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lightsaber
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Re: EASA Directive Requires Indigo to Block ~30% of A321neo Seats on DEL-IST flight

Thu Sep 19, 2019 4:36 pm

WIederling wrote:
edealinfo wrote:
If it wasn't for the EASA directive, they wouldn't have to limit the number of sold seats. Note that Indigo has been operating the A320neo to Istanbul from late March 2019 and had zero issues until the recent EASA directive which changed everything for them.


Which directive?

The Airbus instigated one that is intended to cope with potential CoG issues?

going over our links it is all about having enough fuel for legally reaching a destination up wind ( rather strong ones currently ).

Ugh.. I don't have a link, but the directive is for only one specific coffin corner of the flight regime. Take off or land quicker (which requires more runway) is a fine solution.

I cannot get excited. Regulators are conservative. EASA looked into the MAX and used the NEO as an example of what the MAX should be and instead found an issue at an extreme condition. Airbus is working a software fix. Annoying, not dramatic.

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Re: A320neo Family 'Excessive Pitch' Issue Thread

Thu Sep 19, 2019 4:39 pm

mrbots wrote:
It really just seems like these 50 and 30 year old mid-capacity, mid-range NBs are just being modified and pushed into capacities and ranges they were never intended for leading to these pitch/trim issues. Though I don't see anyone claiming the A320 is "inherently unstable" like they were throwing around at the Max even though the flight behavior seems fairly similar. They're both at a point they require software intervention at extreme edges of the flight envelope. Though, I will also admit I have no qualms about flying either the Neo or the Max (once ungrounded). Hopefully these issues just teach both manufactures they need more thorough testing during the development phase and these pitch/trim issues don't pop up on future updated models (777X, 787-10, etc.) after EIS.

All new aircraft are intentionally being designed less stable or unstable. It is as you note, a need for more testing.

As an I&T lead, I couldn't possibly be biased...

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Re: EASA Directive Requires Indigo to Block ~30% of A321neo Seats on DEL-IST flight

Thu Sep 19, 2019 4:44 pm

lightsaber wrote:
WIederling wrote:
edealinfo wrote:
If it wasn't for the EASA directive, they wouldn't have to limit the number of sold seats. Note that Indigo has been operating the A320neo to Istanbul from late March 2019 and had zero issues until the recent EASA directive which changed everything for them.


Which directive?

The Airbus instigated one that is intended to cope with potential CoG issues?

going over our links it is all about having enough fuel for legally reaching a destination up wind ( rather strong ones currently ).

Ugh.. I don't have a link, but the directive is for only one specific coffin corner of the flight regime. Take off or land quicker (which requires more runway) is a fine solution.

I cannot get excited. Regulators are conservative. EASA looked into the MAX and used the NEO as an example of what the MAX should be and instead found an issue at an extreme condition. Airbus is working a software fix. Annoying, not dramatic.

Lightsaber

edealinfo presented his case as Indigo has to reduce Payload massively due to this EASA directive.
( while available info indicates insufficient reserve fuel due to head winds while trying for a fuller payload.)
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unrave
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Re: A320neo Family 'Excessive Pitch' Issue Thread

Fri Sep 20, 2019 3:50 am

This article on Forbes states that
(1) The excessive pitch issue affects only planes that have the Space Flex cabin installed
(2) Easyjet has solved this issue by "by modifying its on-board software for loading the aircraft, rather than by blocking seats"

Hopefully Airbus comes out with a permanent software fix soon.

https://www.forbes.com/sites/heatherfar ... fe14593f74
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oldannyboy
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Re: EASA Directive Requires Indigo to Block ~30% of A321neo Seats on DEL-IST flight

Fri Sep 20, 2019 7:39 am

edealinfo wrote:
oldannyboy wrote:
Indian airlines are supposedly only leaving the last cargo hold empty, and no-one is dictating them to block all the seats you are mentioning.... That has nothing to do with the COG issues.


They leave the last cargo section empty because there is no bags to carry for the seats that have been blocked!


Yeah, ok mate. Never mind. It's ok.
 
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Re: Indigo Blocks ~30% of Seats on DEL-IST Flight per EASA Directive to Keep Tail-End of A320/A321neo Relatively Empty

Fri Sep 20, 2019 9:55 am

edealinfo wrote:
Indigo pays a HUGE PENALTY for latest DCGA directive stemming from an EASA directive.

Indigo to leave 15% (29 of the 186) seats on A320 Neo and 29% (49 of the 222) seats on A321 Neo unsold, on the Delhi to Turkey flight!


I seem to recall the directive concerns the A320neo only. As they reduce load on A320 and A321 they quite obviously must have other reasons to lighten the load.

Best regards
Thomas
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Re: Indigo Blocks ~30% of Seats on DEL-IST Flight per EASA Directive to Keep Tail-End of A320/A321neo Relatively Empty

Fri Sep 20, 2019 10:58 am

tommy1808 wrote:
edealinfo wrote:
Indigo pays a HUGE PENALTY for latest DCGA directive stemming from an EASA directive.

Indigo to leave 15% (29 of the 186) seats on A320 Neo and 29% (49 of the 222) seats on A321 Neo unsold, on the Delhi to Turkey flight!


I seem to recall the directive concerns the A320neo only. As they reduce load on A320 and A321 they quite obviously must have other reasons to lighten the load.

Best regards
Thomas

The issue effects both planes- EASA had released a directive regarding the A321neo earlier this summer. But I believe the CoG issue (as in, making sure it stays within acceptable range) is more pronounced on the smaller A320neo. With Indigo’s A321neos being denser than most operators it might be more of an issue with them however. I agree though that this sounds more like dealing with excessive weight restrictions due to winds rather than directly because of the directives.

Granted the biggest surprise of the A320 directive is the loading instructions, which seems to imply that airlines were having issues with the aircraft that did not leak out to press.
Last edited by Polot on Fri Sep 20, 2019 11:04 am, edited 1 time in total.
 
VV
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Re: A320neo Family 'Excessive Pitch' Issue Thread

Fri Sep 20, 2019 11:02 am

In my opinion, the term "excessive" in this context is a little bit excessive.
 
