AF447 [Archive] - Page 17

Hyperveloce

30th Jul 2009, 12:09

Hi there.
These Pitot problems have been known for decades. In the late 80s and the early 90s, there was already problems with water/humidity accumulating in the hoose between the probe and the ADR leading to biased airspeeds on Airbuses (and the Boeings may have had their problems too ?). Then Airworthiness directives in the early 2000s to replace the former Sextan (now within Thales) and Rosemount probes by the new models of Thales and Goodrich probes were released, without lasting results, the Pitot obstruction problems reoccurred despite the replacement by the new probes. And the last case between Paris and Rome suggests that a new replacement by the new Thales Pitot probes will not make it. Then let's do what the pilot unions demand, let's buy the new Goodrich probes while Thales prepares a new generation of Pitot probes specifically designed to cope with *increased anti-icing specifications*: if the existing Thales probes already met these specifications (and even more) and if the process of certification does not guarantee that the probes operate in a satisfying manner in real life, then let's review/alter the specifications themselves. The climate change also possibly impacts the high altitude. Maybe they should also include a criteria which says that the performances met during certification should be maintained over a XX % performance level, over YY month, with a ZZ % probability ? (given a specified maintenance process). This would be a way to specify a probe resistance to gradual pollution and obstruction.
The Pitot probes have suffered drain hole defects in the past, partly due to the manufacturing process and susceptibility to corrosion, making the probe vulnerable to pollution.
Similar problems were also observed on the fleet of Mirage 2000:
http://www.defense.gouv.fr/defense/content/download/67654/630213/file/Rapport%20public%20BEAD-air-A-2004-001-A.pdf
See page 55.
Within the Mirage 2000 fleet, the Pitot drain pollution was observed on 30% of the Mirages, 60% in hot/humid areas. Seemingly, this drain gradual obstruction by varied pollutions could make the probe more vulnerable to icing conditions. It was 5 years ago.

Now on he airliners we have at least two available probes:
http://www.goodrich.com/portal/goodrich/images/Goodrich%20Content/Business%20Content/Sensors%20and%20Integrated%20Systems/Products/Literature%20Listing/4004%20Pitot%200851HL.pdf

https://www1.online.thalesgroup.com/col/Air_Transport/pdf/products/bfe/fiche_sensor_probes.pdf
One is designed to improve its anti-icing performance, the other is not.
Roughtly, Goodrich probes are on 2 planes over 3, and Thales probes on 1 plane over 3. Cathay's large fleet of planes has not known any problem with Goodrich (Cathay's saying) while Air France is struggling to make a census of its numerous unreliable speed past cases. Why does AF feel the need to establish an historical sensus of the "unreliable airspeeds" cases ? Is it the only way to get the attention of the manufacturers or the regulatory bodies ?
Jeff
PS) History: Technical Standard Orders from 1948 & 1951 about Pitots
Current Technical Standard Order (http://rgl.faa.gov/Regulatory_and_Guidance_Library%5Crgtso.nsf/0/C8FA4F473570C7C686256DA500459834?OpenDocument)
Current Technical Standard Order (http://rgl.faa.gov/Regulatory_and_Guidance_Library%5Crgtso.nsf/0/C8FA4F473570C7C686256DA500459834?OpenDocument)

PEI_3721

30th Jul 2009, 12:41

Re “… increased frequency of severe weather conditions may be taking the probes beyond their original time of certification design limits.”

Also, consider any changes in the way in which we operate, the routes and altitudes now flown, and perhaps lighter weights in search of economy, all of which could place the aircraft in high risk areas. Add to that, the way in which humans react to bad weather – ‘not been a problem previously’ – ‘it will be OK this time’, 'can deviate too far - must save fuel'.
And especially where the ‘new’ technology radars provide an excellent picture – except the radar might not be able to show some of the hazards, or crews may not have been taught or be able to recall the hazards, i.e. high altitude ice.

syseng68k

30th Jul 2009, 13:10

So, I take it you know exactly where the ice is forming on or in the probe, and can tell Thales and Goodyear exactly what is wrong with their designs so they can fix them post haste? You assume much, http://images.ibsrv.net/ibsrv/res/src:www.pprune.org/get/images/smilies/shiner.gif but in defence, did say in the first sentence that the probes may be working outside their original design limits. The design changes may not be trivial but it is, irrespective of how many years of ‘research’ and committee it takes, an engineering problem with a solution. An extrapolation of an existing, well proven and reliable technology. Thought though, is not good enough. One would expect that there would be a process of continuous research and feedback to identify problems proactively. One incidence of a problem noted, several incidences starts to show a pattern. As for the probe heat controller, it’s not exactly rocket science to design one to prevent overheating.

It seems like there have been many reports of probe icing failures over many years. So how many incidences over time does it take before some sense of urgency is attached to the problem. 1, 5, 10 years worth, or what ?. Not a criticism of engineering, more one of process and I do get the feeling that those who should be driving this are in no particular hurry…

Chris

Lazerdog

30th Jul 2009, 14:00

In some of the photos of the rudder being recovered, it was noted that several static dissipator tufts were missing. Since these are quite flexible, it seems unlikely that impact with the sea would shear them off. Has there been any analysis or discussion of why they were missing?

rgbrock1

30th Jul 2009, 14:07

A week or so ago a report was mentioned of some seemingly aircraft parts washing up on some isolated beach in Guyana. Has anything further come of this, as I've seen
nothing since?
Thanks.

Richard

BOAC

30th Jul 2009, 14:09

rgb - I think somewhere previously it was 'expected' in France 'in August'

Machinbird

30th Jul 2009, 14:21

The problem really seems to be lack of a graceful failure mode of the pitot system and the potential severity of pitot failures on a fly-by-wire aircraft. THAT is the problem will yield best results to an engineering fix. Pitot tubes need to work, but most of the discussion regarding fixing pitot tube problems is really a discussion on the best way to put a band aid on the problem.
The computers that use airspeed need to have a speed input that cannot be completely corrupted by failure of any one class of input. Loss of pitot data should be substituted with SatNav or Inertial speed data in a logical voting progression. Then when pitot data failed, a realistic substitute piece of information could be inserted. This is an engineering problem that engineers can solve. Not cheap ultimately, but compared to the AF447 accident cumulative costs, reasonable.
Sid

Hyperveloce

30th Jul 2009, 14:47

If the BEA needs some aerodynamical/flight mechanics data for the A330 in the transonic regime (say between Mach 0.9 and Mach 1) according to different aerodynamical configurations (spoilers deployed or not or failed, landing gears lowered or not,...), ELSA-chimera can help:
http://img197.imageshack.us/img197/999/aerospoilerm02.jpg
http://img33.imageshack.us/img33/7458/aerospoilerm03.jpg
http://img33.imageshack.us/img33/1743/machbuffetairliner2.jpg
PS) the overspeed of a Learjet 24 (and inconsistant procedures about the airbrakes deployment above MMO)
http://www.airdisaster.com/reports/ntsb/AAR82-04.pdf (http://www.airdisaster.com/reports/ntsb/AAR82-04.pdf)

SaturnV

30th Jul 2009, 16:47

rgbrock, as of July 21, still not definitively identified as coming from either AF 447 or an Ariane

Stabroek News - Hope beach find still not positively identified (http://www.stabroeknews.com/2009/news/local/07/21/hope-beach-find-still-not-positively-identified/)

Regarding the news today of extending the search several months, assuming they can scan about 400 sq km a day, they are now about 10 days into this second phase, and no indication they have found the wreckage yet. And assuming they started the scan in the area they thought most likely to be the impact point, that's rather disappointing. This would now be an area equivalent to a square about 65 sq km on a side that's been scanned without apparent result.

rgbrock1

30th Jul 2009, 17:04

SaturnV:

10 days into an operation that could take months is not long. I'm holding hope that eventually they find something. Until then, they need to scan, scan, scan and more scan
until they find it. The wreckage is down there. Somewhere. And it can be found.
The money and time in doing so will be immense. But, IMHO, well worth the effort
and expense.

stepwilk

30th Jul 2009, 17:12

machinbird, what on earth can satnav or inertial tell you about airspeed, which is the only relevant criterion?

BOAC

30th Jul 2009, 17:20

SaturnV

30th Jul 2009, 17:32

rgbrock, the second phase, the sonar scan, is to take 4-6 weeks and cover 16,000 sq km. The area west of the track is very mountainous, with some peaks that appear to be 2,000 to 3,000 meters high. Large pieces of wreckage that are resting on a steep slope or are in a crevasse would probably present with a smaller vertical profile to a scan, if not altogether hidden entirely.

This may be a very formidable task.

infrequentflyer789

30th Jul 2009, 17:58

I see 'ssk' reports a not dissimilar IAS issue on a A320 (http://www.pprune.org/rumours-news/383142-anomaly-airspeed-data-display-af-a320.html). Are we seeing the same issues on the 737/757/777 ie is it a 'new' wetaher phenomonen or is this somehow ABI common software related?

Short answer: not new. not ABI. At all.

Scenario:Blocked pitot gives unreliable IAS, feeding into autopilot. Based on bad data (overspeed), autopilot pitches up, drops power, then pilots get handed a nearly-stalled plane. Facing multiple warnings including overspeed and stick shaker, pilots ended up stalled, with high AoA leading to compressor stall too, and high vertical speed ocean impact.
Sound like a familiar speculation from this thread ? Yet it as actually a quick summary of my understanding of this crash:Crash One: Birgenair Flight 301 | 12 Jun 2009 | ComputerWeekly.com (http://www.computerweekly.com/Articles/2009/06/12/236425/crash-one-birgenair-flight-301.htm) or Birgenair Flight 301 - Wikipedia, the free encyclopedia (http://en.wikipedia.org/wiki/Birgenair_Flight_301)
Over a decade ago, boeing, not fly by wire, and that is just one example, there are more.

There is just no need to invoke the "evil airbus / fbw removing control from the pilots". Bad IAS (from bad pitot or static data) is a killer, we know that from past experience, and it looks like it still is.

Machinbird

30th Jul 2009, 18:08

Hi stepwilk,
It would not be pure satnav velocity or inertial velocity. That is where the engineering comes in. You generate a computer model of the wind vector, and generate an airspeed validation system (computerized like everything else on the aircraft). The system is looking for any input parameter that is changing faster than preset rates determined by experience. The rates can be adjusted for condition of flight.
The key thing you are trying to avoid with the system is things like a sudden drop off to 0 airspeed or surge to Mach 1.5. Just trying to keep things in the ball park.
Now does it make sense?
Sid

PJ2

30th Jul 2009, 19:02

stepwilk;

The use of GPS groundspeed as well as the use of GPS altitude are both short-term recommended procedures for the loss of pitot-static data. Many of us who fly these aircraft have known this for years and have probably quietly made up our own "response" to loss of pitot-static data by calmly accessing the GPS Nav data on the MCDU, (Multi-purpose Control & Display Unit) on the Airbus or its equivalent on the 777 etc.

Others have made the observation that groundspeed is not airspeed and of course this is an immediately known and appreciated fact by those who fly these aircraft, but the airplane isn't going to do anything aerodynamically dramatic (like lose/gain speed) just because airspeed data alone is lost. The aircraft was fine moments before the loss and so the key is to do nothing, except take over manually and ensure a safe flight path with unchanged thrust levels. Then assess the situation, bring up the GPS page, note the groundspeed and maintain it while the other crew member sorts the event(s) out.

What brought 447 down will almost certainly be a combination of factors/failures rather than one or another system loss, which, individually, would not be mission-critical failures.

Given this, and given the solutions can be imagined as per machinbird's comments, I think this is a promising and already-extant (in use, however informally) solution. Getting to the bottom of a rash of pitot failures would be the first in the triage sequence, however.

Hyperveloce

30th Jul 2009, 19:04

Hi there. There is already an alternative speed scale, the BUSS (Back Up Speed Scale). Not true airspeed though. I don't know how it works, maybe it relies on the interplay between the pich & thrust to derive a scale ? Maybe that the airspeed scale, when it is failing, can be replaced by other usefull scales (for the crew decision) like scales displaying an aerodynamic authority with the aerodynamic margins ?
Jeff

MATELO

30th Jul 2009, 19:07

Quote: A week or so ago a report was mentioned of some seemingly aircraft parts washing up on some isolated beach in Guyana. Has anything further come of this, as I've seen
nothing since?

RGB, This was dealt with at the time on this thread, although not "certain" somebody on here posted pictures of the Arianne rocket booster and the paint matched up exactly with the wreckage found. It looked pretty convincing.

JD-EE

30th Jul 2009, 19:57

RGB - that piece that washed up in Guyana was quite apparently a chunk of a launch vehicle not an aircraft. Another reader here provided links to pictures of that piece in its original location. That pretty much close the case for most people here.

JD-EE

rgbrock1

30th Jul 2009, 20:14

JD-EE and Matelo,

Understood. Then I have to question why the piece of "debris" is on its way to France?????? I would have imagined that the AF447 crash investigators would have been all over this piece of whatever-it-is shortly after its discovery. Would they not have gone to Guyana to examine it? And, if so, wouldn't they have known pretty much with certainty that it is, or is not, a piece of AF447?
It just seems odd that the debris, from whatever it is, was loaded onto a ship headed for France. On the other hand, if it is a piece of an Adriane craft I suppose they wouldn't mind having that back either.

JD-EE

30th Jul 2009, 20:19

Machinbird, I suspect the entire sensor system on aircraft needs to be rethought from 100 year old technology such as tubes that transmit pressure data from the pitot tube location to the computers.

Suppose you migrate to "smart sensors". Things like PIC chips are little more than the cost of their sand these days. The pressure sensor could be built into the pitot assembly with no long tubes to collect crud. The sensor data could be massaged through a calibration table custom to at least the probe design if not the probe itself and then transmitted digitally to the newer ADIRU equivalents. Such a concept would allow for multiple sensors and multiple types of sensors for the same data in the hope that when one type of sensor for a given data item suffered accuracy problems due to ambient conditions the alternate type would not.

In the 1980s it made sense to run tubing. In this century it makes sense to run wire or fiber and accept the degraded inaccuracies. (Double negative intended for the sake of sarcasm.)

JD-EE

JD-EE

30th Jul 2009, 20:27

Perhaps Arianespace is interested in it? JD-EE

LeandroSecundo

30th Jul 2009, 20:57

Hi,

publié le 30 juillet 2009 à 15:53 par EuroCockpit.

Passée relativement inaperçue à l’époque où elle a été rédigée, la note d’information de l’EASA (http://www.eurocockpit.com/docs/EASA_SIB_2009-17_1.pdf) (Agence de sécurité aérienne européenne) du 9 juin 2009
http://www.eurocockpit.com/docs/EASA_SIB_2009-17_1.pdf
sur les problèmes anémométriques mérite un petit arrêt sur image, et un décryptage a posteriori puisque l'on dispose à présent des grandes lignes de la stratégie du BEA qui a décidé - ou qui s’est fait imposer - qu’il convenait de charger l’équipage, voire s’il le faut quelques étages de la compagnie, pour protéger les intérêts économiques européens prioritaires. Et surtout ne jamais dire ou laisser dire - même si c'est désormais un secret de polichinelle - que les sondes Pitot pourraient être à l’origine de la situation inextricable dans laquelle s’est retrouvé l’équipage, entraînant une perte de contrôle de l’appareil.
L’EASA a donc pris la sage précaution de se tenir à distance de ce "service commandé", en rappelant que les problèmes anémométriques doivent être traités par les opérateurs en appliquant les procédures prévues par le constructeur, en commençant par la mise en oeuvre des procédures «memory items», ces actions que l'équipage doit immédiatement effectuer de mémoire sans consulter préalablement aucune check-list.
Un gros tacle pour Air France, qui - on le rappelle - dispose d’une documentation interne (visée par la DGAC) qui ne dit pas la même chose que celle du constructeur (concernant le respect des alarmes décrochage). Une procédure qui, en effet, demande aux pilotes de croire et de réagir immédiatement de mémoire à toute alarme décrochage, alors que cette demande n'existe pas dans les "memory items" du constructeur... Une procédure qui figure toujours dans la documentation officielle d'Air France mais dont une note de service interne a spécifiquement interdit qu'elle soit appliquée en pareil cas par les pilotes (sic), ceci 4 jours - par hasard bien sur - après le crash (note du 5 juin 2009)...
En substance, l’EASA - avant l’heure - a rédigé la page 70 du rapport du BEA qui met silencieusement en lumière ces différences de procédures. L’Europe et le BEA désignent donc Air France et ses équipages, et l’avion peut voler tranquillement. Avec ou sans vitesse indiquée, puisqu’on vous dit que dans tous les cas, il n’y a qu'à faire comme si tout fonctionnait à merveille.
Et de toutes façons, il suffit de piloter au moins aussi bien que les concierges d'Airbus et d’appliquer la bonne vieille méthode «assiette puissance» pour s’en sortir. Au besoin, on peut aussi appeler Monsieur Feldzer - le découvreur d'ouragan - pour connaître l'épaisseur du nuage, bien que cette procédure soit réservée aux imbéciles qui ne savent pas se servir de leurs radars.
Tout ceci, c’était sans compter le nouvel incident survenu le 13 juillet sur A320 avec des nouvelles sondes Thales «BA», incident sur lequel nous reviendrons avec tous les détails nécessaires. C'est la panique dans tous les rayons du bazar et nous aurons aussi l'occasion d'y revenir. Au passage, on note que le réalisme économique du SNPL lui a fait faire marche arrière sur sa demande de changement des sondes Thales par des Goodrich n’ayant jamais connu d’incident : la perte des données de vitesse n’a duré que 7 secondes, alors c’est acceptable. Sans que l’on sache au-delà de quel laps de temps sans indication de vitesse Monsieur Derivry considère que la sécurité des vols est engagée. Plus de sept secondes, mais combien… Huit secondes ? Vingt ? Une minute ? Jusqu’au crash ?
En attendant, Air France a pris une disposition courageuse qui montre à quel point ce problème de sondes Pitot est considéré avec attention, même si Monsieur Gourgeon a maintes fois indiqué que le crash de l'AF447 n’avait rien à voir avec tout cela, ne pouvait pas être lié à cela et avait l'interdiction définitive de venir de cela. En effet, pour bien montrer à quel point il n’y avait - il n'y a et il n'y aura - jamais eu aucun problème de sondes, Air France a décidé de… supprimer tous les ASR (rapports d'incident) s’y rapportant des bases de données internes de la Compagnie.
Sur les 9 incidents rapportés, il n’y a plus aucune trace nulle part d’aucun rapport d'incident d’aucun commandant de bord...
Quelques archives dans la revue «Survol» - parce qu'on n'a pas pu rappeler tous les numéros pour les mettre discrètement au pilon - mais le reste a disparu.
Pour la plus grande joie du BEA qui, finalement, a choisi le camp de l’autre copain de promo 1965… La vie impose parfois des choix cruels, mais Airbus l’a emporté en précisant aujourd’hui, par la voix de Tom Enders, que le constructeur serait prêt à «donner» au BEA une somme de 12 à 20 millions d’euros (une broutille comparée aux chiffres avancés par ailleurs sur les délits d’initiés) pour «étendre les recherches». Imaginerait-on un jour que Boeing puisse financer le NTSB ?
Mais le BEA est sage, même si son «choix» a été facilité depuis qu'il se murmure, dans les "milieux autorisés" et depuis quelques semaines, que la décision irrévocable de trouver rapidement un successeur à Monsieur Gourgeon a déjà été prise au plus haut niveau de l'Etat, la discussion ne portant désormais plus que sur le sort des sous-fifres...

Eurocockpit - Accueil (http://www.eurocockpit.com/index.php)

Use at your own risk any translator :eek:

Bye.

syseng68k

30th Jul 2009, 21:20

Suppose you migrate to "smart sensors". Things like PIC chips are little more than the cost of their sand these days. The pressure sensor could be built into the pitot assembly with no long tubes to collect crud. The sensor data could be massaged through a calibration table custom to at least the probe design if not the probe itself and then transmitted digitally to the newer ADIRU equivalents. Such a concept would allow for multiple sensors and multiple types of sensors for the same data in the hope that when one type of sensor for a given data item suffered accuracy problems due to ambient conditions the alternate type would not.I think you'll find that integrated or close processing of ps data has been around for some time, though don't know if it's used in any current civil ac. Some of the benefits are the elimination of measurement delay caused by tube length, simplified unit replacement and, as you say, connection via standard ac data buses.

The probe issue still nags and nags - Most of the probes i've seen in the past have heaters but no temperature sensing and looking at the data sheets for the two AI fittings mentioned earlier, it looks like they are similar. Why is this of interest ? . Without sensing, it's not possible to have closed loop probe heat control. This means that the probes are getting full power all the time they are switched on. With 300 to 500 watts input typical, it wouldn't surprise me if the probes get almost cherry red hot on the ground, which can't be good for probe life. With a temperature sensor and a decent controller + enough heat capacity, it should be no problem to maintain temperature at optimum levels irespective of load and would also eliminate ground overheating. Otoh, perhaps they use a resistance element with a positive tempco, but it's still a bit primitive.

Iirc, simple 3 term pid controllers are a first year electronics undergrad subject and have been used in industry for decades...

Chris

mm43

30th Jul 2009, 21:24

AB probably already have the equivalent software to provide a Pseudo Air Speed (PAS). The software will provide PAS in every a/c configuration, but like everything else in FBW systems it too needs some external references such as air pressure, OAT and altitude. The a/c configuration clean/unclean, CG, weight, thrust, AoA, pitch, bank angle, spoilers, slats and gear etc., down to and including ground effect should provide a IAS/TAS equivalent to that provided to the ADIRUs from correctly operating Pitots.

Lets face it, the SIM algorithms operate using the same principle.

mm43

Hyperveloce

30th Jul 2009, 21:38

The EASA claims:
"The Aircraft Flight and/or Flight Crew Operating Manuals include procedures for unreliable airspeed indication (Air data system misleading information) and these should be well known by flight crews. Correct application of these procedures by flight crews may be crucial for assuring the safety of the aircraft when such Pitot-static malfunctions occur."
sure, but
1) the Air Caraïbe crew got out without problem by not applying entirely (the stall alarm part) these crucial procedures (and some of its parts being not implementable due to time constraints)
2) how can a crew rely on any procedure when the safety of the plane is immediately impacted by a (false) stall alarm and that the pilot has to take an immediate decision in a context of unreliable airspeeds ? (the AF Paris Antananarivo case)
3) the word "crucial" sounds weird when a month ago Pitot problems posed no safety problems.
I don't understand why the high probability of false stall alarms in this context is never mentioned by the authorities (always mentioning the airspeed loss & pich/thrust procedures).
now, the EASA says it is considering a mandatory change of at least two of the three Pitot probes, so as to have at least two Goodrich probes:
http://www.lexpress.fr/actualites/2/l-ue-voudrait-interdire-un-type-de-capteur-sur-l-airbus-a330_777849.html (http://www.lexpress.fr/actualites/2/l-ue-voudrait-interdire-un-type-de-capteur-sur-l-airbus-a330_777849.html)
I don't even understand why one suspect probe is tolerated on board :ugh: Oh yes, the suspect probe only failed 6 sec. between Paris and Rome a couple of weeks ago. But...How long since they had been introduced ? There should not be any compromise to the safety (all the more if it is about 2000$ per plane).
Jeff, pissed off, and intrigued
PS) Has the NTSB produced any report on the Northwest case of Pitot freezing ?

Litebulbs

30th Jul 2009, 21:40

syseng68k,

The jet has 3 Probe Heat Controllers that use various logic to vary temperature, depending on conditions -

automatically when at least one engine is running, or in flight

manually by switching ON the PROBE/WINDOW HEAT pushbutton.

On the ground, TAT probes are not heated and pitot heating operates at low level (normal power in flight by automatic changeover).

BOAC

30th Jul 2009, 21:52

infrequentflyer789- it was actually a serious question which you have unfortunately misinterpreted.

As far as I am aware, we have a few Boeing accidents caused by blocked pressure sensors - recently an Astraeus operated 757, a bug in the tubes. Yours a wasp in the tubes. Another - ?Peru? by taped over statics. Others I'm sure, I have forgotten. Do we have any events similar to what we are seeing here on other types? The question remains - is this a failure with a common interface link?

