Habsheim
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However, in α-protection mode, the flight control system incorporates a phugoid-damping feedback term in addition to side stick commands when computing the commanded elevator position.
NTSB has done what BEA failed to do.
Reference 8 documents an Airbus simulation of the last 300 ft of the flight, and indicates that the airplane was performing as designed
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Hi CONF iture,
It is and has been since 2001 after several heavy landing incidents. See:
Accident of an Iberian Airbus A320 in Bilbao
You may be protected against stalling, but flying too slowly limits your pitch authority beyond what you might expect in a conventional aircraft.
Edit. I've just noticed your previous comment #160
I agree it may have helped in that particular case (deliberately flown), but the design is to help avoid stalls during windshear GAs etc. Would you prefer the extra couple of degrees of AoA with an increased probability of overshoot beyond stall + then possible wing drop, or the present design?
the design must be firstly detailed, and secondly can be questioned.
Accident of an Iberian Airbus A320 in Bilbao
You may be protected against stalling, but flying too slowly limits your pitch authority beyond what you might expect in a conventional aircraft.
Edit. I've just noticed your previous comment #160
very happy if the system commanded alpha max as requested by the pilot to give a chance to avoid the crash.
Last edited by rudderrudderrat; 26th Dec 2013 at 10:57. Reason: extra text
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@Confiture : Thanks to complete my answer to Rudderruddererrat mentioning alpha max.
Agreed. The Court of Colmar was not able to discover that by themselves, too new technic, unaware "experts" and counter-"experts" of these new technic. Perhaps it could be a legal grief to ask revision of the trial, with that new information.
Originally Posted by Confiture
It was the duty of the BEA, 20 years earlier, to detail such characteristic. NTSB has done what BEA failed to do.
Last edited by Jetdriver; 27th Dec 2013 at 10:43.
Thread Starter
Meanwhile at BA (off-topic)
Quotes from Saint-Ex
"Hi Chris. I was on an A320 fllght the night before the Air France crash. I didn`t think it necessary to mention the aircraft was not one of BA`s as it was so widely reported."
Yes, but many of our readers were too young to be taking an interest in such matters 25 years ago. You're not giving much away, but I presume your flight was as a passenger on a BA a/c? If so, I'd like to apologise for any delay
- we were having a lot of teething probs, both with the a/c and with the systems at the newly-opened Gatwick North Terminal. For example, we were the first short-haul fleet in BA (or, for that matter, the first of any airline operating at Gatwick and elsewhere) to use containerised baggage. I don't know if AF were doing it, although it seems probable, and wonder about Air Inter.
"As far as Flight Safety is concerned you may remember the first BA pilot to be allocated to the Airbus actually headed the Flight Safety department."
You're nearly "right" (pun intended). The first proper BA pilot checked out on the A320 (AYK, the rest of us were all ex-BCAL) was ColinW, who joined us as an Assistant Flight-Manager in the summer. he then masterminded the transfer of the fleet to Heathrow in the October/November, and did a superb job of promoting the A320 in BA. Much later, when BA rationalisation abolished assistant managers, he joined Flight Safety, and eventually headed it.
In 1988, head of Flight Safety was JimP, who wasn't checked-out on the A320 until a year or two later.
"Hi Chris. I was on an A320 fllght the night before the Air France crash. I didn`t think it necessary to mention the aircraft was not one of BA`s as it was so widely reported."
Yes, but many of our readers were too young to be taking an interest in such matters 25 years ago. You're not giving much away, but I presume your flight was as a passenger on a BA a/c? If so, I'd like to apologise for any delay
- we were having a lot of teething probs, both with the a/c and with the systems at the newly-opened Gatwick North Terminal. For example, we were the first short-haul fleet in BA (or, for that matter, the first of any airline operating at Gatwick and elsewhere) to use containerised baggage. I don't know if AF were doing it, although it seems probable, and wonder about Air Inter."As far as Flight Safety is concerned you may remember the first BA pilot to be allocated to the Airbus actually headed the Flight Safety department."
You're nearly "right" (pun intended). The first proper BA pilot checked out on the A320 (AYK, the rest of us were all ex-BCAL) was ColinW, who joined us as an Assistant Flight-Manager in the summer. he then masterminded the transfer of the fleet to Heathrow in the October/November, and did a superb job of promoting the A320 in BA. Much later, when BA rationalisation abolished assistant managers, he joined Flight Safety, and eventually headed it.
In 1988, head of Flight Safety was JimP, who wasn't checked-out on the A320 until a year or two later.
