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AF447

Old 8th Jun 2009, 08:35
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Obie, I am cruising at 2000' above my FMC optimum altitude. Enter cloud and the SAT increases by +20C...By how much would the optimum altitude change in your aircraft?...It happens...unless of course..Sir Richard is correct!

Experts..definitive answer on this one please..real temp rise or indicated due temporary icing effect!

Last edited by Yaw String; 10th Jun 2009 at 17:10.
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Old 8th Jun 2009, 08:38
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Hi Obie

Could I second Bleve's request for a description of the supposed major flaw in his statement?
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Old 8th Jun 2009, 08:52
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Quote:
I would also think you are talking in C as only us stubborn Americans think regularly in F
Yes I am talking °C.

Quote:
I think I would like to avoid areas prone to 30 degree changes.
You don't get any warning or indications that you are about fly into such areas. They are localised and transient events. With experience you start to get a feel where there is an increased risk of it occuring, but that's about it.

My experience, and it seems it is the same as some of the other posters on this thread, is that the common conditions in which large OAT rises have been seen are:

- tropics
- over water
- nearby or recent convective activity
- flying in stratform cloud (appears as widespread speckled green wx radar returns)

The last time I experienced a large OAT rise was over the Pacific Ocean at about 20°N. We were in widespread upper level Nimbostratus cloud. There were no active cells in the nearby region and we assessed the cloud to be from decayed CBs. The radar return was speckled green. Over the space of about a minute (~10nm) the OAT(SAT) went from about -55°C to about -25°C. Fortunately our aircraft had enough excess thrust available to be able to cope with such conditions and we were able to maintain speed and Flight Level.
Well I think you just described a TAT probe icing event there.
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Old 8th Jun 2009, 08:57
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could some one tell me how much a 30 °c temperature change will change mach number?

I've spent hours chasing speed in mountain waves with just 5 or so ° temperature changes. I don't remember the formula for calculating Mach from TAT but I'm sure someone on here has it.
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Old 8th Jun 2009, 09:05
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Just a quick refresher of what density altitude is.....

Density altitude is defined as the altitude at which a given air density is found in the standard atmosphere. For a given altitude, density altitude changes with changes in pressure, air temperature, and humidity. An increase in pressure increases air density, so it decreases density altitude. An increase in temperature decreases air density, so it increases density altitude. An increase in humidity decreases air density, so it increases density altitude. Changes in pressure and temperature have the greatest effect on density altitude, and changes in humidity have the least effect.

With that information, you can see the effect of a temperature change on the aircraft altitude. Note also that entering a area of T/storms may well give rise to an increase in humidity thus an increase in density altitude.

KW
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Old 8th Jun 2009, 09:12
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BT wrote:
But we will all be more careful from now on. And carry more fuel if the sig wx chart looks scarey.
In order to carry more fuel they would have needed to drop some weight elsewhere. They were already at 100% max. TO weight... (233 t) (source AF press conference June 5th)
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Old 8th Jun 2009, 09:13
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amc890

If the rapid rise in displayed temperature was due to TAT probe icing then I would expect that there would be no change in engine thrust. If the outside air temp remains constant, then the Flight Level remains constant and there is no requirement for extra thrust. However as explained previously, if the OAT does increase, there is a need for increased thrust.

In the event I described, the thrust did increase - significantly. In fact we reached max cruise thrust and had to select climb thrust to maintain Flight Level and speed. That is consistent with a real increase in OAT, not a false reading due to TAT icing.
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Old 8th Jun 2009, 09:22
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Bleve

Please read my previous post. Look at the temperature change relationship with density altitude, then, look at how the aircraft would be affected if the TAT probe did ice up (a big if) with a change in temperature, then compare that to a natural change in outside air temperature. The time to change will be the enemy as far as the air data computers are concerned. What the ADC then instructs the A/T an A/P to do can be instrumental in how the airframe and engines maintain their integrity.

KW

Last edited by kwachon; 8th Jun 2009 at 09:25. Reason: spelling, just spent 2 hours flying through T/storms
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Old 8th Jun 2009, 09:22
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"My experience, and it seems it is the same as some of the other posters on this thread, is that the common conditions in which large OAT rises have been seen are:

- tropics
- over water
- nearby or recent convective activity
- flying in stratform cloud (appears as widespread speckled green wx radar returns)"

Bleve,

Thanks for the information. So you don't think I haven't flown much around the world, I can state I have flown across every line of longitude, as far north as Fairbanks and as far south as Perth. I just have never met the conditions you described after over 30 years of flying (US Navy, TWA, ATA, etc). I will say I have never operated in the South Atlantic area.

One learns something new every day in this business.

I do hope they find the "boxes" so we have a clearer picture and less conjecture.
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Old 8th Jun 2009, 09:23
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O.K. Here it is. Regarding the Weather transmission from the flight, misreported/mistranslated in the media as "hard turbulence" seems was earlier reported by this French Media outlet:

French Media wx trsmsn

Using my trusty Google translator here:

Translation via Google

I get:

At 23 hours, twenty minutes before the entry of the Airbus in the airspace of Senegal, the pilot sends a message that crosses a zone of severe turbulence in cumulonimbus clouds charged with electricity and winds. Weather satellites attest
well, not perfect either...... but what do you expect from a computer?