Squawk_ident

30th Jul 2009, 22:04

"Airbus recommends speed sensor switch after crash"

UPDATE 1-Airbus recommends speed sensor switch after crash | Reuters (http://www.reuters.com/article/CMPSRV/idUSLU16943920090730)

LeandroSecundo

30th Jul 2009, 23:21

Hi,

now, the EASA says it is considering a mandatory change of at least two of the three Pitot probes, so as to have at least two Goodrich probes:That's a very strange solution .. seem's a smoke screen .......
So .. if other Pitot case problems in the future on such equipped planes (mixed Pitot brands) it will be :
"It's not my Pitot faulty .. it's the other brand" .. :)

Bye.

Squawk_ident

30th Jul 2009, 23:33

rgbrock1 said

Understood. Then I have to question why the piece of "debris" is on its way to France?????? I would have imagined that the AF447 crash investigators would have been all over this piece of whatever-it-is shortly after its discovery. Would they not have gone to Guyana to examine it? And, if so, wouldn't they have known pretty much with certainty that it is, or is not, a piece of AF447?
It just seems odd that the debris, from whatever it is, was loaded onto a ship headed for France. On the other hand, if it is a piece of an Adriane craft I suppose they wouldn't mind having that back either.

France is in charge of the technical investigation being the State of registration of the aircraft.
From what I have understood from the France2 or France3 reports, the debris that have arrived in France were those found by the Brazilian Navy. About 650 pieces. In August about 450 new ones should arrived. These new debris should be the ones retrieved by the French Navy or vessels. Because nobody in France speaks of any debris found nearby Guyana (Kourou space center), I think that the futur debris will come from the crash area. The French Guyana doesn't have the capacity to receive, handle, analyse the debris and conduct such an enquiry. So everything is sent at Toulouse at the Centre d'Essais Aéronautiques.

The BEA Has published the 30th a communiqué:

Press release 30 July 2009

Flight AF 447 on 1st June 2009

A 330 – 200, registered F-GZCP
The Ifremer oceanographic ship “Pourquoi pas?” is currently on site in the area for the second phase of the search for the flight recorders from AF 447. Work to survey the ocean floor has begun in the area considered to be the most likely, with the aid of a side-scan sonar device and the Victor 6000 ROV and Nautile submarine. The flight recorders’ locator beacons having now ceased transmitting, the next step is to identify the place where the airplane wreckage is located, then to search for the recorders.

The BEA recognizes Airbus’ commitment to participate financially in a continuation of the search if a third phase, over a wider area, appears to be necessary.

About the Ifremer, and for the anedocte, if you go here:
Localisation des navires océanographiques de l'IFREMER (http://www.ifremer.fr/posnav/PosnavWeb/WFAccueil.aspx)
you will notice that the "Pourquoi pas?" is shown at Cabo Verde and she has not moved from there since the beginning of June...

Will Fraser

30th Jul 2009, 23:58

"Not the only cause".....? The first 'cause' without which the chain could not be continued is what's known as the 'procuring cause'. The authorities including Airbus and Air France are playing with language, in my opinion.

Technically they are not incorrect, but they are suggesting that there may have been more than one cause. There can be a combination of events that exacerbate or accelerate outcome, but the pitots are in the 'hot' seat for now. Is it possible for the crash to have happened if the pitots had functioned properly? The answer is yes, but demands accepting coincidental events at long odds.

AB is calling for replacement of Thales (both types? but only two instead of all three). Two questions.

1. Where was their 'request' when the pilots 'demanded' it?

2. Why only two? Not all three? Taking a chance, aren't they?

If the remaining Thales fails, and...........

Since the sampling system uses pairs, only one good pair is left, G-G.
This is a singly redundant system.

Litebulbs

31st Jul 2009, 00:33

Will,

Its money. I imagine most Thales operators have just upgraded any existing AA to AB probes. I am sure that No 1 and No 3 will be changed and it will be a good test bed, to see if the F/O's air data goes haywire, to see if the Capt's and Stby are operating correctly.

It will also be about supply. If the figures are correct, then 400 new probes are going to be needed. I don't know if the ADM's are generic or not. If not, then 400 of them too.

CONF iture

31st Jul 2009, 00:39

About the Ifremer, and for the anedocte, if you go here:
Localisation des navires océanographiques de l'IFREMER
you will notice that the "Pourquoi pas?" is shown at Cabo Verde and she has not moved from there since the beginning of June...

All I can read is :
No position during the search period

... you won't know it if I'm getting or have been stationary ...

Graybeard

31st Jul 2009, 00:52

AOA is the best indicator of stall. Why airliners haven't used it as primary stall warning just puzzles me. Stalling airspeed varies with bank angle and wing loading, but AOA is just that, Angle of Attack, the exact meaurement of stall margin, regardless of bank angle and wing loading.

The stall warning detector on the basic Cessna 150 is a binary AOA device, independent of pitot pressure. Why did the airliners give up that simple redundancy?

GB

Hyperveloce

31st Jul 2009, 01:42

WhyIsThereAir

31st Jul 2009, 01:46

The probe issue still nags and nags - Most of the probes i've seen in the past have heaters but no temperature sensing

The probes I've seen (not a large number, but a few) don't appear to have any formal temperature senesing such as a thermocouple or thermistor in them. However, that doesn't mean they don't have a built-in temperature sensor. They do - the resistance wire heater element itself.

As you doubtless know, resistance wire has a positive temp coefficient, and has a higher resistance as it heats up. This within reason makes the heater elements self-regulating, as the current (and thus heat input) will decrease as the element heats up.

But a smart heater controller can measure the current flow and voltage to the heater, and thus determine the resistance. This, in turn, is a measurement of the temperature of the element. It isn't as sensitive as a thermocouple, but it can be pretty good -- especially since the main goals are to prevent the element burning out from overheat, while providing enough current to keep it above some specified temperature.

A better design would probably divide the heater element into 3 or 4 sections, and possibly add a few thermistors, and thus be able to keep a relatively constant temperature (or any other desired heat profile) on the sensor. As it is, the sensor will be at varying temperatures along the single heater winding, depending on the heat load/loss for that section of heater element.

PEI_3721

31st Jul 2009, 01:54

“ AOA is the best indicator of stall. Why airliners haven't used it as primary stall warning just puzzles me. # 4038
Many (most) airliners use AOA for stall warning and stall identification.
The A330 had AOA and in some modes of operation used it for stall alerting; in this instance it appears that the method of routing AOA information via the ADC was a possible problem.

Re: “EASA says it is considering a mandatory change of at least two of the three Pitot probes …”
EASA’s problem appears to be that having already known of the deficiency ( Instrument External Probes (http://www.sae.org/events/icing/presentations/2007s30duvivier.pdf)), and presumably agreed that crew procedures in the event of unreliable airspeed would be sufficient, this accident may have proved otherwise.
Disregarding hindsight, I wonder how many readers here would have accepted that attitude and power were sufficient for short duration flight without airspeed … of course excepting when in adverse convective weather.

HF in regulation; thinking of all of the alternative scenarios, context, and a judgment call … no blame just a better understanding

Lightning6

31st Jul 2009, 01:55

GB, this AoA based stall detection of the Cessna looks like the AoA law (alpha prot) on Airbuses. But to get an aerodynamical margin, don't we have to compare the AoA to a threshold/a max AoA ? (what is done in the alpha prot). Shouldn't this max AoA depend on the airspeed/altitude ? (Pitot/static)
Jeff

Of course it should, but when you have unreliable indication of airspeed, and possibly altitude, a simple device, as fitted to the C150, would at least give the PIC an indication of his attitude, sometimes the simplest of devices can be useful.

Hyperveloce

31st Jul 2009, 02:20

The following is an extract from Airbus safety First Magazine Issue No 5.

"Back Up Speed Scale (BUSS). 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 BUSS is optional on A320/A330/A340. It is basic on A380, being part of the ADR Monitoring functions.This indication is based on angle of attack (AOA)sensor information, and is therefore not affectedby erroneous pressure measurements.The BUSS comes with a new ADIRU standard (among other new system standards), where the AOA information is provided through the IRs and not through the ADRs. This enables selecting all ADRs off without loosing the Stall Warning Protection. The AOA information provides a guidance area inplace of the speed scale. When the crew selectsall ADRs OFF, then:
•The Back-Up Speed Scale replaces the PFD speed scale on both PFDs,
•GPS Altitude replaces the Altitude Scale on both PFDs.
The Back-Up Speed Scale then enables to fly ata safe speed, i.e. above stall speed and below maximum structural speeds, by adjusting thrust and pitch.

The BUSS will be displayed once all ADRs are switched OFF. Therefore, on aircraft that have the BUSS, when the flight crew cannot identify the faulty ADR(s) when performing the troubleshooting, or when all ADRs are affected, the flight crew will switch OFF all ADRs, and will fly the green area of the BUSS. However, if the safe conduct of the flight is affected,the memory items must still be applied beforetroubleshooting.As the BUSS is associated to the ADR monitoring functions, some unreliable speed situations can be automatically detected (e.g. new ECAM warning “NAV ADR 1+2+3 FAULT”), and some ECAM procedures will lead to the BUSS activation by requesting to switch OFF all ADRs."
(source: PPruNe)
Jeff

Lightning6

31st Jul 2009, 02:51

Hyperveloce...Thanks for that info, something else learnt, it just seems to me that aircraft these days rely too much on computerised electronics (ex-electronics engineer) when a simple flap switch presented in the airflow, directly connected to a warning indicator, would be a cheap and useful way of indicating your AoA without having to faff about turning off your ADR,s under duress, and hoping your BUSS works.

kappa

31st Jul 2009, 03:02

I just read a news report (http://www.bloomberg.com/apps/news?pid=20601087&sid=a_RjA4KU5LOM) on an Airbus advisory. There were many interesting comments, among them, “Sensors from …. Goodrich are the standard on A330/A340 wide-body jets, and are used on 800 of the 1,000 such planes now in service” and “Airbus installed Thales units only when specifically requested by airlines”.

It is an interesting anomaly that Goodrich is a USA based company and Thales is French.

broadreach

31st Jul 2009, 03:33

The vessel was shown at Praia (Cape Verde) on 7-8 June, and at Dakar from 14 July 18:29z to 23 July 08:35z.

Presumably she would have been on station, i.e. searching, from around 10-11 June to around 10 July, then back to Dakar for bunkers, provisions etc. And then back to the search station.

ELAC

31st Jul 2009, 05:38

Quote Will Fraser:

Is it possible for the crash to have happened if the pitots had functioned properly? The answer is yes, but demands accepting coincidental events at long odds.

Why is it that you always jump before looking?

Last week you were ready to believe that rocket garbage was a part of an A330, the week before, what was it? The Rudder Travel Limiter, ALT2, Autopilot Failure Beyond Cheek Gyro Limits? At one time or another you've ascribed cause to so many different factors I've lost count.

You should rethink your statement because you've got it backwards. Is it probable that the crash happened due to the assumed, but still unverified, failure of the pitots? Obviously not, as we now have any number of reports of similar failures occuring which were managed successfully by the crew. It's a serious failure should it occur, but it is not one that should be outside the ability of a normal crew to deal with successfully.

It's not impossible, but it's improbable that this in itself is the "cause". More probable is that it is a result of one of those "coincidental events at long odds" that we can, so far, only speculate about. It would not be demanding acceptance of long odds to recognize that these other factors may be causative but it is taking long odds to describe them, without any supporting evidence, as being subordinate in cause to the issue of the pitots.

ELAC

wsherriff

31st Jul 2009, 06:11

A swept wing aircraft will pitchup in an updraft. CAB Report SA-372 File No. !-0006. Quote: page 16, "The ultimate effect of an updraft is an altitude and noseup increase."

The FLIGHT ENVELOPE PROTECTION PROGRAM will counter the pitchup by pushing the nose over into a dive attitude to protect the aircraft from what it interprets as a stall threat! The pilot will instinctively pull the aircraft's nose up to recover from the dive!. Note; The QANTAS Flight QF72 incident repeated this sequence twice, with numerous passenger injuries!

When you add severe turbulence and massive thunderstorms in the area, there is little doubt what the Flight Data Recorder (FDR) Chart would look
like!

NARVAL

31st Jul 2009, 07:06

About the pitot sensors, although the BEA does not think that they are the cause of the crash, Airbus has acknowledged yesterday that they certainly were at least good for the junkyard and should be replaced by Goodrich sensors, and the EASA has finally decided to do something:
PARIS, July 30 (Reuters) - The European Aviation Safety Agency plans to recommend a ban on the type of speed sensor installed on the Air France (AIRF.PA (http://www.reuters.com/finance/stocks/overview?symbol=AIRF.PA)) Airbus jet which crashed in the Atlantic last month, a spokesman said on Thursday.
A proposed ruling would also ration the number of a newer type of sensor made by same manufacturer, France's Thales (TCFP.PA (http://www.reuters.com/finance/stocks/overview?symbol=TCFP.PA)), to just one per plane, he told Reuters.
This means that at least two of three speed-measuring devices fitted on each jet would have to be supplied by the only other manufacturer, Goodrich (GR.N (http://www.reuters.com/finance/stocks/overview?symbol=GR.N)) of the United States.
The ruling would apply to all Airbus A330 jets equipped with speed sensors -- known as pitot probes -- made by Thales, as well as to the broadly similar A340 airplane.
"EASA will recommend that all A330 and A340 Airbus aircraft currently equipped with Thales pitot probes should be fitted with at least 2 Goodrich probes," said Daniel Holtgen, chief spokesman for the agency responsible for aviation safety in the European Union.
No timescale for the proposed changes was available.
Apparently faulty readings from the sensors are at the centre of an investigation into the crash of an Air France A330 while en route from Brazil to Paris on June 1. The crash during a severe Atlantic storm killed all 228 people on board.
(Reporting by Tim Hepher)
Things are beginning to improve in the closed circuit BEA AF DGAC EASA AIRBUS AIR FRANCE

ernst_mulder

31st Jul 2009, 08:01

A better design would probably divide the heater element into 3 or 4 sections, and possibly add a few thermistors, and thus be able to keep a relatively constant temperature (or any other desired heat profile) on the sensor. As it is, the sensor will be at varying temperatures along the single heater winding, depending on the heat load/loss for that section of heater element.

Isn't it just a maintenance and reliability issue? A constant-on heater is much more durable and safer than one fitted with sensors. Thermistors do break down (at least they do every two years or so in my tumble drier). I think it will be quite difficult even with modern technology to design a IAS meter as maintenance free and reliable as the 200 year old Pitot rubes.

Squawk_ident

31st Jul 2009, 08:20

broadreach said

The vessel was shown at Praia (Cape Verde) on 7-8 June, and at Dakar from 14 July 18:29z to 23 July 08:35z.

Thanks broadreach. Can you please confirm where have you found this information?

HazelNuts39

31st Jul 2009, 13:37

RE: Hyperveloce (#4039)

But to get an aerodynamical margin, don't we have to compare the AoA to a threshold/a max AoA ? (what is done in the alpha prot). Shouldn't this max AoA depend on the airspeed/altitude ? (Pitot/static)The stall warning AoA does have a margin to the AoA corresponding to the stall speed (what you call max AoA). The stall warning AoA is not afffected by airspeed/altitude, weight, loadfactor or airspeed. If erroneous pitot/static produces erroneous stall warning, it's just another fault of the system.

regards,
HN39

CONF iture

31st Jul 2009, 13:42

Presumably she would have been on station, i.e. searching, from around 10-11 June to around 10 July, then back to Dakar for bunkers, provisions etc. And then back to the search station
Ok I hear you broadreach, but there is a difference between "search station" and "stationary on search station"

http://i85.servimg.com/u/f85/11/75/17/84/af447_12.gif (http://www.servimg.com/image_preview.php?i=35&u=11751784)

http://i85.servimg.com/u/f85/11/75/17/84/af447_11.gif (http://www.servimg.com/image_preview.php?i=34&u=11751784)

This must be part of the "transparency" process as seen by the BEA ...

broadreach

31st Jul 2009, 14:23

The position reports come from LloydsMIU's Lloyds Agency network and AIS stations. The call at Praia would have been reported by Lloyds Agents; there's no AIS receiver there. There is an AIS receiver at Dakar. Before you ask, I don't believe there's an AIS station at Fernando de Noronha.

CONF, no doubt there's a difference. "search station" was my own phrase, not AIS's.

vovachan

31st Jul 2009, 15:36

Airbus utilizes design diversity in computers to lessen the chance that redundant systems would fail at the same time in the same way. Funny this principle was never applied to probes.

Hyperveloce

31st Jul 2009, 17:19

There is an AF note (AF Tech Note 34-029) available via the Eurocockpit website : Eurocockpit - Archives (http://www.eurocockpit.com/archives/indiv/E009445.php)
(search the URL with the french key word: forfaiture )
This AF note is dated on the 17th of september 2008.
The two Air Caraïbes incidents occurred during august & in the beginning of september 2008.
They show us that an airspeed deprievation is accompanied with ALTN2, PROT LOST, false stall alarms (with QRH/procedures which may not be so clear is that matter).
The AF note (organizing a census of the unreliable airspeeds cases) basically says that this has no operational impact.
Jeff

glad rag

31st Jul 2009, 17:34

Will Fraser

31st Jul 2009, 17:43

vovachan

What you are referring to is what's known as "Anomalous design".
It is AB's strong suit, and if as you say, some of the mechanicals had undergone the same approach, AF447 would not have happened.

Likewise, BA038 would not have happened, they would have landed safely with one Engine.

It''s a long story, and unknown why it hasn't been discussed before this.

Three separate software systems, but identical pitots ??

rgbrock1

31st Jul 2009, 17:55

Likewise, BA038 would not have happened, they would have landed safely with one Engine.

Will. I'm not sure I understand your reference to BA038? I thought that was a fuel contamination issue ie, ice particles forming on the fuel/oil heat exchangers used on the Trent 800 engines?

Hyperveloce

31st Jul 2009, 18:07

In French, to talk in images, when problems are looming up for exemple over a large human organization (or several), and when everyone or each entity is beginning to protect his own interests (versus the others), we say "ouvrir son parapluie", litteraly "to put up one's umbrella" (before being rained down by problems). A similar idea in English ?
Jeff

EASA & Airbus: procedures about "unreliable airspeeds" should be well known & practiced by all the crew

Airbus: I sell planes with Thales Pitot probes only when my customer asks for them

Other compagnies: "US Airways Group Inc. and Delta Air Lines Inc.’s Northwest unit, the only U.S. operators of A330s, said they had already completed upgrades of the Pitot tubes on their planes with different Thales units following an earlier Airbus advisory" (Bloomberg)
Oh ! an Airbus advisory to install the new Thales Pitot probes you say ?
Cathay: the Goodrich probes on my entire Airbus fleet are like that :ok:

EASA : I don't render the replacement mandatory since I have no guarantee that the new probes will do it.
ok, well, finally, you really should buy some Goodrich now.

Thales: my probes are up to the specifications and have been certified by the French authorities, what's the problem ?

AF: well, this Pitot problems have no operational impact, but we are compiling a census for all of these. For historical purpose ?

Smilin_Ed

31st Jul 2009, 18:16

A similar idea in English ?

It's "CYA". Cover Your A$$.

cribbagepeg

31st Jul 2009, 18:28

The latter *does* lack a little of the elegance of the French expression....

Robert Campbell

31st Jul 2009, 18:39

washingtonpost.com (http://www.washingtonpost.com/wp-dyn/content/article/2009/07/31/AR2009073101195.html?hpid=topnews)

EACA issuing AD requiring at least two Pitot tubes on A330 and A340 be replaced.

The European Aviation Safety Agency plans to propose an airworthiness directive mandating that all A330 and A340 currently fitted with Thales pitot probes must be fitted with at least two Goodrich probes, allowing a maximum of one Thales to remain fitted to the aircraft," said a statement released by the agency based in Cologne, Germany.

Smilin_Ed

31st Jul 2009, 18:41

The latter *does* lack a little of the elegance of the French expression....

Touche`. :)

Will Fraser

31st Jul 2009, 18:45

rgbrock

With all due respect, the topic has become divergent design, a very important idea, one that was used by Boeing in its software developments, as well as AirBus.

It is especially pertinent to ETOPS, since Redundancy was relinquished for Safety critical system design.

Essentially, independently engineered solutions for the same spec. sheet.
It's not exactly spitting in the wind, though it seems like it is reliant on separate approaches to be immune from parallel and identical chain fault.

For example, if the pitots here were different makes, it is quite possible that what failed all three would possibly have failed only one, perhaps due to slight differences in thermal engineering, alloyed surfaces or finish techniques. It is cross applicable to 038 because the 777 has virtually identical plumbing architecture between powerplants, with exact hardware compliance, and of course identical Fuel. It isn't simple to explain, and subject to alot of Flaming, for that reason. What isn't understood irritates easily.

Will

surplus1

31st Jul 2009, 19:03

Airbus utilizes design diversity in computers to lessen the chance that redundant systems would fail at the same time in the same way. Funny this principle was never applied to probes.

Very interesting comment and quite relevant. There are unfortunately other instances in which that 'principle' has never been applied to AB designs and from my perspective they are not at all funny (although I understand your different context use of the term).

Read the following report and it may give you some insight into how AI responds to repeated anomalies experienced in some of their products.

http://www.ntsb.gov/recs/letters/2008/a08_53_55.pdf

If that is how they respond to problems then I have no regrets at never having had the "pleasure" of piloting one of their aircraft.

How would you all like to be flying an A320 that loses all 6 displays and has a standby gyro with a life of 5 minutes? Their SB's and fixes don't work. They change their "new" models but do not retrofit. Sorry, but I'm not impressed.

The same pattern appears to exist with these alleged multiple pitot probe failures and the difficulties they appear to cause. They know there is a problem but, they don't seem to know what it really is and their efforts to eliminate it so far could only be classified as lame.

Tempting fate isn't a game that should be played in commercial aviation, IMHO.

LeandroSecundo

31st Jul 2009, 22:54

Hi,

What isn't understood irritates easily.

For put it simple
The two pilots don't eat the same food :)

Bye.

wes_wall

1st Aug 2009, 00:44

Last night I tuned into the last part of a TV documentary filmed in Australia dealing with thunder storms and the size of ice crystals in ice clouds near and around these systems, but particularly in the cap of a cell. While no definitive conclusion was reached, it was newly discovered that crystals can vary in size by considerable amounts, with corresponding different effects on pitots tubes. Two of their test airplanes while attempting to collect samples, experienced loss of airspeed indications, and had to make emergency landings in the middle of these storms. I am not sure when these tests were done, as I say, I tuned in at the end of the film. Perhaps someone else can provide additional info

alf5071h

1st Aug 2009, 01:56

wes wall, a frequently encountered hazard is the failure to read the thread, and to use the search function:-

http://www.pprune.org/tech-log/376345-air-france-a330-accident-3.html#post4990071

VicMel

1st Aug 2009, 15:15

It would be a great shame if the main conclusion from the loss of AF447 is to change the supplier of the pitots, and consider 'problem solved'. The criticality of IAS seems to be in need of an urgent rethink from a safety/system engineering perspective, too many serious incidents have already occurred involving unavailable/misleading IAS to consider that a simple fix is going to be sufficient.
Three sensors, using the same technology, in the same area on the outside of the aircraft are obviously vulnerable to 'Common Mode Failure' due to rain/ice/debris/birds etc., regardless of the supplier. To then use this vulnerable source to derive a parameter (IAS), which is used by other systems in a way that is critical to aircraft safety should be unacceptable. Is this a case of 'we have always used pitot tubes, they meet the regulations so they are safe, precedent is set'? A method that uses different technologies should be mandated; there are a wide range of technologies already being used for anemometers such as rotating cup or propeller speed, torque on a fixed vane; there are even laser Doppler and ultrasonic anemometers. There seem to be enough alternatives that 3 completely different sensors could be used, and then take the average of the closest 2.
Critical avionic systems should be designed to cope with 'bad data'; garbage in, garbage out is not an appropriate paradigm for safety critical avionic systems; the fundamental problem is an aircraft level safety integration problem, which (IMNSHO) is an issue that needs a lot more attention.
Industry are not to blame (nor are they blameless), they have to work to the the regulations; nothing less, but also nothing more. If a supplier 'over-engineers' their product, they are likely to become uncompetitive. The initiative must rest with the regulatory authorities (FAA, EASA, et al.), it is they that need to raise the crossbar in order to continually improve aviation safety.

