AF447 must go to the Russians who pointed out that in nine fatal LOC cases they had looked at of a/c getting into trouble at high altitudes, eight had crashed within 10 miles of the start of the event. The images below from the Metron report list the cases and show the distribution of distances.




The a/c involved were an A-310, a Tu-154B, two Tu-154Ms, two B737s, an IL-18V, an ATR 72, a MD-82, and if we add AF447, an A-330-200.
One case involved icing, and the Silk Air case may have involved something unusual.

In six cases the LOC started at over 30,000 ft above the crash site, and in eight cases at over 20,000 ft above the crash site, i.e. with plenty of altitude to execute a recovery.

So here we have nine out of ten fatal LOC cases involving a/c manufacturers from different countries, flown by crews from different airlines, regulated by different government authorities, with crews trained under different systems, and using different technologies, some FBW, some not, but all but one of which crashed within ten miles of the start of the incident.

To me as a distant observer there is more than a hint of human factors, or human/machine interface factors, at work here. These data do not prove anything, but do hint (to me) that these (very, very, rare) accidents do happen whether the technology is FBW or not, i.e. human factors or human/machine factors were likely to be important (or dominant) causal factors in the outcome independent of technology, training, nationality, government regulation, or ………

And now back to the microscopes.
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Old 25th Jun 2011, 04:29
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Cool

Hi,

Before new airline pilots receive their licenses or get behind the controls to fly passengers, according to the recommendations, they should receive instruction in small, aerobatic aircraft about how ...
I suggest this woman as chief instructor:
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Old 25th Jun 2011, 06:25
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The aircraft, still trimmed at 2.2deg nose-up pitched up to reach 29deg and the speed had decreased to 145 knots. The captain meanwhile reduced thrust on the no. 1 engine to idle and cut off the hydraulic system in accordance with the flight test order. Immediately after it activated, the autopilot switched to altitude acquisition mode (altitude had been set at 2000 feet on the previous flight phase). This caused the pitch attitude to increase to 32deg in an attempt to reach 2000 feet. The speed decreased further to 100 knots (minimum control speed=118 kts).
ASN Aircraft accident Airbus A330-321 F-WWKH Toulouse-Blagnac Airport (TLS)

Even if this has little or nothing to do with AF447, it shows that also the top guys (AB test pilots) didn't have a clear picture about the situation (alt acquisition mode/versus protections).
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Old 25th Jun 2011, 09:02
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BOAC - Apologies for the slow reply. Details of other aircraft deviating round the weather front can be found in already released BEA reports and in various posts in the threads on this subject. I am sure that if you look you will come across them.

Smilin Ed - What you are referencing are the inputs into the interface. The human factors, the reasons or motivations for the inputs are not covered by aircraft designers. However, as these govern the inputs into the interface they are very important.
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Old 25th Jun 2011, 09:37
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@PickyPerkins

Worth noting that AF447 is an outlier on that table in terms of full incident duration ~4mins 23 seconds which equates to 8,000 ft/min average vertical speed.
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Old 25th Jun 2011, 11:41
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Originally Posted by OC
BOAC - Apologies for the slow reply. Details of other aircraft deviating round the weather front can be found in already released BEA reports and in various posts in the threads on this subject. I am sure that if you look you will come across them.
- is it perhaps that you have missed the 12 deg deviation of AF447 in the report? As far as I know there is no evidence that they 'flew into a CB'.

Last edited by BOAC; 25th Jun 2011 at 12:17.
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Old 25th Jun 2011, 13:33
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I agree, nowhere is there any evidence they flew into a CB. All we know is evidence that the pitot tubes froze up causing unreliable airspeed. Previous similar freeze ups have occured with the A330 with several airlines without flying into CB's.
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Old 25th Jun 2011, 13:54
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To save me hours of searching - can someone quicklink to the report of the 'zoom climb' ?LH 340? over the Atlantic please? I think the analysis of why that beast lept for the heavens would be useful.
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Old 25th Jun 2011, 14:07
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BOAC...Air Accidents Investigation: Airbus A330 C-GGWD and Airbus A340 TC-JDN

Read it carefully. I doubt if there is a relationship between the two behaviours of the aircraft but take a look for yourself and see what you think. The report focuses on a TCAS and AIRPROX event and I don't think does a credible job of explaining the pitch up.

The summary of the behaviour of the A340 in the "zoom-climb" claims that in the overspeed and turbulence, that the AFS reverted to the Alpha Protection Law. From my research, that was changed before this event occurred to inhibit the AoA Protection Law above M0.53. The other frustrating aspect is, the recorder data that is included with the report does not have AoA...the very parameter claimed to have caused the triggering of the AoA Prot Law and the cause of the zoom-climb.

