AF 447 Thread no. 4
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Hi jcjeant,
Because they didn't keep the ND input in for long enough.
They had not diagnosed their problem correctly, and attempted to arrest their ROD with NU side stick inputs.
when PF made nose down inputs the THS don't follow. Why?
They had not diagnosed their problem correctly, and attempted to arrest their ROD with NU side stick inputs.
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Originally Posted by A33Zab
But I get the impression I failed..........
Your line "The FCPC gets ADR & IR information to The FCPC gets ADR & IR information to compensate for speed.." makes me again 'board the train' and ask exactly what ADR info the FCPC gets.to 'compensate for speed.'. You see what bothers me is that I don't think anyone here, and I include the software and system designers, can possibly (or do) understand the intricate processes that system failures can inject. There are simply too may variables and too little 'beta testing' time. It would be a breeze for some clever software writer to give the THS access to a IAS/angle/alt/c of g table and have it automatically adjust its datum concept. He/she might then go away thinking, 'Haven't I done well? One less stream of THS follow-up signals associated with speed change. Look - it KNOWS exactly where it should be for 1g at 230kts, 190kts, etc'
Now, once you 'inject' a speed input into the THS setting you begin to open 'maybe' doors onto the behaviour of the mid-Atlantic 340 and possibly 447 and others. I note the evident resistance in the AB community to accept that anything could be wrong but I do not admire it.
To pick up on MR Optimistic's post #968 - indeed, I did suggest that following a spate of BOEING (everyone see that?) and then the AB PGF THS triggered accident/incidents there should be some physical intervention (a 'wake-up call', if you like) required by a crew to permit THS settings beyond a certain value. This could well have saved 447.
I appears that autotrim, whether it be A/P driven in the 737 or in manual flight, has a lot of fatalities to answer for.
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Hi BOAC,
Sorry - but you are beginning to confuse me now. Have you started the conversion course already?
No one would design a system like you seem to suggest with
How would it know where the C of G was with a full plane load of passengers doing the Conga from the front to the back? (e.g. Last TriStar flight from Dublin)
It might be controlled by FBW - but it's still physically a conventional aircraft obeying the same aerodynamic laws as your Boeing.
Sorry - but you are beginning to confuse me now. Have you started the conversion course already?
Now, once you 'inject' a speed input into the THS setting you begin to open 'maybe' doors onto the behaviour of the mid-Atlantic 340 and possibly 447 and others. I note the evident resistance in the AB community to accept that anything could be wrong but I do not admire it.
It would be a breeze for some clever software writer to give the THS access to a IAS/angle/alt/c of g table and have it automatically adjust its datum concept. He/she might then go away thinking, 'Haven't I done well? One less stream of THS follow-up signals associated with speed change. Look - it KNOWS exactly where it should be for 1g at 230kts, 190kts, etc'
It might be controlled by FBW - but it's still physically a conventional aircraft obeying the same aerodynamic laws as your Boeing.
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Originally Posted by rrat
How would it know where the C of G was with a full plane load of passengers doing the Conga from the front to the back
Anyway, I'd like to move this thread back to a piloting perspective if you would all be patient?
This is what I understand (*? inserted where I am not sure, ? is a normal query). I refer to the point at which the Captain is roused from his bunk and re-enters the flight deck, and my puzzle lies with the fact that for the next *?3 minutes *? the attitude and flight profile of the a/c remains effectively *?unchanged*?
Let's start with the assumption that he arrives on the f/d with a possible sensory awareness of a climb and speed reduction. He *?sees a low or non-existent airspeed indication across the panels*? He *?sees 3 pitch attitudes of 15 degrees*?. He *? sees altimeters at 350 and a VS of 10,000fpm down*? He sees *?TOGA*?. He is otherwise 'untainted' by the excursion of the a/c in the preceding minutes. Why *?does he not recognise it is stalled*?. Does he? Is he then thrown completely off track by the resumption of the stall warning as 'recovery' begins to take effect (throttles to idle etc)? If so, does the *?rapidly unwinding altimeter and VS reading*? not prompt some further attempts?