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Re: Indigo Blocks ~30% of Seats on DEL-IST Flight per EASA Directive to Keep Tail-End of A320/A321neo Relatively Empty

Fri Sep 20, 2019 11:52 am

Polot wrote:
tommy1808 wrote:
edealinfo wrote:
Indigo pays a HUGE PENALTY for latest DCGA directive stemming from an EASA directive.

Indigo to leave 15% (29 of the 186) seats on A320 Neo and 29% (49 of the 222) seats on A321 Neo unsold, on the Delhi to Turkey flight!


I seem to recall the directive concerns the A320neo only. As they reduce load on A320 and A321 they quite obviously must have other reasons to lighten the load.

Best regards
Thomas

The issue effects both planes- EASA had released a directive regarding the A321neo earlier this summer. But I believe the CoG issue (as in, making sure it stays within acceptable range) is more pronounced on the smaller A320neo. With Indigo’s A321neos being denser than most operators it might be more of an issue with them however. I agree though that this sounds more like dealing with excessive weight restrictions due to winds rather than directly because of the directives.

Granted the biggest surprise of the A320 directive is the loading instructions, which seems to imply that airlines were having issues with the aircraft that did not leak out to press.


Thank you for the update.

VV wrote:
In my opinion, the term "excessive" in this context is a little bit excessive.


They just go by the definition, pitch exceeds the command, is hence excessive...

best regards
Thomas
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Re: Indigo Blocks ~30% of Seats on DEL-IST Flight per EASA Directive to Keep Tail-End of A320/A321neo Relatively Empty

Fri Sep 20, 2019 1:23 pm

tommy1808 wrote:
....
VV wrote:
In my opinion, the term "excessive" in this context is a little bit excessive.


They just go by the definition, pitch exceeds the command, is hence excessive...

best regards
Thomas


Can you please be more specific on "pitch exceeds the command".

I do not think the pilot commands a specific pitch. So which "command" did you refer to?
 
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Re: Indigo Blocks ~30% of Seats on DEL-IST Flight per EASA Directive to Keep Tail-End of A320/A321neo Relatively Empty

Fri Sep 20, 2019 1:41 pm

VV wrote:
tommy1808 wrote:
....
VV wrote:
In my opinion, the term "excessive" in this context is a little bit excessive.


They just go by the definition, pitch exceeds the command, is hence excessive...

best regards
Thomas


Can you please be more specific on "pitch exceeds the command".

I do not think the pilot commands a specific pitch. So which "command" did you refer to?


The pitch rate the pilot expects to get from a given input.

Best regards
Thomas
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Re: Indigo Blocks ~30% of Seats on DEL-IST Flight per EASA Directive to Keep Tail-End of A320/A321neo Relatively Empty

Fri Sep 20, 2019 1:55 pm

tommy1808 wrote:
VV wrote:
tommy1808 wrote:
....


They just go by the definition, pitch exceeds the command, is hence excessive...

best regards
Thomas


Can you please be more specific on "pitch exceeds the command".

I do not think the pilot commands a specific pitch. So which "command" did you refer to?


The pitch rate the pilot expects to get from a given input.

Best regards
Thomas


Ok.

So we are taking about take-off here and it is more about the pitch rate of the actual aircraft compared to the one used in the flight manual.

So, my question is what the heck happened during the flight tests and pitch rate model validation?

Isn't that exactly the purpose of flight tests?
 
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Re: Indigo Blocks ~30% of Seats on DEL-IST Flight per EASA Directive to Keep Tail-End of A320/A321neo Relatively Empty

Fri Sep 20, 2019 2:07 pm

VV wrote:
So, my question is what the heck happened during the flight tests and pitch rate model validation?

Isn't that exactly the purpose of flight tests?


"The usual". Behavior expected from intrapolating between the adjacent, actually flown, test points does not match observed behavior.

Best regards
Thomas
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Re: Indigo Blocks ~30% of Seats on DEL-IST Flight per EASA Directive to Keep Tail-End of A320/A321neo Relatively Empty

Fri Sep 20, 2019 4:38 pm

tommy1808 wrote:
VV wrote:
So, my question is what the heck happened during the flight tests and pitch rate model validation?

Isn't that exactly the purpose of flight tests?


"The usual". Behavior expected from intrapolating between the adjacent, actually flown, test points does not match observed behavior.

Best regards
Thomas


Okay.

I must deduce from your explanation that the pitch rate "theta dot" is too high, with possible slightly higher tail strike risk
However, if the rate is made slower, wouldn't it increase TOD a little bit?
 
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Re: Indigo Blocks ~30% of Seats on DEL-IST Flight per EASA Directive to Keep Tail-End of A320/A321neo Relatively Empty

Sun Sep 22, 2019 8:42 am

tommy1808 wrote:
VV wrote:
So, my question is what the heck happened during the flight tests and pitch rate model validation?

Isn't that exactly the purpose of flight tests?


"The usual". Behavior expected from intrapolating between the adjacent, actually flown, test points does not match observed behavior.

Best regards
Thomas



I read again your explanations and still haven't fully understood.

Why does the expected behavior between actually tested points not match the observed behavior?

Isn't there a mathematical model representing the aircraft (from flight dynamics perspective)? I understood that flight tests are to validate that model, including for situations outside the flight tested points.

I am now a little bit confused because it could well mean either the result of the flight test is not correct or the model is not correct. Either way it is confusing for me.

Please give me a little bit more information on this.
 
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Re: Indigo Blocks ~30% of Seats on DEL-IST Flight per EASA Directive to Keep Tail-End of A320/A321neo Relatively Empty

Sun Sep 22, 2019 8:51 am

VV wrote:
tommy1808 wrote:
VV wrote:
So, my question is what the heck happened during the flight tests and pitch rate model validation?

Isn't that exactly the purpose of flight tests?


"The usual". Behavior expected from intrapolating between the adjacent, actually flown, test points does not match observed behavior.

Best regards
Thomas



I read again your explanations and still haven't fully understood.

Why does the expected behavior between actually tested points not match the observed behavior?

