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AF447

Old 31st Jul 2009, 01:55
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Originally Posted by Hyperveloce
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.
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Old 31st Jul 2009, 02:20
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Back Up Speed Scale (BUSS)

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
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Old 31st Jul 2009, 02:51
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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.
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Old 31st Jul 2009, 03:02
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“Airbus Asks Airlines to Use Goodrich Sensors, Not Thales Probes”

I just read a news report 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.
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Old 31st Jul 2009, 03:33
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CONF iture - "Pourquis Pas?" position

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.
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Old 31st Jul 2009, 05:38
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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
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Old 31st Jul 2009, 06:11
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No requirement for AF 447 "Black Boxes"!

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!
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Old 31st Jul 2009, 07:06
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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) 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), 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) 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
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Old 31st Jul 2009, 08:01
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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.
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Old 31st Jul 2009, 08:20
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Pourquoi pas?

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?
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Old 31st Jul 2009, 13:37
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Stall warning AoA

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

Last edited by HazelNuts39; 31st Jul 2009 at 15:28. Reason: minor additions
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Old 31st Jul 2009, 13:42
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Originally Posted by broadreach
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"





This must be part of the "transparency" process as seen by the BEA ...
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Old 31st Jul 2009, 14:23
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CONF iture and Squawk_ident

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.
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Old 31st Jul 2009, 15:36
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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.
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Old 31st Jul 2009, 17:19
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Airspeeds deprievation: Operational Impact=NIL

There is an AF note (AF Tech Note 34-029) available via the Eurocockpit website : Eurocockpit - Archives
(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

Last edited by Hyperveloce; 31st Jul 2009 at 17:44.
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Old 31st Jul 2009, 17:34
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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.

So on the money, it must hurt.
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Old 31st Jul 2009, 17:43
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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 ??
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Old 31st Jul 2009, 17:55
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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?
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Old 31st Jul 2009, 18:07
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"Ouvrir son parapluie"

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

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 ?

Last edited by Hyperveloce; 31st Jul 2009 at 18:25.
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Old 31st Jul 2009, 18:16
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CYA

A similar idea in English ?
It's "CYA". Cover Your A$$.
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