There are many puzzles in this accident, this is another. NB I hope you all notice that 'software' and 'AB' are excluded from the above.
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@BOAC:
Quote:
Originally Posted by A33Zab
But I get the impression I failed..........
- yes, you did. By 'omitting' the vital part "This remark is given in the mentioned FCOM 3.....when a FCTL STAB CTL FAULT is present." which others have now posted you in fact 'raised more questions than you answered'.
Originally Posted by A33Zab
But I get the impression I failed..........
- yes, you did. By 'omitting' the vital part "This remark is given in the mentioned FCOM 3.....when a FCTL STAB CTL FAULT is present." which others have now posted you in fact 'raised more questions than you answered'.
I failed here:
I think you understand but for the ones which do not:
Pls don't consider the THS being locked ....
Pls don't consider the THS being locked ....
ask exactly what ADR info the FCPC gets.to 'compensate for speed.'
Input the accelerometer and rate information from ADIRU, weight and CG from FMGEC, SS input and you will have all ingredients to position the THS.
There are simply too may variables and too little 'beta testing' time
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One such development is the study of electro-hydraulic actuators (EHAs), which could lead to a more-electric aircraft, and already have been tested both on the Iron Bird and in flight.
Since all aircraft systems are controlled from the flight deck, the Iron Bird requires a cockpit for its control, provided by three Airbus Fixed Based Simulators (FBS) along with a mobile visual system – which can be connected to either simulator.
From the flight deck, the Iron Bird can be flown like a standard aircraft, with a computer generating the aerodynamic model and such environmental conditions as air density, air temperature, airspeed and Mach number.
CONTINUED BENEFITS
The team of engineers and pilots who have worked many years with Airbus’ various Iron Birds have a rich backlog of experience, which is valuable when making testing technologies for the safety, efficiency and comfort of the company’s next jetliner products.
Airbus’ previous Iron Birds – which were utilised beginning with the milestone A300B2/B4 and A310 programmes, and followed by the A319/A320/A321, A330/A340 and A380 – are still operational. When called upon, they are used to replay scenarios with the actual hardware and software, providing insights on the situation or to try new enhancements before they are introduced as a modification on the aircraft type.
One such development is the study of electro-hydraulic actuators (EHAs), which could lead to a more-electric aircraft, and already have been tested both on the Iron Bird and in flight.
Last edited by Jetdriver; 8th Jul 2011 at 10:03.
Speed input
BOAC
Your line "The FCPC gets ADR & IR information to The FCPC gets ADR & IR information to compensate for speed.." makes me again 'board the train' and ask exactly what ADR info the FCPC gets.to 'compensate for speed.'
Your line "The FCPC gets ADR & IR information to The FCPC gets ADR & IR information to compensate for speed.." makes me again 'board the train' and ask exactly what ADR info the FCPC gets.to 'compensate for speed.'
When a pilot operates the stick in an aircraft where flight control deflection is not influenced by computers, he will do it by training and habit dependent on the aerodynamic state (TAS) of the aircraft. Going fast, small inputs and small onset rates, slower speeds greater input and maybe faster onset rates. In the F4 in approach configuration and speed the stick could be jerked around without causing any flightpath change, if you did it fast enough. At high mach we needed to be very sensitive with control input not do over g or even get an accellerated stall. The artificial feel produced by a separate pitot system and some weight (bellows and bobweight) helped us with that.
That said i´m not in the clear, on what data the FBW system is doing its job in that area, changing the output to the flightcontrols in relation to different TAS. As there is no artificial feel on the stick, there must be an implemented computer logic to modulate the input to the system to get the correct amount of deflection onset and total deflection in different TAS regimes. Where does this speed value come from or is the system using a logic not depending on speed?
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A33 - I cannot see any point in carrying on this direction since we seem to have a language issue and I do not speak 'anywhere'.
You said
"This remark is given in the mentioned FCOM 3.....when a FCTL STAB CTL FAULT is present."
Now you say
"Don't think so because the remark has nothing to do with the FCTL STAB CTL FAULT"??