Isn't there a mathematical model representing the aircraft (from flight dynamics perspective)? I understood that flight tests are to validate that model, including for situations outside the flight tested points.

I am now a little bit confused because it could well mean either the result of the flight test is not correct or the model is not correct. Either way it is confusing for me.

Please give me a little bit more information on this.


confusion is something to be savored!
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Re: EASA Directive Requires Indigo to Block ~30% of A321neo Seats on DEL-IST flight

Sun Sep 22, 2019 4:19 pm

lightsaber wrote:
Regulators are conservative. EASA looked into the MAX and used the NEO as an example of what the MAX should be and instead found an issue at an extreme condition. Airbus is working a software fix. Annoying, not dramatic.

Hmm.

What I've seen written is that Airbus sifted through collected user data and found a potential issue.
( nothing said about Airbus being creative ( we look at those thing anyway ) or reactive ( could MAX issues also be found on A320 )
Airbus then raised the flag to EASA who then turned it into an official act limiting allowable CoG range for the type
until a software fix is available ( 2020 ).
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Re: Indigo Blocks ~30% of Seats on DEL-IST Flight per EASA Directive to Keep Tail-End of A320/A321neo Relatively Empty

Mon Sep 23, 2019 4:50 am

VV wrote:
Isn't there a mathematical model representing the aircraft (from flight dynamics perspective)? I understood that flight tests are to validate that model, including for situations outside the flight tested points.

I am now a little bit confused because it could well mean either the result of the flight test is not correct or the model is not correct. Either way it is confusing for me.

Please give me a little bit more information on this.


models are always statistical in the sense that you are x.y% sure, whatever sigma authorities want to see, that it represent the actual behavior and so and so % sure that it won´t diverge further than z from the actual aircraft. You fly enough test points to match the number of data points you need to have the required sigma in your model.
All test flight data you get after certification is still compared to and integrated into the model you are using, and if you find that it handles differently you update the crews flying it. Without having read up on the details on this case, i would assume something along the lines of some chaotic aerodynamic interactions just adding up to a relevant difference between model and reality, with an onset rate of the effect that exceeds the fly by wire systems ability to hide.
If memory serves me correctly this excessive pitch issue was discovered by simulation, so the extra data points since certification had improved the model enough to see it.

best regards
Thomas
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Re: Indigo Blocks ~30% of Seats on DEL-IST Flight per EASA Directive to Keep Tail-End of A320/A321neo Relatively Empty

Mon Sep 23, 2019 6:07 am

tommy1808 wrote:
models are always statistical in the sense that you are x.y% sure, whatever sigma authorities want to see, that it represent the actual behavior and so and so % sure that it won´t diverge further than z from the actual aircraft. You fly enough test points to match the number of data points you need to have the required sigma in your model.
All test flight data you get after certification is still compared to and integrated into the model you are using, and if you find that it handles differently you update the crews flying it. Without having read up on the details on this case, i would assume something along the lines of some chaotic aerodynamic interactions just adding up to a relevant difference between model and reality, with an onset rate of the effect that exceeds the fly by wire systems ability to hide.
If memory serves me correctly this excessive pitch issue was discovered by simulation, so the extra data points since certification had improved the model enough to see it.

best regards
Thomas


Reading your explanation above, I have to deduce that the issue is during a relatively dynamic situation like during take-off rotation or during flare at landing.

I am still a little bit confused.

I can understand a kind of scatter in the flight test data, but usually the test is repeated until you have a confidence level that is good enough. It is unlikely there is a "chaotic" aerodynamic interaction during rotation and/or flare. It should have been noticed during flight tests if there are flow separation or highly unsteady aerodynamic situation.

Do you suspect engine-pylon induced separation on the wing?

It is also possible that the mathematical model is highly simplified, perhaps linearly piecewise and this model does not capture the right behavior of the aircraft. In which case it would be even more interesting because it means the flight test points have not been chosen in the right "location".

So yes, I am still a little bit confused on what really happened.
 
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Re: Indigo Blocks ~30% of Seats on DEL-IST Flight per EASA Directive to Keep Tail-End of A320/A321neo Relatively Empty

Mon Sep 23, 2019 6:32 am

VV wrote:
I can understand a kind of scatter in the flight test data, but usually the test is repeated until you have a confidence level that is good enough. .


99% confidence still means a 1% chance to be off. The rest is too specific for me to address.

best regards
Thomas
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Re: Indigo Blocks ~30% of Seats on DEL-IST Flight per EASA Directive to Keep Tail-End of A320/A321neo Relatively Empty

Mon Sep 23, 2019 6:48 am

tommy1808 wrote:
VV wrote:
I can understand a kind of scatter in the flight test data, but usually the test is repeated until you have a confidence level that is good enough. .


99% confidence still means a 1% chance to be off. The rest is too specific for me to address.

best regards
Thomas



I agree that even 100% of confidence on the flight test data points would not be good enough if the mathematical model is overly simplified in a way that it does not allow to capture the aircraft behavior properly.

If I understand you comment, it means that there could be two possible actions:
  • adjust the flight control laws
  • correct the aircraft flight manual

The time needed to do such changes would take about 16 months or more.
 
WIederling
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Re: Indigo Blocks ~30% of Seats on DEL-IST Flight per EASA Directive to Keep Tail-End of A320/A321neo Relatively Empty

Mon Sep 23, 2019 6:20 pm

VV wrote:
The time needed to do such changes would take about 16 months or more.


Software upgrade is destined for H2 2020 afaik.
( no idea where I saw that printed )
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Re: Indigo Blocks ~30% of Seats on DEL-IST Flight per EASA Directive to Keep Tail-End of A320/A321neo Relatively Empty

Tue Sep 24, 2019 6:27 am

WIederling wrote:
VV wrote:
The time needed to do such changes would take about 16 months or more.


Software upgrade is destined for H2 2020 afaik.
( no idea where I saw that printed )


Perhaps it is the plan, but considering the extent of the task, in my opinion it would be introduced into the fleet only in 2021.
 
