A320 and the Miracle on the Hudson
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The issue with the flare was the speed control prior to it that led to the aircraft entering Alpha Prot at 150ft. At impact the aircraft was at 125kts config 2 (F speed would have been about 150kts) at a weight of @150,000lbs (68k) doing 750 fpm. It had very low surplus energy. Certainly not enough to significantly reduce the rate of descent but it was at significant risk of stall or would have been had it not been for the fly by wire protections that did their job. The reason the aircraft refused Sully Alpha Max was that at that point it was unsafe to go there at the rate he requested but it did Max Perform for him.
Confiture will continue to insist that the aircraft failed and that trying to trade a couple of knots close to the stall is a smart idea. He fails to understand the speed and energy regime they were in and is wrong. If they had stalled they would have died. The aircraft prevented this as Sully knew it would hence his abrupt full aft stick. The lesson is that if you have to ditch keep your speed up prior to impact so that you have energy to trade.
The NTSB said that the aircraft max performed but did not explain why Alpha Prot did not give Alpha Max. Below are some snippets from Airbus's submission to the NTSB which explain why the aircraft did what it did. The BEA in their comments at the end of the NTSB report highlight the same things in more detail but I cannot paste them for some reason.
During the remaining portion of the flight, the Aircraft remained in Normal
Law, and on occasion was flown within the alpha protection range. Notably
from approximately 150 ft down to the water impact the Aircraft was in
slats/flaps configuration 2. During this time period the Aircraft was in the
alpha protection mode which allowed the flight crew to remain focused on
their priorities, conversely if the Aircraft had been a non fly-by-wire aircraft,
the flight crew would have had to fly in and out of the stick shaker to
maintain the desired descent profile.
All water entries studies performed either by NACA or later by IMFL lead
to the conclusion that for the A320 aircraft on shallow water, the optimum
configuration is to have:
- Landing gear retracted
- Full slats/flaps configuration for minimum speed
- Pitch around 11°
- Slope around -0.5°
These data translate into a 3.5 ft/sec vertical speed at water impact.
It also shows that in case of water impact with an aircraft pitch below ≈ 8°,
or above ≈15° major airframe structural breakage is expected.
In Flight 1549, the Aircraft’s energy just prior to water impact was
insufficient to significantly decrease the vertical speed during flare, leading
to a water impact at around 13ft/s. Despite this rate of descent at water
impact, the extent of aircraft damages did not prevent a safe evacuation for
all persons on board. Aircraft pitch at water impact was close to the
optimum recommended value.
During the flight time in between the birds and the water impacts, the
Aircraft was flown occasionally within the alpha protection range (around 1
minute 7s), notably from about 150 ft RA down to water impact.
As far as aircraft trajectory is concerned, it has to be noted that the flight
control laws in the alpha protection domain do include some additional
features. AoA protection takes also care of the aircraft trajectory and, thus,
looks after phugoid damping as well as AoA control. There are feedbacks
within the AoA protection law aiming at damping the phugoid mode (low
frequency mode). Without these feedbacks, an aircraft upset from its
stabilized flight point up to constant high AoA would enter a phugoid
(which is, by definition, a constant AoA oscillation) without possibility to
stabilize the trajectory. As a consequence, commanded AoA is modulated:
for instance, if aircraft speed is decreasing and/or pitch attitude is increasing,
pilot's commanded AoA is lowered in order to avoid such a situation to
degrade.
Trying to run simulation without such damping features on the very last
seconds of the flight, without considering what could have been the effect
such features brought upstream during the flight on the overall Aircraft
trajectory and management by the crew would be pure speculation, as not
supported by technical facts.
On the last 10 sec in the air of Flight 1549 , DFDR data show that pitch
attitude is increasing and CAS decreasing. Then, the phugoid damping terms
are non null and are acting in the sense to decrease the finally commanded
AoA vs. the stick command, in order to prevent the Aircraft from increasing
the phugoid features.
It is obvious that achieving the optimum water impact configuration when
engine thrust is available (actually setting a Flight Path Angle of -0.5° on the
FCU), is more easily achievable.
However with a loss of engine thrust, as in Flight 1549, the aircraft energy
management significantly increases the pilot workload. Under these
circumstances, aircraft is still able to reach the optimum water impact
configuration, but this is a demanding task which requires time and
significant pilot focus. Typically, the flare initiation height will be critical to
the achievement of the optimum water entry conditions.
