AF447 Thread No. 3
Peplum and others:
You simply cannot use ground speed.
The wind could easily be 150kts or more in any direction ( I don't kow where you get the idea that 75 is a maximum Peplum, it just isn't). So, if you maintain 400lts GS as you suggest you might be doing 250 or 550 or anything in between. i.e. you have no idea. At near to service ceiling the safe speed range can be as little as 30 kts wide and yet you think it is fine to use a method that has a 300 kt (or more range of error). I can only assume you are not professional pilots to have made such a basic error.
You simply cannot use ground speed.
The wind could easily be 150kts or more in any direction ( I don't kow where you get the idea that 75 is a maximum Peplum, it just isn't). So, if you maintain 400lts GS as you suggest you might be doing 250 or 550 or anything in between. i.e. you have no idea. At near to service ceiling the safe speed range can be as little as 30 kts wide and yet you think it is fine to use a method that has a 300 kt (or more range of error). I can only assume you are not professional pilots to have made such a basic error.
WRT to ground speed the margin is roughly 100kts GS. (~M0,68 - ~M0,86)
The mistake you made is the same one sees over and over again. the 30kts range is IAS. For inertia of the airframe, it's GS that counts. IAS is aerodynamics, Gs is mechanics.
You can't have it both ways, sorry.
GS 400 kts would have been btw much better in any case than GS 110kts (that's what they had roughly). GS should have given them a clue how the thing was plowing through the air. Even if not exact enough for perfect flight, it might have saved the day.
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I do not pretend to be a pro. I'm not. That's not a pilot question. In life, whatever the job you have. When one parameter is vital for you and you don't have it anymore you have to evaluate it.
My thinking is when you do not have anymore reliable IAS, how do you evalute it ? Which clue do you use to evalute it. If not GS, which other do you propose ?
What did source of information they can use to evalute IAS : Ground speed and that's all.
Of course the range of possible speed is narrow at FL350. So, why to pitch-up ?
One wind can be fastet then 75kts, so descend... or praise for it to be less than 75kts but you have to set-up a strategy to replace the automatic pilot and pitot/mach meter did.
Why did they expect climbing to FL380 ? To my knowledge atlimeter was OK. So they should know what they did climbing so high.
Other pilots have reported to live comparable IAS disfunction on airbus and do escape.
Sorry but I do not understand why they do no exploit G.S.
My thinking is when you do not have anymore reliable IAS, how do you evalute it ? Which clue do you use to evalute it. If not GS, which other do you propose ?
What did source of information they can use to evalute IAS : Ground speed and that's all.
Of course the range of possible speed is narrow at FL350. So, why to pitch-up ?
One wind can be fastet then 75kts, so descend... or praise for it to be less than 75kts but you have to set-up a strategy to replace the automatic pilot and pitot/mach meter did.
Why did they expect climbing to FL380 ? To my knowledge atlimeter was OK. So they should know what they did climbing so high.
Other pilots have reported to live comparable IAS disfunction on airbus and do escape.
Sorry but I do not understand why they do no exploit G.S.
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Anyway think one moment. To fly a plane to must evalute the air speed. Because they were high altitude, and the 3 pitot was off, the only indicator effective at this moment was ground speed.
I wonder if this will be the deciding factor for Airbus to implement back-driven sidesticks?
Edit: added "power" to statement above; thought it was obvious.
Last edited by David Horn; 28th May 2011 at 13:52.
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Henra
At the limit of the envelope the margin can be as little as 30kts TAS from Vls to Mmo. MAch and GS have nothing whatsoever to do with it. The aircraft stalled. This is an aerodynamic event. How have you calculated your 'safe' mach numbers because they bear no relation to reality mach .68 could well be below minimum at high level and high weight.
I fail to see what the aircrafts inertia has to do with it. It may have a slight bearing on rate of stall recovery but the important info for stall recovery are aerodynamic. IAS, TAS AoA.
I say agian GS has nothing to do iwth it and only an idiot would use it to handle the aircraft when he has attitude and thrust available to him.
At the limit of the envelope the margin can be as little as 30kts TAS from Vls to Mmo. MAch and GS have nothing whatsoever to do with it. The aircraft stalled. This is an aerodynamic event. How have you calculated your 'safe' mach numbers because they bear no relation to reality mach .68 could well be below minimum at high level and high weight.
I fail to see what the aircrafts inertia has to do with it. It may have a slight bearing on rate of stall recovery but the important info for stall recovery are aerodynamic. IAS, TAS AoA.
I say agian GS has nothing to do iwth it and only an idiot would use it to handle the aircraft when he has attitude and thrust available to him.
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GPS Useless: Fly Attitude
The aerodynamics of the plane is a perfectly good airspeed indicator.