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Re: Indigo Blocks ~30% of Seats on DEL-IST Flight per EASA Directive to Keep Tail-End of A320/A321neo Relatively Empty

Tue Sep 24, 2019 7:04 am

VV wrote:
Perhaps it is the plan, but considering the extent of the task, in my opinion it would be introduced into the fleet only in 2021.

Will the update be applied for old aircraft as well?
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Re: A320neo Family 'Excessive Pitch' Issue Thread

Tue Sep 24, 2019 7:21 am

The articles linked in the beginning state that the excessive pitch occurs during go around procedures, so nose up input plus spooling up the engines to maximum thrust. Also it states that the pitch exceeds the limits of the intended envelope. So in my opinion, the software to protect from excessive pitch, is not correcting enough or fast enough if the air frame rotates to much in this situations. The software update therefore will not be a change in actual software but a change in parameters (or add a new parameters set for cabin flex layout) to update the pitch protection. This parameters are now tested, verified and in 2020 they hopefully will be certified.
 
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Re: Indigo Blocks ~30% of Seats on DEL-IST Flight per EASA Directive to Keep Tail-End of A320/A321neo Relatively Empty

Tue Sep 24, 2019 8:26 pm

unrave wrote:
VV wrote:
Perhaps it is the plan, but considering the extent of the task, in my opinion it would be introduced into the fleet only in 2021.

Will the update be applied for old aircraft as well?


I expect it to be mandatory for eligible airframes. ?
i.e. all NEO ever produced.
it will be part of a regular update for existing frames.

afaics : VV is producing lots of FUD. :-)))
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Re: A320neo Family 'Excessive Pitch' Issue Thread

Tue Sep 24, 2019 8:40 pm

As we don't see any A321's flying themselves into the ground, or pilots reporting fighting with their aircraft to prevent such events from happening it would seem attempts to draw false equivalence in this case serves little purpose. Just sayin'.


THIS!... so the division between Boeing and Airbus fans continues
 
clipperlondon
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Re: A321neo operators alerted over 'excessive pitch' anomaly

Tue Sep 24, 2019 8:49 pm

ukoverlander wrote:
As we don't see any A321's flying themselves into the ground, or pilots reporting fighting with their aircraft to prevent such events from happening it would seem attempts to draw false equivalence in this case serves little purpose. Just sayin'.


Amen to that mate.
 
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Re: A320neo Family 'Excessive Pitch' Issue Thread

Wed Sep 25, 2019 1:49 am

Taking 30-40 plus year old designs and milking and squeezing every sq inch for profit is really what has made this situation. All along, the focus has been on lighter material and more fuel efficient engines. The old times were far better. You had a new design for every category of seat capacities, ranging from a DC9-30 for 80 seats to B727 for 150 seats to A300 for 250 seats and the good old Tristars and DC10s for 300 and beyond, all the way till B747. And every plane had its unique personality. Nowadays they all are the same old boring 2-engine buses trundling along at the golden figure of Mach decimal 82.
 
VV
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Re: A320neo Family 'Excessive Pitch' Issue Thread

Wed Sep 25, 2019 6:06 am

FluidFlow wrote:
The articles linked in the beginning state that the excessive pitch occurs during go around procedures, so nose up input plus spooling up the engines to maximum thrust. Also it states that the pitch exceeds the limits of the intended envelope. So in my opinion, the software to protect from excessive pitch, is not correcting enough or fast enough if the air frame rotates to much in this situations. The software update therefore will not be a change in actual software but a change in parameters (or add a new parameters set for cabin flex layout) to update the pitch protection. This parameters are now tested, verified and in 2020 they hopefully will be certified.


Ok.

So it is not at take off, but only at go-around when the aircraft is light.
So it is not a big deal.

It is still curious they didn't catch it earlier.
 
FluidFlow
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Re: A320neo Family 'Excessive Pitch' Issue Thread

Wed Sep 25, 2019 6:49 am

VV wrote:
FluidFlow wrote:
The articles linked in the beginning state that the excessive pitch occurs during go around procedures, so nose up input plus spooling up the engines to maximum thrust. Also it states that the pitch exceeds the limits of the intended envelope. So in my opinion, the software to protect from excessive pitch, is not correcting enough or fast enough if the air frame rotates to much in this situations. The software update therefore will not be a change in actual software but a change in parameters (or add a new parameters set for cabin flex layout) to update the pitch protection. This parameters are now tested, verified and in 2020 they hopefully will be certified.


Ok.

So it is not at take off, but only at go-around when the aircraft is light.
So it is not a big deal.

It is still curious they didn't catch it earlier.


I would not say that it is not a big deal, the last thing you want is unexpected flight behavior in a go around, when there is already higher than normal workload on the pilot. Thats why the limitations are needed till the software is updated.

Why they did not catch it? That would be good to know for future aircraft and software development.
 
VV
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Re: A320neo Family 'Excessive Pitch' Issue Thread

Wed Sep 25, 2019 7:04 am

FluidFlow wrote:
VV wrote:
FluidFlow wrote:
The articles linked in the beginning state that the excessive pitch occurs during go around procedures, so nose up input plus spooling up the engines to maximum thrust. Also it states that the pitch exceeds the limits of the intended envelope. So in my opinion, the software to protect from excessive pitch, is not correcting enough or fast enough if the air frame rotates to much in this situations. The software update therefore will not be a change in actual software but a change in parameters (or add a new parameters set for cabin flex layout) to update the pitch protection. This parameters are now tested, verified and in 2020 they hopefully will be certified.


Ok.

So it is not at take off, but only at go-around when the aircraft is light.
So it is not a big deal.

It is still curious they didn't catch it earlier.


I would not say that it is not a big deal, the last thing you want is unexpected flight behavior in a go around, when there is already higher than normal workload on the pilot. Thats why the limitations are needed till the software is updated.

Why they did not catch it? That would be good to know for future aircraft and software development.


I still do not understand why a high pitch should be a problem. Isn't alpha more meaningful?

I guess the thrust over weight ratio during the said go-around is quite high and the pitch attitude is only the resulting of the high climb rate. Isn't it just because the flight path is steep?

Is it more about the fact the pilot might not be able to "see" the horizon?