Hyperveloce

1st Aug 2009, 22:01

Quick translation of an ASR summary of the AF census of Pitot problems (08/2008)

Cruising at FL 380, weather radar ON (CAL mode ?), PAX ON, entering a cirrus veil. Suddendly, severe turbulence, A/P manually disengaged, deployment of the airbrakes to avoid MMO, Mach 0.78 selected, airbrakes retracted and A/P reengaged. Then again, new brutal acceleration, A/P automatically OFF, many red echoes on the weather radar, ice is beginning to accrete on the windshield. Altitude is maintained +/- 200 ft.
Many thunderbolts around, key phrase to the PNC in the cabin.
In a blink of an eye, the airspeed rolls back in the red area, recovers its value, then again the two airspeed indications are lost on the PFD and stall alarms are sounded. I was about to implement the stall procedure, before I even had the opportunity to send a MAYDAY, when the airspeeds recovers and are back on displays, then VFR conditions. All flight systems are back, verbal exchange with the cabin crew, they had the time to fasten their seat belt. Message ATC, Dispatch, ATL writing.
________________
fortunate to get the airspeeds back soon enough.
different pitot freezing event durations (between 2 and 4-5 mn, less than 1 mn for the last BA type probe recently), but no time indication here (sounds sudden and of short duration), and the stall alarms occur immediately
I don't get why people focus on airspeeds problems in the media, ok it is a problem but a problem with a clear solution (pich & thrust), but the very difficult troubleshooting (fault isolation) and the false stall alarms in this context seem to be the real evil, a problem pilots are seemingly not very well trained to.
Jeff
PS) These Pitot problems seem to have increased very rapidly in 2008 on the Thales AA, despite new maintenance rules adopted in 2003, why ? (this may be an explanation for the apparent lack of reactivity of the authorities, they may have been taken by surprise). Problems with the drain manufacturing qualifity were observed on certain AA probes, but if the pollution removal was correctly operated, does this suggest that the problem could be a gradual corrosion (aging accentuated by the initial manufacturing process) ?
PPS) I don't know whether AF had correctly evaluated the problems posed to air safety as seen through the cases it was gathering or through the Air Caraïbe cases, but I would like to know whether these ASR related to Pitot problems had been communicated to the DGAC, BEA, Airbus and to the EASA.
PPPS) CS-25 -General Certification Considerations -
.../...
(ii) Airspeed.
Display of airspeed in the cockpit is a critical function.
Loss of all airspeed display, including standby, must be assessed in accordance with CS 25.1333(b). *
Loss of primary airspeed display for both pilots must be improbable
Displaying hazardously misleading airspeed simultaneously on both pilots’ displays, coupled with the loss of stall warning or overspeed warning functions, must be Extremely Improbable.
_________________
could this kind of requirement be the reason why the stall warning or overspeed functions are still available in alternate law 2, even if the airspeeds are corrupted (ADR Disagree), even if this stall/overspeed warnings are largely plagued by false alarms ?
In the same vein, I really wonder why the (false) speed trends are still displayed on the PFD when the airspeeds are corrupted ? The AF 908's PF reacted to stall alarms because he was reading -50 kts of speed trend while the stall warning sounded at FL350 (these -50kts are most likely a measure of the roll back due to the obstruction, but indeed this must be a worrying signal at high altitude where the aerodynamic margin is reduced). This makes two misleading signals (plus the misleading procedure about stall warnings) and an immediate decision to take. Plus a possible airspeed chase by the A/THR to set the stage (and degrade the aerodynamic margin). Plus night hand flight & possible turbulences. Plus workload and attention split.

ArthurBorges

2nd Aug 2009, 07:37

"CYA" indeed, or, in air force jargon "Watch my six" and variants, as where "six o'clock" means "right behind you."

NARVAL

2nd Aug 2009, 10:03

Quote Hyperveloce : Displaying hazardously misleading airspeed simultaneously on both pilots’ displays, coupled with the loss of stall warning or overspeed warning functions, must be Extremely Improbable.
This casts doubts on the way the certification process is thought and approved…There are fine engineers and test pilots at Airbus, but it seems that the problem lies « upstream » in the process. The FHA (functional Hasard Assessment) studies the failures analysis and their threat to the safety. This is studied in part 1309 of FAR 25, with an advisory circular (AC 1309) explaining how to understand and enforce the rules…If I understand it correctly, you must look closely at the different causes especially if the failure comes from false raw data, or bad transcription, or erroneous comparisons etc…That is the Failure Mode and Effects Analysis. It seems to me, but I shall be happy to be corrected, that this has not been done thoroughly as far as the « Pitots » and their information are concerned. It was understood (wrongly) that a single event (in this case the icing of the three probes) could not interfere, or pollute, all the channels downstream. Thus angle of attack measurements with perfecly health vanes is polluted by erroneous airspeed indications…The Perpignan crash of a 320, even if due to reckless decisions in a hasty test-flight, should have started a strong reaction from the BEA as far as the « Vote-validated inputs control » is concerned.
Many cases are not covered by the certification in those new generation airplanes, and apart from changing the probes (which should have been a prudent recommandation by the BEA…but no, it is Airbus and EASA who make the move ) it will be necessary to strenghten and question the certification process.
Will it be done without pressure from the pilots ? Rather unlikely, I fear.

syseng68k

2nd Aug 2009, 10:47

litebulbs:
WhyIsThereAir:

So I guess a lower voltage is applied on the ground (ie: V/2 = P/4) to mitigate overheating, but it's still not optimal. One of the advantages of having temperature sensing and closed loop control is more capable bite in terms of ice detection, heating element or temp sensor failure. Agreed, the simplest solution may do the job 90% of the time and should be the most reliable since there are fewer parts, but in my experience, the electronics part of any modern system design is usually the most reliable, assuming conservative design rules. The problems are nearly always with the mechanical bits and of course connectors.

As for resistance elements, most of the commonly available resistance wires have only a small positive tempco. For example, nichrome is around 300 ppm per degree C, so they must be using some pretty fancy alloys for the function to get the (?) square law characteristics required.

Chris

HotDog

2nd Aug 2009, 11:01

In 33 years of various jet aircraft operations equipped with dual Pitot/Static probes, never had any airspeed indication problems due to probe icing. Perhaps they should go back a few years in technology and recyle some of the pitot tubes from the Arizona aircraft cemeteries.:ok:

WojtekSz

2nd Aug 2009, 12:43

is there any correlation between the pitot icing cases geographical/flight level location and other newly developed patterns in weather (possibly to global warnimg ?)

As this is recently happening much more frequently there must be some reason to this:
- technical design - unlikely as there is still substantian number of planes with the same technology being used for last 10 years and more
- flight patterns - i have no knowledge to check this - needed input from more experienced, but the only thing that comes to my mind is smaller plane separation due to higher traffic (mignt not be the case when flying to/fro SA)
- weather patterns - most probable as we are still learning about the weather phenomenon internal structure. Warmer seas (an clearly established fact) mean more energy available to build higher cb and transport huge masses of air and water into high elevations

The production/certification tests are based on some standard repeatable conditions which may be currently not standing up to real life requirements

Hyperveloce

2nd Aug 2009, 15:18

On October 19, 2002, about 2000 eastern daylight time (EDT) [or 0000 coordinated universal time (UTC)], a Boeing 757-200, TF-FII, operating as Icelandair flight 662, experienced a stall while climbing from flight level (FL) 330 (i.e., 33,000 feet) to FL 370. The flight lost about 7,000 feet during the recovery and then diverted to Baltimore-Washington International Airport (BWI), Baltimore, Maryland. There were no injuries to the 191 passengers or 7 crewmembers and no damage to the airplane.

ANALYSIS/CONCLUSIONS

During the takeoff roll as the captain was about to call "eighty" knots, the first officer called "hundred." The captain noted that the standby airspeed indicator agreed with the first officer's and decided to continue the takeoff and address the anomaly of his airspeed indicator after takeoff. The pilots indicated that EICAS messages appeared and disappeared several times after takeoff and during the climb, including the messages MACH/SPD TRIM and RUDDER RATIO. Checklists for MACH/SPD TRIM and RUDDER RATIO messages did not mention an unreliable airspeed as a possible condition. The modifications associated with Boeing Alert Service Bulletin 757- 34A0222 (and mandated by FAA Airworthiness Directive 2004-10-15 after the incident), which had not been incorporated on the incident airplane, would have provided a more direct indication of the airspeed anomaly. According to information in the Icelandair Operations Manual, these EICAS messages (in conjunction with disagreements between the captain and first officer airspeed indicators) may indicate an unreliable airspeed. Overspeed indications and simultaneous overspeed and stall warnings (both of which occurred during the airplane's climb from FL330 to FL370) are also cited as further indications of a possible unreliable airspeed. The crew did take actions in an attempt to isolate the anomalies (such as switching from the center autopilot to the right autopilot at one point during the flight). However, this did not affect the flight management computer's use of data from the left (captain's) air data system, and the erroneous high airspeeds subsequently contributed to airplane-nose-up autopilot commands during and after the airplane's climb to FL370. During the climb the captain's indicated airspeed began to increase, and the overspeed warning occurred. The first officer indicated that at this time his airspeed indication and the standby airspeed indication both decreased to about 220 knots and his pitch attitude felt high. Despite agreement between the first officer and standby airspeed indications and the pilots' belief that the captain's airspeed indicator was inaccurate, control was transferred from the first officer to the captain. Pitch attitude continued to climb and airspeed continued to decay after the captain assumed control. The airplane's pitch attitude became excessively high until the airplane's stick shaker activated and the airplane stalled. Although stall recovery was eventually effected and the airplane was leveled at FL300, the lack of appropriate thrust and control column inputs following the stall delayed the recovery. Evidence from the investigation indicates that anomalies of the captain's airspeed indicator were caused by a partial and intermittent blockage of the captain's pitot tube. The reason for the blockage was not determined.
Source:
http://www.rnf.is/media/skyrslur/2002/M-08602_AIG-34,_flugatvik_TF-FII_vid_Baltimore_skyrsla_NTSB.pdf (http://www.rnf.is/media/skyrslur/2002/M-08602_AIG-34,_flugatvik_TF-FII_vid_Baltimore_skyrsla_NTSB.pdf)

PJ2

2nd Aug 2009, 17:09

Jeff;

Around 1990 or so I had this very scenario occur on a 767 during climbout over the Rockies one dark, overcast winter night. The captain's airspeed was the problem as the F/O's airspeed compared correctly with the Standby Airspeed. We flew the F/O's airspeed to destination and the Captain's airspeed slowly corrected as we descended into warmer air (relatively speaking - it was minus 15 or so), on final.

The same EICAS messages occurred to us as did on the Icelandic 757. We did not have to use pitch-power responses as my airspeed was unaffected. We wrote it up of course.

As industry experience shows, the problem, although extremely rare, isn't new, isn't isolated to the Airbus A330 and almost never leads to an accident if the causes and the procedures for dealing with the failure are understood. Going back to "old designs" is not the solution.

BOAC

2nd Aug 2009, 17:40

Agreed, PJ, nothing new under the sun, and it has been happening since the first pilot took off with his pitot head cover or static port plug in place, but as I said before (4031 and earlier) what appears to be new is either a multiple failure of probes or some software effect. All the 'examples' we are getting here involve ONE of the sensors. I think, however, the ?AeroPeru' crash had all the statics blocked?

Will Fraser

2nd Aug 2009, 17:48

So the question becomes what is different about the bus' reaction to discrepant a/s? Are we certain that three pitots failed on 447? No.
What is AB's plan for unreliable air speed driven a/p? I'm reading about pitot/a/p problems in Boeing, in climb, and single failure as well.

If the AD calls for r/r of two pitots only, and AB believes all three failed on 447, you see the problem? Something doesn't fit.

Smilin_Ed

2nd Aug 2009, 17:53

If the AD calls for r/r of two pitots only, and AB believes all three failed on 447, you see the problem? Something doesn't fit.

Could the folks who wrote the AD be aware of a logistics problem, i.e. there are only so many Goodrich probes available so they're spreading them out over the entire fleet? Agreed that something doesn't fit, at least from where I sit.

Will Fraser

2nd Aug 2009, 18:04

With autos not selling, tire sales are off, Goodrich isn't that busy. I'm convinced it's money, and I'm not the only one. AF and AB are in a tough spot.

Smilin_Ed

2nd Aug 2009, 18:30

Goodrich doesn't make auto tires anymore. They sold the tire brand to someone else, maybe a Japanese company, and are strictly in the aerospace business now. I think they make landing gear, wheels, and brakes. Didn't realize they were in the pitot tube business too until this came up.

HazelNuts39

2nd Aug 2009, 18:42

Smilin,
Didn't realize they were in the pitot tube business too until this came up.

I believe the 'pitot tube business' was previously called "Rosemount".

regards,
HN39

HazelNuts39

2nd Aug 2009, 19:01

RE: Hyperveloce (#4076)

The Conclusion of the the NTSB Airplane Incident Report:
The National Transportation Safety Board determines the probable cause(s) of this incident as follows:
The captain's improper procedures regarding stall avoidance and recovery.
Contributing to the incident were ...

Pilots MUST respect stall warning.

regards,
HN39

pax2908

2nd Aug 2009, 19:13

It is reasonable to assume that more is known than publicly available. There has been a lot of speculation concerning the probes. So I am assuming that by now a significant number of probes have been inspected, and problems were found. Possibly, corrosion has been mentioned; if so, it is only a matter of time before some pictures become available? Or, are the probes being replaced without a clue of what's going on?

ernst_mulder

2nd Aug 2009, 20:48

As a non-pilot I have a question. I know this is off-topic but it has been bugging me reading this forum.

What I do not understand is the sequence "IAS declines - stall warning sounds - stall procedure initiated". If the IAS declines during a well defined stable cruise with a specific engine thrust I would think that the stall warning and IAS would immediately be suspect. In fact a stall procedure at this stage might even be unsafe.

Graybeard

2nd Aug 2009, 21:01

Am I missing something regarding faulty airspeed on the 757/767? The pilot seeing erroneous airspeed just has to reach forward and switch to Alternate ADC.

GB

SPA83

2nd Aug 2009, 21:11

TSO C16, Air-speed tubes (electrically heated), requires compliance
to the performance specifications of SAE Aerospace Standard AS393. SAE
AS393A includes a test to demonstrate deicing and anti-icing capability, but only temperature and airspeed are specified. Liquid water content is not specified but it influences heat requirements. Although functioning of pitot probes are evaluated in natural icing conditions during certification test programs, there is no requirement to flight test at the Appendix C or X icing limits because the low probability of finding those conditions imposes a burden. The airframe manufacturer is responsible for showing the pitot heat is adequate for the Appendix C and Appendix X icing conditions. If not obtained in flight test, analysis or icing tunnel test data should be submitted.
Although Appendices C and X of part 25 only consider the liquid
water content of icing conditions, recent cloud characterization research has indicated that approximately 40 percent of icing condition events consist of liquid water drops and ice crystals (mixed-phase icing conditions). The ice crystal environment may be more critical than liquid water for thermal systems since more energy is required to evaporate the ice crystals.

JD-EE

2nd Aug 2009, 22:17

syseng68k, what use is a closed loop control of you do not know the sweet spot for applying the sensor and have a way of doing so without destroying the probe's calibration? I strongly suspect that presuming the entire probe is all at one temperature is a serious mistake.

Something changed in the last few years that is affecting the probes of at least one manufacturer rather adversely. It's not global warming, the time frame is wrong to declare that. We've been cooling this last decade. So let's look, instead, at things like probe maintenance, probe mounting, flight regimes used, and so forth.

That might be some worthwhile study even if it does not apply to the accident under discussion here. I've certainly seen no proof that this is what happened to AF447. "It's too simple," is the way I'd describe it as a cause. AF447 was more likely done in by a rather rare cascade of failures, perhaps improper radar settings (lack of training), perhaps asleep in the cockpit, perhaps distracted by preparations for the 4 hour crew change, perhaps it involved engine icing, perhaps any number of things mentioned here. (Maybe some of them can be surmised from noting the strange position at which the plane apparently hit the ocean with a very strong vertical velocity component. A really good "it went down here" position might sharply limit the flight (or spin) profiles that could have taken place. That would also require some good guesses at just how high a vertical velocity component was needed to cause such a breakup.)

Look to things that somewhat limits the probability that it's a daily event for other AF447 flights before this one. I note one, it was particularly dark with very little illumination from the Moon. That limits any visual horizon for orientation. That happens half or less of each month. Another is the somewhat exceptional storm. And, yes, icing on pitot probes seems to be an exceptional event. But is this enough for explaining why it's only happened once since A340s were flying that route at that time of day? (Does the flight more commonly have its 4 hour crew change happen at a different position in the flight? Could this have been caused by the captain being overdue in the cockpit leaving the F/Os preoccupied with "where is he?")

JD-EE

PJ2

2nd Aug 2009, 23:43

BOAC;

Yes, the Aeroperu had the statics taped over with clear tape while the airplane was washed. The Birgenair 757 pitot loss cause was undetermined but there was a theory that mud-dauber wasps had built a nest in one of the pitot tubes. The current issue is disconcerting for sure. Because of the autoflight system depth of component and software integration the effects can be very distracting and initially difficult to assess while the airplane's warning systems settle down. Cascading failures can be very distracting, but that is not the primary issue here. The key is to do nothing and change nothing because the airplane was just fine moments before the event. The issue here is surprise and confusion not the loss of data and that is not a situation which will inevitably lead to a LoC.

GB, not sure who you're asking re "the pilot seeing erroneous airspeed" and re the point you're missing. I don't recall a lot about the 1990 incident and what we did but if it was my post your asking about, the point you're missing is obvious I think - the unreliable airspeed problem was essentially a non-event. We determined which indicator was correct using the Standby ASI and we flew the airplane to destination without further incident.

I don't recall any drills in the books which called for switching ADRs as, at the time, there was no such thing as an unreliable airspeed. We just used our heads and made it up as we went and it worked just like it should. The Birgenair and Aeroperu accidents occurred in 1996 I believe.

mulder:
I would think that the stall warning and IAS would immediately be suspect. In fact a stall procedure at this stage might even be unsafe
In my opinion, you are correct. "Respect the stall warning" must be understood as meaning, respect "legitimate" stall warnings. We expected (but did not get) an overspeed warning when the captain's ASI exceeded the barber pole, (Max operating speed). We would have ignored the overspeed warning in that case.

DJ77

3rd Aug 2009, 11:48

In US terminology, incidence is defined as the angle between the reference chord line of the wing and the longitudinal axis of the fuselage. As far as I know, this angle generally lies in the range 0 to 3 deg. With this definition, we have in level flight:
Pitch attitude = Angle of Attack - incidence.

The A330 "Unreliable Speed Indic. / ADR Check Proc." contains a table of Pitch / Thrust values. In this table, for parameters corresponding to AF447 known data at the time of the events, ie:

clean configuration,
cruise phase,
gross weight > 190 t,
FL250 – FL 370,

you can read:

Speed = 260 kt,
Pitch attitude = 3.5 deg,
N1 = 90%.

The pitch attitudes values in the table are rounded to the closest 0.5 deg.

The report on the ACA incident says (page 11) that the "STALL" audio alarm is triggered when the AoA exceeds a predetermined value that depends on

Flaps or Slats position,
Speed or Mach (???),
Active control law (normal, alternate or direct).

Then it states that two STALL audio alarms occured during the incident for AoAs of 4.48 deg and 4.31 deg respectively. Those values were obviously obtained from FDR data. A note adds that the STALL alarm is triggered at a threshold AoA of 4.2 deg. I believe that this value only applies in the configuration of the incident and was obtained from Airbus personnel.

It may look stange that AoA depends on airspeed but probe litterature generally speak of "local AoA" and "corrected AoA". An important design stage for AoA probe installation is to find a place on the fuselage where the correction is quasi linear relative to airspeed. This is done experimentally in wind tunnel. One would expect that if the associated Air Data Computer detects unreliable airspeed, it uses a default conservative correction factor. Alternatively, the warning computer could use increased margins, which would account for the threshold AoA dependancy upon the active control law.

Since the configurations of the ACA flight and AF 447 were very close (cruise, clean, about same weight, same level), It seems very likely that AF 447 experienced STALL alarms. Moreover, if the 4.2 deg AoA threshold value is true, the formula:
Pitch attitude = Angle of Attack - incidence
3.5 deg = 4.2 deg - incidence
shows that, at this weight and flight level, even taking into account rounding and using zero incidence, the a/c is very close (less than one deg) to the stall warning alarm threshold. A little pitch up move of the sidestick or a small updraft could trigger it.

Posted by HazelNuts39: Pilots MUST respect stall warning

That is fairly true. This alarm is in the category of "time critical warnings", like GPWS or windshear alarms, that require immediate crew awareness and corrective action. Crew Resource Management teaches that when such an alarm occurs, it's not the time to start wondering what caused it, but to act.
The PF of the ACA flight fortunately did not perform the stall recovery procedure because he was convinced the plane was not stalled. This conviction was certainly based, among other cues, on the fact that he had been controlling airspeed manually for some time when the airspeed rollback event occurred. In fact, FDR data show they exited the event at the same airspeed they entered it. They did respect the stall warning in an appropriate way since they voluntarily ignored it.

Contrary to ACA, the A/T was controlling airspeed aboard AF447, until it disconnected. The crew was not at the same level of awareness about the airspeed before the indicators went astray. If a STALL alarm sounded, which I think is very likely, they logically respected the alarm the standard way: nose down, full thrust then ... loss of control ?

The main cause of the accident could be ... failure of the crew to disregard a false alarm.

HazelNuts39

3rd Aug 2009, 12:11

RE: PJ2 (#4090)

"Respect the stall warning" must be understood as meaning, respect "legitimate" stall warnings.

I’m inclined to question the wisdom of advocating “respect only ‘legitimate’ stall warnings”. Firstly, I believe that the risk involved in the appropriate response to stall warning tends to be overstated, considering that in most of these incidents the stall warning occurs after the speed has been reduced to turbulence penetration speed, typically Mach 0.78 – 0.80. Secondly, I believe that we (several posters including myself) may have been wrong in assuming that these stall warnings are “false”.

To elaborate on the first point:
(a) from ASR on FGNIH AF908 CDG-TNR -
Suivi immédiatement de l'alarme STALL STALL STALL (sans l'alarme cricket associée) avec indication de TOGA LK. Comme j'avais toujours le speed trend à moins 50 Kts, j'ai piloté l'avion en manuel avec mise en descente et léger virage à droite pour sortir de l'AWY. L'avion répondant très mollement avec sur le PFD CDB plusieurs régressions de vitesse dans le bandeau rouge inférieur. (...) Descente jusqu'au FL 340. La vitesse avion étant redevenue correcte j'ai débrayé l'ATHR pour sortir du TOGA LK. Les indication de vitesse étant similaires coté CDB et OPL, ...
and (b) from NTSB Report on Icelandair B757 incident; Icelandair Stall Recovery Training; as per Boeing 757 Flight Crew Training Manual; see source document for Approach-to-Stall Recovery procedure -
A stall must not be confused with the stall warning that alerts the pilot to an approaching stall. Recovery from an approach to a stall is not the same as recovery from an actual stall. An approach to a stall is a controlled flight maneuver; a stall is an out-of-control, but recoverable condition.

To elaborate on the second point, I would like to re-examine information provided in the Air Caraibe memo:
On page 12 - la check-list « UNRELIABLE SPEED INDICATION » ... , dans sa partie développée en 3.02.34 page 17, celle-ci stipule «RELY ON THE STALL WARNING THAT COULD BE TRIGGERED IN ALTERNATE OR DIRECT LAW. IT IS NOT AFFECTED BY UNRELIABLE SPEEDS, BECAUSE IT IS BASED ON ANGLE OF ATTACK ».
On page 11 - l'alarme « STALL » se déclenche deux fois pour un « AOA » de 4.48° puis 4.31°. NB 5, seuil pour le déclenchement de l'alarme « STALL » : « AOA »=4.2°
On page 6 - «HIGH ANGLE OF ATTACK PROTECTION»: (...) Faisant suite à un problème technique et dans le cadre d'une reconfiguration de la loi de pilotage en « ALTERNATE LAW 1 », il existe une nouvelle protection appelée « LOW SPEED STABILITY » laquelle s'active entre 5KT et 10KT au dessus du décrochage. La profondeur passe alors en « DIRECT LAW». Néanmoins, un ordre qui peut être surpassé par le pilote et visant une diminution de l'assiette est introduit pour maintenir une marge par rapport à la vitesse de décrochage. Une alarme sonore « STALL » s'active. Sur le « PFD » les vitesses « Va PROT » et « Va MAX » sont remplacés par Vsw. Pour terminer, il faut souligner que le givrage des sondes « PITOTS » et « TAT » entraîne au préalable l'apparition du message « F/CTL ADR DISAGREE » qui engendre à son tour le passage en « ALTERNATE LAW 2 » avec dans ce cas la perte de la protection « LOW SPEED STABILITY ».