Thread Starter
Quote from Dozy Wannabe:
"Is he talking about the A320 that almost landed on Crawley High St?"
Perhaps you could supply some details?
"Is he talking about the A320 that almost landed on Crawley High St?"
Perhaps you could supply some details?
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It was the duty of the BEA, 20 years earlier, to detail such characteristic.
NTSB has done what BEA failed to do.
When the design prevents Sully to obtain a better touchdown, and Asseline, as wrong as he was in the first place, to avoid the trees, the design must be firstly detailed, and secondly can be questioned.
NTSB has done what BEA failed to do.
When the design prevents Sully to obtain a better touchdown, and Asseline, as wrong as he was in the first place, to avoid the trees, the design must be firstly detailed, and secondly can be questioned.
But...
- Is it prooved that a higher AoA would have permitted to clear the trees? After reading the current thread, I'm under the impression it's not sure, far from it... Plus as awblain said:
- With this in mind, why do you point a finger at the BEA? I'll quote its website: The safety investigation, whose sole objective is to prevent future accidents and incidents, includes the gathering and analysis of information, the drawing of conclusions, including the determination of cause(s) and/or contributing factors and, when appropriate, the making of safety recommendations (European Regulation 996/2010 article 2 part 14).
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Originally Posted by rrr
You may be protected against stalling, but flying too slowly limits your pitch authority beyond what you might expect in a conventional aircraft.
On the contrary, what happens here is a total disconnection between the elevator movement and the sidestick displacement even if beyond alpha prot the sidestick should directly command the alpha ... That leaves the pilot out of the loop ... how really are deflected my elevators ?
I agree it may have helped in that particular case (deliberately flown), but the design is to help avoid stalls during windshear GAs etc. Would you prefer the extra couple of degrees of AoA with an increased probability of overshoot beyond stall + then possible wing drop, or the present design?
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On the contrary, what happens here is a total disconnection between the elevator movement and the sidestick displacement even if beyond alpha prot the sidestick should directly command the alpha ... That leaves the pilot out of the loop ... how really are deflected my elevators ?
If the only way to keep the pilot in the loop is, in your eyes, strictly proportionnal stick and surfaces displacements, then I understand you don't like FBW aircraft. I suppose you weighted pro and cons?
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Hi AlphaZuluRomeo,
I think the B777 FBW system would satisfy CONF iture. Page 3. Design Philosophy. http://www.davi.ws/avionics/TheAvion...ook_Cap_11.pdf
"What should be noted, however, is that none of these features limit the action of the pilot. The 777 design utilizes envelope protection in all of its functionality rather than envelope limiting. Envelope protection deters pilot inputs from exceeding certain predefined limits but does not prohibit it. Envelope limiting prevents the pilot from commanding the airplane beyond set limits. For example, the 777 bank angle protection feature will significantly increase the wheel force a pilot encounters when attempting to roll the airplane past a predefined bank angle. This acts as a prompt to the pilot that the airplane is approaching the bank angle limit. However, if deemed necessary, the pilot may override this protection by exerting a greater force on the wheel than is being exerted by the backdrive actuator. The intent is to inform the pilot that the command being given would put the airplane outside of its normal operating envelope, but the ability to do so is not precluded. This concept is central to the design philosophy of the 777 Primary Flight Control System."
I guess the same is true in pitch control.
If the only way to keep the pilot in the loop is, in your eyes, strictly proportional stick and surfaces displacements, then I understand you don't like FBW aircraft.
"What should be noted, however, is that none of these features limit the action of the pilot. The 777 design utilizes envelope protection in all of its functionality rather than envelope limiting. Envelope protection deters pilot inputs from exceeding certain predefined limits but does not prohibit it. Envelope limiting prevents the pilot from commanding the airplane beyond set limits. For example, the 777 bank angle protection feature will significantly increase the wheel force a pilot encounters when attempting to roll the airplane past a predefined bank angle. This acts as a prompt to the pilot that the airplane is approaching the bank angle limit. However, if deemed necessary, the pilot may override this protection by exerting a greater force on the wheel than is being exerted by the backdrive actuator. The intent is to inform the pilot that the command being given would put the airplane outside of its normal operating envelope, but the ability to do so is not precluded. This concept is central to the design philosophy of the 777 Primary Flight Control System."
I guess the same is true in pitch control.
