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AF447

Old 8th Jun 2009, 04:53
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BRE
 
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If I remember correctly from aerodynamics lectures, there is no other reliable way to measure airspeed.

One could use Doppler radar, but that would involve tracer particles. Or one could use a propeller which might give somewhat reliable readings below 300 knots but would completely miss static air pressure.

A GPS derived speed signal might be helpful but lacks information about wind speed and static pressure.
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Old 8th Jun 2009, 05:16
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Retraction

Guys my post on page 24 to Airpolice may have a error in it. Several readers have correctly brought into question the 0200? keyboard crew acars report assumption and it's source. I committed the cardinal sin of quoting and believing a journo report with the term "hard turbulence" instead of a real source. My apologies. The Air France Press Release in English, which is also fishy says:

The aircraft hit a zone of stormy weather with strong turbulence at 2am this morning (universal time), i.e. 4am in Paris. An automatic message was received from the aircraft at 2:14am (4 :14am in Paris) indicating a failure in the electric circuit a long way from the coast.
2nd PR from the bottom

Of course, to re-emphisize: the acars images from French TV are not consistent with what you would expect to see with any electrical problem. All we have at this point is images of that leg report to maintenance via French TV? Right? What we need now is the actual image, or at least some sources of the acars wx report from the crew to [Flight Following] Ops. [The PIREP]

Can anybody provide the source of the last manual transmission? [a credible source, such as an corporate or government spokesperson addmission?]

Thanks

CC

p.s. You guys were right to question that.

Last edited by Captain-Crunch; 8th Jun 2009 at 07:29. Reason: [added clarification in brackets]
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Old 8th Jun 2009, 05:46
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_____________________


JACDEC SPECIAL ACCIDENT REPORT

Not sure if (or why ) this source is discredited- you asked me to remove prior ACARS message list,
but perhaps pertinent?
If so, further discrediting of rumored radio ( voice? ) transmission ,
" heavy turbulence ."


19:03 - Departure at Rio de Janeiro-GIG - ~22:05 AF 447 is passing Natal and is heading out over the Atlantic at 35.000 feet and with 450 knots - 22:33 last radio contact, AF 447 passing INTOL waypoint - 22:48 AF 447 left controlled airspace of CINDACTA 3, north of Fernando de Noronha Island - ~23:00 AF 447 entered a zone of thunderstorm clounds and turbulences - 23:10 ACARS message indicates that the autopilot was disengaged, fly-by-wire systen reverts to alternate law, data from both pitot static ports lost, TCAS antenna at fault - 23:11 both air data units flight computers (ADIRU) failed, standby attitude indicator (ISIS) lost - 23:12 diagreement of ADIRU data - 23:13 two flight management computers (PRIM1 + SEC1) failed - 23:14 AF 447 sent an automated message indicating an electrical problem and a possible loss of cabin pressure - 23:20 - estimated passing of waypoint TASIL - 02:33 alarm war raised and the search rescue mission began -


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Old 8th Jun 2009, 05:57
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My experience is that some pilots don't fully understand the true significance of a sudden outside air temperature rise (and yes they do occur - I have seen temperature rises of 20-30 degrees).

When we are flying at a constant Flight Level we are in fact flying at a constant 'indicated' altitude. The true height of this Flight Level above mean sea level (AMSL) will vary with the outside air temperature. In cold air it is lower, in warm air it is higher. So when we encounter a sudden increase in outside air temperature, to maintain a constant Flight Level the aircraft has to increase it's true altitude AMSL. ie it has climb against gravity, (but in the flight deck the altimeter and VSI will still show level flight because we are flying a constant Flight Level ie 'indicated' altitude.)

Now to climb against gravity we have to add energy and this ideally comes from the engines increasing thrust. Where the problem arises is if we are cruising near max altitude and the aircraft is cruise thrust limited. If the engines are at max thrust, they can't add any more energy. With the autopilot maintaining a constant Flight Level, but the true altitude increasing, the only available source of energy is speed. ie speed is converted into height and the aircraft's speed reduces. And as has been mentioned before, if you're in 'coffin corner' a stall is not too far away. The only solution is to descend and you may not have much time to make that descision.
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Old 8th Jun 2009, 06:32
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Further to my previous post, a possible scenario might be (and in no way am I suggesting that this did happen):

Aircraft flies through heavy weather and encounters turbulence and icing.
Pitot probes ice up resulting in numerous system failures.
Aircraft flies into a suddenly warmer airmass.
Autopilot maintains constant Flight Level, but with increase in OAT and increased weight due to ice build up, engines are at max thrust and can't maintain airspeed.
Crew are distracted dealing with the system failures and don't notice or have no reliable indication of decreasing airspeed.
Icing on wings results in a higher than normal stall speed.
Ice build up is asymetric so one wing stalls before the other.
Spin ......