I’m taking the text quoted from page 12 for what it says: stall warning in alternate or direct law is based on AoA; it is not affected by unreliable speeds.
Likewise for the facts quoted from page 11: two stall warnings occurred at AoA’s 4.48 and 4.31 degrees, for a threshold of 4.2 degrees. In other words, these are valid stall warnings as per system design.
The text on page 6 is not entirely clear to me. Does it mean that stall warning in Alternate Law 1 occurs at an AoA corresponding to ‘between 5 and 10 kt’ above stall speed? In that case the stall warning margin in Alternate Law 1 ‘as per system design’ would be about twice the regulatory minimum of 3 knots or 3 percent, which ever is greater. This could make sense in view of the lost alpha-prot protection, while the stall warning margin in Normal Law is presumably closer to the regulatory value. The last sentence (Pour terminer ...) is not understood. If it means that stall warning is lost, that would contradict the procedure which aims to retain stall warning by keeping one ADR ‘online’.

regards,
HN39

PS: After writing the above, I read DJ77's #4091, but decided to post my contribution anyway because I think it's still valid. DJ77's last paragraph raises the question: Would the occurrence of a stall warning normally trigger an ACARS message?

Hyperveloce

3rd Aug 2009, 13:40

Hi there. Thank you D77, PJ2, all, for these reasonning.
-The Air Caraïbe report states that the stall warnings are triggered as soon as the AoA exceeds 4.2° (can't we find the tables for these AoA thresholds as a function of the aerodynamical configuration & the Mach ?), so indeed, a downdraft of ~10 kts would be sufficient to biase the AoA so as to induce a stall alarm ?
-In most of the known recent cases (about Pitot icing & corrupted airspeeds), stall warnings were sounded, in one occurence it was an overspeed warning. The freezing event durations seem to lie between 1mn and 4-5mn (3mn average).
-It appears that some pilots (were about to) react(ed) to the stall alarms
-The simulation trainings only implement true stall/overspeed alarms justified by conditions in most cases known and prepared beforehand.
-Facing a decision about a stall warning, wouldn't a pilot consider both the cost of disreguarding a justified stall warning and the cost of taking in account an undue stall warning ? (depends on where the PF thinks his plane is within the flight envelope)
-Which are the signals a pilot should consider to make his decision about stall warnings ? (ADR disagree context)
D77 suggests that the Air Caraïbe crew may have had a better, real time awareness of their airspeeds/thrust (A/THR manually OFF) than the AF 447 crew when they faced the stall warnings.
A cross-checking in the BUSS fashion (pich/altitude time evolution for a given pich,thrust)
A cross(checking in the OCTAVE fashion: airspeeds directly compared to GPS ground speed corrected by the OCTAVE
wind database (time required for that ? accuracy versus the aero margins ?)
.../...
on the contrary what would be the false friends to avoid when you have to decide about stall alarms ?
the speed trends if they are maintained/still displayed on the PFDs !
the part of the unreliable airspeeds procedure that tells to take stall alarms in account (and to disreguard the
ECAM warning "risks of undue stall warnings")
.../...
If it appears that the AF 447 may have lost control in high altitude cruise because it reacted badly to a stall alarm, it should be possible to assess the amount of time required to increase the airspeed from Mach 0.80 (~cruise speed) to Mach 0.85 (reaching MMO) then to Mach 90 (severe overspeed) under a few hypothesis ( thrust ; descent angle )
couples ?
Does anone understand why one of the planes which went through a Pitot freezing event (with the deluge of similar ECAM messages) found itself in TO/GA LK ? (the A/THR was manually disengaged before)
Jeff
PS) stall/ overspeed warnings are not transmitted by the ACARS

jshg

3rd Aug 2009, 14:17

On the A330 in manual thrust if speed drops below a certain point, ( 'alpha floor', close to the stall), auto thrust re-engages at TOGA power (thrust lock). The only thing that will stop it is if auto thrust is unserviceable.

Hyperveloce

3rd Aug 2009, 14:49

Yes jshg, I have also read that the TO/GA LK could only result from the activation of the alpha prot (the AoA law was only available before the ADR disagree and the deluge of ECAM alerts, it is lost in ALTN2). The thrust index N1 will also be locked if the A/THR fails, then "THR LK" will flash on the FMA at the top of the PFD (the PF should not miss it if he is hand flying the plane ?) when the ECAM will display "AUTO FLT A/THR OFF". Will the FMA diplay THR LK or TOGA LK if the N1 was full thrust (TO/GA) when it was locked ?
If one of the planes (Pitot freezing) found itself in TO/GA LK after the ADR disagree, does it suggest that its alpha prot had activated just before ? If the A/THR was manually set to OFF, it shouldn't have been chasing airspeeds in this case (but wouldn't the alpha prot. also reduce the AoA or the pich ?)
As the AF 447 is the only case with an engaged A/THR when the problems occured, I would really like to know whether there is a mean to confirm that an A/THR in managed speed mode can chase declining airspeeds (thus reducing the margins left to the pilots). But whether it was an alpha prot. activation or an A/THR chasing declining airspeeds, the result would be similar: the automation reducing the margins of the pilots/crew before it threw the towel ? The next question would be to know whether these two possibilities can remain outside the situational awareness of the crew (taking in account the context).
In any case, assuming that the pich was lowered and the thrust was increased either by automation or the crew, I feel it would be really interesting to know if the crew had only 30 sec and 60 sec before the plane reached MMO and Mach 0.9 (for example assuming a 2° descent from FL350 and TOGA). To know how much time left the crew had to recognize/acknowledge the overspeed situation.
(actions: thrust on idle, airbrakes deployed, severe overspeed: lower the landing gear ?)
keeping in mind the possible PRIM1/SEC1 voluntary reset (between 02:13:15 and 02:13:30): if the airbrakes were deployed, they would have been retracted by this event whether it be automatic or manual.
Jeff

DJ77

3rd Aug 2009, 15:17

HazelNuts39:

The text on page 6 is not entirely clear to me. Does it mean that stall warning in Alternate Law 1 occurs at an AoA corresponding to ‘between 5 and 10 kt’ above stall speed?

Yes, that's what it means.

The last sentence (Pour terminer ...) is not understood. If it means that stall warning is lost, that would contradict the procedure which aims to retain stall warning by keeping one ADR ‘online’.

My tentative translation:
"Finally, it is worth noticing that PITOT and TAT probes icing entails first the << F/CTL ADR DISAGREE>> message pop up, which then generates switching to <<ALTERNATE LAW 2>> and, in this case, loss of <<LOW SPEED STABILITY>> protection."

the <<LOW SPEED STABILITY>> protection is described in the first part of the paragraph. Since the system can no longer determine if there remains a valid airspeed, it seems logical to cancel the protection. That does not preclude stall warnings based on AoA.

btw, I doubt that TAT probe icing plays a role in this sequence.

BOAC

3rd Aug 2009, 15:33

Back to the AB experts please. Again apologies if I am going over old ground, but the reading of the thread remains a challenge.

I understand the ABI instruction is to 'respect the stall warning', but to me it looks as if there will not be one?

From my reading of the 330 FC section, it appears that in ALT 1 there will be an IAS driven stall warning, but in ALT 2 with 2 ADRs out there will not, and with 3 out there will be also no overspeed warning.

Obviously there cannot be a reliable 'overspeed' detection, but I cannot see why an AoA triggered stall warning is denied in a worst case scenario of no IAS to work on. Are AB pilots actually happy with this or should the warning be available? (E&OE of course:)) Surely this is the only 'long-stop' left to a crew with multiple IAS failures?

Smilin_Ed

3rd Aug 2009, 15:46

I continue to get the feeling from this conversation that at least some pilots feel that a stall warning requires instantaneous action to prevent a major upset. When I mentioned this earlier, someone, I forget who, reassured me that flying a Bus in AF442's situation was NOT like trying to balance on a bowling ball. Is there not time to assess the situation and take deliberate response vs. instantaneous reaction? Would they not have had time to determine whether a stall warning was legitimate? What's the rush? If, unlike the Colgan and Turkish crews, the AF crew was not asleep, would not a thoughtful assessment of the situation be the prudent course?

Also, are angle of attack data not derived from a vane (or whatever) independent of the pitot/static, ADIRU, gyro, and inertial systems? Would not a glance at an independent AoA readout be the way to verify or validate a stall warning while in cruise. Is there such a readout?

Will Fraser

3rd Aug 2009, 16:07

I agree with SmilinEd. Just because one sees a warning is no reason to go into Panic mode. My sense of this crew tells me with their experience and skill, they were calm and professional. As A330 pilots, they were the best informed and current in type than any, "Stall? mmm...what gives?".

One can get carried away with 'nonchalance', however. That 1011 that plopped in the swamp had everyone fixated on a broken green lamp. That's taking 'detachment' a bit far.

HazelNuts39

3rd Aug 2009, 17:13

RE: Smilin Ed (#4098) and Will Fraser (#4099)

Smilin,
The issue we're discussing has nothing to do with AB vs the rest of the world. A distinction needs to be made between stall avoidance and stall recovery. Stall warning warns that stall is approaching, it is NOT identification that the airplane is stalled. Stall warning begins when AoA exceeds a threshold below the stall, and continues until AoA is reduced below the threshold. Stall avoidance demands prompt response. No panic, just a gentle reduction of an abnormally nose-high attitude will stop the warning. The immediate effect of pitching down is to reduce AoA. The reduced lift causes the airplane to descend so that it will pick up some speed. Meanwhile the engines will have spooled up to provide the extra thrust that will recover the lost altitude. If you don't respond, the stall warning may cease while maintaining pitch and thrust, e.g. if it has been caused by an upward gust. If you allow the stall warning to persist, you don't know whether you are close to the warning threshold or close to stalling. In the latter case, a more agressive maneuver may be called for to avoid stalling. If you do stall, no need to panic either - the airplane has demonstrated safe stalling characteristics in many (hundreds?) stalls before type certification. You will loose a couple of thousand feet, will see some unusual attitudes and g-levels, but if you stay cool you will end up straight and level. You may have some explaining to do after you get home - like that Icelandair captain.

regards,
HN39

Hyperveloce

3rd Aug 2009, 17:38

Well, if you get stall alarms at a flight level of 350 and if you see -50 kts of speed trend (trend over 10 seconds) on your PFD, isn't it a powerfull invitation to think quick, given your thin margin ? (probably <50 kts at FL350 ?). No need to panic of course, but you have to take this decision just after being rained down with multiple ECAM alerts, aural and visual alerts, and after having lost most of your flight protections. Maybe you had a little time to think about these multiple signals, to try to understand all these confusing signals displayed on the ECAM and the PFDs, then a new problem arises, you hear that your plane is stalling. No need to panic, but a clear & quick analyzis in a high workload & confusing situation ? The misleading signals: the stall warnings themselves, the airspeeds, the airspeed trends, the ECAM warning about "risks of undue stall warnings" and the SOPs urging you to take stall warnings into account (and to disreguard the ECAM warnings).
Sorry but I know how I feel when my PC goes haywire, produces strange & conflicting signals, and when my troubleshooting book or service is of no help. I how it can be frustrating, although I have all my time to comprehend between two coffees, in a flat world. I can't figure out how I would be, if I had only tens of seconds to solve a very confusing problem, with a plane to handfly in the same time with no visibility, in the night, buffeted in a tropical thunderstorm. I guess I would really be tempted to reboot the failed automation, but I am not a pilot.
All I know are past incidents, and past incidents show that some pilots are taking the stall alarms (and some other flight parameters) seriously. And some other incidents show attempts to reboot the PRIM/SEC inflight to regain a normal law. I don't know if you have the time to think, but in certain situations, you don't even have the time to send a MAYDAY.
Jeff
----------------
PS) Are there formulae or tables to compute the time needed to reach Mach 0.85 and Mach 0.90 starting from FL350, Mach 0.80, according to several descent angles (1°,2°,3°...) and different thrust levels (N1=0.85, 0.90, 0.95, Max) ? is it possible to compute the same thing but with a banking angle ?
----------------

Smilin_Ed

3rd Aug 2009, 18:02

HN39, my comment/questions are not unique to AB to any other manufacturer. It just happens that this is an AB accident. I still think the attitude on this thread, regardless of make of plane, seems to be that response to a stall warning has to be super fast. Does it? If the crew is awake and the plane seems to be flying OK, there's no need to panic and consequently take the wrong action. Just deliberate assessment of the situation followed by appropriate action.A glance at the AoA, should quiet any fears. IMHO, there should be an independent AoA readout available at all times.

24victor

3rd Aug 2009, 18:42

ELAC explained the reason why some time back. This is getting to be a really long thread........

Rgds.

24V

Actually, the instrument exists and has been an available option for FBW Airbus's for at least 16 years, and probably since the introduction of the A320 in 1989. If you look at a cockpit photo you can even see the "blank" in the upper left corner of the Capt.'s instrument panel where the AoA indicator is meant to be fitted. The problem is not the lack of the instrument, just an unwillingness of the airline's to pay for an instrument that they don't consider necessary.

ELAC

Will Fraser

3rd Aug 2009, 18:47

Regardless of the many opinions surrounding such a corporate position, ELAC has framed the discussion, a discussion that transcends this thread, and may or may not have something to do with the fate of AF447, Rocket junk and histrionic writing aside.

JD-EE

3rd Aug 2009, 20:16

Smilin Ed, if the occupants of the flight deck were paying attention to their instruments rather than doing something silly like reading their Playboys or playing canasta they should have a good awareness of what the AP has the plane doing. So if there is a sudden stall warning for no known good reason why should they act by doing something which might be wrong. If they are in the correct regime and an input to the stall warning system went sour almost anything they do other than intentionally ignoding the warning would be the wrong thing.

You ARE doing something when you intentionally sit there and make no changes.

JD-EE

PJ2

3rd Aug 2009, 20:33

Jeff;
Are there formulae or tables to compute the time needed to reach Mach 0.85 and Mach 0.90 starting from FL350, Mach 0.80, according to several descent angles (1°,2°,3°...) and different thrust levels (N1=0.85, 0.90, 0.95, Max) ? is it possible to compute the same thing but with a banking angle ?
No. Such tables would serve no useful purpose or solve no problem which carries risk. No airline pilot has a right to expect that such tables would be used or useful, mainly because most seasoned pilots know pretty well what it would take.

To regain speed at high altitude it takes a very long time in level flight especially if the air is warm, (ISA + 15 and warmer). However, speed can increase very rapidly even with a 0-degree pitch or perhaps 1, maybe 2 degrees at most, depending upon power setting and what the air is doing around you. Most transports cruise at 2deg NU or so - some slightly higher, others a bit lower and it is of course, dependant upon IAS. A five degree nose-down pitch is a very serious pitch down and 10 degrees could be defined as a loss of control without speed/Mach limit.

It's very simple and explained very well in Davies. The L/D curve for a jet transport when Davies wrote back then and still today, is very shallow. The airplane will slide along the curve left and right, very easily where as for propeller-driven aircraft the curve is much more "U" shaped mainly due to the thrust and drag offered by the large disc(s) described by the props.

BOAC

3rd Aug 2009, 20:35

Guys - where is this 'stall warning' you keep talking about going to come from? Is it not determined they were in Alt 2 Law with at least two ADR's 'suspect'?

HazelNuts39

3rd Aug 2009, 21:21

RE: Smilin Ed (#4102)

I still think the attitude on this thread, regardless of make of plane, seems to be that response to a stall warning has to be super fast. Does it?
Generally speaking, no. The time available for an action to avoid stalling depends on how rapidly the stall is approaching. Most airplanes, including the A330 in Normal Law, will have a stall warning margin of the order of 3 percent of the stall speed. In certification tests to determine the stall speed, the speed is reduced at the rate of 1 knot per second until the airplane stalls. If the stall warning is set to occur 5 knots above stall speed, then it would occur 5 seconds before the airplane stalls.
A glance at the AoA, should quiet any fears. IMHO, there should be an independent AoA readout available at all times.
I'm sure any testpilot would agree totally. However, I'm told that, generally speaking, airline pilots have no use for an AoA indicator.

regards,
HN39

Hyperveloce

3rd Aug 2009, 21:24

Jeff;
It's very simple and explained very well in Davies. The L/D curve for a jet transport when Davies wrote back then and still today, is very shallow. The airplane will slide along the curve left and right, very easily where as for propeller-driven aircraft the curve is much more "U" shaped mainly due to the thrust and drag offered by the large disc(s) described by the props.
Thank you PJ2, I will try to find your reference. I did a very simple computation a while ago, but I have no experimental data to validate this, do you think it could be plausible ?
http://img34.imageshack.us/img34/2411/machpoint.jpg
This would suggest that it takes a little bit more than 30 s to exceed the MMO, a little bit more than 1 min to reach Mach 0.88, and more than 2mn to reach Mach 0.89 (with a N1=0.95 and a 2° descent)
Jeff

Smilin_Ed

3rd Aug 2009, 22:40

Based on responses to my queries, it seems to me that fear of stalling out in cruise is misplaced. One has to wonder where this fear comes from. Training? Were not the stall warning features implemented primarily for approach phases?

DJ77

4th Aug 2009, 09:39

Based on responses to my queries, it seems to me that fear of stalling out in cruise is misplaced. One has to wonder where this fear comes from

Smilin, if I stalled, my main fear would be to see your arse flying in the cabin.

HazelNuts39

4th Aug 2009, 09:55

RE: DJ77 (#4091)

DJ,

I believe industry practice is that the aircraft longitudinal axis (x-axis) is the reference for angle of attack (alpha), flight path angle (gamma) and pitch angle (theta). All angles are positive upwards. The relation between these angles is given by:

theta = gamma + alpha

From the ATSB Interim Report on the A330/QF72 accident:
For an A330, during all phases of flight, the typical operational range of AOA is +1
degree to +10 degrees. In cruise, a typical AOA is +2 degrees.

It may look strange that AoA depends on airspeed but probe litterature generally speak of "local AoA" and "corrected AoA". An important design stage for AoA probe installation is to find a place on the fuselage where the correction is quasi linear relative to airspeed. This is done experimentally in wind tunnel.

A calibration curve for the relation between vane angle and airplane AoA is established during flight tests. I assume that this calibration is used in the ADIRU to convert the alpha-vane output to AoA.

Stall warning AoA is normally not affected by airspeed or mach, but it is possible that the calculation algorithm applies a Mach-bias at high Mach.

regards,
HN39

Smilin_Ed

4th Aug 2009, 10:14

Smilin, if I stalled, my main fear would be to see your arse flying in the cabin.

Not to worry then. Except for an occasional trip to the loo, I'd be tightly strapped in. :)

DJ77

4th Aug 2009, 10:41

re: HN39 (#4112)

HN39, I agree, if the x axis is the reference for AoA then theta = gamma + alpha. Then in level flight [gamma = 0]: theta = alpha. By the way, the choice of a reference for AoA is somewhat arbitrary.

This still leaves AF447 less than 1 deg away from stall warning, if the 4.2 deg AoA triggering threshold is true.

DJ.

BOAC

4th Aug 2009, 11:07

I'll ask again! In ALT2 WHAT is going to trigger the stall warning please?

Hyperveloce

4th Aug 2009, 11:48

Acoording to the Air Caraïbe ASR, the stall warnings are triggered as soon as the AoA exceeds a threshold which is a function of:
-the aerodynamic configuration (slats/flaps)
-the airspeed (kts) or mach point
-the control law (normal, alternate, direct)
I wonder if this AoA/speed threshold computation is the same as alpha floor & alpha max computations (excepted that the AoA law/alpha prot. will no longer take over to control/protect the plane since it is no longer active, but will only sound a warning as soon as the AoA threshold is exceeded). Does anyone know how these alpha threshold are computed ? (where can we find the AoA threshold tables ?)
Jeff

DJ77

4th Aug 2009, 11:52

I'll ask again! In ALT2 WHAT is going to trigger the stall warning please?

AoA.

BOAC, I may be wrong but I suspect you are mixing up "low speed protection" and "stall warning", the former being some kind of enhanced stick nudger and the later being an audio alarm .
DJ.

DJ77

4th Aug 2009, 12:07

Not to worry then. Except for an occasional trip to the loo, I'd be tightly strapped in. http://images.ibsrv.net/ibsrv/res/src:www.pprune.org/get/images/smilies/smile.gif

You better be !

More seriously, stalling an airliner in normal operations involves many risks that a sound captain cannot allow himself to take. eg: passenger or cabin crew injuries, inflight collision, engine flameout, aircraft damage, and more.

HazelNuts39

4th Aug 2009, 12:22

RE: DJ77 (#4114)

dj,

By the way, the choice of a reference for AoA is somewhat arbitrary.
Just think of the whole airplane, rather than any particular part of it (wing section and 'incidence' vary considerably along the wingspan). Anyway its not important which reference is used, but you must use it consistently.
This still leaves AF447 less than 1 deg away from stall warning, if the 4.2 deg AoA triggering threshold is true. With cruise AoA typically 2 degrees, wouldn't that leave 2.2 degrees?

regards,
HN39

funfly

4th Aug 2009, 12:33

fundemental question;
If I fly my (small) aircraft into an active Cu and the conditions in there cause my pitot tube to ice over resulting in my loss of control.....
Is it really the pitot tube failure that has caused the crash?

BOAC

4th Aug 2009, 12:39

DJ - all I have to go on as non-Airbus is 'Smart Cockpit' which says that 'Low Speed Stability' (which it says incorporates the audio stall warning) is ABSENT in ALT2 with 2 ADR disagree. I take it you are saying the audio is still available?

HazelNuts39

4th Aug 2009, 12:50

RE: Hyperveloce (#4116)
Does anyone know how these alpha threshold are computed ?No, you would have to ask Airbus Flight Test/Engineering. If you were in their shoes, this is what you could do:

You do a stall test (or several) in the particular configuration. Starting at a speed well above the stall, you gradually reduce airspeed until the airplane stalls. From the recorded data, you derive a curve of CL vs alpha (see for example page 5 in the Lutz presentation). On that curve you select an alpha-max. The CL at alpha-max defines the reference stall speed. If you want the minimum stall warning margin required by regulation, you calculate a speed equal to 103 percent of stall speed, and the corresponding CL. With that CL you go into the CL-alpha curve to find the stall warning threshold. Bear in mind that you may select a stall warning margin greater than the regulatory minimum.

regards,
HN39

Hyperveloce

4th Aug 2009, 16:33

RE: Hyperveloce (#4116)
No, you would have to ask Airbus Flight Test/Engineering.

Thank you HN39. Yes: CFD, wind tunnels, flight tests, and the return of experience will shape these AoA tables. But wouldn't it be of interest, for a pilot, to know these limits ? Aren't they the limits of his own authority as a pilot ? (before the automation overules him). Not knowing these limits could lead to a bad surprise from the automation: one day, nearing the limits of the flight envelope, these tables could activate a primary reflexes of the plane & litterally sort the pilot out of the control loop ? In fact, this already happened. Wouldn't it be usefull for a pilot who is handflying his plane (all the more in a critical phase, say at landing/take off) to know/be warned that the automation is about to take over the plane in a surprising move ?
Jeff
PS) Assuming a pilot decides to apply the stall procedure (in reaction to several stall warnings) and lowers the nose (and possibly increases the thrust if there is a margin left). Two flights have initiated a descent and departed from their initial route to avoid a possible traffic but they recovered their airspeeds rapidly during the descent and stabilized their altitude. How would the crew monitor the consequences/results of their actions (stall procedure) in the absence of airspeeds ? If these latter do not recover their normal values as rapidly as in the two previous cases, when would a crew abord his descent ?
Is it only necessary to get a couple of ADRs in agreement to recover the airspeeds and the normal display on the PFDs or is it required that the 3 ADRs are simultaneously consistent ?
Where is the GPS ground speed & altitude displayed in the cockpit ?
PPS) About the crew reaction to stall warnings: wouldn't it make a difference that the crew be {CoPi 32 yrs; CoPi 37 yrs} or {CPT 58 yrs; CoPi 32 yrs} if stall alarms sounded like in several cases of Pitot event ? If yes, is it probable that a crew rotation had occured before 02:10Z ?
..............CPT.... CoPi37....CoPi32.....................................
ATPL ......1990... 2001...... 2000* (*) only the theoretical part
Flight Hrs 10988* 6547...... 2936 (All types) (*) CaravelleXII,A320,Boeing 737
Flight Hrs 1747.... 4479 .... 807.. (A330/A340)
South Am 16....... 39........ 5..... (flights toward south America)

Smilin_Ed

4th Aug 2009, 18:11

DJ77:
More seriously, stalling an airliner in normal operations involves many risks that a sound captain cannot allow himself to take. eg: passenger or cabin crew injuries, inflight collision, engine flameout, aircraft damage, and more.

