AF 447 Thread No. 12
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Cause and Effect
Stall warnings are not connected directly to stick movements, they are caused by airplane condition (angle of attack).
Initially the speed was normal. The yank back on the stick then pointed the aircraft 15 degrees nose high. That ATTITUDE at that ALTITUDE caused massive loss of speed, that loss of speed reduced lift, that loss of lift caused the aircraft to adopt a downwards flight path, the backstick of Bonin caused the ATTITUDE to remain very high, the attitude and flightpath together make for a high angle of attack, that causes stall warning. And of course the low "maximum angle of attack" at high Mach number makes for the possibility that the stall warning already went of during the pullup, while real airspeed was not extremely low yet.
If just around that time, an abrupt stick forward movement is started, but already stopped when reaching approximately neutral stick, then the aircraft does not really have time to react by decreasing pitch attitude.
Crucial mistake in your reasoning is, that the sounding of stall warning at the moment of forward stick movement, would convince Bonin of the need to pull back again. For every pilot, it should be bread and butter, that stall warning requires relaxing of back pressure, requires forward stick movement, not aft stick movement.
The only instance of stall (warning) requiring you to pull, would be in a negative stall (that is, with so much negative g applied, that the negative angle of attack is too great - however, that condition can only be concocted in an aerobtic aircraft. In a civvie airliner it could only occur when the horizontal tailplane has broken off and the wreck is then pitched forward by the negative pitch moment of the wing alone - and the wing would soon fail structurally - read accident report of Itavia DC-9 near Ustica in circa 1980 ).
Quote
Once in very high AoA, any Nose Down produces remarkable acceleration and negative g. Sufficient to cause reversal by pilot of ND command. The record shows this? Add to this the return of STALLSTALL, and recovery is foreclosed, demonstrably....Unquote
Application of forward stick would not magically produce negative g and massive acceleration. First, the whole aircraft would have to react (that takes time), the g load would decrease a little bit, slowly the angle of attack would decrease, thereby decreasing, slowly, the enormous amount of drag from the extreme angle of attack, and then initially slowly, the speed would increase. Then of course, matters would pick up pace and then again, carefully, aft stick would be applied to keep acceleration reasonable, acceleration (that is g!!!, not the increase of airspeed) reasonable, so as not to stall again, etcetera etcetera.
Perhaps you are under they impression that, while having the airplane act as a piano, falling through the air, that the crew was subjected to zero (or perhaps a little) negative g. Not so, it was falling steady state, more or less, and everything inside would be pulled into their seats by gravity with the normal load of approximately 1 g.
Initially the speed was normal. The yank back on the stick then pointed the aircraft 15 degrees nose high. That ATTITUDE at that ALTITUDE caused massive loss of speed, that loss of speed reduced lift, that loss of lift caused the aircraft to adopt a downwards flight path, the backstick of Bonin caused the ATTITUDE to remain very high, the attitude and flightpath together make for a high angle of attack, that causes stall warning. And of course the low "maximum angle of attack" at high Mach number makes for the possibility that the stall warning already went of during the pullup, while real airspeed was not extremely low yet.
If just around that time, an abrupt stick forward movement is started, but already stopped when reaching approximately neutral stick, then the aircraft does not really have time to react by decreasing pitch attitude.
Crucial mistake in your reasoning is, that the sounding of stall warning at the moment of forward stick movement, would convince Bonin of the need to pull back again. For every pilot, it should be bread and butter, that stall warning requires relaxing of back pressure, requires forward stick movement, not aft stick movement.
The only instance of stall (warning) requiring you to pull, would be in a negative stall (that is, with so much negative g applied, that the negative angle of attack is too great - however, that condition can only be concocted in an aerobtic aircraft. In a civvie airliner it could only occur when the horizontal tailplane has broken off and the wreck is then pitched forward by the negative pitch moment of the wing alone - and the wing would soon fail structurally - read accident report of Itavia DC-9 near Ustica in circa 1980 ).