Last edited by Bleve; 8th Jun 2009 at 07:30.
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Old 8th Jun 2009, 06:34
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"My experience is that some pilots don't fully understand the true significance of a sudden outside air temperature rise (and yes they do occur - I have seen temperature rises of 20-30 degrees)."

Bleve,

Not to doubt you, but where have you experienced such large changes at the higher flight levels such as FL350? I would also think you are talking in C as only us stubborn Americans think regularly in F (they force me to use C when flying). In my experience at the higher levels, maybe I have seen a change of 3 to 4 degrees C at a constant FL over a lapse of time. Of course, if you are in the middle of a big CB, you are no longer at any one flight level for any period of time. I think I would like to avoid areas prone to 30 degree changes.

To me, 40C isn't hot but 104F is cooking. Oh wait, they are the same.
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Old 8th Jun 2009, 06:38
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where have you experienced such large changes
In the tropics, in and near convective weather, just like the conditions AF447 were in.
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Old 8th Jun 2009, 06:49
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Quote:
where have you experienced such large changes
In the tropics, in and near convective weather, just like the conditions AF447 were in.
Are you talking degrees F then?
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Old 8th Jun 2009, 06:53
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Bleve....you theory is very plausible. Likewise I believe a lot of crews havent a notion of the significence of TAT/SAT temp changes and the impact on flight. this is no way reflects on this accident as we are just guessing what happened.

I also reckon all the acars msg's re prim's/ sec's/adr's where transmitted when the aircraft was out of control.
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Old 8th Jun 2009, 07:09
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If I remember correctly from aerodynamics lectures, there is no other reliable way to measure airspeed.

One could use Doppler radar, but that would involve tracer particles. Or one could use a propeller which might give somewhat reliable readings below 300 knots but would completely miss static air pressure.
There most certainly are ways of measuring gas flow velocity; there is a huge industry making sensors which do this. Ultrasonic, coriolis, you name it. The raw data will not be the same as a pitot tube (which doesn't measure TAS anyway) but could be corrected back to read an "IAS" like a pitot tube does.
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Old 8th Jun 2009, 07:31
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ACARS Messages

Christy Sweet,

Thanks for posting the link to the list of messages. Don't have a maintainence manual but...

FYI - Auto pilot will disconnect at ALTN LAW activation - involuntary disconnect indicated by "AUTO FLIGHT AP OFF" message. ALTN LAW probably activated by multiple ADR disagree / Flags on PFD (same thing).

Also the first (memory) items on the QRH Unreliable Airspeed Checklist if actioned are: Autopilot/Flight Directors and Auto Thrust off.

NAV TCAS FAULT is just a by-product of the ADR problem.

I doubt the ISIS (3-in-1 Standby Instrument) was fully lost: only the Airspeed part as the Attitude is a separate electric gyro powered by the DC Essential or Hot Battery Bus. ISIS Altitude is raw data from the standby static vents (does not go through Air Data Modules) - While pitot icing is likely I feel it is unlikely that the static vents iced up too. So ISIS attitude and ALT should have been reasonable. At the very least ISIS Attitude should have been good

PRIM 1 Fault and SEC 1 Fault - All PRIMs & SECs have ADIRU input but in the case of the SECs it is only Yaw rate - in anycase PRIM 2,3 and SEC 2 were still OK according to the ACARS messages which should have been ample to fly the aircraft. Bit of a mystery there. BTW - I understand QANTAS Flight 72 had slightly different messages i.e. PRIM 1 PITCH FAULT, then PRIM 2 PITCH fault. After that they tripped to ALTN LAW and had no more control problems as it was NORMAL law (improper activation of low speed protection) that was faulty.

If I am reading the messages correctly the Advisory at 0214z (last message) was ATA 31 meaning pressurisation. The pressurisation Advisories applicable are cabin rate > +/- 1800 fpm or Cabin Alt . >8800' - this could be possible without breakup or structural depressurisation as the CPC's (Cabin pressure controllers) may have been getting incorrect data from the ADIRUs.

Whatever happened they certainly had their hands full
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Old 8th Jun 2009, 07:52
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Credible Sources

ChristySweet,

I'm just having trouble remembering how we knew that there was an ACTUAL acars keyboard message sent, and the exact wording. I'll re-read the whole thread I guess.

Your link to the german web page is NOT a credible source. Do you understand this? You can't keep picking things out of the air. Your previous posting of erroneous information needed to be taken down. Do you understand this?