As for "What do you need for speed calculation?" my point is I do NOT need a 'speed calculation' and nor should the THS.
rrat "No one would design a system like you seem to suggest with" - your confidence is most impressive. Does it extend to knowing that no-one would design a system to shut off the stall warning in flight whilst the a/c is still stalled?
You said
"This remark is given in the mentioned FCOM 3.....when a FCTL STAB CTL FAULT is present."
Now you say
"Don't think so because the remark has nothing to do with the FCTL STAB CTL FAULT"??
As for "What do you need for speed calculation?" my point is I do NOT need a 'speed calculation' and nor should the THS.
rrat "No one would design a system like you seem to suggest with" - your confidence is most impressive. Does it extend to knowing that no-one would design a system to shut off the stall warning in flight whilst the a/c is still stalled?
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Hi BOAC,
It doesn't need to know the C of G. We need to prove the C of G is within limits for TO & Landing and to estimate the stab trim setting for take off.
When it's airborne, the FMGC will estimate the VLS using config, fuel distribution and previously entered ZFW C of G. However the FAC will display the real VLS using measured Angle of Attack.
No - it certainly doesn't extend that far and there is no mention in FCOM either. With hindsight, I hope AB change that logic on the stall warning inhibit and include WoW, Radio Alt logic etc. instead.
With "Stall Stall" blaring at them as the Captain entered the Flight Deck at FL 350, I believe we would not be having this dialogue.
we are talking datums, sir. If it don't know that, you are 'dead in the water' as they say.
When it's airborne, the FMGC will estimate the VLS using config, fuel distribution and previously entered ZFW C of G. However the FAC will display the real VLS using measured Angle of Attack.
Does it extend to knowing that no-one would design a system to shut off the stall warning in flight whilst the a/c is still stalled?
With "Stall Stall" blaring at them as the Captain entered the Flight Deck at FL 350, I believe we would not be having this dialogue.
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Hi,
rudderrudderrat
I'm in complete disagreement with your statement.
This is no need of long ND input fot change the THS deflection.
Any input (up or down) is followed (a response) by a movement of the THS ..up or down (in the flight law they were)
But the BEA note .. tell that the "THS remained in a full up position to the end of the event" ...
So despite nose down inputs ..
BEA again:
So the aircraft was responding to the nose down inputs orders .. but the THS not !
It's something not right there !
rudderrudderrat
Because they didn't keep the ND input in for long enough.
They had not diagnosed their problem correctly, and attempted to arrest their ROD with NU side stick inputs.
They had not diagnosed their problem correctly, and attempted to arrest their ROD with NU side stick inputs.
This is no need of long ND input fot change the THS deflection.
Any input (up or down) is followed (a response) by a movement of the THS ..up or down (in the flight law they were)
But the BEA note .. tell that the "THS remained in a full up position to the end of the event" ...
So despite nose down inputs ..
BEA again:
"At 2 h 12 min 02, the PF said "I don’t have any more indications", and the PNF said "we have no valid indications". At that moment, the thrust levers were in the IDLE detent and the engines’ N1’s were at 55%. Around fifteen seconds later, the PF made pitch-down inputs. In the following moments, the angle of attack decreased, the speeds became valid again and the stall warning sounded again."
It's something not right there !
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Hi jcjeant,
"After the autopilot disengagement:
„„the airplane climbed to 38,000 ft,
„„the stall warning was triggered and the airplane stalled,
„„the inputs made by the PF were mainly nose-up,
„„the descent lasted 3 min 30, during which the airplane remained stalled. The angle of
attack increased and remained above 35 degrees,
„„the engines were operating and always responded to crew commands."
They lowered the nose at some stage but then received the stall warning again. The report doesn't say that they continued to inject nose down inputs after that event. All it says is that they were mostly nose-up.
Do you think they were still pushing down hard at impact? The last recorded values were a pitch attitude of 16.2 degrees nose-up, a roll angle of
5.3 degrees left and a vertical speed of -10,912 ft/min.