Quote
Once in very high AoA, any Nose Down produces remarkable acceleration and negative g. Sufficient to cause reversal by pilot of ND command. The record shows this? Add to this the return of STALLSTALL, and recovery is foreclosed, demonstrably....Unquote
Application of forward stick would not magically produce negative g and massive acceleration. First, the whole aircraft would have to react (that takes time), the g load would decrease a little bit, slowly the angle of attack would decrease, thereby decreasing, slowly, the enormous amount of drag from the extreme angle of attack, and then initially slowly, the speed would increase. Then of course, matters would pick up pace and then again, carefully, aft stick would be applied to keep acceleration reasonable, acceleration (that is g!!!, not the increase of airspeed) reasonable, so as not to stall again, etcetera etcetera.
Perhaps you are under they impression that, while having the airplane act as a piano, falling through the air, that the crew was subjected to zero (or perhaps a little) negative g. Not so, it was falling steady state, more or less, and everything inside would be pulled into their seats by gravity with the normal load of approximately 1 g.
Last edited by EMIT; 31st Jul 2017 at 18:35. Reason: typo
"...For every pilot, it should be bread and butter, that stall warning requires relaxing of back pressure, requires forward stick movement, not aft stick movement..."
The first Stall Warn interrupted what was a brisk movement forward of the Stick. According to the graph, the Warning stopped, Bonin continued forward stick movement, and then gently added aft pressure to stick. Don't forget, he may have suspected coffin corner, and was trying to be judicious with Pitch. He also was trying to arrest the descent his ND started, with aft stick.
Pull back, Stall. Push forward, Overspeed.
"...Perhaps you are under they impression that, while having the airplane act as a piano, falling through the air, that the crew was subjected to zero (or perhaps a little) negative g. Not so, it was falling steady state, more or less, and everything inside would be pulled into their seats by gravity with the normal load of approximately 1 g..."
Now you are in Deep Stall. With your experience of Deep Stall, and a two hundred ton aircraft squatting on a cushion of thin air, you say forward stick produces gentle response?
I would say no. A brick, or any portion of it, losing its cushion, will accelerate quickly, and perhaps even start a tumble. If 447, balanced thusly, was stable or thereabouts, do you think pilot would risk stability to gain unwanted airspeed, exacerbating the already novel and robust instability in the Roll?
But this is Deep Stall. I refer to first Stall Warn, as shown in the report.
I have flown this maneuver, albeit in a small plane. Unless rudder and aileron are strictly controlled, the aircraft acts like a man trying to stand on a bowling ball. It leaks to the side, falls forward, or even seems to slip backward. It is exhilarating, and without prior experience, I suggest would be intimidating, to say the least.
The first Stall Warn interrupted what was a brisk movement forward of the Stick. According to the graph, the Warning stopped, Bonin continued forward stick movement, and then gently added aft pressure to stick. Don't forget, he may have suspected coffin corner, and was trying to be judicious with Pitch. He also was trying to arrest the descent his ND started, with aft stick.
Pull back, Stall. Push forward, Overspeed.
"...Perhaps you are under they impression that, while having the airplane act as a piano, falling through the air, that the crew was subjected to zero (or perhaps a little) negative g. Not so, it was falling steady state, more or less, and everything inside would be pulled into their seats by gravity with the normal load of approximately 1 g..."
Now you are in Deep Stall. With your experience of Deep Stall, and a two hundred ton aircraft squatting on a cushion of thin air, you say forward stick produces gentle response?
I would say no. A brick, or any portion of it, losing its cushion, will accelerate quickly, and perhaps even start a tumble. If 447, balanced thusly, was stable or thereabouts, do you think pilot would risk stability to gain unwanted airspeed, exacerbating the already novel and robust instability in the Roll?
But this is Deep Stall. I refer to first Stall Warn, as shown in the report.
I have flown this maneuver, albeit in a small plane. Unless rudder and aileron are strictly controlled, the aircraft acts like a man trying to stand on a bowling ball. It leaks to the side, falls forward, or even seems to slip backward. It is exhilarating, and without prior experience, I suggest would be intimidating, to say the least.
Last edited by Concours77; 31st Jul 2017 at 19:17.
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But this is Deep Stall. I refer to first Stall Warn, as shown in the report.