Questioning any information that we discuss, is NOT discrediting anything. O.K? It is what makes pprune so powerful. I am impressed with the caliber of some of the contributors: such as the acars guys, the techs and many others. Not every one, however, can contribute Christy, because it is outside of your area of expertise. Stick to what you know.

For new people, who just won't bother to read the whole thread (and I know it is long,) or who don't have time, a good summary of what we've been covering is here: (and you should read it!)

Wiki - Air France Flight 447

I will update that wiki page when we decide how credible the acars pirep transmission is. Note: wiki is a living document, and is constantly changing. Many items there are being debated right now to be tossed out. The process is impressive.

CC

Alternatively, here are the source images: ACARS Leg Report scroll to the bottom for the big ones.

.

Last edited by Captain-Crunch; 8th Jun 2009 at 08:22.
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Old 8th Jun 2009, 07:54
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Bleve…very good point, and another good reason to consider your optimum FL when requesting cruise level, especially when around CB activity or other potential turbulence situations.
I remember enroute Cun-Mxp, 2000’ above optimum in B767…..random track, with colleague on same routing, 20 mins behind. Enjoying 160kts average tailwind.

On encountering an unforecast 30nm band of mod/severe CAT at 30W, I had already made Pan calls on 121.5 and 128.95 to descend without clearance, ….when,.... my clearance came through on HF.

My colleague was duly warned and requested the same. Lucky to have been off busy OTS.
Downside of random track being no prior warning from traffic ahead…..
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Old 8th Jun 2009, 07:58
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Bleve has said, and I quote:

"Now to climb against gravity we have to add energy and this ideally comes from the engines increasing thrust. Where the problem arises is if we are cruising near max altitude and the aircraft is cruise thrust limited. If the engines are at max thrust, they can't add any more energy. With the autopilot maintaining a constant Flight Level, but the true altitude increasing, the only available source of energy is speed. ie speed is converted into height and the aircraft's speed reduces."

Of course, all airline pilots, even brand new First Officers on jet a/c, know that this statement has a major flaw based on lack of knowledge.

Hopefully Bleve will do some research, or at least speak to some of his pilot friends, and withdraw his statement!
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Old 8th Jun 2009, 08:01
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All this technical discussion is of little value. We will never know. The DFDR records the output of the sensors. Sensors that had failed. I suggest that even if they find the blackbox, it will only add to the mystery.

What we do know is that the aircraft flew into a huge TS and didnt come out in one piece.

How many pilots that fly across the Atlantic would divert 100nm from track to go around a TS like this? -bearing in mind that that same TS will probably make the HF unusable. I have gone 80nm off track to avoid. Scarey with no radio contact, although it was a random track, not a NAT track 60nm from the next one, although TCAS is a nice backup.

If you had carried min fuel and diverting 100nm around weather would mean that you couldnt make your planned destination would you still go around it? Probably less than said yes to the first Q. But we will all be more careful from now on. And carry more fuel if the sig wx chart looks scarey.
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Old 8th Jun 2009, 08:11
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I would also think you are talking in C as only us stubborn Americans think regularly in F
Yes I am talking °C.

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.
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Old 8th Jun 2009, 08:14
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BL..I am learning much from reading this thread. All real experience threads are valid and the inspired technical discussions should help us all be better aviators.
Nothing wasted here!
Sad & regrettable circumstances........we will all try to learn from their loss!

Pprune at its best!
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Old 8th Jun 2009, 08:21
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Of course, all airline pilots, even brand new First Officers on jet a/c, know that this statement has a major flaw based on lack of knowledge. Hopefully Bleve will do some research, or at least speak to some of his pilot friends, and withdraw his statement!
OK Obie, no need to be cryptic, so for my benefit and the others reading this thread, what is the major flaw?
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Old 8th Jun 2009, 08:25
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Like Bleve and others I've seen temp rises in the order of 20-30 degC passing through the ITCZ between Japan and Australia on many occasions. Usually the first thing I'd notice is that the aircon can't deal with it and you can smell/feel the cabin air become more humid and then notice the SAT rising rapidly. A good reason not to operate right up at or above optimum in that neighbourhood. Once out of the hi-temp area the SAT decreases just as quickly.

Diversions around thunderstorm activity of well over 100nm are not that uncommon in oceanic airspace, I've done plenty over the years.

Regards,
BH.
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Old 8th Jun 2009, 08:30
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amc890

I think, as you suggest, TAT probe icing is the reason for apparent sudden transient temperature rise. The probe would be shielded from ambient air for a few seconds until the ice melted.
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