Anyway...these things are complicated. Maybe I'm mis-reading it all.
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Old 25th Jun 2011, 14:49
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Interesting, PJ (many thanks for the link). I disagree (from a position of ignorance on the AB system!) with your 'doubt' of a 'relationship' - ignoring the trigger for a/p dropout, we appear to have a similar manouevre induced by the FCS and not the crew, resulting a (co-incidental) 'arrival' at FL380 after a 6000fpm zoom during which the IAS decayed below Vls. OK, I'm easily swayed by these things, but???????

I do not understand why the alpha reached 'alpha-prot' all on its own? It then goes on to say that if the sidestick is left untouched in pitch, alpha remains at alpha-prot, and that application of full back stick would take it to alpha-max and that a determined nose-down input is required to stop this. So, this a/c,all on its own, raised the nose to alpha-prot and climbed - with no crew action to cause it. The report goes on

"For 18 seconds after the autopilot disengaged the aircraft remained within 200 feet altitude of FL 360 but once AoA law was invoked at 14:21:50 hrs, the aircraft’s attitude began to pitch nose-up. The pitchup trend continued for 17 seconds reaching a peak of 15° nose-up shortly before the first nose-down sidestick command was applied. Throughout this phase the aircraft climbed rapidly (reaching a peak rate of about 6,000 ft/min) due to the increase in lift created by the flight control system’s capture of alpha prot. The aircraft reached its apogee at FL 384 at 14:22:28 hrs where the airspeed had decayed to 205 KIAS and 0.67 Mach even though full thrust had been applied."

I then am told that there is no indication in this system to the crew that this 'law' has been invoked? I am struggling to see, through my ignorant eyes, why this is not relevant to 447? I know, different type and 'history', but is there not an Occams Razor lurking here?
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Old 25th Jun 2011, 15:17
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Originally Posted by BOAC
... I am struggling to see, through my ignorant eyes, why this is not relevant to 447? I know, different type and 'history', but is there not an Occams Razor lurking here?
Note this report was discussed on these forums as soon as the crash site located - the 'zoom-climb' to loose speed and stall from height being the simplest explanation Mr Occam could suggest. But clear air turbulence, daytime, 4 engines ... no Unreliable Airspeeds or Alternate 2 law - so very different protections active. Trying to match pilot inputs and the resulting elevator, Stab. and engine speeds to the resulting flightpath from the low res FDR plots in this report is still quite a challenge - what sense and scale is on the 'SS1 PT'? Compare/contrast the higher quality better labelled plots in the QF72 first interim report Investigation: AO-2008-070 - In-flight upset, VH-QPA, Airbus A330-303, 154 km west of Learmonth, Western Australia, 7 October 2008 , which is relevant with respect to the dynamic response of an A330 at FL370 but control system glitches not believed to be directly related to AF447?

Last edited by sensor_validation; 25th Jun 2011 at 15:36.
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Old 25th Jun 2011, 16:00
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There are at least 5 computer systems monitoring airspeed: 2 FMGECs and 3 FCPCs (a weird architecture for me but what do I know?).

The previous 2 or 3 days discussions suggested the following possible sequence of events (of course open to discussion):

Pitot 1 tip freezes. ADR1 output indicates rapidly decreasing airspeed/Mach.

FCPCs and the AFS part of FMGECs detect the discrepancy and launch monitoring functions:

AFSs quickly reject ADR1 (tolerance threshold = 20 kt for 0.45 s) and uses remaining ADRs

FCPCs would reject ADR1 if its error relative to median CAS was still above 16 kt after 10 seconds. In the meantime, having detected the median CAS value decreased more than 30 kt in 1 second they launch the “median CAS monitoring function”:

• Master FCPC (FCPC1) broadcasts it intends to change the flight control law from normal to ALT2.

• Master FMGEC/AFS receives the ALT2 request from FCPC1, disengages AP and A/THR then acknowledges the message.

• Receiving acknowledgment that AP and A/THR are off, FCPC 1 activates ALT2 law and notifies other FCPCs.

• All FCPCs start computing flight control commands according to ALT2 law, using limited pitch rate feedback and gains for an initial period of 10 seconds. “F/CTL ALT LAW” is displayed on the ECAM. At this stage, ALT2 law is temporary. If at the end of the monitoring period the median CAS value is found less than the value registered at the start of the period minus 50 kt, ALT law will be latched.

• At some point before the end of the monitoring process FCPC2 loses connectivity with ADR1. For FCPC2 the median CAS becomes the average of ADR 2 and 3 CAS values, practically unchanged compared to the initial value.