Turbine D,
Point taken, but there is no other way to describe the Stall. It didn't help having full Nose Up Trim, and under slung engines at full chat (which induces nose up). Once the wing unloaded, and THS remained all NU, the elevators became trim tabs. Also, this aircraft is longitudinally stable, it resists emphatic changes in Pitch something the "trim tabs" though recorded, had little effect...upon.
Once the aircraft "settled in", it may actually have seemed docile. But the recovery shouldn't have been necessary anyway. As Wiedehopf points out, in Alternate Law, the 330 becomes a different "beast".
Point taken, but there is no other way to describe the Stall. It didn't help having full Nose Up Trim, and under slung engines at full chat (which induces nose up). Once the wing unloaded, and THS remained all NU, the elevators became trim tabs. Also, this aircraft is longitudinally stable, it resists emphatic changes in Pitch something the "trim tabs" though recorded, had little effect...upon.
Once the aircraft "settled in", it may actually have seemed docile. But the recovery shouldn't have been necessary anyway. As Wiedehopf points out, in Alternate Law, the 330 becomes a different "beast".
Last edited by Concours77; 31st Jul 2017 at 21:45.
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Vessbot,
Perhaps this will help you on stall understanding:
http://www.sftentx.com/files/75234188.pdf
Perhaps this will help you on stall understanding:
http://www.sftentx.com/files/75234188.pdf
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Nothing indicates it was impossible to get out of that stall situation with proper flight control inputs.
The main culprit and obstacle was that unbelievable fully nose up auto trimmed THS ...
Deep Stall. Nomenclature. Critical to a technical approach, without doubt.
1. How did it get there?
2. What made it (functionally) not recoverable?
3. What issues in the AC design made it (inadvertently) fatal?
Three poorly designed, inadequate pitot systems, due to be replaced by a line that did not take seriously the vulnerability of the aircraft in conditions that were frankly typical of the airspace. Threat of a pilot strike finally got them to take action....
Full thrust, bleeding energy, loss of lift at the outer wing, Chronic NU command. Direct Law in Roll, the betrayal of the STALLWARN system, turbulence, cockpit disarray (visitor). Delayed recognition of the loss of speeds display and Normal Law by pilot crew. (Fifteen seconds). One can make the argument that the loss of speeds and Normal Law, caused by Thales Pitots, was the direct and sole cause of the ultimate impact with the ocean.... "Shoulda, Woulda, Coulda...."
Then the piece de resistance, a full up HS.
Stall entry unnoticed, and a mental lock on issues other than those that would cause a recovery.
The word "cascade" comes to mind. This is not a simplistic and isolated wreck.
1. How did it get there?
2. What made it (functionally) not recoverable?
3. What issues in the AC design made it (inadvertently) fatal?
Three poorly designed, inadequate pitot systems, due to be replaced by a line that did not take seriously the vulnerability of the aircraft in conditions that were frankly typical of the airspace. Threat of a pilot strike finally got them to take action....
Full thrust, bleeding energy, loss of lift at the outer wing, Chronic NU command. Direct Law in Roll, the betrayal of the STALLWARN system, turbulence, cockpit disarray (visitor). Delayed recognition of the loss of speeds display and Normal Law by pilot crew. (Fifteen seconds). One can make the argument that the loss of speeds and Normal Law, caused by Thales Pitots, was the direct and sole cause of the ultimate impact with the ocean.... "Shoulda, Woulda, Coulda...."
Then the piece de resistance, a full up HS.
Stall entry unnoticed, and a mental lock on issues other than those that would cause a recovery.
The word "cascade" comes to mind. This is not a simplistic and isolated wreck.
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It looks very much like flying 'on the wrong side of the drag curve' this is a stable state and if your aircraft has sufficient power then the lift is supplemented by the power from the engines as they have a significant upward vector due to the nose high angle and the aircraft will happily fly straight and level at below its normal stall speed 'sitting' on the power. Can be fun if you can see what you are doing.
If the aircraft is at height and power to weight ratio is not good or power is reduced the aircraft will drop - quite fast - as AF447 did. The nose high attitude must be maintained and for that the tail plane had motored into full nose up 'trim' - and every throttle increase with underslung engines also assisted the nose up attitude. This is not a classic stall.