The situation should be the same for all aircraft. High thrust over weight ratio combined with high lift devices is not exceptional, especially for long-range aircraft during go around.

Anyway, I do not know much about it and that's why ask a lot of questions. A high pitch should not be a concern unless the response from the pilot is not appropriate. After all the pilot is the last defense to avoid an incident or accident.
 
WIederling
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Re: A320neo Family 'Excessive Pitch' Issue Thread

Wed Sep 25, 2019 7:12 am

FluidFlow wrote:
Why they did not catch it? That would be good to know for future aircraft and software development.


What I haven't seen mentioned is by how much pitch is exceeded and in what kind of special conditions.

Space Flex changes mass distribution but it also changes the moment of inertia
and thus has impact on initiating/stopping rotation.
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FluidFlow
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Re: A320neo Family 'Excessive Pitch' Issue Thread

Wed Sep 25, 2019 8:03 am

WIederling wrote:
FluidFlow wrote:
Why they did not catch it? That would be good to know for future aircraft and software development.


What I haven't seen mentioned is by how much pitch is exceeded and in what kind of special conditions.

Space Flex changes mass distribution but it also changes the moment of inertia
and thus has impact on initiating/stopping rotation.


How much exceeded I could not tell either, never saw this but the condition is given: It occurs when the aircraft is in flare mode.

@ VV

If pitch becomes to big, or too high too fast, it could possibly lead to a stall. It takes time to spool up the engines and develop maximum thrust. If the pitch becomes too high before the thrust is there, airspeed will drop significantly and that is not good. Also it could lead to over corrections by the pilot due to unexpected high pitch.
 
VV
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Re: A320neo Family 'Excessive Pitch' Issue Thread

Wed Sep 25, 2019 11:22 am

FluidFlow wrote:
WIederling wrote:
FluidFlow wrote:
Why they did not catch it? That would be good to know for future aircraft and software development.


What I haven't seen mentioned is by how much pitch is exceeded and in what kind of special conditions.

Space Flex changes mass distribution but it also changes the moment of inertia
and thus has impact on initiating/stopping rotation.


How much exceeded I could not tell either, never saw this but the condition is given: It occurs when the aircraft is in flare mode.

@ VV

If pitch becomes to big, or too high too fast, it could possibly lead to a stall. It takes time to spool up the engines and develop maximum thrust. If the pitch becomes too high before the thrust is there, airspeed will drop significantly and that is not good. Also it could lead to over corrections by the pilot due to unexpected high pitch.


I do not necessarily agree high pitch is the important parameter for stall. Angle of attack is.

If I understand well, pitch is relative to ground reference whereas angle of attack is relative to the aerodynamic reference.

Therefore a high pitch (theta) during a high climb gradient (gamma) is not necessarily a stall problem as long as the angle of attack (alpha) is below the alpha max.

Perhaps you can explain better your position?
 
FluidFlow
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Re: A320neo Family 'Excessive Pitch' Issue Thread

Wed Sep 25, 2019 11:42 am

VV wrote:
FluidFlow wrote:
WIederling wrote:

What I haven't seen mentioned is by how much pitch is exceeded and in what kind of special conditions.

Space Flex changes mass distribution but it also changes the moment of inertia
and thus has impact on initiating/stopping rotation.


How much exceeded I could not tell either, never saw this but the condition is given: It occurs when the aircraft is in flare mode.

@ VV

If pitch becomes to big, or too high too fast, it could possibly lead to a stall. It takes time to spool up the engines and develop maximum thrust. If the pitch becomes too high before the thrust is there, airspeed will drop significantly and that is not good. Also it could lead to over corrections by the pilot due to unexpected high pitch.


I do not necessarily agree high pitch is the important parameter for stall. Angle of attack is.

If I understand well, pitch is relative to ground reference whereas angle of attack is relative to the aerodynamic reference.

Therefore a high pitch (theta) during a high climb gradient (gamma) is not necessarily a stall problem as long as the angle of attack (alpha) is below the alpha max.

Perhaps you can explain better your position?


I think in this case it is semantics: An aircraft pitches upwards, so it increases its pitch and AoA, it does not angle up. You could write it increases its angle of attack but that also increases pitch during the flare (pitch is in general really low in this phase, I think 0-10)°. Anyway during flare the aircraft is really slow and engines in general in idle. In this stage of the flight increasing pitch will lead to a reduction in airspeed. Yes AoA is one possible indicator when a stall sets in, this AoA is dynamic and a function of airspeed. If you keep your airspeed and increase your AoA you eventually stall. If you keep your AoA constant and slow down you eventually stall. So if you pitch up and your airspeed drops quick you stall your aircraft when the alpha (pitch) protection does not kick in fast enough because it cant reduce your pitch input.

So pitch up --> airspeed reduced --> AoA increases --> max AoA (Stall angle) reduces --> now if the pitch protection does not kick in fast enough the actual AoA exceeds the max AoA --> Stall. Now if you are slow enough you can stall your aircraft at AoA=0.

This means that during this stage of the flight if you need to go around your pitch up has to be limited controlled by the actual airspeed and the predicted change of airspeed. It probably takes a buffer value into account to how fast the engines produce enough thrust to guarantee climb at a certain pitch and limits the pitch up (rotation) during the spooling up time. This guarantees that at no point during the go around the actual AoA exceeds the max AoA and therefore stalls.
 
VV
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Re: A320neo Family 'Excessive Pitch' Issue Thread

Wed Sep 25, 2019 5:12 pm

FluidFlow wrote:
VV wrote:
...

I do not necessarily agree high pitch is the important parameter for stall. Angle of attack is.

If I understand well, pitch is relative to ground reference whereas angle of attack is relative to the aerodynamic reference.

Therefore a high pitch (theta) during a high climb gradient (gamma) is not necessarily a stall problem as long as the angle of attack (alpha) is below the alpha max.

Perhaps you can explain better your position?