"After the autopilot disengagement:
„„the airplane climbed to 38,000 ft,
„„the stall warning was triggered and the airplane stalled,
„„the inputs made by the PF were mainly nose-up,
„„the descent lasted 3 min 30, during which the airplane remained stalled. The angle of
attack increased and remained above 35 degrees,
„„the engines were operating and always responded to crew commands."
They lowered the nose at some stage but then received the stall warning again. The report doesn't say that they continued to inject nose down inputs after that event. All it says is that they were mostly nose-up.
Do you think they were still pushing down hard at impact? The last recorded values were a pitch attitude of 16.2 degrees nose-up, a roll angle of
5.3 degrees left and a vertical speed of -10,912 ft/min.
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@BOAC:
As for "What do you need for speed calculation?" my point is I do NOT need a 'speed calculation' and nor should the THS
Excuse me for not writing 'the perfectly english' which you only understand, next posts - if any - will be adressed to all but you. I can only write 'anywheres'.
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Re: Asking what would the the second thing to do after looking at AoA value when hearing STALL STALL.
Nope
. So you have your AoA value, lets say it's Seven.
If that's the first thing you look at it must be key to the subsequent process that you plan to apply. So what do you do next? What is so important about the AoA number that the aircraft is telling you in your subsequent decision process. If you need to question the stall warning then why do you believe the actual AoA, it's coming from the same system....
Me, the first thing I'd look at is a horizon (an AoA indicator of sorts of course, but which also tells me whether my wings are level. Two birds with one stone....)
BOAC's attitude is interesting, a remarkable desire to blame the aircraft with zero evidence to go down that track. One wonders if this is relevant to this accident, the CVR should be key to working out the contributing factors, one wonders what else was said. Perhaps a "What's it doing now" ???
Nope
. So you have your AoA value, lets say it's Seven.If that's the first thing you look at it must be key to the subsequent process that you plan to apply. So what do you do next? What is so important about the AoA number that the aircraft is telling you in your subsequent decision process. If you need to question the stall warning then why do you believe the actual AoA, it's coming from the same system....
Me, the first thing I'd look at is a horizon (an AoA indicator of sorts of course, but which also tells me whether my wings are level. Two birds with one stone....)
BOAC's attitude is interesting, a remarkable desire to blame the aircraft with zero evidence to go down that track. One wonders if this is relevant to this accident, the CVR should be key to working out the contributing factors, one wonders what else was said. Perhaps a "What's it doing now" ???
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Originally Posted by PA
a remarkable desire to blame the aircraft with zero evidence to go down that track.
No-one ready to answer my poser with a serious response?
Primary and Secondary Pitch=Control
In case anyone is getting the wrong impression, let me chip-in an important point to this THS discussion.
BOAC is focussed on discussing the THS as if it is used as a primary flight control. This is not the case on FBW Airbuses, just as it is not the case on an A300 or A310, or on B707 through B777. They are not like Gums's Viper, which uses the whole horizontal stabiliser (tailplane) as an elevator.
On all these jet transports, primary pitch control is provided by the elevator, as per DHC-1 Chipmunk or Cessna 150. On those aircraft, the pilot then adjusts a trim tab on the elevator itself, which provides an aerodynamic load to hold the elevator at the position the pilot wants. This position is reflected by the control stick.
On large jet transports, speeds, CG and high-lift devices are so much more variable that, on the approach, the elevator would be in a very high position. In other words, the primary control of pitch would be already near the limit of its travel. This is plainly unsatisfactory. The solution is to provide a secondary pitch control, in the form of the all-moving horizontal stabiliser, which trims the aircraft in pitch to enable the elevators to return to neutral. The control column will also return to neutral. On Airbuses, FBW or not, this is referred to as the THS.
When hand-flying an A310 or B767, the PF makes pitch commands with the control column. The elevators move. When the PF achieves the pitch effect he/she wants, he trims the THS to enable himself to relax pressure on the column. All jet transports have an autopilot (AP) which uses the same technique as the pilot. When it trims the THS, we call that auto-trim.