The aircraft is now in a stable nose high state dropping faster than its forward speed. Unwittingly, PNF by insisting that PF kept the wings level assisted in the maintenance of the stable state. Had PF lost the roll control the aircraft would have rolled out of its stable state - perhaps before the tail had motored to full NU. That would have provided a more 'conventional' LOC that they may have recovered from. As it was they sat on the wrong side of the drag curve all the way to the surface.
If the aircraft is at height and power to weight ratio is not good or power is reduced the aircraft will drop - quite fast - as AF447 did. The nose high attitude must be maintained and for that the tail plane had motored into full nose up 'trim' - and every throttle increase with underslung engines also assisted the nose up attitude. This is not a classic stall.
The aircraft is now in a stable nose high state dropping faster than its forward speed. Unwittingly, PNF by insisting that PF kept the wings level assisted in the maintenance of the stable state. Had PF lost the roll control the aircraft would have rolled out of its stable state - perhaps before the tail had motored to full NU. That would have provided a more 'conventional' LOC that they may have recovered from. As it was they sat on the wrong side of the drag curve all the way to the surface.
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787 is, I believe, slightly different in that if speed is unavailable it calculates a synthetic airspeed from AOA and other data both for display and use in the control laws. This might have been developed with an eye on the vulnerability of C*U to loss of U.
C*U hasn't been without its problems though:
https://www.flightglobal.com/news/ar...d-data-423735/
https://www.atsb.gov.au/media/577302...-149-final.pdf
Pitot icing, plane's computers can't cope, yet again (even with the synthetic airspeed).
to quote the second link:
In response to a previous, similar event on another B787-8, the FAA published an airworthiness directive warning flight crew not to make large abrupt magnitude flight control inputs in response to
unrealistic drops in airspeed.
Boeing also revised the flight control software to limit the rate of elevator feel reduction with drops in airspeed. This will specifically allow the column to stay at a higher feel force to mitigate large and abrupt unintentional pitch inputs.
unrealistic drops in airspeed.
Boeing also revised the flight control software to limit the rate of elevator feel reduction with drops in airspeed. This will specifically allow the column to stay at a higher feel force to mitigate large and abrupt unintentional pitch inputs.
Another salient quote from that report:
In this case, the crew showed a high level of professionalism in response to a weather related event. The crew demonstrated high levels of communication and coordination, promptly applied checklists and procedures.
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You guys seem really wedded to the definition of "deep stall" being limited to the particular blanked stabilizer phenomenon in T-tails. Or otherwise diminished pitch authority. Fine, I'll live with it. Nevertheless, this airplane was very deeply stalled.
And Turbine D, there's no need to act like an
about it.
This is an interesting point. Normally, if you asked anybody, they would say that a transport airplane should have docile stall characteristics, so as to limit workload (and potential for further upset) in a recovery. Now, it seems to me at least plausible that this docile behavior contributed to a lack of stall identification by the crew. Talk about a double edged sword!
Well, everything I wrote about the airline flying experience wrt. the maintenance of basic flying skills outside the normal airline profiles, applies equally to non-Airbus types. So, we'd be in a real pickle if we apply that solution industry-wide! (I know you're being tongue in cheek, of course.)
And Turbine D, there's no need to act like an
about it.I have flown this maneuver, albeit in a small plane. Unless rudder and aileron are strictly controlled, the aircraft acts like a man trying to stand on a bowling ball. It leaks to the side, falls forward, or even seems to slip backward. It is exhilarating,
[...]
Also, this aircraft is longitudinally stable, it resists emphatic changes in Pitch something the "trim tabs" though recorded, had little effect...upon.
Once the aircraft "settled in", it may actually have seemed docile.
[...]
Also, this aircraft is longitudinally stable, it resists emphatic changes in Pitch something the "trim tabs" though recorded, had little effect...upon.
Once the aircraft "settled in", it may actually have seemed docile.
Well, everything I wrote about the airline flying experience wrt. the maintenance of basic flying skills outside the normal airline profiles, applies equally to non-Airbus types. So, we'd be in a real pickle if we apply that solution industry-wide! (I know you're being tongue in cheek, of course.)