For a given weight and cg, the pitch angle (nose up/down), as shown on the Attitude Indicator, will indicate airspeed. Pitch down, and the plane speeds up; pitch up and the plane slows down. It's there staring at the pilot throughout every flight.
Oh, that happens to be the basic of the Unreliable Airspeed Indicator training.
Of course, some 35 years ago, the FAA began preaching that pitch controls altitude and power controls speed, and too many bought into it, but that's for another thread..
For a given weight and cg, the pitch angle (nose up/down), as shown on the Attitude Indicator, will indicate airspeed. Pitch down, and the plane speeds up; pitch up and the plane slows down. It's there staring at the pilot throughout every flight.
Oh, that happens to be the basic of the Unreliable Airspeed Indicator training.
Of course, some 35 years ago, the FAA began preaching that pitch controls altitude and power controls speed, and too many bought into it, but that's for another thread..
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For inertia of the airframe, it's GS that counts.
What did source of information they can use to evalute IAS : Ground speed and that's all.
at FL380 it was probably indeed down to 30kts but going there was not a good idea in the first place. The idea of peplum to go to a lower altitude where the margin is wider and to go to a reasonable GS is better than what happened here, even though not perfect. It is not a good strategy to fly the plane by GS but it could be used to check plausibility of one's own assumptions about what is going on. GS can't be trumped and if GS says 110kts, you get a clear pitcure about what's wrong.
@Zorin_75:
No contradiction:
For flying it's IAS that counts.
Inertia (i.e. Decelleration/accceleration) happens based on TAS. (Rho/2 * V_TAS ^2).
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Well done Zorin. Its pitch and power that would save them.
Pitch alone tells you nothing by the way, Graybeard, since a moderate pitch with a high angle of descent=high AoA as in this case.
I hope the non pilots can now accept that GS without air data is just meaningless for aerodynamics, absolutely meaningless.
Pitch alone tells you nothing by the way, Graybeard, since a moderate pitch with a high angle of descent=high AoA as in this case.
I hope the non pilots can now accept that GS without air data is just meaningless for aerodynamics, absolutely meaningless.
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busTRE:
A moderate pitch with high angle of descent means not enough power to hold altitude. Use power as needed to control altitude.
This assumes a non-stalled wing, of course, which such events begin with.
Pitch alone tells you nothing by the way, Graybeard, since a moderate pitch with a high angle of descent=high AoA as in this case.
This assumes a non-stalled wing, of course, which such events begin with.
Last edited by Jetdriver; 28th May 2011 at 20:47.
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Zorin_75: From an engineering perspective; invalid (faulty) air data from non- design-redundant sensors appear to be the weakest link imho, triggering a cascade of errors thereafter.
Band-aid, extrapolated solutions just don't fly with me. If someone is going to give a pilot or a computer Air Data, then sure as aunt betty make it dependable, fail-safe Air Data. It's really just that simple. Alternatively, a crew of two pilots, and MacGyver might suffice.
Band-aid, extrapolated solutions just don't fly with me. If someone is going to give a pilot or a computer Air Data, then sure as aunt betty make it dependable, fail-safe Air Data. It's really just that simple. Alternatively, a crew of two pilots, and MacGyver might suffice.
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I suggested this on the initial AF447 thread, and didn't get much response, but I don't see why it would not work:
As long as you have a valid IAS, you systematically compare it to GS using GPS and compute wind speed and direction from that. You store this value. If the IAS fails, you use this stored value to correct the GPS-derived GS to get an estimated AS.
Except in the case of severe wind shear, why would this not work?
You could present the estimated AS as a range, with some degree of uncertainty, incorporating previous variations in wind speed, if any, or just an uncertainty factor (perhaps growing over time) to account for possible changes in wind speed.
As long as you have a valid IAS, you systematically compare it to GS using GPS and compute wind speed and direction from that. You store this value. If the IAS fails, you use this stored value to correct the GPS-derived GS to get an estimated AS.
Except in the case of severe wind shear, why would this not work?
You could present the estimated AS as a range, with some degree of uncertainty, incorporating previous variations in wind speed, if any, or just an uncertainty factor (perhaps growing over time) to account for possible changes in wind speed.
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Whilst i can see the argument for pitch & power as overriding targets, as a non pilot, surely there is more to it than that? For example, during the previous hr or so of the flight (at FL350) there must have been an "average" values for pitch, power and GS, that have been clearly demonstrated to "fly" the airframe in a sensible trim.
So surely, in the case of upset, these values would have been a nice place to start trying to aim for, no matter what your AS instruments are saying to you?? Clearly, under no conditions would a groundspeed of 110kts be acceptable (unless you are flying into the MOTHER of all headwinds, which the rest of the flight would have demonstrated to be false??)