I think in this case it is semantics: An aircraft pitches upwards, so it increases its pitch and AoA, it does not angle up. You could write it increases its angle of attack but that also increases pitch during the flare (pitch is in general really low in this phase, I think 0-10)°. Anyway during flare the aircraft is really slow and engines in general in idle. In this stage of the flight increasing pitch will lead to a reduction in airspeed. Yes AoA is one possible indicator when a stall sets in, this AoA is dynamic and a function of airspeed. If you keep your airspeed and increase your AoA you eventually stall. If you keep your AoA constant and slow down you eventually stall. So if you pitch up and your airspeed drops quick you stall your aircraft when the alpha (pitch) protection does not kick in fast enough because it cant reduce your pitch input.

So pitch up --> airspeed reduced --> AoA increases --> max AoA (Stall angle) reduces --> now if the pitch protection does not kick in fast enough the actual AoA exceeds the max AoA --> Stall. Now if you are slow enough you can stall your aircraft at AoA=0.

This means that during this stage of the flight if you need to go around your pitch up has to be limited controlled by the actual airspeed and the predicted change of airspeed. It probably takes a buffer value into account to how fast the engines produce enough thrust to guarantee climb at a certain pitch and limits the pitch up (rotation) during the spooling up time. This guarantees that at no point during the go around the actual AoA exceeds the max AoA and therefore stalls.


I do not think it is a question of semantics.

The only thing that should trigger a stall is probably excessive AoA (alpha).

So if your reasoning is true that pitch is AoA then when the AoA reach a certain threshold the AoA warning will be triggered, it may be the stick shaker or stick pusher or I do not what. In that case we should then talk about AoA excess and not "excessive" pitch. Even then I know that the AoA protection (stick shaker or pusher or whatever) is far from stall and there are several margins, including the maneuver margin.

One comment above mentions the issue is during go-around and I just do not see any stall risk because you have the AoA protection (stick shaker or pusher or whatever). In addition there is an envelope protection too. It should not stall even if the pilot pulls the stick like mad.

If I understand well your logic, with which I do not fully agree, the excessive pitch is a concern during flight phases close to the ground because the pitch attitude might cause a tail strike and not stall.

So no, it is still unclear what the issue is and if there is an issue I do not understand why it is called "excessive pitch" unless it is close to the ground.

It would be nice if someone can enlighten properly us on this.
 
WPIAeroGuy
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Re: A320neo Family 'Excessive Pitch' Issue Thread

Wed Sep 25, 2019 9:41 pm

FluidFlow wrote:
VV wrote:
FluidFlow wrote:

How much exceeded I could not tell either, never saw this but the condition is given: It occurs when the aircraft is in flare mode.

@ VV

If pitch becomes to big, or too high too fast, it could possibly lead to a stall. It takes time to spool up the engines and develop maximum thrust. If the pitch becomes too high before the thrust is there, airspeed will drop significantly and that is not good. Also it could lead to over corrections by the pilot due to unexpected high pitch.


I do not necessarily agree high pitch is the important parameter for stall. Angle of attack is.

If I understand well, pitch is relative to ground reference whereas angle of attack is relative to the aerodynamic reference.

Therefore a high pitch (theta) during a high climb gradient (gamma) is not necessarily a stall problem as long as the angle of attack (alpha) is below the alpha max.

Perhaps you can explain better your position?


I think in this case it is semantics: An aircraft pitches upwards, so it increases its pitch and AoA, it does not angle up. You could write it increases its angle of attack but that also increases pitch during the flare (pitch is in general really low in this phase, I think 0-10)°. Anyway during flare the aircraft is really slow and engines in general in idle. In this stage of the flight increasing pitch will lead to a reduction in airspeed. Yes AoA is one possible indicator when a stall sets in, this AoA is dynamic and a function of airspeed. If you keep your airspeed and increase your AoA you eventually stall. If you keep your AoA constant and slow down you eventually stall. So if you pitch up and your airspeed drops quick you stall your aircraft when the alpha (pitch) protection does not kick in fast enough because it cant reduce your pitch input.

So pitch up --> airspeed reduced --> AoA increases --> max AoA (Stall angle) reduces --> now if the pitch protection does not kick in fast enough the actual AoA exceeds the max AoA --> Stall. Now if you are slow enough you can stall your aircraft at AoA=0.

This means that during this stage of the flight if you need to go around your pitch up has to be limited controlled by the actual airspeed and the predicted change of airspeed. It probably takes a buffer value into account to how fast the engines produce enough thrust to guarantee climb at a certain pitch and limits the pitch up (rotation) during the spooling up time. This guarantees that at no point during the go around the actual AoA exceeds the max AoA and therefore stalls.


Stall is dependent on AoA and AoA alone. Speed does not matter. If you reduce speed and maintain AoA your lift will decrease and you’ll no longer be in 1g flight.
-WPIAeroGuy
 
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Re: A320neo Family 'Excessive Pitch' Issue Thread

Thu Sep 26, 2019 12:01 am

WPIAeroGuy wrote:
FluidFlow wrote:
VV wrote:

I do not necessarily agree high pitch is the important parameter for stall. Angle of attack is.

If I understand well, pitch is relative to ground reference whereas angle of attack is relative to the aerodynamic reference.

Therefore a high pitch (theta) during a high climb gradient (gamma) is not necessarily a stall problem as long as the angle of attack (alpha) is below the alpha max.

Perhaps you can explain better your position?


I think in this case it is semantics: An aircraft pitches upwards, so it increases its pitch and AoA, it does not angle up. You could write it increases its angle of attack but that also increases pitch during the flare (pitch is in general really low in this phase, I think 0-10)°. Anyway during flare the aircraft is really slow and engines in general in idle. In this stage of the flight increasing pitch will lead to a reduction in airspeed. Yes AoA is one possible indicator when a stall sets in, this AoA is dynamic and a function of airspeed. If you keep your airspeed and increase your AoA you eventually stall. If you keep your AoA constant and slow down you eventually stall. So if you pitch up and your airspeed drops quick you stall your aircraft when the alpha (pitch) protection does not kick in fast enough because it cant reduce your pitch input.

So pitch up --> airspeed reduced --> AoA increases --> max AoA (Stall angle) reduces --> now if the pitch protection does not kick in fast enough the actual AoA exceeds the max AoA --> Stall. Now if you are slow enough you can stall your aircraft at AoA=0.