As an aside there is a reason the QRH and ECAM do not direct you to use the Yellow Electric Pump in a Green and Yellow Hyd failure. It will overheat and you will lose it very quickly.
Confiture will continue to insist that the aircraft failed and that trying to trade a couple of knots close to the stall is a smart idea. He fails to understand the speed and energy regime they were in and is wrong. If they had stalled they would have died. The aircraft prevented this as Sully knew it would hence his abrupt full aft stick. The lesson is that if you have to ditch keep your speed up prior to impact so that you have energy to trade.
The NTSB said that the aircraft max performed but did not explain why Alpha Prot did not give Alpha Max. Below are some snippets from Airbus's submission to the NTSB which explain why the aircraft did what it did. The BEA in their comments at the end of the NTSB report highlight the same things in more detail but I cannot paste them for some reason.
During the remaining portion of the flight, the Aircraft remained in Normal
Law, and on occasion was flown within the alpha protection range. Notably
from approximately 150 ft down to the water impact the Aircraft was in
slats/flaps configuration 2. During this time period the Aircraft was in the
alpha protection mode which allowed the flight crew to remain focused on
their priorities, conversely if the Aircraft had been a non fly-by-wire aircraft,
the flight crew would have had to fly in and out of the stick shaker to
maintain the desired descent profile.
All water entries studies performed either by NACA or later by IMFL lead
to the conclusion that for the A320 aircraft on shallow water, the optimum
configuration is to have:
- Landing gear retracted
- Full slats/flaps configuration for minimum speed
- Pitch around 11°
- Slope around -0.5°
These data translate into a 3.5 ft/sec vertical speed at water impact.
It also shows that in case of water impact with an aircraft pitch below ≈ 8°,
or above ≈15° major airframe structural breakage is expected.
In Flight 1549, the Aircraft’s energy just prior to water impact was
insufficient to significantly decrease the vertical speed during flare, leading
to a water impact at around 13ft/s. Despite this rate of descent at water
impact, the extent of aircraft damages did not prevent a safe evacuation for
all persons on board. Aircraft pitch at water impact was close to the
optimum recommended value.
During the flight time in between the birds and the water impacts, the
Aircraft was flown occasionally within the alpha protection range (around 1
minute 7s), notably from about 150 ft RA down to water impact.
As far as aircraft trajectory is concerned, it has to be noted that the flight
control laws in the alpha protection domain do include some additional
features. AoA protection takes also care of the aircraft trajectory and, thus,
looks after phugoid damping as well as AoA control. There are feedbacks
within the AoA protection law aiming at damping the phugoid mode (low
frequency mode). Without these feedbacks, an aircraft upset from its
stabilized flight point up to constant high AoA would enter a phugoid
(which is, by definition, a constant AoA oscillation) without possibility to
stabilize the trajectory. As a consequence, commanded AoA is modulated:
for instance, if aircraft speed is decreasing and/or pitch attitude is increasing,
pilot's commanded AoA is lowered in order to avoid such a situation to
degrade.
Trying to run simulation without such damping features on the very last
seconds of the flight, without considering what could have been the effect
such features brought upstream during the flight on the overall Aircraft
trajectory and management by the crew would be pure speculation, as not
supported by technical facts.
On the last 10 sec in the air of Flight 1549 , DFDR data show that pitch
attitude is increasing and CAS decreasing. Then, the phugoid damping terms
are non null and are acting in the sense to decrease the finally commanded
AoA vs. the stick command, in order to prevent the Aircraft from increasing
the phugoid features.
It is obvious that achieving the optimum water impact configuration when
engine thrust is available (actually setting a Flight Path Angle of -0.5° on the
FCU), is more easily achievable.
However with a loss of engine thrust, as in Flight 1549, the aircraft energy
management significantly increases the pilot workload. Under these
circumstances, aircraft is still able to reach the optimum water impact
configuration, but this is a demanding task which requires time and
significant pilot focus. Typically, the flare initiation height will be critical to
the achievement of the optimum water entry conditions.
As an aside there is a reason the QRH and ECAM do not direct you to use the Yellow Electric Pump in a Green and Yellow Hyd failure. It will overheat and you will lose it very quickly.