DJ, I think you misunderstood what I was getting at. My point is that with appropriate situational awareness, a flight crew should instantly be able to recognize whether a stall warning is real or spurious. Of course a stall is a serious matter, but if the cockpit crew is awake they shouldn't have to reflexively carry out some rote procedure without reflecting on it for a few seconds. From most of the posts here, I gather that some of our brethren here are spring-loaded to do things that might not be appropriate. I was asking people knowledgeable in AB operations whether a stall warning is something to panic over. From the responses, I gather not. There should be plenty of time to decide on the proper response.

Regards,

Ed

DJ77

4th Aug 2009, 19:57

RE BOAC (#4121)
Not being AB myself, I just try to understand the FCOM (Smart Cochpit and another source). I understand that "low speed protection" is a flight control function (ATA 27) while "audio stall warning" is generated by the Flight Warning Computer (see "smart cockpit", ATA 31, Indicating and Recording Systems 1-31-10 Page 4). I may be wrong but I think these two functions are completely independent.

DJ77

4th Aug 2009, 20:35

RE: HN39 (#4119)
With cruise AoA typically 2 degrees, wouldn't that leave 2.2 degrees?

I found the 3.5 deg cruise pitch attitude in the "Unreliable Airspeed Indication / ADR check proc." (FCOM 3.02.34 P21). I acknowledge it is for an IAS of 260 kt. Nominal IAS at M 0.80 / FL 350 is 273 kt so the pitch attitude at M 0.80 may be perhaps a half deg lower. Remember however that Air Caraïbe started and ended their 1 min and 26 sec airspeed rollback at exactly M 0.80. One can think that their airspeed did not vary much in between and still they had two stall warnings.

Regards,

DJ.

DJ77

4th Aug 2009, 21:36

Smilind_Ed (#4124),

I generally agree with your post, except on one point: you don't really have "plenty of time". Look, a stall warning should normally never happen aboard an airliner. If it happens, you must have missed something big or ... it is spurious. If you cannot determine which is true almost instantly, you have to take the safest course of action: believe the alarm. Usually, this cannot hurt and you buy time to analyse later. Otherwise, you would need to mobilise cognitive resources to analyse the available parameters and that takes time, very possibly too much time. We are only humans.

Regards,

DJ.

Smilin_Ed

5th Aug 2009, 00:03

DJ, I guess we need to define "plenty of time". Five seconds, ten seconds? In a couple of seconds, a properly alert crew should be able to say to themselves, "Hey look, the airspeed just dropped and we got a stall warning, but the plane keeps on flying normally. Must be a failure of the airspeed indicators." As long as you're cruising smoothly do you really want to push over and add power, or whatever? I wouldn't think so but that's why I think an independent AoA indicator would be appropriate. Lately there has been a rash of erratic airspeed indications reported. It turns out that there have been incidents going back some time. Apparently the airlines don't want to pay for it but until the erratic airspeed problem is solved, if I were flying one of these, I'd like to have an AoA gauge. That way I wouldn't unnecessarily disturb the passengers.

safetypee

5th Aug 2009, 01:20

Re the stall discussion; ‘all warnings must be respected’, is generally true. Great care is taken to ensure that technology has a very low false warning rate for critical warnings – hazardous situations, but in some circumstances the crew are also alerted to an impending hazardous situation, e.g. TAWS - Amber alerts, then Red warnings. Crews, in normal circumstances are not required to, and should not attempt to identify ‘false’ warnings.

In conventional aircraft, many stall ‘warning’ systems have two levels.
An alert level is given before the aircraft stalls, e.g. 1.05 -1.1 Vs, where usually stick-shake provides additional awareness. Somewhat misleadingly, the majority of alerting signals are called “stall warning” (vice alerting), but the recovery action only requires avoidance of the approaching stall.
The actual stall (Vs) is defined by an identification signal (stall ident); often via a stick push which cues the full recovery action.

In aircraft such as the A330, there may be no requirement for one or both parts of a stall identification system, particularly where control/AOA limiting protections are used.
However, when flying in a reversionary mode – the loss of the protections, aspects of a conventional stall ‘alert’ are used.
AFAIK the setting of this alert provides the crew with information that they are approaching a stall and that ‘avoidance’ action is required (an alert). This is not necessarily stall recovery, just the alleviation of the impending situation.

I doubt that many crews either have or even those with this knowledge (as applicable to the A330) would be able to recall and apply it in such difficult circumstances – no display of primary information, unreliable airspeed, convective weather.
In the absence of specific training, any crew might well revert to old habits – basic training, a full-stall recovery.
In this, there may be similarities with the Colgan Air accident.

It appears that the specific combination of circumstances in this accident is very, very rare. Remove any one of the main contributions and the outcome could have been significantly different – note previous incidents.
The design assumptions about the use of alternative stall awareness, procedures for unreliable airspeed, and even the continued airworthiness status after reports of pitot problems were probably justifiable before this event; - after, now with hindsight, a change is required.

Will Fraser

5th Aug 2009, 01:41

my question safetypee would then be, if a/s (indications) are lost, and the STALL alert appears, does the pilot know if it is appropriate to 'recover', or merely to 'avoid'. I somehow have a hard time envisioning the small stick vibrating, and then articulating 'forward' at Stall. Wouldn't you think an AI would be critical at such a time as well, rather than 'optional' ??

safetypee

5th Aug 2009, 01:52

Re “does the pilot know if it is appropriate to 'recover', or merely to 'avoid'”.
The emphasis of my text was that the indication would only require avoidance - perhaps a subsequent nose drop or roll asymmetry would indicate a stall.
I do not know what specific procedures are recommended for an alert level, but I would suspect a small nose down pitch adjustment and application of power.
AFAIK the ‘alert’ is audio only.

DJ77

5th Aug 2009, 08:06

Hyperveloce:
Is it only necessary to get a couple of ADRs in agreement to recover the airspeeds and the normal display on the PFDs or is it required that the 3 ADRs are simultaneously consistent ?

The FCOM don't say airspeed indications, either exact or erroneous, are removed from the PFDs and ISIS (otherwise, you could not sort them out in case of ADR DISAGREE).

How would the crew monitor the consequences/results of their actions (stall procedure) in the absence of airspeeds ?

There are other cues, like pitch/thrust or pitch/vertical speed relationships.
As was already mentionned by others, stall warning procedure is different from stall recovery. the former was very well described by HazelNuts39 in post #4100.

DJ.

HazelNuts39

5th Aug 2009, 08:23

Has there been a single confirmed false stall warning in all these unreliable airspeed incidents?
regards,
HN39

Hyperveloce

5th Aug 2009, 10:31

-during the two Air Caraïbe, the crew got two series of stall warnings a few (~30s and ~40s for the 2nd incident) seconds after the deluge of fault reports & the loss of flight assistances and protections (severe turbulence penetration proc.: N1 fixed between 81 and 82%, Mach 0.80).
-during a flight between Paris and Antananarivo (flight AF 908), FL370, A/THR OFF, Mach 0.80, after a similar sequence of faults, the crew immediately faced stall warnings although the A/THR was TO/GA locked (-50kts of speed trend), and decided to initiate a descent (and a departure from the initial route to avoid traffic during the descent).
-flight AF 422 (FGLZT) Paris/Roissy-Bogota, entering a cirrus veil at FL370, severe turbulence, A/P manually disengaged, deployment of the airbrakes to avoid MMO, Mach 0.78 selected, airbrakes retracted and A/P reengaged. Then again, new brutal acceleration, A/P automatically OFF, many red echoes on the weather radar, ice is beginning to accrete on the windshield. Altitude is maintained +/- 200 ft. Many thunderbolts around, key phrase to the PNC in the cabin. Suddenly the airspeed rolls back in the red area, recovers its value, then again the two airspeed indications are lost on the PFD and stall alarms are sounded. The PF was about to implement the stall procedure when the airspeeds recovered.
Over 6 recent known cases (incl. the two cases investigated by the NTSB), 4 produced stall warnings a few seconds (40s max for the AC case) after the classic sequence of faults had occurred, one produced a late overspeed warning (Northwest flight ?). If these weren't false alarms, this would be a very strange combination of coincidences, how to explain that without obvious alterations of the flight parameters (or with a thrust increase to TO/GA), the planes initially in stabilized cruise flight were approaching a stall in a blink of an eye, in all these cases ?
Jeff
PS) when you read the account of these flights, you don't really get the feeling that the crew had "plenty of time" (say more than 15-20 s) to think about the stall alarms, and you don't get the feeling that these were "smooth" quiet flights when the sequence of problems occurred. In the case of the AF 422, the turbulences had increased just before the event (maintaining altitude +/- 200 ft) and most of the flights had disengaged their A/THR (turbulence penetration), AF 447 excepted. There was a large number of sudden & confusing events concentrated within 1 or 2 minutes.

HazelNuts39

5th Aug 2009, 12:01

Hyperveloce

5th Aug 2009, 12:40

Hyperveloce:
The FCOM don't say airspeed indications, either exact or erroneous, are removed from the PFDs and ISIS (otherwise, you could not sort them out in case of ADR DISAGREE).

My wording was not precise enought, sorry for that. The Air Caraïbe safety report explains how the PFD are reconfigurated in the event of an ADR disagree: "SPD LIM", RED FLAG (like in the AF 447 ACARS btw) and many of the following indicators are lost: VLS, S, F, the green dot, Vtrend, Vmax, VFEnext, Vsw (resulting from the CAS monitoring process which excluded the 3 ADR and triggered the ALTN2 and PROT LOST). Though we know that the Vtrend is still displayed (-50 kts during the Paris-Antananarivo flight), and I wonder if it is opportunate in the case ADR disagreement event.
But in the case of the AF 422, when it is said "réapparition de la vitesse puis conditions VMC", what does exactly mean "réapparition de la vitesse" ? Back to the normal PFD speed display with all the previously lost speeds indicators ?
There are other cues, like pitch/thrust or pitch/vertical speed relationships.
As was already mentionned by others, stall warning procedure is different from stall recovery. the former was very well described by HazelNuts39 in post #4100.
DJ.
Yes, I was assuming that the nose had been lowered a bit (and maybe the thrust had been increased) with the idea to avoid stalling conditions, not to recover from these (and in my thinking
, these would tend to be spurious). Is the pich&thrust procedure only applicable to maintain a constant altitude (zero vertical speed) or is it easily implementable during a descent ? Once the plane is in descent, given moderated turbulence and probably no outside clues, how much time would you need to monitor the time evolution of {pich; thrust; altitude evolution or vertical speed} to get a sufficient confidence about your flight point ? Because it seems that 10s, 30s or 50s could lead to different outcomes if my rudimentary computations bear a sufficient degree of representativity.
Jeff
would there be also the opposite case (overspeed alarms, nose up/climbing and critical loss of speed in high altitude, nose up stall) ?

Hyperveloce

5th Aug 2009, 13:10

RE: Hyperveloce (#4134)

Jeff,
The Air Caraibe incidents have been properly analysed and the stall warnings have been found to be valid. I strongly suspect that the other events have been similarly analysed with the same result. The only result of Air Caraibe's meeting with Airbus 'engineers' in Toulouse has been that Airbus "would consider a possible amendment of the checklist" (my own words). Has the checklist been amended?
regards,
HN39
I don't know if the check-list has been amended (Airbus said it was working on it at the end of 2008) and if it was, if it could explain the differences shown by the BEA report between Airbus and AF SOPs.
I agree with you HN39, that AC report shows that the AoA exceeded the 4.2° threshold when the stall alarm sounded. But this 4.2° threshold is probably different under a normal law and normal airspeeds ? (since it is derived from these two parameters, and from the aerodynamical config.). Hence to me, this event would not be independant from the event "Pitot freezing" and to prove my point or disprove it, the only piece of information needed would be to get the normal AoA threshold (under a normal law) and compare it to 4.2°. I don't know if the AoA exceeding 4.2° was a definitive sign of a "valid"/real stall (probably not, since the plane's AOA reached 4.48° without entering a stall or having shown precursors of a stall), or if it was an AoA threshold with a margin to take in account the degraded situation (ALTN2).
Besides, there are two stall warnings, the one triggered by the alpha prot. (lost in ALTN2) and the one mentioned above (comparison to 4.2°). In this latter case, the stall warning comes with the cricket sounds: the AC crew heard the cricket when the stall warnings sounded, but not all the other crew: the AF 908 reported "stall warnings without the cricket sound".
Jeff

HazelNuts39

5th Aug 2009, 13:42

RE: Hyperveloce (#4136)

Jeff,
Stall avoidance, properly executed, is very gentle. Few, if any, person in the cabin would even notice it in still air, and even less in turbulence.
Perhaps it needs to be explained that, unlike most other warnings, stall warning continues as long as AoA exceeds the warning threshold, and ends when AoA is reduced below that threshold. Thats where the avoidance ends and 'normal' flight is resumed.
regards,
HN39

Hyperveloce

5th Aug 2009, 14:01

I sincerely hope that every pilot flying Airbuses have read this Air Caraïbe flight safety report.
Among the last ACARS messages are the PRIM1/SEC1 faults.
The Air Caraïbe and the Qantas flights tried to reset their master flight computer in the hope to regain the normal law for the rest of the flight (Qantas was advised by the ground maintenance/technical center).
Counting from the A/P and A/THR OFF event, the unreliable airspeeds events have never lasted more than 3mn. Taking an upper range duration of 3mn would give us ~02:13:30Z, which is the time when the PRIM1 and SEC1 fault appear, the plane was probably already loosing altitude rapidly (if we exclude the high dive scenario, with 20 000, 30 000 or 40 000 fpm vertical rates). We are sure that the airbrakes (if they were deployed before) were retracted at this moment. The other planes reset their PRIM only after they had stabilized the situation.
Jeff
http://img401.imageshack.us/img401/9919/pitotfreezing.jpg

augustusjeremy

5th Aug 2009, 14:22

The Air Caraïbe and the Qantas flights tried to reset their master flight computer in the hope to regain the normal law for the rest of the flight (Qantas was advised by the ground maintenance/technical center).In the Qantas flight episode the a/c left normal law only when PRIM 1 was reset after the crew turned it off and PRIM 2 became master.

Actually the crew was trying to end the uncommanded pitch down events that maybe were happening because the a/c didn't change to alternate law as it should.

Hyperveloce

5th Aug 2009, 15:04

About PRIM1 & PRIM2 PRIM master changed from PRIM 1 to PRIM 2 between the two pich down events. PRIM master changed from PRIM 2 to PRIM 1 after the 2nd pich down event. About PRIM3, after the 2nd pich down The flight crew reported that, after returning the aircraft to 37,000 ft, they commenced actions to deal with multiple ECAM messages. They completed the required action to deal with the first message (NAV IR1 FAULT) by switching the captain’s ATT HEADING switch from the NORM position to CAPT ON 3 position, and then cleared that message. The next message was PRIM 3 FAULT. The crew completed the required action by selecting the PRIM 3 off, waiting 5 seconds and then selecting it on again. .../...
During one of the conversations, maintenance watch suggested that the crew could consider switching PRIM 3 off, and this action was carried out. This action did not appear to have any effect on the scrolling ECAM messages, or the erratic airspeed and altitude information.
----------------------------------
hence you are right augustusjeremy, there was already an ECAM message indicating a PRIM3 FAULT when this latter was reset. I am surprised to read that the Qantas flight had also erratic airspeeds & altitude information ? Jeff
PS) the Air Caraïbe PRIM reset:
http://img2.imageshack.us/img2/1346/primresetac.jpg
PPS) Stall warnings are a typical signature of unreliable airspeeds events (Airbus):
http://henrimarnetcornus.20minutes-blogs.fr/media/00/00/196453185.jpg

HarryMann

6th Aug 2009, 02:15

Personally a lot of the comment and opinion on a good few pages recently, makes me 1) worried;
2) think that:

a) The bigger picture is how much 'real life', 'real stall' experience the handling pilot has... it sounds like a stall or an approach to stall warning to some airline pilots is a rare thing - frightening. Isn't this almost de rigeur in sim training, many stalls, in all flight modes - and refreshed regularly as matter of course

b) the only time an approach to stall is really anything other than (initially) a light and progressive push on the stick, is late in the approach. At any other sensible altitude, either totally ignoring stall approach warning or the obverse - loads of power and a heavy nose-down response - seems unlike anything sensible or ordained.
Always, especially if in doubt, ease the stick forward straight away whilst checking immediately the std scan instruments.. and thrust.

c) With the momentum and energy of 200 tons, a slippery shape and at cruise speed, if thrust is as expected, surely nobody has ever had to whack the throttles open and pitch heavily nose down (the two are anyway to some extent counter balanced in the shorter term).

d) If an incipient approach to stall with 35,000' to play with, cannot be handled with a natural small pitch down in the first instance, without fear or fright, then that's not a safe aeroplane. So I presume it is, and plenty of cruise thrust-loss and climb at low thrust incipient stalls are thrown into the training - it must be 2nd nature to fractionally lower the nose immediately - but that's all for a good few seconds.

e) If turbulence, of a strong or severe nature is present it changes the whole picture.... barely mentioned in much of the recent discussion on imagined events and (re) actions to indications and warnings. But wherever you are in almost all dynamic phases of pitch, a buffet, stick shake or airspeed warning still should produce that natural reflection almost immediately, followed by heightened awareness of where the craft is in pitch, attitude and power and trim state. As was pointed out earlier, that was probably all Buffalo shaker required in reality and should have absolute 'programmed in' natural response, from first flight in a glider, a 152, countless sim flights & checks, right up to an A380 for real - if not, we are in serious trouble in the skies.

The big unknown is not so much the way the airspeed might have gone haywire over seconds or minutes - but the onset and if severe turbulence, the level, type and wavelength - was that a big factor. Something we can imagine, pontificate about but really just don't know - it could have been a very big factor, or not a factor at all.

My comments are really not pointed at the AF447 situation, more, why are we even discssuing what is/should be hard-wired as a stall approach response?
Because the a/p kicked out so unexpectedly?

That should be expected in severe turbulence and expectation implies high situational awareness (airspeed/picth/power/trim etc)
If not expected then we have a) a/p fault b) flight data fault. c) something has broken or you've hit something.

Sorry to drag this out... I'm left with a question.

How much manual handling sim-time and real flight-time is built up per thousand hours in heavy to severe turbulence conditions (i.e. when it would perhaps be expected the a/p would find itself on or beyond limts) ?

PJ2

6th Aug 2009, 03:58

HarryMann;
How much manual handling sim-time and real flight-time is built up per thousand hours in heavy to severe turbulence conditions (i.e. when it would perhaps be expected the a/p would find itself on or beyond limts) ?
A thousand hours is, for most major carrier transport pilots, about 12 to 18 months of "hard time" depending upon contracts. (Putting in 85hrs of hard time in a month for an airline pilot is risking high fatigue levels). A 330 captain on long haul operations may get 3 landings a month, perhaps 4, maybe 5 on rare occasions. Domestic crews will do 75 to 90 landings a month and about the same hard time.

From my own experience, almost all crews engage the autopilot above 3000ft. Very few fly to 10,000ft/FL100 and almost nobody flies to cruise altitude. Disconnection can occur at about the same altitude on approach - 3000ft, but most crews disconnect below 1000ft, and many at around 400ft.

At 1500ft on approach, an airliner is just over two minutes to touchdown.

Out of a typical flight, I would estimate the first five minutes and the last 3 minutes are hand-flown, the usual exceptions applying.

If the typical number of landings applies per month, a long-haul crew member may be getting, at the most, 30 minutes of hand-flying per month or about 6, perhaps 9 hours of hand-flying during the 12 to 18 month period. A domestic pilot would be doing the number of landings per month times about 7 minutes but it's more difficult to estimate for short-haul.

There is NO hand-flying taught or encouraged in the simulator except for the requisite steep turns and approaches to stall on an initial aircraft checkout. There is NO standby instrument practise and, very rarely, we did a raw data, (no flight directors) hand-flown, (including manual thrust levers), ILS. These approaches are usually between a bit ropey and a go-around but some are spectacularly, beautifully hand-flown with the loc/g-s or airspeed "painted" on the gauge face. Over the years, hand-flying was discouraged more and more and finally the authority to disconnect was removed from the FCOM except in circumstances where workload was low, (no traffic, no weather).

I have never in 35 years of sim work, carried an airliner into the stall. Such work was and should be test-pilot work as no airline pilot ever expected to have to deal with a full stall and certainly not a spin in a heavy transport.

With four, likely five recent accidents in which the crew lost control and stalled their aircraft resulting in a fatal accident, perhaps times and expectations and reasons for studying the full stall, have changed.

Within limits, we never had altitude restrictions within which we had to recover and we always watched for the secondary stall from pulling to hard or not enough nose-down. Jet Upset maneuvers were never done nor trained. We practised EGPWS and TCAS escape maneuvers.

I don't know how much of this reflects others' experience.

HarryMann

6th Aug 2009, 11:10

PJ2

Thankyou.

You're not the one in the firing-line, but I would then like to ask generally, how is the handing back of an aircraft to manual flight in what may inevitably be a 'less than trained for' state - condoned as acceptable - in the larger scheme of things.

I have obviously lost the plot in the last 30 years making these seemingly simple (and silly?) deductions of 'a training and skills maintenance system fit for likely purpose, '... or the industry has lost the plot - in one crucial area - if not more?

An accident that may not be thought to be in this category - AA587 wake turbulence handling - trained for specifically - but (allegedly) improperly.

PJ2

6th Aug 2009, 15:50

HarryMann;
how is the handing back of an aircraft to manual flight in what may inevitably be a 'less than trained for' state - condoned as acceptable - in the larger scheme of things.
I hope others who have perhaps left the thread but visit it to see what's changed, might offer their views on this subtle but important question.

The intoxication with automation largely through the substantial crew-cost-reductions have moved the industry thinking a very long way away from "focus on skills" since I joined in the early '70's. The focus is on "managing" the airplane, not flying it. The philosophy works almost all the time because automation is very good at "normal" and is, in my view, a tremendous safety enhancement. But like designing wings, engines and other bits, any "improvement" always comes with a cost, a compromise which is almost always obvious and economically acceptable in the trade. In my view, it is "the intoxication" that has blinded the usual awareness of those costs when the discussion turns to automation. I remember very well the introduction of the 767 with just two pilots. Like the Douglas Company's DC8, the "new" 767 cockpit design would have long seat rails so the First Officer could "travel" back to the panel and manage the fuel and whatever else was back there. In the case of the DC8 I guess the regulator (wisely in my view) didn't go for a two-pilot, four-engine airliner in the 60's but the 767 arrived with an Observer Seat and not a Second Officer seat.

When the 320 was introduced, veteran pilots raised on cables and pulleys saw the automation compromise instantly and began cautioning against loss of situational awareness, loss of the third set of eyes and something new that they called "mode confusion". I have many articles from AW&ST on this phenomena as I think it was an historical moment in aviation that would have consequences - it wasn't that it was hard to see - it was because of the wholesale, unquestioning adoption of automation as a panacea to cost, the arrival of which came during yet another mini-recession and "trouble at the airlines". It also came during the implementation of de-regulation in the US, where "cost-advantage" drove many agendas. "Intoxication" is not too light a term when looking back.

At the time, nobody knew anything about the airplane and the instructors were literally 24hrs ahead of the students. I think the introduction was successful in large part because of the flying and thinking skills of the pilots at the time. When the 320 began doing something we didn't understand, we simply disconnected and hand flew it until we sorted it out - not a big deal.

I don't think the same circumstances would be quite as possible today. Too many pilots are afraid to disconnect the autoflight/autothrust systems and fly just for the fun of it and managements are fearful of this very fact and my experience has been that instead of training, after an all-weather approach or other handling incident they tighten the reins and prohibit manual-flying even more. The philosophy has a logical outcome and that is a loss of skill accompanied of course by the subtle loss of confidence in one's ability to take over.