The big question, is what parameters and causal factors lead the 3 pilots to incorrectly determine the necessary actions to recover?
Like all things in this world, everything is a compromise, i'm sure we could build an "uncrashable" aircraft, but no one would be able to afford to buy or fly it!
The most important thing, is that if clear and accurate action/response recomendations are forthcoming, that these are precisely implemented.
Unfortunately, there are no absolute answers in risk management, it's a "make the best job you can with the resources availible" problem.
So surely, in the case of upset, these values would have been a nice place to start trying to aim for, no matter what your AS instruments are saying to you?? Clearly, under no conditions would a groundspeed of 110kts be acceptable (unless you are flying into the MOTHER of all headwinds, which the rest of the flight would have demonstrated to be false??)
The big question, is what parameters and causal factors lead the 3 pilots to incorrectly determine the necessary actions to recover?
Like all things in this world, everything is a compromise, i'm sure we could build an "uncrashable" aircraft, but no one would be able to afford to buy or fly it!
The most important thing, is that if clear and accurate action/response recomendations are forthcoming, that these are precisely implemented.
Unfortunately, there are no absolute answers in risk management, it's a "make the best job you can with the resources availible" problem.
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spagiola: I think that would work (in a brief sensor fault condition), but estimated values degrade with elapsed time and environmental transcients as you say - wouldn't it just be better to be able to depend on reliable air data?
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THS Problem on a Falcon 7X
Another leak (not verified): http://jacno.com/prov/images/extrait-fdr-cvr.png
See posts #83 and #84 on this page (in french): Forums Aviation Civile • Afficher le sujet - Airbus Rio-Paris : les dessous cachés des enquêtes
A THS related incident involving a Falcon 7X and the subsequent release of an EAD http://jacno.com/prov/EASA_EAD_2011-0102-E_1.pdf and the grounding of the world's Falcon 7X fleet.
Are both AF447 and this Falcon 7X sharing some software or hardware components ?
Comments ?
Regards.
See posts #83 and #84 on this page (in french): Forums Aviation Civile • Afficher le sujet - Airbus Rio-Paris : les dessous cachés des enquêtes
A THS related incident involving a Falcon 7X and the subsequent release of an EAD http://jacno.com/prov/EASA_EAD_2011-0102-E_1.pdf and the grounding of the world's Falcon 7X fleet.
Are both AF447 and this Falcon 7X sharing some software or hardware components ?
Comments ?
Regards.
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From an engineering perspective; invalid (faulty) air data from non- design-redundant sensors appear to be the weakest link imho, triggering a cascade of errors thereafter
Still, such a failure shouldn't (and doesn't need to) lead to losing control of an aircraft. Any accident is a chain of events with often many contributing factors. So far, large pieces of the puzzle are still missing.
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I am curious as to what caused the initial upset ( with a climb rate in excess of 7000 fpm) according to flights website. The statemet that the Captain briefed the crew about turbulence ahead is a little ambiguous. Did he mean immediately ahead ? or just a reminder that it was forecast on the flight ? That question is relevent ? Altough they did make an initial turn of 12 degrees just prior to the upset. I guess they were avoiding weather .
Also , could there be a link to this and the QF 330 incident where they unexpectantly had an upset ? Cant recall all the details of that incident , apart from unexpected , climb or desent .
Also , could there be a link to this and the QF 330 incident where they unexpectantly had an upset ? Cant recall all the details of that incident , apart from unexpected , climb or desent .
davionics, #353
Absolutely. There's no engineering reason why it can't be fixed either.
They have had years to deal with it as well. I know pilots are a hairy
chested breed who don't like to make a fuss and think that they can
handle any situation, but my argument is that they should never be
expected to handle some of them. I think the regulators will need to
have much sharper teeth in future, both to overcome industry inertia
and airline beancounter interests.
Doesn't the A380 have a laser based or alternative air speed sensor
as a option ?...
Band-aid, extrapolated solutions just don't fly with me. If someone is
going to give a pilot or a computer Air Data, then sure as aunt betty
make it dependable, fail-safe Air Data. It's really just that simple.
going to give a pilot or a computer Air Data, then sure as aunt betty
make it dependable, fail-safe Air Data. It's really just that simple.
They have had years to deal with it as well. I know pilots are a hairy
chested breed who don't like to make a fuss and think that they can
handle any situation, but my argument is that they should never be
expected to handle some of them. I think the regulators will need to
have much sharper teeth in future, both to overcome industry inertia
and airline beancounter interests.
Doesn't the A380 have a laser based or alternative air speed sensor
as a option ?...