On a FBW Airbus, the AP works much the same, using auto-trim. When hand-flying, the PF does not need to trim the THS manually: the auto-trim does it. (Several American jets had a crude version of this 40 years ago, called control-wheel steering [CWS]). This only applies in Pitch-Normal and Pitch-Alternate laws. In Pitch-Direct law, the PF does his own THS-trimming.
AF447 left its cruise altitude in Pitch-Alternate law, and most of us think that this was retained for the rest of the flight (but lacking any high-AoA protections). The EFCS interpreted the PF's stick commands in pitch according to its C* terms of reference, applied the appropriate elevator when necessary, and then trimmed the THS to enable the elevators to return to neutral. The reason it trimmed the THS all the way to minus 13 degrees (13NU), was to avoid reaching full-travel UP on the elevators.
At any stage during that up-trimming process, or even after it, what would have happened if the PF had pushed the stick fully forward? The EFCS would have selected full down-elevator, and started trimming the THS in the nose-down-trim direction.
BOAC is focussed on discussing the THS as if it is used as a primary flight control. This is not the case on FBW Airbuses, just as it is not the case on an A300 or A310, or on B707 through B777. They are not like Gums's Viper, which uses the whole horizontal stabiliser (tailplane) as an elevator.
On all these jet transports, primary pitch control is provided by the elevator, as per DHC-1 Chipmunk or Cessna 150. On those aircraft, the pilot then adjusts a trim tab on the elevator itself, which provides an aerodynamic load to hold the elevator at the position the pilot wants. This position is reflected by the control stick.
On large jet transports, speeds, CG and high-lift devices are so much more variable that, on the approach, the elevator would be in a very high position. In other words, the primary control of pitch would be already near the limit of its travel. This is plainly unsatisfactory. The solution is to provide a secondary pitch control, in the form of the all-moving horizontal stabiliser, which trims the aircraft in pitch to enable the elevators to return to neutral. The control column will also return to neutral. On Airbuses, FBW or not, this is referred to as the THS.
When hand-flying an A310 or B767, the PF makes pitch commands with the control column. The elevators move. When the PF achieves the pitch effect he/she wants, he trims the THS to enable himself to relax pressure on the column. All jet transports have an autopilot (AP) which uses the same technique as the pilot. When it trims the THS, we call that auto-trim.
On a FBW Airbus, the AP works much the same, using auto-trim. When hand-flying, the PF does not need to trim the THS manually: the auto-trim does it. (Several American jets had a crude version of this 40 years ago, called control-wheel steering [CWS]). This only applies in Pitch-Normal and Pitch-Alternate laws. In Pitch-Direct law, the PF does his own THS-trimming.
AF447 left its cruise altitude in Pitch-Alternate law, and most of us think that this was retained for the rest of the flight (but lacking any high-AoA protections). The EFCS interpreted the PF's stick commands in pitch according to its C* terms of reference, applied the appropriate elevator when necessary, and then trimmed the THS to enable the elevators to return to neutral. The reason it trimmed the THS all the way to minus 13 degrees (13NU), was to avoid reaching full-travel UP on the elevators.
At any stage during that up-trimming process, or even after it, what would have happened if the PF had pushed the stick fully forward? The EFCS would have selected full down-elevator, and started trimming the THS in the nose-down-trim direction.
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Originally Posted by rrrat
With "Stall Stall" blaring at them as the Captain entered the Flight Deck at FL 350, I believe we would not be having this dialogue.
At around 2 h 11 min 40, the Captain re-entered the cockpit. During the following seconds, all of the recorded speeds became invalid and the stall warning stopped.
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Hi,
Very nice !
But .. as you I read the BEA note .. and in this note it's :
The THS remained full up deflection to the end of the event
So you don't answer the question...
Why (or how) THS will stay (nothing move even 1°!!) full up to the end of the event ... when we know that nose down inputs were performed ...
How you explain this this contradiction (for me) in the BEA note ?
Hi jcjeant,
"After the autopilot disengagement:
„„the airplane climbed to 38,000 ft,
„„the stall warning was triggered and the airplane stalled,
„„the inputs made by the PF were mainly nose-up,
„„the descent lasted 3 min 30, during which the airplane remained stalled. The angle of
attack increased and remained above 35 degrees,
„„the engines were operating and always responded to crew commands."