Given the propensity these days for many, and certainly the media, to instantly come to extreme conclusions more out of habit than thinking, I must caution that these are very black-and-white pictures that are being painted in this and other posts of mine; - the reality is far, far more subtle than is being stated. But these posts, already too long, would be a book and a very dry one at that, which no one would ever read. The industry is NOT falling apart at the seams but instead is coming to terms with the same kinds of changes pilots and managements did when the piston era yielded to the jet era beginning around 1954 or so, a phenomena that most pilots saw and commented about from 1988 on. These are observations made by many in the industry at the time, and today. "Listening" however, is a lost art. "I'll see it when I believe it" is the outcome.

The question you ask is, "Is the industry concerned about Loss of Control, (LoC)?" and I would submit, "no, not yet" as a tentative response. But it should be on their radar, given the four, likely five recent stalling accidents by crews ranging from veteran to relatively inexperienced.

My own response would be somewhat "actuarial" as opposed to ideological. "The loss of skill is condoned" by airline managements by virtue of the changed focus of initial and recurrent training regimes towards "managing the cockpit" instead of flying the airplane, and by virtue of the strong, overwhelming success of automation's introduction and presence.

As always, an informed, (through the heavy use of collected flight data, LOSA programs and crew reports) and measured response is indicated, "a bow towards manual flight with a view to re-familiarization and re-building", not a wholesale revising of priorities, would be something to consider as a viable response. It is as much attitude as it is foundational skills that has changed.

rgbrock1

6th Aug 2009, 16:15

PJ2:

Although I work in the IT industry which has nothing to do
with aviation your comments on automation and blind reliance on the same, struck a chord within me.
I see automation all the time in my industry. We call it the "lights out" environment where most, if not all, the day-to-day functioning of a data center is automated. Management loves it because it allows them to "cut costs" and eliminate positions or, worse, outsource.
Automation is good. When used wisely. It is very bad when blind reliance is enacted. I have all too often seen automation "mask" some very undesirable problems. With very ugly consequences.
To me it is, and always will be, a matter of knowing what lies behind the automation ie, what is the automation doing and how can I ascertain if what being automated is indeed being correctly automated. It's not an easy task by any sense of the imagination. In computer terms I liken it to the differences between MS Windows and operating systems like VMS, Linux and Unix. Windows, as we all know, is more or less a point-n-click world. VMS, Linux, Unix and MVS (IBM) are command line interfaces. Such interfaces allow you to access the very guts of the operating system, should you feel so inclinded. Windows does not for the most part. But, and this is a big but, if you do know what lies behind the point-n-click world then you are in a much better position to control that environment. Most people nowadays in the IT world, have no idea what lies behind their GUI environments. To know what is going on within a given system, at all times, without blind reliance on automation and/or point-n-click, brings one a much better understanding of the environment then one without such knowledge. And allows one to be much more "aware" of what is going on in a given system.
I think some of this can be extrapolated to some aspects of aviation, specifically to the fbw environment. Perhaps I'm incorrect in this as I am not involved in aviation but I think the underlying principles of my assertion are valid.

PJ2

6th Aug 2009, 18:08

rgbrock1;
The notion of "understanding" has changed according to economic and therefore "cultural" needs from mere mechanical how-to, to knowing one's role but not knowing what is underneath the required adaptions we all have made. That change began around 1970 when the post-war economy began to be dismantled.

It is inconvenient to commerce to have, seek or require understanding beyond what is needed to be known about one's small participative-footprint within the larger system. The notion of "NTK" - Need To Know is an adaptive term, perhaps a euphemism, has been applied to aircraft since the introduction of the 320. When many of us began flying, we had to be able, from memory, to draw aircraft systems, draw complex terminal areas and know what made an aircraft tick. We had to know aerodynamics, high-altitude flight and how to draw then analyze weather systems. I knew captains who would draw the entire route weather, analyzing frontal systems in 3 dimensions and where the icing was to be expected. No longer. "Dumbing Down" is the label applied to what has happened since 1970 or so but because today we have "normalized the deviance" we accept that people can "talk on the surface" ad nauseum and be taken seriously as knowledgeable when in fact "flying" has become "managing" a machine.

Therefore, whether it is something as pervasive and institutionalized as a democracy, or whether the environment is an aircraft cockpit, one needs certain tiny, targeted pieces of information to function within the narrowly-defined band of competency, the exceedance of which is not encouraged in either environment.

Whether one comprehends what one is doing with a click of the mouse in a Windows environment, (especially in Vista :ugh:) or what is going on underneath the push of the ALT knob on the FCU of a 320/330/340/380 type is immaterial to the task at hand. In such an environment, one's knowledge is limited to, and is, "outcome driven", and is not "needs (comprehension) driven".

We can't change culture of course but we can, through philosophical approaches, comprehend the underlying assumptions of seemingly "stupid" behaviours and alter and otherwise tweak slightly these behaviours towards original-but-masked goals, in this specific case, towards flight safety.

Phantom Driver

6th Aug 2009, 20:14

PJ2:
Excellent analyses. In aviation, technology grows in leaps and bounds, but as far as the good old human interface is concerned,we are forever reinventing the old wheel. Favourite long time quote-"Man has oft more need to be reminded than informed". Thus history just keeps on repeating itself when we read the Human Factors/CRM/(aka Airmanship) aspects of these accident reports.

Re:Manual flying: This subject has been covered ad nauseam in previous threads. But the current thread has brought the issue back into the spotlight. Well, another old favourite (courtesy of Andy Capp)-"The older I get, the better I was".Our skills inevitably degrade with age and lack of practice. But putting macho aspects aside, the fact is-todays aircraft are designed to be flown/managed with the automatics. Todays ATC/RVSM/RNP environment has no place for inserting (rusty) manual flying, (no matter what 411A thinks!) and the proof lies in the FDAP program that many airlines practice (quite rightly) to trap the unwary, the rusty, the cowboys.

Quite rightly so; I don't know about you,but when I am riding down the back, I don't want to be subjected to some wild ride while the guy up front tries to polish up his manual flying skills (not) , while the PM is working like a one-armed paper hanger doing config changes & RT/MCP/MCDU work, as well as frequency changes, at the same time as trying to monitor the Ace's not-so-hot flying on a dark night on a typical European or elsewhere RNAV SID or STAR.Don't laugh;I have seen it on quite a few occasions while sitting on the jumpseat as augmenting Captain.

Where I do agree with you 100 per cent is the failure to address these issues in the simulator. We should be doing far more raw data manual flying in the sim on recurrent training (maybe not on base checks;jeopardy involved here); if you can't hack it, serious questions need to be asked; and yet, as you say, this is not happening! Apparently, on the 777, some operators do the V1 cut in the sim b/checks with the TAC (Thrust Assymetry Compensator) on! Don't even have to think too hard about which rudder to push! Where is the sense in that? A big wakeup call is needed. Automation works most of the time,but you better be ready when the gremlins strike.

Hyperveloce

7th Aug 2009, 12:54

Hi there. I know that the question was largely discussed, and I remember Takata's contributions. When we use the NOAA/OSCAR currents which are observational (SHOM currents are predictions, the result of a 3D model), it seems that these data are able to describe the debris drift between the 6th of June and the 20th of June and the rotation of the current direction from north north east to north north west. The NOAA/OSCAR time series (not the current maps) show that the current speed nearly doubled between the two periods June 1 - June 6 and June 6 - June 9 (from 0.125 to 0.215 m/s): the drift range between these two period should be roughtly similar. This would give an area for the debris on June the 1st marked by the interrogation marks. Would it suggest that the initial small departure of 3NM to the west of the SALPO-TASIL route (seen on the last known positional ACARS at 02:10Z) has become a large turn to the west ? Maybe not a U-turn but a substantial route alteration (>90°) ?
Jeff
http://img13.imageshack.us/img13/6560/debriscurrentstraj.jpg

SaturnV

7th Aug 2009, 14:45

Jeff, my feeling based on the drift was that there was a deviation to the west of the track. I have always felt, based on the search grids June 2-5, if there was a deviation to the east of the track, the search would have discovered the debris a lot sooner. I won't speak for takata as to whether he eventually abandoned his idea that the plane did a 180 or attempted to.
_______________
I am both a bit surprised and a bit disconcerted that there is no news of the sonar having picked up any targets worthy of investigation by the mini-subs. The sonar sweeps probably have covered nearly half of the area they intended to sweep at this point, and one would expect they would start with the area they thought the plane most likely impacted the sea. If that is the case, they would now be moving the grids significantly greater distances to the north of the last reported position, and west of the track. Even if the boxes are never retrieved, the impact point can be critical to several theories for how and when the plane came to fall into the sea.

JD-EE

7th Aug 2009, 19:42

Probe Finds Airspeed Sensors Failed on at Least 12 U.S. Flights (http://www.foxnews.com/story/0,2933,538122,00.html)

This suggests that loss of airspeed indication alone should not have brought down AF447. There must have been some other relatively unique factors involved. I believe this lends weight to PJ2's comments along this line. Probe icing is not enough by itself to account for the problem.

I might wonder if the relative lack of light outside the cockpit made it impossible during heavy turbulence to maintain proper attitude. Remarks here indicate that in severe turbulence, when you may need it the most, attitude indication, and indeed all the instruments, become very difficult to read. Would that combination be sufficient to account for AF447?

This also suggests to me that there has been a bad pitot probe problem for quite some time, particularly with the Thales probes. Thales is already hedging itself with the whine that they built their probes to AirBus specifications. I see some blame shifting and finger pointing rather than efforts to fix a bad situation. I also see some indication that this problem may have been covered up for quite some time now.

It's expensive to replace these probes unless the public learns enough to demand it. With the relatively low caps on liability for deaths that airlines face there is the specter of a lost plane here and there is a simple "business expense". The plane itself costs more than the payouts for the deaths, I believe. That gives me pause to think about flying, as if the TSA hassles are not enough for that.

JD-EE

pax2908

8th Aug 2009, 11:06

HarryMann

8th Aug 2009, 11:35

There appears to be no laws of dynamic similarity that would make a scaling up of the whole pitot probe inaccurate and I'm stretching myself to think of a problem with a 50 or 100% bore increase.
Airborne contaminants are generally small and large ones less likely to be homegeneously distributed, e.g. windborne detritus. Meaninga larger one might be more prone to detrital blocking but not 2 or all 3. Neither would one be as prone to complete blockage.

Obviously there is an optimum scale for a pitot probe, but has it been chosen too small.. key criteria to be considered are also inspection, cleaning, repair and corrosion (relative blocking ability)

I also can't see why the entry bore cannot be modelled smaller than the main bore and drain, as long as full pressure recovery is achieved, Q will be measured when V=0 at the transducer face. This could prevent larger scale detritus entering at all...

However, the manufacturers I accept, know a damn sight more than myself - even Thales - but are maybe working to a poorly conceived set of specifications (e.g. size, cost etc) that may indeed be quite historical and never reviewed for sensibility in many, many years...

Hyperveloce

8th Aug 2009, 12:28

On the French speaking web site, they have published the details of an incident which occurred "a few months before" AF447. In that case, maintenance have found that the three probes had the water drainage holes blocked. My question is again a naive one: in such a case, the problem is considered to be solved once the drains are cleared and the pipes flushed (as per the Airbus procedure), OR is there a mechanism to at least trigger more frequent inspections? For sure if maintenance is done correctly, then it should NOT be normal to find all 3 probes with the drains blocked?

I think we can find an AESA air worthiness directive from 2003 whose purpose is to increase the maintenance frequency on the Pitot probes. Another AESA paper describes manufacturing problems on the drain of certain AA probes resulting in a rapid obstruction, poor water drainage and poor performances in case of heavy rains or icing conditions (even if you have an efficient heater). Maybe we see now the difficult aging of these AA probes. But whatever, when the French Air Force lost a Mirage 2000 five years ago, the military did not wait for a similar problem to reoccur: the AF conducted a large study on its entire Mirage 2000 fleet to get complete statistics over a period of time, to analyze the risk and its evolution, and to adapt the maintenance. Has it been done on these airliners ? Jeff

pax2908

8th Aug 2009, 15:51

Re. to HV (post# 4154). Following your suggestion I was able to find a few ADs which seem relevant.

The most recent (2003-148) is for A300/A310 and Thales AA probes with low serial numbers; it refers to a manufacturing defect of the drain hole; and requires to perform the Thales procedure to clean/repair the probes. This AD seems very similar to two ADs isssued in November 2002 applying to Thales AA probes with s/n lower than 4760 (2002-586 for A320, and 2002-594 for A330/A340).

These ADs are in response to airspeed discrepancies reported by "an A320 operator".

I was not able to find, in these ADs, a direct reference to the increase in maintenance frequency. Also I was not able to find anything more recent from the EASA web site. I do believe that Airbus has been following this closely.

Will Fraser

8th Aug 2009, 16:33

good spark

IMO the answer has been available for some years, and lifting the 'rug' merely emphasizes what needs to happen. Whether its static electricity, dissimilar metals, or salt corrosion, the Pitots are being changed. The issue isn't pitots, it's recognition and response. It has become painfully obvious where on the list of priorities Aviation 'safety' reposes. Feigning mystery and taking years to act has become de rigeur.

funfly

8th Aug 2009, 17:45

PJ2
Is it just possible that the automation of aircraft has contributed to;
a. lower costs thereby keeping the aviation industry afloat and
b. improved overall safety.

Could it be that it is inevitable that there will be aircraft crashes when systems fail and the controls are put in the hands of pilots trained as managers rather than pilots.
This could be the 'cost' of sustaining the industry and maintaining an overall safer flying environment.

It may just be that we get far less disasters using computer systems to fly the airctaft than if we relied only on live pilots - however well trained and experienced.
Expecting any pilot to cope with situations that are outside of the ability of the computer systems might just be asking too much.

In a situation where an aircraft knowingly entered weather for which the aircraft was not designed maybe one cannot question the systems if they fail.

Don't shoot me, I am being Devils advocate with these questions in order to suggest alternatives - we seem to be stuck on 'real pilots are better' & 'bring back the old days'

PJ2

8th Aug 2009, 19:21

funfly;
Don't shoot me, I am being Devils advocate with these questions in order to suggest alternatives - we seem to be stuck on 'real pilots are better' & 'bring back the old days'
On the contrary the point you raise is an excellent one. No "Devil's Advocacy" here - what you say is the truth. It is a long acknowledged fact that automation has dramatically reduced industry costs and enhanced flight safety. The weight savings in hydraulics and other mechanical solutions to flight controls and landing gear operation alone on the A320 design were significant. The reliability and accuracy of automation is nothing short of spectacular and is nowhere more beautifully demonstrated than on a Category IIIb ILS autoland approach in RVR600 conditions, (forward visibility 600 feet). The safety factor has increased exponentially too, with automated peripherals such as TCAS II, EGPWS, FANS and ACARS all of which have prevented untold numbers of fatalties. Don Bateman's (of Honeywell) invention, GPWS has prevented untold numbers of CFIT accidents.

In short, automation has been a hugely positive net change for commercial aviation. Computerization has made exponential changes in flight safety in related areas through ATC capabilities, (radar & transponders, predictive tracking) and weather prediction and modelling and disemination of this information rapidly and widely through the internet, (Like many crews could, I used to start my flight planning in the uninterrupted calm of the hotel room some four hours before departure, downloading the flight plan onto the laptop and studying the weather etc). Mechanical and technical reliability of aircraft have made system and engine issues almost a thing of the past. Engine shutdowns are rare compared to the piston era where arriving from an overseas flight on all four was an event.

Aircraft instrumentation accuracy, the introduction of flight management guidance computers, satellite communications all have contributed to reducing vertical, lateral and longitudinal separation standards, putting more airplanes into the sky safely. The introducion of RVSM standards reducing vertical separation from 2000ft above FL290 to 1000ft literally doubled available airspace both domestically and over the ocean.

Automation can mitigate the effects of fatigue because it doesn't get distracted, lose situational awareness or suffer from any of the other very elementary human frailties such as vertigo or fear. Automation is a fine and "loyal" servant, used wisely and intelligently.

Except for the kind of respect that this profession used to (deservedly) garner but has been lost by the processes herein described, the call isn't for a "return" to the old days - not at all. In fact, were we to do that under the watch of present industry leaders and regulators I strongly suspect the accident rate would skyrocket immediately. It's hypothetical however and as such is a meaningless argument - we're not going back.

Automation has one major, huge fault however and we all know what it is. That fault is the subject of the entire thrust behind this dialogue - computers and automation is dumber than a bag of hammers - it is GIGO, all the way down. Automation will fly an airliner smoothly, accurately, beautifully, straight into the ground, (and has) or will, if pilots permit, stall the aircraft, even the Airbus.

The secondary effects of automation is loss of situational awareness and loss of flying and thinking skills. Loss of instrument scan may be a tertiary effect.

This conversation is really about "support" for the best flight safety enhancement the industry has ever had - a skilled, trained and experience airline pilot. That enhancement is the least expensive of all the changes which have occurred to take flight safety where it has gone since the 50's.

"Support" means respect for the capabilities and contributions of a professional airline pilot. "Respect" means paying a wage that one can raise a family on, buy a house on, retire on. You aready know that Captain Sullenberger (and every pilot at US Airways, United and a few other major carriers) don't have pensions even though they paid into them.

Support means training intelligently, effectively, using flight data programs and LOSA information upon which to base curriculae and not just training to pass the ride and tick the box. That requires infrastructure, staffing, and a longer-term vision than quarterly results. That means that some things which do not directly produce "profit" must nevertheless be supported and not be targeted under the constant drive to cut costs where "lack of production" is perceived. I have seen it written and heard it said from the executive levels of airlines, sometimes couched in euphemisms, sometimes not, that pilot augmentation for long-haul operations is merely so much union feather-bedding. An enlightened use of human factors knowledge in combination with the substantial science already available on circadian rhythms, just for starters, is needed. When the FAA comes to actually believe there is need for change, we know that the problem is serious and has been for decades and decades. In Canada, the problem remains unrecognized and undiscussed except among flight safety groups and advocates. Despite their words on flight safety, IATA has in the past been one of the more vocal groups speaking/lobbying against any changes in flight time and duty day regulations.

Support means acknowledging that, just like other professions, it takes time to grow experience and that one does not just pick such things from trees.

"Experience" means time, but the pipeline is drying up. Young people don't want to be "airline pilots" these days for all the obvious reasons that are both succinctly and clearly expressed here by many, the finest expression coming from Captain Sullenberger before Congress in February.

Young pilots need to be shown how it was and how it ought to be. Ms. Shaw likely never understood the disadvantages of the lack of such support and guidance because to those who are starting out, everything is "normal". Those who have lived the career for some time, know (and knew) better.

This is a tall order which almost certainly will never be filled until industry itself recognizes the problem. At present, there is "no elephant in the living room" and most managements are "satisficed".

We cannot say if loss of control accidents will trend upwards or not. Preventative strategies which produce "nothing" as a successful result, (ie, no incidents, no accidents) are extremely difficult to implement and defend when the MBAs come looking for where to cut costs and especially where the executive levels don't comprehend how flight safety work is done.

Out of experience however, we can say that given fertile ground as described and not just incidental opportunity where the holes line up, untoward trends in aviation will continue and may increase.

These aren't wholesale, massive changes being called for. They are a change in stance - The belief that an airline pilot can be made by giving the candidate 250hrs of simulator and then putting them in the right seat of an A320 or B747 and expecting that the captain will not be alone should something serious occur, is the lack of support being discussed here. It is money, nothing else, that drives this kind of thinking.

So your question is a good one I think. It needs far more examination and discussion than one little posted response. It is at the heart of the important questions, "wither aviation, wither the profession of 'airline pilots', wither flight safety?".

HarryMann

8th Aug 2009, 22:17

PJ2

Wow! :D

What a shame a collection of such erudite responses aren't going to be published in an Airline Aviation Safety Journal - or would there be no-one of any influence subscribing to their mailing lists within the industry these days? :rolleyes:

Clear_Prop

8th Aug 2009, 22:21

Will, I think part of the logic behind the recommendation to replace only 2 of the 3 probes is due to the emerging idea that 3 identical units are more likely to suffer the same problem at the same time than differing units; coupled with the lack of firm hard data characterising the exact nature of icing / blockage at this time.

It is not known as fact whether the BF Goodrich units are impervious to similar issues, so the recommendation allows some additional redundancy in the form of component variation.

Will Fraser

9th Aug 2009, 00:28

Clear Prop

If as you say the theory behind leaving a suspect Thales probe on speaks of divergent design, bravo. DD is not additional redundancy, it's a form of fault isolation due to engineering approach. Keep in mind that the new Thales has a failure on record already. To my knowledge, the Goodrich replacements are unblemished, thus far.

I'd like to believe the remaining Thales is related to 'improved' safety considerations, unfortunately, it is a face saving crumb thrown to France.

I would not rule out that the Thales is vulnerable due to drain block. The inspect/clean/reinstall may be the fly in the ointment. If the drain is blocked even a little, water plugs the tube. If ICE was the issue, the Goodrich would likely have logged some failures, (they may have).

cessnapuppy

9th Aug 2009, 03:30

Automation can mitigate the effects of fatigue because it doesn't get distracted, lose situational awareness or suffer from any of the other very elementary human frailties such as vertigo or fear. Automation is a fine and "loyal" servant, used wisely and intelligently. The problem is that MOST automation has NO situational awareness, as situational awareness is recognizing not only where you ARE, but remembering where you WERE and knowing the difference. The way auto pilots and most flight systems are written now is as if you jump out of a plane on a skydiving trip. While freefalling, your two feet for a moment are firmly on the back of the fellow sky diving below you. as he spreads his arms and decelerates, you gain 'gravity' relevant to his speed and thus, UNBUCKLE AND DISCARD YOUR PARACHUTE *good luck with the remaining 10,000 feet, sucker! ----- Ludicrous? (not the singer) but that's how A/P ,F/C software is written today! Sure, there are minor bits of pseudo intelligence , what I call 'digital common sense' like storing the last 15 seconds of a probe's readings to be able to discard 'noise' of intermittent fluctuations but that's not applied across the board. Most sampling and decision making is using that very instant of data and until corrected will allow a plane coming in to land: 800ft, 700ft, 600ft, -82 ft!!! to instantly cut engines (we already landed, whoopee!) and fall short of the runway. Obviously, if the autopilot had situational awareness, it would discard the sudden drop from 600ft to -82 ft as being unsustainable and invalid and do something else (automatic TOGA?) handing over to the pilot WOULD not be a good option, I think as there would be no time.

averow

9th Aug 2009, 04:40

Excellent summary. As I get older and more experienced in my profession, sometimes I realize that the best response to a dire computer generated warning is to simply do nothing: scan instruments and perform a quick "reality check" but not take aggressive action unless warranted....

Cheers ! :ok:

lomapaseo

9th Aug 2009, 12:57

The problem is that MOST automation has NO situational awareness, as situational awareness is recognizing not only where you ARE, but remembering where you WERE and knowing the difference.

An example of situational awareness would be the FADEC systems on engines.

They compare multiple inputs and when they disagree (presumed fail) the FADEC latches at the last known reliable condition of flight.

PJ2

9th Aug 2009, 14:40

lomapaseo;
An example of situational awareness would be the FADEC systems on engines.
I think I understand what you mean and I think we understand that there may be as much a philosophical meaning as a semantic one here. No software is "aware". My very simple understanding of software is, while software can mimic learning, software doesn't "learn" in the meaning of the term we usually understand. While I am aware that those that work in AI will likely take issue with such views, the kind of sofware that guides an airliner is by comparison, pretty basic, an algorithm, without the ability to anticipate or recall in a human way. cessnapuppy touches on this in an interesting way. The processors and memory capacity are similarly pretty basic as are the displays. The trade is perhaps in robustness.

For a number of reasons, I am not sure that "fuzzy logic" solutions are suitable to airline work. I may be missing something but I don't think the problems of flight are that complex that such a sophisticated approach is necessary. The problems driving change and "improvement", (sometimes known as "progress"...), are all about cost, not physics.

BOAC

9th Aug 2009, 16:16

The great benefit the human brain has over the artificial is the capacity to 'think outside the box' which by definition AI cannot do. I fear also that the human pilots are on the way to losing that faculty too.