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For the sake of argument, let's assume you switch off the engines (fuel cut-off) and continue to glide at 150 KIAS. How long before your hyd pressure drops below say 2000 PSI (without extending the RAT and engines windmilling somewhere between idle and 0 RPM)?
I guess it would depend on the number and degree of flight control deflections, but could you glide for say a minute and have enough pressure to flare? Or even extend flaps a bit?
Just like in a car you have 4-5 full brake pedal deflections before accu pressure is gone once you turn off the engine...
Just wondering...
I guess it would depend on the number and degree of flight control deflections, but could you glide for say a minute and have enough pressure to flare? Or even extend flaps a bit?
Just like in a car you have 4-5 full brake pedal deflections before accu pressure is gone once you turn off the engine...
Just wondering...
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Aircraft did not fail … it just refused.
Their job is to deliver Alpha Max and certainly not to prevent to benefit from it.
Why would you stall at Alpha Max ... !?
Airbus would not be too happy to hear that one.
Do you remember what is Alpha Max ?
See how you can benefit from it on the LIFT side.
Just what you need, WHEN you need it : Flare time !
Originally Posted by Ashling
Certainly not enough to significantly reduce the rate of descent but it was at significant risk of stall or would have been had it not been for the fly by wire protections that did their job.
Why would you stall at Alpha Max ... !?
Airbus would not be too happy to hear that one.
Do you remember what is Alpha Max ?
See how you can benefit from it on the LIFT side.
Just what you need, WHEN you need it : Flare time !
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There is a difference between theory and practise which is why Alpha Prot damps the input, if required, to prevent overshooting the max value.
You cannot flare an aircraft with the energy levels they had, at least not in any meaningfull way, but you can most definately stall it. That would be catastrophic in this instance. It is not worth the risk which is why the aircraft protected them but at the same time gave them the maximum performance it could.
You asked for an explanation, its all in Airbus's submission and that of the BEA at the end of the NSTB report. You clearly could not be bothered to read those prior to your last post or you refuse to accept that phugoids exist and need to be mitigated against. You do not know better thsn the NTSB (who did not criticse the aircraft or its FBW) or the BEA and you definately do not know the aerodynamic qualities of the aircraft better than the manufacturer.
You cannot flare an aircraft with the energy levels they had, at least not in any meaningfull way, but you can most definately stall it. That would be catastrophic in this instance. It is not worth the risk which is why the aircraft protected them but at the same time gave them the maximum performance it could.
You asked for an explanation, its all in Airbus's submission and that of the BEA at the end of the NSTB report. You clearly could not be bothered to read those prior to your last post or you refuse to accept that phugoids exist and need to be mitigated against. You do not know better thsn the NTSB (who did not criticse the aircraft or its FBW) or the BEA and you definately do not know the aerodynamic qualities of the aircraft better than the manufacturer.
Last edited by Ashling; 1st Oct 2011 at 09:04.
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APU
IFLY_INDIGO how come the airplane was in normal law after dual engine failure? FCOM says that if flight control computers detect G+Y hyd failure, it goes into alternate law. isn't it?
The NTSB concludes that, despite being unable to complete the Engine Dual Failure checklist, the captain started the APU, which improved the outcome of the ditching by ensuring that a primary source of electrical power was available to the airplane and that the airplane remained in normal law and maintained the flight envelope protections, one of which protects against a stall.
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There is a difference between theory and practise which is why Alpha Prot damps the input, if required, to prevent overshooting the max value.
How many more protections are you ready to make up on this aircraft ?
Alpha Max is not already enough 3 degrees short of Alpha Stall. Do you need another Alpha to protect you from approaching Alpha Max. What is the code name for such Alpha ?
Does Alpha Phugoid look nice ?
Appendix D had been read for a long time.
I would not have missed it for anything :
Despite what pretend Mister Langewiesche or the BEA in the Appendix D, I believe Sully would have obtained a better touchdown on his own without the protections interfering with his experience.
Sully would not have got a single of those phugoid oscillations by being allowed to raise the nose on the flare.
Not at that altitude.
Not in that time frame.
Better attitude Lower RoD just positive stuff.
Originally Posted by Appendix D page 6
Furthermore, it is not certain that, without the phugoid oscillation damping function, it would have been possible to meet all the recommended parameters.
Do you think they would only have tested without that POD function ?
Not a chance, too proud to have to admit that flaring in Direct Law may have been as good as flaring in their complex Normal Law with the indispensable magical Phugoid Oscillation Damping function.