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Aside from the fact that CONF's assertion that, in the Hudson incident, the protections "prevented a perfect touchdown" is a fiction to which he appears to be the only subscriber - the NTSB were freer to look into aircraft behaviour in their report as there were far fewer preceding factors (barring the birdstrike itself) to write up. In true half-informed fashion, some of the press wrote up the behaviour as "assisting" the landing on water, but since when have any of you ever taken the press seriously? An attitude which is entirely understandable given the frequent mistakes and mischaracterisations they make.
RRR - we don't know exactly what the B777 systems would have done in a similar scenario, but based on the understanding I have, the servos driving the yokes would have significantly increased resistance to the pilot's inputs the closer the aircraft came to maximum permissible alpha. This in turn would have increased the physical effort required to pull up. The behaviour may be more akin to a conventional setup in some respects, but the systems would still have in effect been "fighting" the pilot's inputs.
"Crawley High St." refers to an incident related in a dead-tree book I owned, the first edition of 'The Tombstone Imperative' by Andrew Weir. It apparently happened to a G- registered A320 in July 1988 and was tangentially related to the Bangalore and Strasbourg accidents (i.e. autoflight-related). Given the lack of online references I can find I can only think it must have come from a CHIRP or similar reporting regime.
Last edited by DozyWannabe; 26th Dec 2013 at 21:19.
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Originally Posted by AZR
Is it prooved that a higher AoA would have permitted to clear the trees? After reading the current thread, I'm under the impression it's not sure, far from it...
With this in mind, why do you point a finger at the BEA? I'll quote its website: ...
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Hi rudderrudderrat,
Thanks, I'm aware of the different philosphies when it come to protections/limits. I know that a number of pilots feel like they would rather have the ultimate control, and hence don't like the A because it's like "the damn thing is better than I'm" (sometimes).
But that's not the point, here: in an A320 as in a 777, command (stick/yoke) and elevator are disconnected, and their relative displacement not (always) proportionnal. That's any FBW with anything else than Direct Law. E.g. C* law.
Hi CONF iture,
So now, the elevators were un-cooperative? Feels like the great return of the killer plane (and/or computer).
Now we're at rudderrudderrat'point. I dare say I fail to see how the aircraft should have saved the day, while not (hard) imposing hard limits to the crew...
With "cooperative" elevators as you put it, and stick full back (human reaction just before impacting the trees), stall is on the way = worse end-result.
How many years later?
Once again, I share the regret. The NTSB did? Yes. We're happy it did? Yes. We agree on that. I just feel it's not fair to write that the BEA "should have".
Thanks, I'm aware of the different philosphies when it come to protections/limits. I know that a number of pilots feel like they would rather have the ultimate control, and hence don't like the A because it's like "the damn thing is better than I'm" (sometimes).
But that's not the point, here: in an A320 as in a 777, command (stick/yoke) and elevator are disconnected, and their relative displacement not (always) proportionnal. That's any FBW with anything else than Direct Law. E.g. C* law.
Hi CONF iture,
Now we're at rudderrudderrat'point. I dare say I fail to see how the aircraft should have saved the day, while not (hard) imposing hard limits to the crew...
With "cooperative" elevators as you put it, and stick full back (human reaction just before impacting the trees), stall is on the way = worse end-result.
Once again, I share the regret. The NTSB did? Yes. We're happy it did? Yes. We agree on that. I just feel it's not fair to write that the BEA "should have".
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Originally Posted by AZR
With "cooperative" elevators as you put it, and stick full back (human reaction just before impacting the trees), stall is on the way = worse end-result.
Thread Starter
Dozy Wannabe's Crawley scenario (off topic)
Quote from Dozy Wannabe:
" 'Crawley High St.' refers to an incident related in a dead-tree book I owned, the first edition of 'The Tombstone Imperative' by Andrew Weir. It apparently happened to a G- registered A320 in July 1988 and was tangentially related to the Bangalore and Strasbourg accidents (i.e. autoflight-related). Given the lack of online references I can find I can only think it must have come from a CHIRP or similar reporting regime."
In those days NDB approaches were still available at LGW, using the Locator-NDBs west and east of the airfield (on the extended centrelines of Rwys 08R/26L respectively, about 4nm from their thresholds). With TRK-FPA available on the A320 FD (and with a better PFD display than we had enjoyed on the FPA-equipped A310), we were using it - sometimes with the AP engaged - to provide a form of track and glide-slope guidance (the latter as an alternative to the cumbersome step-down technique, which was still standard in most airlines).