Will Fraser

9th Aug 2009, 16:52

BOAC

I'm seeing some overlap between this thread and the Colgan accident.
Your last post focuses directly on the interface of Automation and manual flight. It isn't a stretch to say that the heightened hazard is at handoff. AF447 and Colgan both had a/p drop in a charged and atypical F/D setting. It is unknown what the exact chain was in 447, except to say that the a/c was lost in/at the time frame in question; with Colgan the a/p disconnect happened just prior to shaker.

With 447, the challenges appear to be IAS and/or weather related, with Colgan pilot error(s). Either way, training 'to the moment' is under review.
In 447 the 'errors' in question appear to be mechanical in origination, with Colgan, likely PE. Either way, it's of interest where the training in both instances takes the discussion. Pitch and Power.

It's inescapable that the default is manual flight. 447 aside, I've noticed broad similarities in many of the more recent accidents. Turkish, Perpignan, Colgan, Birgenair, even Continental off runway, these are accidents whose direct cause was a loss of Pitch awareness/control. 447 may have been. It may be simplistic, especially for the more detail oriented, but to the extent that tragic consequences have resulted, a focus and consequent discussion of basic flight issues seems to need to be had.

Personally, I don't think it's necessary to start Stall training ATP's. It seems to be something else that is present, or lacking. If a disease can be prevented, it doesn't need to be treated.

John Farley

9th Aug 2009, 17:09

Some (me and my 330 mate) see it as a pity that when airspeed info is lost the automatics are not programmed to hold the appropriate attitude and power thus allowing the crew to concentrate on comms and possible fixes without the need to handle the aircraft at the same time.

stepwilk

9th Aug 2009, 17:24

But isn't that why there are two of you? What I learned--okay, 40 years ago--was that if you had a problem, the captain gave either himself or his first officer the job of flying/controlling the aircraft, while the PNF got out the emergency checklists, sent necessary comms and did the troubleshooting. Try to both do it and you can put an entire L-1011 into the Everglades without even knowing it....

lomapaseo

9th Aug 2009, 17:32

PJ2

I don't think the problems of flight are that complex that such a sophisticated approach is necessary. The problems driving change and "improvement", (sometimes known as "progress"...), are all about cost, not physics.

I suspect that there is room for understandings here. Let's put aside the cost aspect as it tends to divert these kinds of discussions.

Generally the idea behind a product design function is to provide what the pilot wants (cost is a later gate that it must pass). So IMO the discussion should be arround the area of what the pilot needs.

IF "improvement and progress" are the desired output. Then the idea is to agree on what constitutes this and proceed from there. For this problem area I was tending along the thinking that the crew needed the confidence to take the time to sort out the changing situation. So I was following the thread hint (my read may have been wrong here) that a computer could not help much here. Thus my response was aimed at the example of how the computer can best be trusted vs the rapid responses of man.

pax2908

9th Aug 2009, 18:13

There was some discussion about what is the appropriate reaction to a stall warning. Now, it is not clear at this time whether or not there was a stall warning in this case. But even if a stall warning can not be issued in ALTN2, I think it remains possible that it happened earlier? For example, in case the initial CAS drop has been below the 30kt/second threshold?

testpanel

9th Aug 2009, 18:26

It's inescapable that the default is manual flight. 447 aside, I've noticed broad similarities in many of the more recent accidents.

I´m with you, bufalo and amsterdam crash; they both were able to crash a, for the rest, perfect a/c!
I use those 2 crashes during my profchecks, and yes I am no crash-investigator nor expert, but i do have "some" hours both up-front and behind in the sim. And i have seen a tendency among pilots to fixate instead of AT LEAST 1 (ONE) PILOT FLYING!

vovachan

9th Aug 2009, 19:09

I remember reading some impressions by a russian test pilot of, among other things, an A310. He was rather down on the stall behavior. The stall came on at low AoAs with little or no warning, and the ac lost lateral stability rather dramatically and pitched up making the situation worse. He described the ac as a case of the mfg trying to compensate for the ills of an aerodynamically questionable platform with electronic doodads.

Granted that AF447 is a different plane, although sharing the same gene pool as the A300/310, how sound IS the airframe? When the electronic protections cut out under less than optimal conditions and the pilots are required to manually fly what may be an evil-handling airframe?:hmm:

Will Fraser

9th Aug 2009, 19:10

At cruise, a/p is at its most practical and important aspect. To select a/p only to sit on the edge of the seat and birddog every bump and discrepancy is to eliminate the need for it. On a sophisticated transport, autoflight is a form of commanded complacency. So its disconnect (uncommanded) of course comes at an inopportune moment. After a series of warnings, chimes, and an uncertainty in the F/D, one pilot needs to retrieve the checklists and troubleshoot, solo ? Yes, because the PF needs to update his scan, 'get' the panel and the 'feel' starting with Pitch and Power, from a degraded (of course) SA. The PNF is at an immediate disadvantage, all the alerts are after the fact (of course), and there are many. Both Pilots are behind the a/c. The a/p was behind enough to need to disconnect. No matter the reason, an unexpected a/p disconnect demonstrably causes problems, some of which seem to have gone unaddressed.

IcePack

9th Aug 2009, 19:20

Un-Substantiated rumor doing the rounds that the a/c may have reached 47000 ft during it's upset. (Convective lift?)
Sorry if this has already been posted. I believe it is a result of further analysis of the recieved ACAR's reports. However I repeat only a rumor.

proteus6

9th Aug 2009, 19:29

Can you back up your statement regarding the A310 stall? I don't think what you say makes any sense, details please?

Tree

9th Aug 2009, 21:31

The Russian test pilot's comments reminded me that I am not enamoured with the FCC's on AI products making rudder inputs without the pilot's knowledge or desire (yaw damper inputs excepted). Watching any video of the 380 shows substantial rudder inputs and reversals on short final.

HarryMann

9th Aug 2009, 21:55

The stall came on at low AoAs with little or no warning, and the ac lost lateral stability rather dramatically and pitched up making the situation worse.

Unlikely indeed if we're talking subsonic well short of Mcrit

HarryMann

9th Aug 2009, 22:14

IF 35,000 > 47,000 ft

4 minutes at 50 ft/s (a v. high thermal climb rate in the troposhere, 20 ft/s is quite normal)

If a/t out, manual flight, the throttles would need to be cut quick if encountering that sort of thermal bubble. And going 'over the falls' out the backside of that could be quite an experience.

IF...

singpilot

10th Aug 2009, 01:25

I once crossed 11000' over the top of a line just west of Chicago. I was young and dumb, and a senior guy was in the left seat. We started at FL370. Big bump, and we started going up. Throttles closed, A/P off, nose down as far as we dared, MMO approaching, boards up, up and away we went.

Topped out at FL440 in a G2, idle power, boards up (Ceiling FL450).

Chicago center had no one above us (it was ISA+10) as I remember (Thank you Lord). They shut anyone from following us after that. The guy in front of us busted his service ceiling (an MD80 that started at FL330).

We drifted back down to FL 370 with the boards up, throttles closed, and tried to stabilize the cabin altitude.

After that, I had a personal rule about crossing rapidly building lines.

Don't.

The 47000' rumor for an A330? As clean as that airframe is, above SVC ceiling, at night, in or above wx, no horizon (visual or artificial), possibly no A/S display?

No way you'd walk away from that one. But then we already knew that.

Dave Gittins

10th Aug 2009, 05:58

I am just dumbfounded - As there is nothing I have seen or read to even start a rumour of AF447 getting to FL 470. We have no survivors, no FDR or CVR. no radio calls, no radar coverage and Tim Vasquez's weather evaluation all conspiring against it.

Lets keep speculation within reasonable limits or state some logic behind the rumour. :ugh:

PJ2

10th Aug 2009, 06:03

singpilot;

It's the one scenario that could explain the ACARS Cabin Alt message. That said, all here would certainly require more data and it just hasn't appeared and hasn't been posited as "something new" from the ACARS messages. Other than being mentioned in the list and the limits explained, it's not dealt with in the section explaining the messages.

grizzled

10th Aug 2009, 08:14

DG -- While I agree that there is nothing to substantiate a specific altitude as high as FL470, there is considerable relevant logic that supports a hypothesis of a rapid climb significantly past, say, FL 410.

I have seen nothing that would rule out a thermally driven rapid climb in the given circumstances, whereas I have certainly seen many posts on this thread suggesting scenarios that are either highly implausible, or even ruled out.

As PJ2 suggests, such a scenario is one possible explanation for one of the as yet unexplained ACARS messages.

FWIW, I am one of those who is still somewhat optimistic with regard to the data recorders being located. Soon I hope.

HarryMann

10th Aug 2009, 09:36

Could it be, not the ACARS messages, but the method of transmission & reception that offers such data...
I have no knowledge of this technology and from what I've read previously and reasoning that 2 miles in altitude would require timing to absurd limits, triangulation too, can only ask that experts here knock my suggstion back quickly and categorically!

Dave Gittins

10th Aug 2009, 10:12

grizzled I am not immune to any well reasoned hypotheses but having just read Tim Vasquez's analysis again, he draws the conclusion that whilst nothing can be ruled out, there is no evidence of significant or extraordinary activity in the ITCZ that night or any unusual updrafts. His diagram at fig 13 shows the 447 just through an area of suspected updrafts but he also notes that updraft strength is generally lower in oceanic Cbs than overland Cbs.

That said, if I experienced a sudden and dramatic updraft I would likely put the left wing down and try to make a descending 180 .. which perhaps tends towards the "turnback" theory popular a few thousand posts back.

As you say, roll on the FDR & CVR being found ... it's surely only a matter of time.

HarryMann

10th Aug 2009, 10:35

...he draws the conclusion that whilst nothing can be ruled out, there is no evidence of significant or extraordinary activity in the ITCZ that night or any unusual updrafts.Maybe not unusual from a met aspect, but is it common to fly through the centre of such updrafts, which he also admits I believe, could have been topping out at 51,000 ft, having burst through the surrounding tropopause ...

which could have happened that dark and stormy night?

HarryMann

10th Aug 2009, 10:45

IF...

Another outside odds 'fit' might be that having to fly pitch and power once A/S seemed unreliable, if they followed AFM and did so, and if they realised their climb-rate, pulling the thrust back would have been 'difficult to justify', at least intially.

syseng68k

10th Aug 2009, 12:05

I think I understand what you mean and I think we understand that there may be as much a philosophical meaning as a semantic one here. No software is "aware". My very simple understanding of software is, while software can mimic learning, software doesn't "learn" in the meaning of the term we usually understand. Semantics… No computer has real ‘intelligence’, but systems can be designed to be adaptive or more or less ‘aware’ as required, for a particular application. The problem is that the more complex the algorithm, the more likely there are to be corner cases that the designers didn’t consider and there are many complex interacting variables involved in the control of an ac. Thus, the kiss principle applies and is especially relevant in safety critical applications since the simpler the system, the easier it is to test and show that it is demonstrably correct and deterministic.

For a number of reasons, I am not sure that "fuzzy logic" solutions are suitable to airline work.

A sort of half way house between a completely dumb control system and ai. At a basic level, it takes the weighted values of many inputs and perhaps time to compute an output value or decision.

An example of where such an approach might be usefull in avionics is the pitot failure situation. Assume level flight for some period, constant as and with ground speed from gps and perhaps doppler. A computer keeps track of these sensors, their rates and their relationship over a several minute period, as well as other variables of interest such as aoa, vertical speed, attitude etc. The historical set and running averages can be used to predict the next set of values to a fair degree of accuracy over a short timescale. If any single value falls outside a defined window, or exceeds rate limits at next sample time, the system may resample to filter noise before rejecting the sensor. It then makes a best effort estimate from remaining sensors and presents that to the user, together with alarms for the suspected failing sub system and degraded accuracy of data. Such an approach becomes even more relevant where the outputs from one subsystem become dependent inputs for others. ie: systems can and should be designed to prevent domino effect failure. The key thing is that, whatever the overall system design, it should degrade gracefully and produce unambiguous data at all times. It fails completely if it is unable to do this, or gives up in such a way as to present the controlled entity to the user in an unknown state...

Chris

Bergerie1

10th Aug 2009, 13:54

I retired from active flying nearly 15 years ago, so I must not fall into the trap of thinking that more ‘stick and rudder’ flying is the only panacea for some of the problems that are manifesting themselves today. The last aircraft I flew was the B747-100/200 series!

Having been out of the loop for the last few weeks I have missed much of the discussion in PPRUNE about AF447. Now that I have had the chance to read back through some of the comments in this thread it seems to me that we are in danger of straying from the essentials.

First, we still don’t know what happened. There is some evidence that the Thales pitot tubes may have been at fault. Equally, I found Tim Vasquez’s analysis of the weather very informative (see www.weathergraphics.com/tim/af447/ (http://www.weathergraphics.com/tim/af447/) ). But it is still all speculation.

Second, we must accept that however good aviation systems have become there are phenomena out there that exceed anything we can reasonably expect to survive. I have recently been sailing along the south coast of Ireland and have been reminded of the so-called ‘freak waves’ which can in some cases reach heights of 30 mtrs. It is worth remembering that, world-wide, over the last two decades, more than 200 super-carriers - cargo ships over 200m long - have been lost at sea. Eyewitness reports suggest many were sunk by high and violent walls of water that rose up out of calm seas. In the air, thunderstorms have the power to wreak similar havoc and must be treated with the greatest of respect.

Third, while reading this thread, the emphasis has shifted from what little is known about AF447 to a more general and very valid discussion on handling skills and automation. Harry Mann and PJ2 discussed stalling (6 Aug). My view is that current pilots do not know enough about the stall characteristics of their aircraft simply because this is treated at such a superficial during training. D.P. Davies (Handling the Big Jets, 3rd edition, page 110) suggests that aircraft achieve stall warning speeds on somewhere between 1 in 100 and 1 in 1000 flights; and stall speed on around 1 in 100,000 flights. When he wrote this book he also compared this with engine failure rates at that time of approx 1 in every 1000 flights en-route and 1 in 100,000 on take-off near V1. Since then, engines have become much more reliable but we still seem to have accidents caused by stalling. I would argue that, in modern training, more emphasis should be placed on handing stalls. I used to do C. of A. test flights on VC10s, B707s and B747s and was surprised at how many line pilots were so concerned about the safety of such manoeuvres. Clearly this was because of their comparative lack of exposure. The controlled conditions of a test flight are one thing, with few surprises. At FL350 on a dark night in turbulence it would be another matter, but I am sure more adequate simulator training would improve skills and increase confidence.

Fourth, with so much of the operation now being done using automation, it is clear that situational awareness and manual handling skills are declining. Phantom Driver (6 Aug) quite rightly says that he does not want to have a wild ride while some guy up front tries to polish up his handling skills. PJ2 (also on 6 Aug) highlights how little manual handling is done these days on the route and that next to NO time is spent on hand-flying on the simulator. He has also written at length (8 Aug) on the positive effect that modern automation has had on flight safety – if we went back to the old methods I am convinced that the accident rate would increase. Therefore, the issue is to decide what training is relevant to the modern situation. I think that PJ2, Harry Mann and Phantom Driver would all agree that what is needed is a thorough analysis of exactly what needs to be trained and then to revise conversion and recurrent training schedules so that they reflect more closely the current risks rather than those of yesteryear. I also think that more hand-flying in the simulator, with exercises specifically designed to increase confidence in taking over manually after unusual problems, would be of great benefit to increase confidence and manual skills. Perhaps, exercises of this sort would have helped the Turkish crew at Amsterdam.

Fifth, one final thought – this thread and many others following an accident tend to wear a ‘hair shirt’. Accidents always hit the headlines, and then we rake over the coals at great length. However, the quiet, competent saving of an extremely hazardous situation is hardly noticed – unless it happens under the gaze of the press on the Hudson River! Perhaps we should spend a little more time celebrating the remarkable things that are achieved by our colleagues every year.

Squawk_ident

10th Aug 2009, 15:51

10/08/09 Number 09-099
http://ad.easa.europa.eu/blob/easa_pad_09_099.pdf/PAD_09-099_1

Phantom Driver

10th Aug 2009, 16:34

Bergerie 1:

Hopefully some Heads of Training will take in these points. The sad fact is, too many of us old timers (yours truly included) and the younger ones weaned on automation, have forgotten how to "fly"!

I always recall a DC10 accident some years ago at (Boston?)--short(ish) runway, wet snow; auto thrust system had a known history of faults. On this occasion, it held Vref+20 all the way down the approach. This was noted and commented upon by the crew, but nothing was done to rectify the situation. A/C landed hot and aquaplaned off the end in to the river.

The accident report made note of the fact that the Captain had not flown with A/T out for the past 5 years and so was reluctant to disconnect and fly manual throttles. Similar ingrained habits seen in the Qantas 744 incident at Bangkok; idle reverse was (apparently) the current SOP, resulting in another overrun on a wet runway following an aborted G/A (Captain over riding F/O's decision?).

David Beaty had some interesting things to say about all this in his "Human Factors in Air Accidents". In stressful times we all, of course, tend to revert to the habit which is most comfortable, as tunnel vision sets in. A pity really,because the lessons have always been there. As some old sage (Samuel Johnson, if memory serves correctly) wrote-"Man has oft more need to be reminded than informed".

In the Air Force (love ém or hate ém!}, the instructors used to delight in drilling into us -"You Fight as you Train"; seems like the same lessons could well be carried across into our Airline ops. We really do owe it to the customers.

Hyperveloce

10th Aug 2009, 17:09

I have seen nothing that would rule out a thermally driven rapid climb in the given circumstances, whereas I have certainly seen many posts on this thread suggesting scenarios that are either highly implausible, or even ruled out.

Hi there !
Please, could you be more specific about the either implausible or ruled out scenarii ? On my own, I have seen nothing that would acertain this hypothesis of a rapid climb at FL470 (why 470 ? no overshoot in the thermal imagery, no updraft detected by the AMDAR flight 25 mn before on the same track but at FL325 - wind 3.6m/s@319° , conditions can change rapidly though). Does this scenario of a rapid climb even require a freezing event of the Pitots ? It would be a coincidence ? (Pitot freezing event & rapid/uncontrolable climb)
Where would be the problem with a possible unfortunate reaction of the automation and the pilots in a context of unreliable airspeeds, misleading signals in the cockpit and in the procedures, high workload and false stall alarms, that would have degraded the aerodynamic margin at high altitude and rendered the plane highly vulnerable to turbulence even moderated ? (loss of control in a Learjet fashion)
Jeff

Will Fraser

10th Aug 2009, 17:11

Proposed AD

Though the new Thales # is 'yet to be proven as robust....as Goodrich...' it stays at position 2, Goodrich on the other two stations. With a recent failure on the Thales r/r on the 320, the logic of this AD (proposed) is classic. Classically confused.

augustusjeremy

10th Aug 2009, 17:56

Does this scenario of a rapid climb even require a freezing event of the Pitots ? It would be a coincidence ? (Pitot freezing event & rapid/uncontrolable climb)

Technical, accurate and objective.

syseng68k

10th Aug 2009, 20:24

Or, what happens if the protections kick out and a pilot with VERY GOOD skills
gets handed a compromised aircraft in the midst of moderate to extreme turbulence and with instrument readings which are misleading, at best? Nothing at all good I fear.After reading this thread for several weeks, that's about the best summary i've seen to date. :ok:

I'n not qualified to comment as a commercial pilot and it's some years since I did any flying, but it amazes me that there are not more events with systems that degrade to such a condition and just at the time when the crew need them the most.

One could say not smart enough by half...

mm43

10th Aug 2009, 21:10

Hyperveloce;

Careful examination of the OSCAR/NOAA surface current data provides 065°T x 22.5cm/sec at 3°N 31°W over the 5 day period centered on 2 June 2009. I have therefore examined the positions in which bodies were recovered from on 6/7/8 June and constructed a likely current line based on what we know, i.e. that for the 3 days just mentioned and a calculated rate for the 5 - 6 June of 19cm/sec (9NM/day) back to the time of the accident at about 02:14:30Z on 1 June of 22.5cm/sec (10.5NM/day).

The reason for using the bodies as a check on the current is that they will have initially sunk to a point of equilibruim, and provided the depth was not too great, the water temperature would have commenced the decomposition process. Then over a period of time each of these bodies would have gained enough buoyancy to become visible on or near the surface - which explains the number of days it took to find those that they did. The point is that the bodies will have been subject to little or no leeway effects due to the surface wind. SHOM data shows that large easterly vectors on the surface become small westerly vectors the deeper you go, which helps to explain why some debris items floating with possibly little or no windage have been found to the east of the general drift line in which the bodies were found.

The reduced size graphic below shows 2 significant cumulonimbus cells, the one on the track and another left of the track shortly after passing ORARO. It seems that each of these mesoscale cells has played a part in this incident.

http://i846.photobucket.com/albums/ab27/mm43_af447/af447-lkp-lge-3b.jpg

I surmise that for some unknown reason the WX radar has not revealed the presence of the cell the a/c penetrated at around 0209, but when everything turned pear shape at 0210 the PF made a decision to get out of the ITCZ and commenced a lefthand 180 and descent hand flying the a/c with somewhat degraded control systems provided in Alternate/Direct law. Singpilot described his experience a few posts back, but the conditions in the cockpit of AF447 were surely somewhat different.

The lefthand turn was unfortunately taking the a/c toward the Cb cell NNW of ORARO.

What happened during the SATCOM outage between 0213 and 0214 is of course speculative, but at some point in this rapid descent it can be assumed that IAS became available and an effort was made to stabilize the rate of descent. If a nose up attitude was adopted, the updraft associated with the next Cb cell may have resulted in a flameout of both engines.

Well the graphic shows the general idea, but if the current vector at 3°N 31°W was in fact 055°T x 20cm/sec, the impact point would have been about 10NM further east. This would give better GS but with a tighter turn - to be expected if the speedbrakes were deployed.

Here is the link to the full scale graphic.

http://i846.photobucket.com/albums/ab27/mm43_af447/af447-lkp-lge-3.jpg

mm43

HarryMann

10th Aug 2009, 23:18

What the guy describes is basic bad stall behaviour whereby the A310 raises its nose when approaching a stall and flies itself deeper into a stall.

Somebody's going to have to be a lot more specific before this rumour is taken seriously..

Under what configuration, trim, a/s and MNo did the suggested behaviour manifest?

Then we might be able to establish how relevant it is to this thread, if it is a correct & thoroughly objective assertion.

PJ2

11th Aug 2009, 01:58

mm43;
If I may enquire, for the mathematically-challenged among us, how the radius of the turn was calculated? I would just like to understand as my very amateur reading and use of the formula from Kermode's "Mechanics of Flight" is a nominal six and three-quarter miles for a 25deg bank turn at 463kt, (532mph) groundspeed and a time of about 330 seconds for the full 180. Hand flown the turn could be made tighter of course. Speed brakes do not tighten a turn, btw, bank angle does however.

r= v^2/(g.tanθ), where;

radius is in feet, velocity is in fps, g = 32.2, Tan of 25deg = 0.4663

Found a better formula from one of our bretheren in Tech to plug into Excel:
=ROUNDUP(POWER(D2,2)/((TAN(F2/(180/PI())))*68625),3), apparently used by PAN Ops, (Link) (http://www.pprune.org/tech-log/159674-radius-turn-formula.html#post1707074),
D2 = TAS value
F2 = Angle of bank.
Result is in NM

If the turn began at the "LKP", the yellow circle describes an 81,000ft diameter circle, or roughly 13.5 nm.
http://i277.photobucket.com/albums/kk76/batcave777/AF447TurnRadius2009-08-10_183022.jpg

mm43

11th Aug 2009, 04:30

PJ2;

If I may enquire, for the mathematically-challenged among us, how the radius of the turn was calculated?Didn't even try and calculate the radius of the turn - these guys were on a roller coaster with combination of ascending / descending air and an inherited tail wind. As I said, if the speed brakes (meaning to trade speed for a higher bank angle and less Gs) had been used they would have pulled a tighter turn, but I have no idea how awkward hand flying might be in alternate/direct law - and in these conditions.

A more direct path to the calculated impact point is likely as it provides for a steeper descent and ultimately a slower IAS when they attempt to level off. Someone might like to comment on how effective the rudder would be in direct law at near stall speed pulling TOGA with only one engine. Remember, the BEA stated the vertical stabilizer damage showed the tail was rotating to port on impact and I couldn't help but wonder if only No.1 was operational.