This means that during this stage of the flight if you need to go around your pitch up has to be limited controlled by the actual airspeed and the predicted change of airspeed. It probably takes a buffer value into account to how fast the engines produce enough thrust to guarantee climb at a certain pitch and limits the pitch up (rotation) during the spooling up time. This guarantees that at no point during the go around the actual AoA exceeds the max AoA and therefore stalls.


Stall is dependent on AoA and AoA alone. Speed does not matter. If you reduce speed and maintain AoA your lift will decrease and you’ll no longer be in 1g flight.

I do think there is a bit of talking past each other. Yes, speed has a 2nd order impact on stall (reducing speed reduces the local Reynolds number which shifts stall location a tiny bit).

I think the concern was a sudden loss of lift ehich, since more change AoA is required to acheive the desired lift, one is more likely to experience the scenario. At high speed, controls and habit slow AoA changes reduce to he risk. Heck, the 1.5G limit might be exceeded to take the airframe to stall at speed. ;)

A software upgrade, not a big deal.

Lightsaber
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WPIAeroGuy
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Re: A320neo Family 'Excessive Pitch' Issue Thread

Thu Sep 26, 2019 3:21 am

lightsaber wrote:
WPIAeroGuy wrote:
FluidFlow wrote:

I think in this case it is semantics: An aircraft pitches upwards, so it increases its pitch and AoA, it does not angle up. You could write it increases its angle of attack but that also increases pitch during the flare (pitch is in general really low in this phase, I think 0-10)°. Anyway during flare the aircraft is really slow and engines in general in idle. In this stage of the flight increasing pitch will lead to a reduction in airspeed. Yes AoA is one possible indicator when a stall sets in, this AoA is dynamic and a function of airspeed. If you keep your airspeed and increase your AoA you eventually stall. If you keep your AoA constant and slow down you eventually stall. So if you pitch up and your airspeed drops quick you stall your aircraft when the alpha (pitch) protection does not kick in fast enough because it cant reduce your pitch input.

So pitch up --> airspeed reduced --> AoA increases --> max AoA (Stall angle) reduces --> now if the pitch protection does not kick in fast enough the actual AoA exceeds the max AoA --> Stall. Now if you are slow enough you can stall your aircraft at AoA=0.

This means that during this stage of the flight if you need to go around your pitch up has to be limited controlled by the actual airspeed and the predicted change of airspeed. It probably takes a buffer value into account to how fast the engines produce enough thrust to guarantee climb at a certain pitch and limits the pitch up (rotation) during the spooling up time. This guarantees that at no point during the go around the actual AoA exceeds the max AoA and therefore stalls.


Stall is dependent on AoA and AoA alone. Speed does not matter. If you reduce speed and maintain AoA your lift will decrease and you’ll no longer be in 1g flight.

I do think there is a bit of talking past each other. Yes, speed has a 2nd order impact on stall (reducing speed reduces the local Reynolds number which shifts stall location a tiny bit).

I think the concern was a sudden loss of lift ehich, since more change AoA is required to acheive the desired lift, one is more likely to experience the scenario. At high speed, controls and habit slow AoA changes reduce to he risk. Heck, the 1.5G limit might be exceeded to take the airframe to stall at speed. ;)

A software upgrade, not a big deal.

Lightsaber


Right. During slow speed flight the airplane will naturally be at a higher AoA , and therefore closer to the critical AoA. If a sudden pitch up maneuver is performed, such as a go around, the aircraft pitch rate can exceed the rate at which it can respond to enevelope protection, which could lead to a low altitude stall. That would most certainly be deadly. I’m glad Airbus caught this, but to say this isn’t a big deal is treating it too lightly.
-WPIAeroGuy
 
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Re: A320neo Family 'Excessive Pitch' Issue Thread

Thu Sep 26, 2019 6:01 am

WPIAeroGuy wrote:
lightsaber wrote:
WPIAeroGuy wrote:

Stall is dependent on AoA and AoA alone. Speed does not matter. If you reduce speed and maintain AoA your lift will decrease and you’ll no longer be in 1g flight.

I do think there is a bit of talking past each other. Yes, speed has a 2nd order impact on stall (reducing speed reduces the local Reynolds number which shifts stall location a tiny bit).

I think the concern was a sudden loss of lift ehich, since more change AoA is required to acheive the desired lift, one is more likely to experience the scenario. At high speed, controls and habit slow AoA changes reduce to he risk. Heck, the 1.5G limit might be exceeded to take the airframe to stall at speed. ;)

A software upgrade, not a big deal.

Lightsaber


Right. During slow speed flight the airplane will naturally be at a higher AoA , and therefore closer to the critical AoA. If a sudden pitch up maneuver is performed, such as a go around, the aircraft pitch rate can exceed the rate at which it can respond to enevelope protection, which could lead to a low altitude stall. That would most certainly be deadly. I’m glad Airbus caught this, but to say this isn’t a big deal is treating it too lightly.


Okay.

So you said it is not "not a big deal" (note the double not).

This said, I still do not understand why it is called an excessive pitch when all the latest comments are talking about AoA (or alpha) and a potential stall.

My understanding is that there is a speed margin on top of which you have the maneuver margin and there could potentially be margin for icing too. In general the stall warning (stick shaker of pusher or whatever) is triggered below even the AoA with the above mentioned margins.

Is there any concern even those margins could be "eaten" too?

So far, I understood from the explanations above that the situation can be an issue when the aircraft is light, during low speed/low energy conditions and with the application of TOGA thrust for a go around. Did I understand well?

From what I understand, the issue is not during high rate of climb situation, because the AoA which (I think) is equal to the pitch minus the flight path (Alpha = theta minus gamma) should not be a concern even if the pitch is high.

Please enlighten us more.
 
WPIAeroGuy
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Re: A320neo Family 'Excessive Pitch' Issue Thread

Thu Sep 26, 2019 11:52 am

Stall speeds are just representations of AoA and will vary with aircraft weight, but will be constant at AOA, icing notwithstanding because now you’re changing the airfoil shape.