Some pretend that computerized aircrafts are less complex ...
Ashling, would you provide the FCOM's references about that Phugoid Oscillation Damping function. I must admit I have probably missed it ... or not ?
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Phugoid oscillations are to do with short term longnitudinal stability in this case. Its another way of explaining why its easy to over control close to the stall and end up in the stall. Ever flown a low speed scissors in air combat ?
There is no Alpha Phugoid, I did not say there was and neither do the BEA or Airbus. Kindly refrain from misrepresenting what others say.
You very sarcasticaly say "indepensable" "magical" when referring to the aircrafts protections. Did you design it?, did you test it? No, thought not yet you suggest you know better than those who did.
The NTSB criticised Airbus for not fully explaining the Alpha Prot function in the FCOM and in training BUT THEY DID NOT CRITICISE THE PERFORMANCE IT GAVE ON THE DAY.
The jet was at 150,000 lbs (68k), 750 Fpm Rod and almost 25 kts !! below the speed for the configuration they were in. That is a bad bad place to try to flare from. To put that in context its the equivelant of trying to flare a jet close to max weight from 20 - 25 kts below Vref without power. You seem to say that you can flare effectively from this position and then accuse me of not understanding what a flare means. Unbelievable. Makes me wonder if you are even a pilot.
Your contention seems to be to free the pilot up to fly right to the stall, for what benefit ? A small reduction in rate of descent at best. At what risk ? A stall leading to catastrophy. The risk reward trade is all wrong and obviously so. You cannot risk a stall in a ditching and if you think commercial pilots are able to finnesse their handling, without prior practise, to do this then you are a bigger fool than I take you for.
You are hell bent on denegrating Airbus when it was Airbus that gave the Captain the care free handling he needed to protect him in those last few crucial moments before impact. You refuse to accept that it was the speed control that prevented the aircraft from being able to flare effectively not the FBW. That protected him.
You have got your focus all wrong.
There is no Alpha Phugoid, I did not say there was and neither do the BEA or Airbus. Kindly refrain from misrepresenting what others say.
You very sarcasticaly say "indepensable" "magical" when referring to the aircrafts protections. Did you design it?, did you test it? No, thought not yet you suggest you know better than those who did.
The NTSB criticised Airbus for not fully explaining the Alpha Prot function in the FCOM and in training BUT THEY DID NOT CRITICISE THE PERFORMANCE IT GAVE ON THE DAY.
The jet was at 150,000 lbs (68k), 750 Fpm Rod and almost 25 kts !! below the speed for the configuration they were in. That is a bad bad place to try to flare from. To put that in context its the equivelant of trying to flare a jet close to max weight from 20 - 25 kts below Vref without power. You seem to say that you can flare effectively from this position and then accuse me of not understanding what a flare means. Unbelievable. Makes me wonder if you are even a pilot.
Your contention seems to be to free the pilot up to fly right to the stall, for what benefit ? A small reduction in rate of descent at best. At what risk ? A stall leading to catastrophy. The risk reward trade is all wrong and obviously so. You cannot risk a stall in a ditching and if you think commercial pilots are able to finnesse their handling, without prior practise, to do this then you are a bigger fool than I take you for.
You are hell bent on denegrating Airbus when it was Airbus that gave the Captain the care free handling he needed to protect him in those last few crucial moments before impact. You refuse to accept that it was the speed control that prevented the aircraft from being able to flare effectively not the FBW. That protected him.
You have got your focus all wrong.
Last edited by Ashling; 4th Oct 2011 at 19:50.
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Make up your mind Ashling, is it a protection or it is not ?
If it prevents the aircraft to approach Alpha Max it has to be a limitation ...
Now a question for you :
If High AoA protection when activated prevents an aircraft to approach Alpha Max (in this case by 4 degrees), when will we ever reach Alpha Max that Airbus is so proud of ?
NTSB did not criticize Airbus – They just mention that the flight envelope protections did not allow an increase in AoA despite the fact that a margin of 4 degrees existed before reaching Alpha Max, not Alpha Stall, Alpha Max.
Where did I refuse that maintaining more speed to the water would not have helped for the flare ?
Please quote ?
FBW has nothing to do either, don’t be confused.