As mentioned in the earlier post, the calculated impact point could well be 10NM further east which would fit in well with the bank angle you have indicated and what appears to have been a rapid descent. Subject to the OSCAR/NOAA surface current data being reasonably accurate, I wouldn't be too supprised to find the "Pourquoi pas?" somewhere close by.

BTW, your circle is tangental to 0209, but moving it on 30 secs would allow the circumference to pass through the LKP at 0210. Thanks for the bank angle calcs and link.

mm43

PJ2

11th Aug 2009, 05:23

Cheers, mm43 - interesting work as was takata's. Along with others, I too, think they'll find the wreck and the recorders.

Wannabe Flyer

11th Aug 2009, 05:37

Out of curiosity

CVR and Data Recorders not found, bulk of wreckage not found. At what stage/time frame will the investigation committee "give up"?

In such instances what do they list in the investigation report? Has this happened before in any incident?

:bored:

HarryMann

11th Aug 2009, 11:07

Not directly relevant but as far as rapid descents and dives are survivable and the likely results of such... here is a copy of a post elsewhere on this board...
Saha Air 707 loses 2 on climbout (http://www.pprune.org/rumours-news/383867-saha-air-707-loses-2-climb-out-2.html)

http://i895.photobucket.com/albums/ac157/Entaxei/B7073ENGINE1500X1000SIZE686.jpg

N712PA a JT3 engined 707 from Pan Am's initial 6 lost the No 4 engine over France on 25th February 1959 in a training incident, it landed at Heathrow and was repaired in the Pan Am hangar.

N712PA had been involved in a near 30,000 ft dive over the Atlantic three weeks earlier where it got close to Mach 1 ...possible autopilot malfunction ..... No 3 does'nt look to clever either!! ..... nobody checked the engine mounts?.

Mods read/allow/delete as required

Hyperveloce

11th Aug 2009, 11:50

Hey there !
Thank you very much mm43 for this nice work.
I visualize the final trajectory in a very similar way than yours, two aspects expected maybe:
- this large route deviation would be unvoluntary, this would be the horizontal trace (large roll perturbation) of the high altitude cruise loss of control, this would occur as a consequence of a large exceedance of the MMO (Mach>0.89-0.90) and this severe overspeed would require ~1mn or over to occur
: the tight turn would start around ~02:11:00Z
- this turn would not be a constant load factor turn (a part of a circle) with such a high constant curvature radius but a trajectory where the shortest radius (highest load factor, highest roll) is at the beginning of the initial route departure and where it decreases (roll is being controlled) in less than one minute.
This tight turn would probably go with a rapid loss of lift/altitude ?
Once the roll is back under control, the pilots were in position to try to regain control in the vertical plane ? (AoA/incidence, pich). This would be the final part of the trajectory: rather linear in the horizontal plane and in the vertical plane, a rapid loss of altitude (~10 000 fpm), the AoA/incidence decreasing in a first time to regain the aerodynamical authority (also with the loss of altitude and the increasing air density - stall recovery) and increasing again to generate enought vertical Gs to try to break the catastrophic descent. The plane being "en ligne de vol" (straight horizontal trajectory / wings leveled, small horizontal speed component / speed mostly vertical, possibly a slight nose up)

http://img148.imageshack.us/img148/15/finalhorizontaltrajecto.jpg

Indeed the drifting of the bodies or of the debris can be very different if you look where was recovered the left wing spoiler (this latter, recovered north of TASIL, seems like an outlier in the debris distribution, it has not been much deviated westward by the westernly surface winds derived from the satellite scatterometers, see windscat). I will have another look to the surface current values over the first days of June since I have used values slightly lower than yours (and much lower than the SHOM values).

I am studying the slopes distribution of the seabed in the area where the debris should have been colocated the 1st of June at 02:15Z. I wish to validate my computations before I produce any graph results (missing values in the numerical terrain model) but it appear that between 5% and 10% of the seabed slopes are between 25° and 50°, using a 1.25km square bin resolution (narroy faults, slope details finer than this 1.25 km are lost/not observable). This bathymetry must be a real pain: towing up and down the multibeam sounder with the relief, varying scanning speed/resolution as a function of the slope, etc... Would it be a luxury to send another high resolution sounder to probe this area ?
Jeff

Hyperveloce

11th Aug 2009, 12:08

Hey Harrymann. This seems highly relevant to me, I have also been searching such cases to validate my little speed computations (as a function of the thrust, angle of dscent, altitude, etc...). On the DC-8 cases (reaching Mach 1.012 around FL410 starting over FL500 and Mach 0.82), it would require 3 mn of a 5° controlled dive but I haven't found this historical details:
http://img411.imageshack.us/img411/5642/dc8overmach1valid.jpg

singpilot

11th Aug 2009, 13:27

Do y'all remember a post by me several pages ago about how (aerodynamically) clean most airliners are?

That when heavy (and even when not), they will accellerate happily to MMO and beyond with a 'mild' pitch excursion (or an expedited descent, perhaps along with a temp change/wind shear/shift)?

Look at the data from the DC-8 'dive'..... 5 degrees of nose down pitch.....

This in a 1960's DC-8 at high altitude.

So now, put yourself near performance cruise ceiling, at night, at cruise, and get distracted by..... anything. Forget WX, AltLaw, DirLaw, all the rest.

Find yourself hand flying a perfectly normal airplane. That's not a stretch.

5 degrees nose down is not far away. How long did it take to get to the surface? More than 5 degrees nose down.... That's not a stretch.

I'm just saying, I know how easily it gets fast.

Now put back in what we do know. AltLaw, DirLaw. WX. Possibly missing/faulty info displayed.

Not pretty.

HarryMann

11th Aug 2009, 14:25

This in a 1960's DC-8 at high altitude.Yes, but surprisingly those wings were thinner, less super-critical, more sweep and could well have had higher Mcrit, surprisingly - just less optimised for the 'exact' cruise condition and fuel volume/sweep trade-offs..

I doubt you'd get an A330 above M 1.0 (in one piece) :rolleyes:

Also, the lower by-pass, or even pure jets of that day, had much less momentum drag and indeed, the naceles also likely again, a higher Mcrit

Ditto fuselage diameter

But I'm not arguing your general case-making and assertions...

Hyperveloce

11th Aug 2009, 15:24

Several airliners have exceeded their MMO, the China Airliner sustained more than +5 vertical Gs, even Airbuses, but with light excursions beyond their MMO (Mach 0.86-0.87). These ones recovered after a few thousands feet altitude loss.
I have read in an Airbus flight testing manual that the high speed stability could be tested, by inducing a voluntary/controlled overspeeding phase, waiting for the protection law to activate. It was indicated in any cases "DO NOT EXCEED MACH 0.90". I don't know about any Airbuses or Boeings having closed or exceeded Mach 0.90 in a single piece and survived. One Boeing has probably largely exceeded this limit largely during a high dive at medium altitude (and has gone supersonic ?) but it broke into pieces before the surface impact. It the middle of a mesocluster of tropical thunderstorms, nearing the highest top Cb cell tower, I really wonder whether you need to operate a large excursion beyond the MMO to loose your flight stability margins and really be vulnerable to turbulence. I also wonder about the detrimental impact of the spoilers during a significant excursion beyond the MMO (there was a problem in the overspeed procedures of the Learjet about this aspect, the one of the manufacturer and the one of the pilot being different, but I also know that the wing/airframe geometry of a Learjet and of an Airbus are not the same)
Jeff

Bergerie1

11th Aug 2009, 15:36

Hyperveloce
The B747 has been taken up to M0.99 True by Boeing and 0.98 during UK certification, and the handling remained good throughout. I don't know about the Airbus types.

M.Mouse

11th Aug 2009, 16:52

Worldwide-Aviation.net (http://www.worldwide-aviation.net/index.php?option=com_content&view=article&id=127:klm-grounds-a330-fleet&catid=34:airilnes&Itemid=61)

robertbartsch

11th Aug 2009, 17:10

When the French investigators concluded that 447 hit the water intact based on compression evidence from recovered wreckage, does this include or exclude the stabilizer?

Apparently, the tail was recovered >50 miles from much of the rest of the recovered wreckage and the automated electronic messages transmitted to AF indicate a decompression event ocurred earlier?

vapilot2004

11th Aug 2009, 17:20

The BEA has stated that the vertical fin broke away from the fuselage due to impact. Something about how the attach points were distorted and forces were assumed to come from the rear.

Machaca

11th Aug 2009, 18:12

No A330 groundings -- Worldwide-Aviation.net issues retraction:

Rectification - KLM Grounding A330 Fleet
(http://www.worldwide-aviation.net/index.php?option=com_content&view=article&id=127:klm-grounds-a330-fleet&catid=34:airilnes&Itemid=61)
Rectification following an article earlier today with regard to KLM suspectingly grounding its A330 fleet. Confirmed sources around the airline have told Worldwide-Aviation.net that all Airbus A330 in service of KLM are still in operation. Replacement of the pitot probes is an ongoing process and it is not expected that this would form a problem maintaining the current flight schedule.

HarryMann

11th Aug 2009, 21:59

and the automated electronic messages transmitted to AF indicate a decompression event ocurred earlier?

No, they don't, certainly not explicitly, maybe read this thread back a bit first to get some proper background.

singpilot

12th Aug 2009, 01:40

As I remember (AirChina, Kalitta, and others) the 747 tends to shed outer panels of stab/elevators and gear doors with Mach+ excursions.

Not a regime that I'd ever want to explore.

Then the 747SP's were certified (as I remember) even faster than normal 747's? Maybe they operated faster, sorry, can't remember.

Do I remember that an elevator or a piece of one was recovered in the AF447 debris?

Dave Gittins

12th Aug 2009, 04:11

Whilst the pitot issues have concentrated pretty much on Air France, the world fleet of 1000 A330 and A340s - and a host of other Airbuses - extends way beyond that.

What is the picture with the types of pitots in use elsewhere and any need to exchange Thales for Goodrich.

I say this with a very personal interest as I am due to fly as SLF on a Qatar Airways A330 from Doha to Manchester in 2 weeks time and would like to have some insight.

augustusjeremy

12th Aug 2009, 04:39

Only from Airbus ?

Graybeard

12th Aug 2009, 15:06

About ten years ago, an Evergreen Intl A/L 747-100 converted to cargo, enroute KJFK-KANC at night over Canada, had A/P roll computer do a slow rollover, and the plane went supersonic in the dive. They landed at nearest airport, and may have replaced a few panels. The plane continued in service for more years. Actual speed was retrieved from the fdr.

GB

Will Fraser

12th Aug 2009, 15:20

Avoiding too fine a point on the topic, it is of note that at least three separately discovered control surfaces were discovered. I haven't followed the drift/current discussions; BEA would conclude that the a/c impacted as a complete airframe. The Vertical Stabilizer, Rudder (attached), a spoiler (left, inner) and a portion of the Elevator were of note prior to the conclusion by BEA that the a/c held together until the last. Since the discussion is drifting in a 'shedding parts' direction, I thought I'd remind us of the evidence, though I'm not implying that is what happened. Since Upset can occur in either of two seperate trends, it appears BEA have selected the Stall rather than the overspeed, shed metal format. BEA's statement is possible, but I question its status as a conclusion.

Hyperveloce

12th Aug 2009, 15:43

Hyperveloce

12th Aug 2009, 15:47

Hyperveloce

12th Aug 2009, 15:59

Since Upset can occur in either of two seperate trends, it appears BEA have selected the Stall rather than the overspeed, shed metal format. BEA's statement is possible, but I question its status as a conclusion.
Hey Will. Can't a severe overspeed end up into a stall ? (high speed stall/mach buffet).
To me, there is no contradiction between an initial overspeed and a stall (or even two: a stall by exiting the upper limit at high altitude during the overspeed, then, after a nearly successfull recovery/flight point back again within the envelope, exiting the lower limit of the flight envelope due to an overcorrection at low altitude).
Jeff
PS) Has NTSB scheduled any report of its investigations ?

Will Fraser

12th Aug 2009, 16:01

Jeff

I think their opinion that the a/c remained whole is meant to include not shedding parts, a Stall and descent to the Ocean. If overspeed, and the potential for elevator failure, spoiler separation, and VS loss, well you see their problem. A kind of Reverse postulation that precludes airframe failure, which would be my goal if I had an opportunity to claim it for a principal in the accident. I think that more is included in the BEA's assessment than is justified in evidence.

Hyperveloce

12th Aug 2009, 16:57

Even if the BEA could get some clues about the impact conditions, and will get a more accurate view after the CEAT analysis, the BEA cannot know about pieces of the airframe it hasn't recovered, hence it would be difficult to understand how the BEA could suggest that the structural intergrity of the plane was not compromised at all. In my understanding, the BEA position is only that the plane had not suffered a mid-air break up or a major control surface failure (that would have rendered it uncontrollable) like a VS loss. There had been some speculation about a catastrophic structural failure in altitude. Given this, I don't think that the BEA interim report says that no spoiler was lost for example. But his was a young airframe.
Jeff
BEA interim report (page 72):
"leur examen visuel montre que l’avion n’a pas été détruit en vol ; il paraît
avoir heurté la surface de l’eau en ligne de vol, avec une forte accélération
verticale."
"their visual examination (of the debris) shows that the plane did not brake up in mid air ; .../..."

rgbrock1

12th Aug 2009, 17:04

Hyperveloce:

quote/hence it would be difficult to understand how the BEA could suggest that the structural intergrity of the plane was not compromised at all. In my understanding, the BEA position is only that the plane had not suffered a mid-air break up or a major control surface failure (that would have rendered it uncontrollable) like a VS loss. There had been some speculation about a catastrophic structural failure in altitude./endquote

Isn't the theory of the airframe not breaking up at altitude suggested by the absence of flail-type injuries on the recovered bodies?

EmBee

12th Aug 2009, 23:45

Aero-Instruments to offer pitot tubes for Airbus aircraft (http://www.flightglobal.com/articles/2009/08/05/330592/aero-instruments-to-offer-pitot-tubes-for-airbus-aircraft.html)

mm43

13th Aug 2009, 02:15

Hyperveloce;

The spoiler you referred to was I think the port outer which was picked up by a merchant ship north of TASIL on 13 July. If it had detached on account of an overspeed event, then that would help to explain its recovered position not falling within the range of expectation provided by the surface current/wind data. This would also fit in with the high Gs roll/bank to port and the high speed descent toward the suspected crash site as postulated by you in a recent post.

http://i846.photobucket.com/albums/ab27/mm43_af447/af447-quikscat.gif

I have extracted the Quikscat mean surface (+10m) winds from the NOAA site and determined that the mean surface wind at 3°N 30°W for the period 1 - 7 June was from 069.3°T x 11.06 knots (5.69m/sec). The vertical stabilizer has a very low profile to windage, in fact the only significant airfoil was the small piece of empennage skin rolled up and inward on the forward end. The leeway for the v/s shown on the graphic below was 221°T x 11.1NM with reference to the general position of the 5 bodies recovered on 7 June. Without knowing the precise timings for either position (which could have been any time between sunrise and sunset) there is some room for positional error.

http://i846.photobucket.com/albums/ab27/mm43_af447/af447-current-vs-3.jpg

The effective windage factor calculated from the graphic is 0.74% which doesn't seem unreasonable. Applying the same factor to the Quikscat data provides a leeway of 249.3°T x 12.8NM over 6.5 days. Sun shadow on a photo taken at the time of the v/s recovery indicates that the sun was near or on the meridian, i.e. 1400z. However, when comparing the Quikscat data with the MSL analysis during the period in question, the wind vector should be more northerly. Putting that aside, the calculated result puts the v/s where it should be +/- a couple of miles.

mm43

surplus1

13th Aug 2009, 19:48

While I'm neither supporting or rejecting an in-flight break up, those searching for baggage should consider that an in-flight break up can mean a rather wide variety of things. Peraps the empennage came off and the rest remained intact until impact. Perhaps a wing partially failed, but the remainder remained intact. Perhaps the horizontal tail surfaces failed downwards and the rest remained intact. In-flight break up does not necessarily translate to hundreds or even tens of tiny pieces. It just means some type of structural failure prior to impact of the whole, which precluded the ability to recover from an in-flight upset.

You all need to be as creative in your thinking about structural failure as you are about drift patterns, ocean currents, ice crystals in pitot tubes and 180 deg turns. At this point all that we have is a mystery, therefore anything is possible.

JD-EE

13th Aug 2009, 23:30

Will asked a fair question, "What gives you the confidence to quote "60-120 mph" ??"

That is pure conjecture considering the terminal velocity of a human (about 120MPH) and the wings. I doubt it'd hit flat at 200 MPH with both wings present. (With only one wing it would not hit flat at all.) It might have hit faster if the pilot had been in a poorly controlled dive and managed to try to pull up as he saw the ocean. That would account for the flat or almost flat attitude, the tail breaking off as it did, and would likely give a faster velocity vector when contacting the ocean.

If I understand the construction of the pressure vessel and the interior the pressure vessel does not support much weight at all. That is all handled by an interior cabin construction. That way the pressure vessel would not be punctured by a lot of small holes supporting heavy weights. Thus it would be sort of like dropping a cigar tube on its side with the cigar in it. You'd get crumpling on the bottom that hits the ground. But the top would not crunch down. That's an extreme example. But it gives the idea behind my thinking. Mass as well as deceleration is needed to crunch the cabin.

Some evidence indicates a break near the front of the wing. That is how the galley and other parts "escaped". And it explains the crew rest facility pieces. If that happened before the rest of the fuselage crunched with its circular integrity removed you can explain the distribution for the recovered passenger bodies.

The chief arguments regarding a break-up in mid air involve getting the debris to where it was found given the ocean currents and the missing items you'd expect to see from a breakup. This would be items of luggage from the hold rather than the sparse couple things found that are generally overhead bin items.

The breakup scenario also requires the plane to remain in a relatively stable attitude until after the last message. It also requires the plane to remain enough in one piece to hit the ocean more or less flat. And you have to break off the VS in the mode seen. (Remember my demo concept of pulling pages out of a three ring binder. You can figure out how you pulled the paper out by the tear patterns. And the VS is very much like that piece of paper right down to the "three ring binder" mounting.)

I'd believe breakup in the air if you can prove God or weather could swat at a plane mashing its tail forward and up without leaving marks on its rear edges.

JD-EE

HarryMann

14th Aug 2009, 00:41

IF the a/c broke up at a decent height, the main bits would then have dropped to the surface at a high speed.

Would they ? The engines would, a centre section section wouldn't tumble 'that*' fast, with main wing panels attached.

*What is 'high speed'?

The surface impact would probably have been extreme and the a/c would have been reduced to smallish pieces.Would it? More likely if striking as a whole unit ?

Although a lot of these would have sunk, many would have floated. More than the bits that have been found.. Not so in the case of the Comets, which 'definitely' broke up at altitude...

The only real difference, is that here we'd have a few more pieces floating, due to composite construction... seems they stayed attached?

============================
We seem to be not only wantonly urinating, but to windward with a lot blowing back in our faces here... :)

Someone's going to be right, but probably more by chance than genuinely educated deductive reasoning :rolleyes:

So I think BBF's conclusion is probably right, it agrees with BEAs and currently is the more likely occurrence, but some of the conjecture on kinematic and aerodynamic behaviour requires more rigorous justification.

Something may well have bent or broke at high altitude, but just as likely in thicker air at low altitude if control was compromised (which obviously it was, one way or another)....

BarbiesBoyfriend

14th Aug 2009, 01:04

Harry

After the Lockerbie accident, when the a/c came apart ahead of the wing L/E , the rest of the a/c came down with enough force to dig a crater 200 feet wide and 60'- 80' deep, closing the M74 for 2 days. They found the engines........

If the AF had a similar break up, I doubt you'd find the galley a-floating on the briny.;)

wes_wall

14th Aug 2009, 01:15

Very early in this thread, I posted the following, but cannot find it now. This is copied from my word processor

Again, I think that there is a good possibility that the airplane may have gone down intact. I based this on the thus far slow or lack of discovery of a debris footprint. Had the airplane failed at altitude, given the altitude, speed, and winds aloft, then one could reasonably expect an extended area of debris which would track with the airplane as it descended. I doubt it would have been difficult to locate.

To compare, I recall all too well the Lockerbie situation with the inflight breakup of PA and the area that was affected. The heavy portion fell in the village, and nearby area, but countless other items extended for miles. Some large, some small.

On the other hand, MS990 created only two relatively small debris field in the Atlantic. One 62 X 66 meters, and the other 83 X 73. This airplane entered the water mostly intact

I still think that the airplane reached the water with the fusillage together, with some failure occuring on impact. This would account for the varied distribution of bodies compared to the seating chart. Had the cabin broke at or around R & L 2, a good case can be made for the galley.

rgbrock1

14th Aug 2009, 12:31

Interesting the Lockerbie has been brought up. (I, unfortunately, remember it all too well.) We know for a fact that Pan Am 103 broke apart at altitude. I'd like to correlate this with the recovered bodies from 103 and AF 447. If we all remember, although 103 broke apart at altitude many of the recovered bodies were fully clothed. (Reference: "my boy", "the man in the suit", etc.) So, in answer to someone's query earlier this week: because the bodies that were recovered from AF 447 were clothed, or not, I believe is indicative of nothing as far as a break up at altitude or not.
Perhaps i"m incorrect.
Then again, this supposition does nothing toward understanding what the CAUSAL factors of AF 447's destruction were. :ugh:

Dutch Bru

14th Aug 2009, 13:18

Yet another dozen pages added to this thread because a few contributors refuse to read or otherwise ignore the "evidence" to date that BEA brings forward in its preliminary report which leads BEA to declare it is likely that the aircraft hit the water intact.

Allow me to paste here some quotes from pages 38 to 40 of the said report:

"The identified debris thus comes from all the areas of the plane."

"Part of the radome was found, representing approximately a fifth of its
circumference along its upper part."

"The galley, identified as G2, located at the level of door 2 on the right-hand
side, was not very distorted. Baskets and racks were compressed in the lower
part of both galley carts."

"The distortions observed in the metal vertical reinforcements of a toilet door
showed evidence of significant compressive forces."

"Fragments of the walls of the flight crew rest module were crumpled and
those of the ceiling were deformed downwards. The floor was curved under
the effect of a strong upward pressure from below. The connecting brackets
between the floor and the walls were bent backwards."

"Observations of the tail fin and on the parts from the passenger (galley, toilet
door, crew rest module) showed that the airplane had likely struck the surface
of the water in level flight, with a high rate vertical acceleration."

Assuming on what was there in terms of clues at the time of the publication of the report, I gues this sounds all perfecty plausible. To doubt the official investigating body and contrary to BEA's concrete findings speculate otherwise on NO evidence at all is irresponsible and a waste of space.

The final report will take into account all clues and evidence that has and, for now, will become available, hopefully when the wreckage and the recorders are found.

Clear_Prop

14th Aug 2009, 23:31

DutchBru:

To doubt the official investigating body and contrary to BEA's concrete findings speculate otherwise on NO evidence at all is irresponsible and a waste of space.

Is it? Are you sure? So accepting on blind faith the hastily assembled preliminary observations of the official investigators' hypotheses based on some very limited bits of evidence is ok is it? I dont see much yet that can be labelled as "concrete findings" from anyone, even BEA.

I dont mean to single you out on this DB, because your response was quite valid and yes I agree it is frustrating to read the same things coming back again and again. However, whether we like it or not, iteration is a hugely important aspect of any kind of problem solving. It is only annoying in this forum because it is inconvenient; it doesn't fit neatly into a single-thread debating format.

So, either we take the view DB alludes to that there is no point whatsoever to this thread and we should just let the investigators do their job...

...or we allow this thread to stand as a collective demonstration that the aviation community will not accept less than the highest standard of problem solving in this case.

Whether the investigators take heed of some of the additional cognitive reasoning being offered by contributors to this forum, or not, they will surely be aware that this is one of the key places at which their findings MUST stand up to criticism.

Unfortunately in the field of problem solving it is NOT sufficient to say "Oh I wish people would shut up about x,y,z because they were mentioned 130 pages ago" because unless these things churn over and get re-evaluated obvious missing links will stay missing. It took a 13 year old kid to point out the that dial-up could become DSL due to an obvious oversight by an entire industry.

- I agree it is frustrating to read all the repitition though, particularly in such a complicated case. I would propose to the moderators that AF447 should temporarily occupy its own section within Pprune - with seperate sub-threads for the main debating issues, general news and a summary; until such a time as the evidence, reporting, speculation and debate of each nuance begin to gravitate towards something conclusive.