They lowered the nose at some stage but then received the stall warning again. The report doesn't say that they continued to inject nose down inputs after that event. All it says is that they were mostly nose-up.
Do you think they were still pushing down hard at impact? The last recorded values were a pitch attitude of 16.2 degrees nose-up, a roll angle of
5.3 degrees left and a vertical speed of -10,912 ft/min.
"After the autopilot disengagement:
„„the airplane climbed to 38,000 ft,
„„the stall warning was triggered and the airplane stalled,
„„the inputs made by the PF were mainly nose-up,
„„the descent lasted 3 min 30, during which the airplane remained stalled. The angle of
attack increased and remained above 35 degrees,
„„the engines were operating and always responded to crew commands."
They lowered the nose at some stage but then received the stall warning again. The report doesn't say that they continued to inject nose down inputs after that event. All it says is that they were mostly nose-up.
Do you think they were still pushing down hard at impact? The last recorded values were a pitch attitude of 16.2 degrees nose-up, a roll angle of
5.3 degrees left and a vertical speed of -10,912 ft/min.
But .. as you I read the BEA note .. and in this note it's :
The THS remained full up deflection to the end of the event
So you don't answer the question...
Why (or how) THS will stay (nothing move even 1°!!) full up to the end of the event ... when we know that nose down inputs were performed ...
How you explain this this contradiction (for me) in the BEA note ?
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Hi HN39,
If he did hear it initially, shortly afterwards it stopped. I would guess that he assumed the crew had "respected" the stall warning and the aircraft was no longer stalled. It would take some time to absorb what he was witnessing and diagnose a continued stall (especially without the stall warning).
It's a pity that the stall warning sounded again after they made the correct (ND) input.
Hi jcjeant, - I can only explain the stab trim remained full NU, if the pilot inputs were mostly NU. If the full report shows they were attempting to unstall the aircraft with nose down inputs - but the stab remained full nose up - then AB have a huge re-design problem. I don't think that's the case.
Do you assume the captain did not hear the warning when he entered the Flight Deck?
It's a pity that the stall warning sounded again after they made the correct (ND) input.
Hi jcjeant, - I can only explain the stab trim remained full NU, if the pilot inputs were mostly NU. If the full report shows they were attempting to unstall the aircraft with nose down inputs - but the stab remained full nose up - then AB have a huge re-design problem. I don't think that's the case.
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Originally Posted by rrat
Amongst the 13,630 + posers you've made, which one is the serious one
"It would take some time to absorb what he was witnessing and diagnose a continued stall" - how long would it take you? I'm pretty sure how long it would take me.
CS - I have flown all those systems. I know how they work (well, the 'crude' ones anyway). I have flown all-flying tails, elevators only, locked and unlockable elevators and follow-up tails.
jcjeant,
I can see why you infer that the BEA is contradicting itself, but that is not necessarily the case. As I explain in my post above. the THS reached 13 NU because the EFCS was trimming out a large amount of up-elevator. My GUESS is that the recorded 13NU represents the most that the auto-trim was capable of. Call it full-travel if you like.
Once the THS reached full-travel, the EFCS was probably having to apply more and more up-elevator to achieve what it wanted (i.e., what it thought the PF wanted). The brief nose-down inputs made by the PF may not have been sufficient to push the elevators into a down position. Unless and until that happened, the THS would remain where it was.
I can see why you infer that the BEA is contradicting itself, but that is not necessarily the case. As I explain in my post above. the THS reached 13 NU because the EFCS was trimming out a large amount of up-elevator. My GUESS is that the recorded 13NU represents the most that the auto-trim was capable of. Call it full-travel if you like.
Once the THS reached full-travel, the EFCS was probably having to apply more and more up-elevator to achieve what it wanted (i.e., what it thought the PF wanted). The brief nose-down inputs made by the PF may not have been sufficient to push the elevators into a down position. Unless and until that happened, the THS would remain where it was.