On your side you’re not ready to consider that a margin of 4 degrees existed in the aerodynamics (NTSB BEA Airbus do not refute this, do they ?) before reaching Alpha Max (which is not Alpha Stall Ashling … just not yet) and therefore the potential to improve the touchdown, as Sully was trying to, was a reality that the flight envelope protections refused to authorize.
You prefer to scare around with a catastrophe scenario … go ahead, but remember, Alpha Max is not Alpha Stall, and if Normal Law is afraid of the phugoid oscillations, just give Direct Law to Sully, I’m sure he will deal OK with them.
Still nothing in the FCOM on the Phugoid Oscillation Damping function … ?
If it prevents the aircraft to approach Alpha Max it has to be a limitation ...
Now a question for you :
If High AoA protection when activated prevents an aircraft to approach Alpha Max (in this case by 4 degrees), when will we ever reach Alpha Max that Airbus is so proud of ?
NTSB did not criticize Airbus – They just mention that the flight envelope protections did not allow an increase in AoA despite the fact that a margin of 4 degrees existed before reaching Alpha Max, not Alpha Stall, Alpha Max.
Originally Posted by Ashling
You refuse to accept that it was the speed control that prevented the aircraft from being able to flare effectively not the FBW.
Please quote ?
FBW has nothing to do either, don’t be confused.
On your side you’re not ready to consider that a margin of 4 degrees existed in the aerodynamics (NTSB BEA Airbus do not refute this, do they ?) before reaching Alpha Max (which is not Alpha Stall Ashling … just not yet) and therefore the potential to improve the touchdown, as Sully was trying to, was a reality that the flight envelope protections refused to authorize.
You prefer to scare around with a catastrophe scenario … go ahead, but remember, Alpha Max is not Alpha Stall, and if Normal Law is afraid of the phugoid oscillations, just give Direct Law to Sully, I’m sure he will deal OK with them.
Still nothing in the FCOM on the Phugoid Oscillation Damping function … ?
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However, when in normal law, regardless of the pilot's input, the computers will prevent excessive maneuvers and exceedance of the safe envelope in pitch and roll axis.Taken from the flight control section of the 320 FCOM
No Flight Crew Manuals mention all the aerodynamic characteristics of an aircraft. In this instance Airbus elaborated by explaining that the FBW reduced the input due to Longnitudinal Damping (Phugoid). Its a technical way of saying that its easy to overcontrol close to the stall which we all should appreciate especially as the aircraft has a pitch up tendancy close to the stall as highlighted in Safety First which you referenced in another thread.
If you seriously think you can flare an aircraft effectively from 25 odd knots below the manoever speed for the weight and config they were in you are deluded.
Further if you think they would have been better off in Direct Law then you are mistaken. In Direct Law the aircraft is free to stall. At the speed they were at the Stall Warning would have been hammering away for quite some time and there is no AoA gauge and no way of knowing how close to the stall you are. Are you really saying that in Direct Law 25 knots slow on the manoever speed with the stall warning blaring away that the right thing to do is pull.
If it had been a Boeing the stall warning would have been blaring away too, allied to the stick shaker and again no AoA indication so no way to know how close you are to the stall and no feel due to the stick shaker.
Sully did not have to worry about that. He was in an Airbus in normal law, thanks to his actions, that allowed him care free handling and gave him maximum performance. He would emphaticaly have been considerably worse off if he had been in alternate or direct law whatever speed profile he flew.
I am well aware Alpha Max is not Alpha stall. There is a margin for a reason. I am also well aware that there was a gap of 3 AoA to Alpha Max when they impacted due to the FBW mitigating Sully's full aft input. Unlike you I am willing to accept that there was a reason that the FBW mitigated this input. Airbus and the BEA have explained that reason and you still insist you know best. I did not design or certify the aircraft and neither did you. You have no basis in fact for denegrating the design or performance of the aircraft because you do not have the data to base that judgement on. You should take note that the NTSB, who have no axe to grind in Airbus's favour, do not criticise the aircraft or its design.
I am not an aerodynamicist but my practical experience is that it is very very easy to overcontrol close to the stall. It takes finesse and current practise to operate in that regime. Any large aggressive inputs will lead to a stall. Thats why you pull to the buffet then squeeze into it in a Max Rate Turn. At low speed the buffet band is even easier to pull through. So if a pilot makes a full aft stick input in that regime then it is no surprise to me that the aircraft mitigates it. Its exactly what I would have expected.