"...Because the Aircraft remains safe even when the pilot pulls on the stick to the stop thanks to the high angle of attack protection, Airbus position is that no additional alerts about low speed/energy situations is needed at high altitude because large altitude loss due to stall cannot occur on Airbus Fly-By-Wire aircraft.
Moreover, no additional stall warning or stick shaker is needed with this kind of protection. Stall warning is only re-introduced on airbus aircraft when the angle of attack protection is lost (loss of normal laws)...."
ASHWG LAA Report_15 March 2010 Final Version_Appendix 1
Fair enough. What of performance after reversion to alternate Law? Stall Warn should compel action. If ignored, or dismissed, there is no other resolution for Airbus pilot. Shaker is unmistakable, irrevocable and emphatic compulsion to act.
So. Why the waiver from FAA? I would understand the waiver if clearly limited to Normal Law, the alpha Prot is its own Stall Warn, and cannot be overridden.
Alternate Law is a "different" airplane, should it not be required to meet minimum standard of other aircraft?
Roll in Direct? Perhaps a clever way to introduce instability in Roll, and a clever way to provide Nose Down, independent of crew? Unstable roll axis is perhaps the only Stall cue they would receive? Did Bonin outfox the airplane, and himself, by learning to manage the new roll? Or was the aircraft supposed to roll until the nose dropped, by design? Stick and rudder by program?
What this crew needed was instability in the descent, not docility. They were focused on stability as always, like all good Airbus drivers?
Moreover, no additional stall warning or stick shaker is needed with this kind of protection. Stall warning is only re-introduced on airbus aircraft when the angle of attack protection is lost (loss of normal laws)...."
ASHWG LAA Report_15 March 2010 Final Version_Appendix 1
Fair enough. What of performance after reversion to alternate Law? Stall Warn should compel action. If ignored, or dismissed, there is no other resolution for Airbus pilot. Shaker is unmistakable, irrevocable and emphatic compulsion to act.
So. Why the waiver from FAA? I would understand the waiver if clearly limited to Normal Law, the alpha Prot is its own Stall Warn, and cannot be overridden.
Alternate Law is a "different" airplane, should it not be required to meet minimum standard of other aircraft?
Roll in Direct? Perhaps a clever way to introduce instability in Roll, and a clever way to provide Nose Down, independent of crew? Unstable roll axis is perhaps the only Stall cue they would receive? Did Bonin outfox the airplane, and himself, by learning to manage the new roll? Or was the aircraft supposed to roll until the nose dropped, by design? Stick and rudder by program?
What this crew needed was instability in the descent, not docility. They were focused on stability as always, like all good Airbus drivers?
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I ve tested several times a very good malfunction in the box: Volcanic ash. It is a nasty one because both engines are not usable and all your pitots are blocked. 777 is a democracy, if 2 out of the 3 pitots are blocked the ADM that are in majority reporting the same speeds are "winners into the election" for best data. In other works you will be prompted with erroneous speed for a while, till you hit 80 kts IAS and then the last ADM will be "elected". Back to that malfunction, your best friend would be the weather briefing with winds (predicted) and GPS ground speed since you cannot apply pitch, power, performance trick.
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WX
Preflight WX: charts were outdated and crew simply could not read them properly as on page 5.
AF are in the stone age regarding WX as they did not do provide any satellite indications!
AF 447 LE PLAN DE VOL AF447-Plan de vol. - ppt télécharger
AF are in the stone age regarding WX as they did not do provide any satellite indications!
AF 447 LE PLAN DE VOL AF447-Plan de vol. - ppt télécharger
re-hash of old stuff
Great point(s) Vessbot
Years ago, like thread 5 or 7 or 9, I tried to make the point that the 'bus must have nice stability and low buffet when at a high AoA. So defeating any of the remaining "protections" ( God, how I hate what that term implies) by holding a nose up command as the speed rapidly decreases makes for a "smooth" stall entry and except for the degraded roll control laws the sucker just sits there happy and descending at 10,000 feet per minute.