IIRC, there was a known incident in which the crew mis-selected a VS (vertical speed) instead of an intended FPA (flight-path angle). With the original ergonomics of the A320 AFS, the format of the shared VS/FPA display of the resulting selected VS on the FCU would not necessarily have alerted a crew to the mistake. The latter would soon become evident, however, by an excessive pitch-down, and rising VS.
Until corrected, such a mis-selection could quickly take the a/c below the normal approach profile. It would not, however, affect the tracking in azimuth. Crawley High Street is a couple of miles due south of Gatwick - nowhere near the approach paths for either runway.
If such an incident was considered hazardous, an MOR would have been submitted by the crew and/or ATC (hopefully both), which should remain on record. If not, but one or both pilots felt it needed to be made known, an anonymous 'Chirp' report might have been filed for the information of other UK-licensed crews. Unless and until we can find one or the other, your scenario remains mysterious.
" 'Crawley High St.' refers to an incident related in a dead-tree book I owned, the first edition of 'The Tombstone Imperative' by Andrew Weir. It apparently happened to a G- registered A320 in July 1988 and was tangentially related to the Bangalore and Strasbourg accidents (i.e. autoflight-related). Given the lack of online references I can find I can only think it must have come from a CHIRP or similar reporting regime."
In those days NDB approaches were still available at LGW, using the Locator-NDBs west and east of the airfield (on the extended centrelines of Rwys 08R/26L respectively, about 4nm from their thresholds). With TRK-FPA available on the A320 FD (and with a better PFD display than we had enjoyed on the FPA-equipped A310), we were using it - sometimes with the AP engaged - to provide a form of track and glide-slope guidance (the latter as an alternative to the cumbersome step-down technique, which was still standard in most airlines).
IIRC, there was a known incident in which the crew mis-selected a VS (vertical speed) instead of an intended FPA (flight-path angle). With the original ergonomics of the A320 AFS, the format of the shared VS/FPA display of the resulting selected VS on the FCU would not necessarily have alerted a crew to the mistake. The latter would soon become evident, however, by an excessive pitch-down, and rising VS.
Until corrected, such a mis-selection could quickly take the a/c below the normal approach profile. It would not, however, affect the tracking in azimuth. Crawley High Street is a couple of miles due south of Gatwick - nowhere near the approach paths for either runway.
If such an incident was considered hazardous, an MOR would have been submitted by the crew and/or ATC (hopefully both), which should remain on record. If not, but one or both pilots felt it needed to be made known, an anonymous 'Chirp' report might have been filed for the information of other UK-licensed crews. Unless and until we can find one or the other, your scenario remains mysterious.
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Well, for one thing because the engines will be trying to pitch the plane nose-up as they begin to provide power. Without the flight control system counteracting this tendency, even neutral elevator could allow the aircraft to overshoot 17.5 degrees in very short order.
What the computers do is not especially clever, the advantage they have is that they can detect and counteract unwanted deltas (changes) in attitude much faster than a human. Again, nothing in the documentation states that full back-stick will command alpha max instantaneously - indeed experience shows that it can take up to around 20-30 seconds to stabilise enough to reach 17.5 degrees. Thus the BEA did not "fail" to do anything - only if Airbus's documentation claimed instant alpha max would the aircraft's behaviour have needed more thorough examination.
@Chris Scott - thanks for the input. I suspect "Crawley High St." was a bit of journalistic licence on the part of the author. I mentioned it only because Saint-Ex mentioned BA, and to the best of my knowledge that was the only BA A320 to have any difficulty around that time.
@rudderrudderrat - the other thing important to remember about the High Alpha modes is that they are designed to allow for a limited amount of roll authority to be retained even at alpha max. What the flight control systems are doing is assimilating all the external forces acting on the aircraft along with the control inputs and responding to control demands while maintaining a stable flight regime. In this case you have the increase in thrust from the podded engines causing an increase in pitch attitude, as well as a somewhat belated full back-stick demand. The Bilbao case you link seems to highlight what us engineers call an unknown "edge case" (i.e. a scenario that was unaccounted for in the original design, and sometimes results in non-optimal behaviour). However it also demonstrates that if Airbus are presented with evidence of such an occurrence, they can and will turn around a fix and will announce it publicly even before the final report is written.
EDIT : Looking at the report on the Iberia Bilbao incident:
http://www.smartcockpit.com/download...rd_Landing.pdf
It seems that the problematic aggressive phugoid damping was initiated by a tailwind gradient which manifested itself as an excessive reduction in airspeed (a delta of around -10kts over one second). The EFCS logic incorrectly considered this to be a result of phugoid motion and applied nose-down elevator to arrest the pitch-up demand.