I've contributed more than enough now so for the time being I'll leave it to others to keep this going if they so desire.
No Flight Crew Manuals mention all the aerodynamic characteristics of an aircraft. In this instance Airbus elaborated by explaining that the FBW reduced the input due to Longnitudinal Damping (Phugoid). Its a technical way of saying that its easy to overcontrol close to the stall which we all should appreciate especially as the aircraft has a pitch up tendancy close to the stall as highlighted in Safety First which you referenced in another thread.
If you seriously think you can flare an aircraft effectively from 25 odd knots below the manoever speed for the weight and config they were in you are deluded.
Further if you think they would have been better off in Direct Law then you are mistaken. In Direct Law the aircraft is free to stall. At the speed they were at the Stall Warning would have been hammering away for quite some time and there is no AoA gauge and no way of knowing how close to the stall you are. Are you really saying that in Direct Law 25 knots slow on the manoever speed with the stall warning blaring away that the right thing to do is pull.
If it had been a Boeing the stall warning would have been blaring away too, allied to the stick shaker and again no AoA indication so no way to know how close you are to the stall and no feel due to the stick shaker.
Sully did not have to worry about that. He was in an Airbus in normal law, thanks to his actions, that allowed him care free handling and gave him maximum performance. He would emphaticaly have been considerably worse off if he had been in alternate or direct law whatever speed profile he flew.
I am well aware Alpha Max is not Alpha stall. There is a margin for a reason. I am also well aware that there was a gap of 3 AoA to Alpha Max when they impacted due to the FBW mitigating Sully's full aft input. Unlike you I am willing to accept that there was a reason that the FBW mitigated this input. Airbus and the BEA have explained that reason and you still insist you know best. I did not design or certify the aircraft and neither did you. You have no basis in fact for denegrating the design or performance of the aircraft because you do not have the data to base that judgement on. You should take note that the NTSB, who have no axe to grind in Airbus's favour, do not criticise the aircraft or its design.
I am not an aerodynamicist but my practical experience is that it is very very easy to overcontrol close to the stall. It takes finesse and current practise to operate in that regime. Any large aggressive inputs will lead to a stall. Thats why you pull to the buffet then squeeze into it in a Max Rate Turn. At low speed the buffet band is even easier to pull through. So if a pilot makes a full aft stick input in that regime then it is no surprise to me that the aircraft mitigates it. Its exactly what I would have expected.
I've contributed more than enough now so for the time being I'll leave it to others to keep this going if they so desire.
Last edited by Ashling; 6th Oct 2011 at 11:54.
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fly-by-wire
hi there,
Need your help.i am a young commercial pilot and i just got my licence recently.i am preparing for an interview with a certain airline.from my understanding they will ask me a few questions about how "fly-by-wire" works and i havnt the slightest clue.if u could be so kind as to take a few minutes and just briefly explain to me how it works,i would be forever grateful to you.
thanks in advance
Need your help.i am a young commercial pilot and i just got my licence recently.i am preparing for an interview with a certain airline.from my understanding they will ask me a few questions about how "fly-by-wire" works and i havnt the slightest clue.if u could be so kind as to take a few minutes and just briefly explain to me how it works,i would be forever grateful to you.
thanks in advance
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However, when in normal law, regardless of the pilot's input, the computers will prevent excessive maneuvers and exceedance of the safe envelope in pitch and roll axis.Taken from the flight control section of the 320 FCOM
- Yes - Alpha Max is part of the safe envelope in pitch.
- Yes - The computers will prevent exceedance of Alpha Max, not exceedance of (Alpha Max minus 4 degrees).
I am well aware Alpha Max is not Alpha stall. There is a margin for a reason.
If it had been a Boeing the stall warning would have been blaring away too, allied to the stick shaker and again no AoA indication so no way to know how close you are to the stall and no feel due to the stick shaker.
Anyway IIRC a few procedures in the Boeing recommend to even go to the stick shaker if necessary. Is it because the Danger to stall is so great Ashling ?
Aslo, again IIRC, the Pitch Limit Indicator on Boeing shows the AoA margin to the stick shaker.
Question still stands Ashling :
If High AoA protection when activated prevents an aircraft to approach Alpha Max (in this case by 4 degrees), when will we ever reach Alpha Max that Airbus is so proud of ?