• The 10 seconds period ends. Because their final median CAS value is beyond the 50 kt tolerance, FCPC1 and FCPC3 signal normal law unavailable. They also reject ADR1. FCPC2 finds its median value in tolerance and able to compute normal law.

• Before latching ALT law, the FCPC priority logic must be invoked otherwise the master FCPC would force other FCPCs to change law and would never relinquish mastership.

• Priority logic grants mastership to FCPC2 because it is claiming the highest level of flight control law.

• End of “median CAS monitoring function”.

Now comes perhaps the most arguable part of this scenario. Pitot2 and Pitot3 start icing simultaneously but not as fast as Pitot1. CAS does not decay fast enough to trigger another “CAS monitoring function”. However, it triggers the AoA protection law instead, due to the “phase advanced AoA calculation” similar to the TC-JDN A340 Airprox incident. That this function is now inhibited above M 0.53 is irrelevant in this case since the measured Mach number was soon showing less than that.

The A/C start a zoom climb, trying to maintain about Alpha Prot AoA, apparently confusing the PF beyond any understanding.

Perhaps all of the above is just garbage but:
1/ The claim found in the Airbus FCTM that simultaneous obstruction of two pitots is “highly improbable” is a weak case when there is a common cause. These pieces of hardware are built under tight tolerances, live the same life in the same environment and pitots 2 and 3 occupy exactly symmetric positions on the fuselage (contrary to pitot1). Additionally, ice ingestion is not a slow process at cruising speed when the Ice Water Contents in atmosphere reaches 9 g per cubic meter.

2/ I believe the “phase advanced AoA calculation” uses a time derivative of CAS in order to anticipate the interception of Alpha Prot speed and prevent any slower speed. AoA may not be precise or stable enough and its variation is not linear with speed.

Last edited by DJ77; 27th Jun 2011 at 13:28. Reason: 1 wrong End of Line character deleted
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Old 25th Jun 2011, 16:12
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The previous 2 or 3 days discussions suggested.....
that none of the three pilots had any idea what's going on.

This, in a modern, highly sophisticated airplane.......

Optimum interface? I'm afraid no!
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Old 25th Jun 2011, 16:18
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Feedback Systems (Testability and Diagnosability)

PJ2,

When trying to understand this "things" we must remember they are "complex feedback Systems" eventually with crew actions affecting final results (crew with his own feedbacks not always logical and understandable by us).

Many years ago i worked (Testability of complex electronic Systems) in diagnosing "complex digital circuitry" full of feedback loops. The only way we found adequate to diagnose a faulty circuit down to the component level was "to open the feedback loops" at least, momentarily.

The simple reason is: When there is a certain failure, the "feedback loops" make the "failure" appear also in the inputs of the System. And this was for a Hardware in a lab, in a bench with all necessary stuff (Digital storage scopes, logic analyzers, recorders, etc.)

When investigating incidents (e.g. AIRPROX) or accidents (AF447) i suspect the current FDR´s may be not are enough to provide all the required details (e.g. the WRG fault) to allow a definitive conclusion.
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Old 25th Jun 2011, 16:27
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Ridiculous Pitot redundancy implemented

Considering Airbus SAS didn´t have supply of "hotter" Pitot´s a much safer approach would be to put several Pitot´s in selected locations of the a/c and feeding a reliable "voting scheme" subsystem.

The "redundancy" used in this design may be is "amplifying problems".

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Old 25th Jun 2011, 17:02
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In Annexe 1 of the French version of the first interim BEA report, Meteo France's analysis of Meteosat 9 imagery indicated AF447 flew into a cloud with tops of 500 to 520, while in an area where mature convective storms were embedded within layers of cumulus, altocumulus, and stratocumulus.

Dans la nuit du 31 mai au 1er juin 2009, au-dessus de l’océan, la ZCIT est le siège d’une activité orageuse marquée mais discontinue : on distingue plusieurs amas convectifs (multicellulaires) séparés par des zones de Cumulus, Stratocumulus et Altocumulus.
....
On constate qu’à 2 h 07 les températures les plus froides sont de l’ordre de -75 °C à -80 °C, alors que la tropopause se situe entre les FL500 et FL520, avec une température voisine de - 80°C : certains des cumulonimbus de l’amas ont atteint l’altitude de la tropopause et leur stade de maturité, mais l’imagerie ne révèle aucun développement vertical exceptionnel du point de vue climatologique, qui serait caractérisé par un « overshoot ».
Vasquez concluded the cloud tops were FL560 at about 2 h 10.

What sort of cloud does one find at FL500 in the ITCZ?
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Old 25th Jun 2011, 18:22
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pj2

many thanks again for one of many useful links

Last edited by foster23; 25th Jun 2011 at 18:33.
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