I can understand that the crew could not readily accept that they were deeply stalled. Ask a "delta" pilot like me in my early years, of any type - F-102, Mirage, F-106, Vulcan, Concorde, and so on. Very smooth transiton from lift to no lift and plenty drag and vertical velocity you do not want. My recollections of the Deuce was it had a "buzz", but no wing rock or buffet that I had in the other 3 or 4 planes I flew. But the bottom fell out on short final if you pulled back a lot with low power. So I cut some slack for the crew recognizing their stall entry, but only a little. Lack of understanding the confusing degraded control laws and failure to just hold whatever control inputs were there when the aero sensors went tits up and the AP kicked out did not help at all. Lastly, as CONF pointed out, the THS trimming while in a backup mode was the icing on the cake.
I am not gonna demand all the newer folks here go back thru the thousands of posts where we dissected this terrible crash, but maybe using the "search" features one could see "deep stall", "longitudinal stability", control law regression, and many more aspects of the crash.
You guys seem really wedded to the definition of "deep stall" being limited to the particular blanked stabilizer phenomenon in T-tails. Or otherwise diminished pitch authority. Fine, I'll live with it. Nevertheless, this airplane was very deeply stalled.
And Turbine D, there's no need to act like an
about it.
And Turbine D, there's no need to act like an
about it.
I can understand that the crew could not readily accept that they were deeply stalled. Ask a "delta" pilot like me in my early years, of any type - F-102, Mirage, F-106, Vulcan, Concorde, and so on. Very smooth transiton from lift to no lift and plenty drag and vertical velocity you do not want. My recollections of the Deuce was it had a "buzz", but no wing rock or buffet that I had in the other 3 or 4 planes I flew. But the bottom fell out on short final if you pulled back a lot with low power. So I cut some slack for the crew recognizing their stall entry, but only a little. Lack of understanding the confusing degraded control laws and failure to just hold whatever control inputs were there when the aero sensors went tits up and the AP kicked out did not help at all. Lastly, as CONF pointed out, the THS trimming while in a backup mode was the icing on the cake.
I am not gonna demand all the newer folks here go back thru the thousands of posts where we dissected this terrible crash, but maybe using the "search" features one could see "deep stall", "longitudinal stability", control law regression, and many more aspects of the crash.
Moreover, no additional stall warning or stick shaker is needed with this kind of protection. Stall warning is only re-introduced on airbus aircraft when the angle of attack protection is lost (loss of normal laws)...."
ASHWG LAA Report_15 March 2010 Final Version_Appendix 1
Fair enough. What of performance after reversion to alternate Law? Stall Warn should compel action. If ignored, or dismissed, there is no other resolution for Airbus pilot. Shaker is unmistakable, irrevocable and emphatic compulsion to act.
So. Why the waiver from FAA? I would understand the waiver if clearly limited to Normal Law, the alpha Prot is its own Stall Warn, and cannot be overridden.
Alternate Law is a "different" airplane, should it not be required to meet minimum standard of other aircraft?
Does there not seem to be a large omission here, gums?
Each time the crew experienced the STALLWARN, it should have been preceded by a stick shaker.
If, in AltLaw, the "cannot Stall" morphs into an aircraft that can not only Stall, but does so so subtly that a separate device must be required ?
It occurs to me that if the shaker was shaking without stop all the way down they may have tumbled to the state of the aircraft?
ASHWG LAA Report_15 March 2010 Final Version_Appendix 1
Fair enough. What of performance after reversion to alternate Law? Stall Warn should compel action. If ignored, or dismissed, there is no other resolution for Airbus pilot. Shaker is unmistakable, irrevocable and emphatic compulsion to act.
So. Why the waiver from FAA? I would understand the waiver if clearly limited to Normal Law, the alpha Prot is its own Stall Warn, and cannot be overridden.
Alternate Law is a "different" airplane, should it not be required to meet minimum standard of other aircraft?
Does there not seem to be a large omission here, gums?
Each time the crew experienced the STALLWARN, it should have been preceded by a stick shaker.
If, in AltLaw, the "cannot Stall" morphs into an aircraft that can not only Stall, but does so so subtly that a separate device must be required ?
It occurs to me that if the shaker was shaking without stop all the way down they may have tumbled to the state of the aircraft?