As there was no such tailwind gradient at Habsheim, and the airspeed deltas were much less extreme, I reckon it unlikely that phugoid damping applied here.
What the computers do is not especially clever, the advantage they have is that they can detect and counteract unwanted deltas (changes) in attitude much faster than a human. Again, nothing in the documentation states that full back-stick will command alpha max instantaneously - indeed experience shows that it can take up to around 20-30 seconds to stabilise enough to reach 17.5 degrees. Thus the BEA did not "fail" to do anything - only if Airbus's documentation claimed instant alpha max would the aircraft's behaviour have needed more thorough examination.
@Chris Scott - thanks for the input. I suspect "Crawley High St." was a bit of journalistic licence on the part of the author. I mentioned it only because Saint-Ex mentioned BA, and to the best of my knowledge that was the only BA A320 to have any difficulty around that time.
@rudderrudderrat - the other thing important to remember about the High Alpha modes is that they are designed to allow for a limited amount of roll authority to be retained even at alpha max. What the flight control systems are doing is assimilating all the external forces acting on the aircraft along with the control inputs and responding to control demands while maintaining a stable flight regime. In this case you have the increase in thrust from the podded engines causing an increase in pitch attitude, as well as a somewhat belated full back-stick demand. The Bilbao case you link seems to highlight what us engineers call an unknown "edge case" (i.e. a scenario that was unaccounted for in the original design, and sometimes results in non-optimal behaviour). However it also demonstrates that if Airbus are presented with evidence of such an occurrence, they can and will turn around a fix and will announce it publicly even before the final report is written.
EDIT : Looking at the report on the Iberia Bilbao incident:
http://www.smartcockpit.com/download...rd_Landing.pdf
It seems that the problematic aggressive phugoid damping was initiated by a tailwind gradient which manifested itself as an excessive reduction in airspeed (a delta of around -10kts over one second). The EFCS logic incorrectly considered this to be a result of phugoid motion and applied nose-down elevator to arrest the pitch-up demand.
As there was no such tailwind gradient at Habsheim, and the airspeed deltas were much less extreme, I reckon it unlikely that phugoid damping applied here.
Last edited by DozyWannabe; 27th Dec 2013 at 14:54.
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The behaviour may be more akin to a conventional setup in some respects, but the systems would still have in effect been "fighting" the pilot's inputs.
In a conventional system (direct control cable and without or with counterweight) there will have the same effect that is to say an application force to the controls which will increase with deflection requested ... it does not comes to fighting .. but simply to the laws of physics and that is exactly what is reproduced in the 777 system
When you pilot a Tiger Moth .. the system is no fighting your inputs .. it's simply physical laws in action
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In normal situations yes, but the forces applied to counter the inputs when in an envelope protection mode on the B777 will be noticeably greater than they would be if it were simply emulating aerodynamic resistance. In that mode it's not trying to mimic old-fashioned controls, it's trying to tell the pilot they are in danger of departing the flight envelope by significantly increasing flight control resistance. It's a modern, digitally-controlled descendant of the old "stick-push" systems, but it acts pre-emptively. A Tiger Moth won't do that.
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Originally Posted by DozyWanabee
Again, nothing in the documentation states that full back-stick will command alphamax instantaneously - indeed experience shows that it can take up to around 20-30 seconds to stabilise enough to reach 17.5degrees. Thus the BEA did not "fail" to do anything - only if Airbus's documentation claimed instant alpha max would the aircraft'sbehaviourhaveneededmore thorough examination.
As a computer guy who had responsibility of methods choices in our research center, I would NEVER have accepted to register such "systems"(?) without the complete boolean tables showing how passing from EVERY mode to another is managed, and due description of ALL the transient regimes ASWELL theoric and from experience.
I wonder why the BEA and other safety agencies did not see or/and point that lack of computer science method.
Many lifes are deliberatly sacrified by unresponsible engineers (probably able and taught to perform much more, that fact does the things still worse) playing only stats of opportunity to be paid by criminal blind airlines and unaware persons on board and their family.
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CONF iture - "When the design prevents Sully to obtain a better touchdown,"
http://www.ntsb.gov/doclib/reports/2010/aar1003.pdf
pdf pages 65, 73, 106, 107 of 216. Lack of airspeed, and not the airplane, was the primary problem.
http://www.ntsb.gov/doclib/reports/2010/aar1003.pdf
pdf pages 65, 73, 106, 107 of 216. Lack of airspeed, and not the airplane, was the primary problem.