Here's the source statement:

A 23 heures, soit vingt minutes avant l'entrée prévue de l'Airbus dans l'espace aérien du Sénégal, le pilote envoie un message signalant qu'il traverse une zone de fortes turbulences, dans des cumulo-nimbus chargés d'électricité et des vents violents. Les satellites météo attestent
Anybody Speak French? Wanna confirm that the google translation is right?

Thanks,

So it seems "Severe" is the word we are dealing with here. Ten minutes before the chit hit the fan.

Crunch - Out
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Old 8th Jun 2009, 09:24
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Bleve

You're logic and train of thought is on the money me thinks.

And when you are at coffin corner and there is nothing left but to descend but the a/c is telling you something else and you believe it for any number of reasons

Disaster beckons.

The other equally important hole on the cheese, is why no diversion?

Last edited by VR-HFX; 9th Jun 2009 at 05:47.
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Old 8th Jun 2009, 09:27
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Gumby,
So you don't think I haven't flown much around the world
I never thought that for one moment. If I gave that impression I am sorry - it was never my intent.
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Old 8th Jun 2009, 09:31
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Captain-Crunch


It reads after Senegal:

The pilot sent a message indicating he was passing through an area of strong turbulance within Cumulous Nimbus clouds with lightning and violent winds.

KW
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Old 8th Jun 2009, 09:32
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qu'il traverse une zone de fortes turbulences,
Fortes= Strong.
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Old 8th Jun 2009, 09:35
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Anybody Speak French? Wanna confirm that the google translation is right?
I'm afraid "fortes turbulences" is just blurry terminology like "strong turbulences".


Found this on a French aviation website:



- CAT légère : 75% des cas
- CAT modérée : 15 à 20% des cas
- CAT sévère : 5 à 10% des cas
- CAT violente ou extrême : 1% des cas


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Old 8th Jun 2009, 09:36
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Further to the French message in Captain Crunch's post.

The pilot sends a message signalling that he is crossing....
later on
electricity and violent winds -

Only a few words left out but necessary I think.
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Old 8th Jun 2009, 09:38
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amc890

If the rapid rise in displayed temperature was due to TAT probe icing then I would expect that there would be no change in engine thrust. If the outside air temp remains constant, then the Flight Level remains constant and there is no requirement for extra thrust. However as explained previously, if the OAT does increase, there is a need for increased thrust.

In the event I described, the thrust did increase - significantly. In fact we reached max cruise thrust and had to select climb thrust to maintain Flight Level and speed. That is consistent with a real increase in OAT, not a false reading due to TAT icing.
You can get thrust changes. Are you sure the thrust ref didn't reduce toward and beyond the thrust required even to the point that you had to select climb thrust and in fact increase thrust at that point, because everything you describe including selecting climb or even cont thrust is still screaming TAT probe icing to me. I'll see if I can find some reference material from a QRH.

EDIT
Note; not Airbus material
One or more of the following may be evidence of TAT
probe icing:
•The autothrottle disconnects and the
reference/target EPR and reference EPR displays
blank
•The thrust levers are not aligned with the engine
EPR displays
•The engine EPR displays are not aligned with the
thrust levers aligned
•A decrease or increase in the reference/target EPR
displays at a constant altitude and speed
•The engines are unable to achieve the maximum
continuous or the maximum climb rating with thrust
levers fully forward
•The TAT display remains constant and near 0
degrees C during climb, cruise, or descent

Last edited by amc890; 8th Jun 2009 at 09:49.
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Old 8th Jun 2009, 09:45
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Hello,
I think a "coffin corner" due to a sudden change in the air temperature is a strong possibility.
My question is not about what did make the flight fall.... is about why the AF crew didn´t avoid that CB (more than 35,000 feets tall), specially when an IB flight behind them requested a change of route to avoid this (and one could supose that the AF crew listened the request)...pilots use to avoid this areas.
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Old 8th Jun 2009, 09:52
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Hello,
I think a "coffin corner" due to a sudden change in the air temperature is a strong possibility.
My question is not about what did make the flight fall.... is about why the AF crew didn´t avoid that CB (more than 35,000 feets tall), specially when an IB flight behind them request a change of route to avoid this (and one could supose that the AF crew listened the request)...pilots use to avoid this areas.
I think this is the very first question. The whole thing would be ressumed in two questions:

1) Why did it enter the CB, 2) What happened inside?

For the first question, several things have been argued, most of them banned, such as the problem with the radar on AB.
What I find intringuinly is why this forum is banning pilots who weekly fly the leg SouthAmerica - Europe on AB330/340 and knows very well what they are talkin´ about...
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Old 8th Jun 2009, 09:55
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Exclamation

I just happened to run into this article. Not sure if it was posted yet.

Could this be pure coincidence considering the threats at EZEIZA?

Key Figures In Global Battle Against Illegal Arms Trade Lost In Air France Crash (from Sunday Herald)

Key figures in global battle against illegal arms trade lost in Air France crash
ARGENTINA: Argentine campaigner Pablo Dreyfus and Swiss colleague Ronald Dreyer battled South American arms and drug traffickingFrom Andrew McLeod

AMID THE media frenzy and speculation over the disappearance of Air France's ill-fated Flight 447, the loss of two of the world's most prominent figures in the war on the illegal arms trade and international drug trafficking has been virtually overlooked.

?
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