A light airplane will respond to elevator/pitch input faster (lower moment of inertia) and the application of thrust will create a nose up pitching moment. Combined these could put you in a stall before the envelope protection can respond.

Since this is a dynamic condition, the envelope protection needs to account for the fact that the aircraft will not respond instantaneously. So I’m guessing they’re lowering the threshold in these cases.
-WPIAeroGuy
 
Charlie757
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Re: A320neo Family 'Excessive Pitch' Issue Thread

Wed Oct 02, 2019 12:33 am

Alarming to think this is what cabin densification is doing. The implementation of that galley and toilet layout (spaceflex) which is impossible for crew to work out of, and the addition of 6 extra seats on A320’s is something these aircraft were never designed for (hence the last row having no windows. A good solution would be to get rid of this awful ‘spaceflex’ design
 
1989worstyear
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Re: A320neo Family 'Excessive Pitch' Issue Thread

Wed Oct 02, 2019 12:49 am

acechip wrote:
Taking 30-40 plus year old designs and milking and squeezing every sq inch for profit is really what has made this situation. All along, the focus has been on lighter material and more fuel efficient engines. The old times were far better. You had a new design for every category of seat capacities, ranging from a DC9-30 for 80 seats to B727 for 150 seats to A300 for 250 seats and the good old Tristars and DC10s for 300 and beyond, all the way till B747. And every plane had its unique personality. Nowadays they all are the same old boring 2-engine buses trundling along at the golden figure of Mach decimal 82.


CO2 emission taxes might finally provide the impetus for a new large NB, but right now, "the market" is content with the 1988 Hair Metal Plane with New Engines or the 1968/1997 Frankenplane who has been Maxed-out.
Stuck at age 15 thanks to the certification date of the A320-200 and my parents' decision to postpone having a kid by 3 years. At least there's Dignitas...
 
estorilm
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Re: A320neo Family 'Excessive Pitch' Issue Thread

Wed Oct 02, 2019 3:16 pm

WPIAeroGuy wrote:
lightsaber wrote:
WPIAeroGuy wrote:

Stall is dependent on AoA and AoA alone. Speed does not matter. If you reduce speed and maintain AoA your lift will decrease and you’ll no longer be in 1g flight.

I do think there is a bit of talking past each other. Yes, speed has a 2nd order impact on stall (reducing speed reduces the local Reynolds number which shifts stall location a tiny bit).

I think the concern was a sudden loss of lift ehich, since more change AoA is required to acheive the desired lift, one is more likely to experience the scenario. At high speed, controls and habit slow AoA changes reduce to he risk. Heck, the 1.5G limit might be exceeded to take the airframe to stall at speed. ;)

A software upgrade, not a big deal.

Lightsaber


Right. During slow speed flight the airplane will naturally be at a higher AoA , and therefore closer to the critical AoA. If a sudden pitch up maneuver is performed, such as a go around, the aircraft pitch rate can exceed the rate at which it can respond to enevelope protection, which could lead to a low altitude stall. That would most certainly be deadly. I’m glad Airbus caught this, but to say this isn’t a big deal is treating it too lightly.

I wouldn't say it would most certainly be deadly - as others have eluded to, it requires a number of parameters to be met (including, apparently, a high density spaceflex-fitted NEO, probably at a light weight) while performing a go-around-type maneuver.

Even then, the very core design of the flight envelope protections have significant authority to prevent the situation from becoming deadly. It's likely what was detected simply had more to do with HOW the aircraft was SUPPOSED to perform, which no longer fell within the realm of "normal" as far as A32X handling is concerned (ie. how pilots are trained, what they expect a given input to perform, pitch rates, etc). They need to modify the software so that any variation of cabin layout and type (ie NEO) act the same way for continuity, certification requirements, etc.

Commonality within Airbus products has always been a huge selling point, not just with operators but with pilots as well - I'm sure they're highly motivated to get every element of the NEO to act like any other 320-family AC.

A couple other notes, firstly why it "wasn't caught" - I'd imagine they did extensive flight control and software studies / reprogramming during the NEO design/development program, which was fine (the original NEO cabin layout was not part of the issues being reported here from what I understand). However with the introduction of SpaceFlex cabins later on, I'm assuming the same level of aerodynamic and control studies weren't done.

Another note is the fundamental (and physical) design of the aircraft versus the MAX, since many in this thread continue to draw direct comparisons between the two aircraft. From an aerodynamic point of view (as far as I understand it) we are talking about VERY different issues here. The behavior is similar, but the root cause is not. The engines on the NEO are in a nearly-ideal location, both CG and vertically as far as center-of-thrust is concerned (as opposed to the MAX). This issue w/NEO is from a true CG / weight location problem (again, due to layout). Applying TOGA power at slow speeds (regardless of load/CG) on the MAX will result in (as I understand it) a VERY unexpected pitch-up, even with MCAS the plane still does this, it just "has a system to correct it" kinda. Conversely, on the NEO you need to have the right plane in the right cabin configuration at the right weight to encounter this, and even then there are control systems in place to prevent loss of control - the behavior itself is very undesirable though.

As far as fixes are concerned, the two aircraft are on different planets here. The NEO has all the computing power and redundancy it could ever need - it already calculates and protects AoA issues with triple-redundancy on both CEO/NEO. Beyond the flight protection aspect, the very handling and behavior of the plane is FBW, thus if ANY condition during any regime is undesirable, you can tweak the behavior in the core FBW and not rely on a protection in the first place.

When Airbus implements this fix, technically a SpaceFlex high-density NEO can execute a TOGA/missed at light weight and act EXACTLY like a CEO/NEO. THIS is the definition of grandfathering and commonality as far as I'm concerned. Conversely, regardless of whatever MCAS fix is eventually implemented on the MAX, the plane will always exhibit that pitch behavior. They're just concerned about protection afterwards. That's a different definition of "grandfathering" in my book, but oh well. It should work fine when fixed.

Unfortunately the MAX engineers have NONE of this capability; not the sensors, computers (both number and computing power), nor the ability to alter the actual/core flying characteristics in a flexible way - you simply have add-on things to change how it flies, and it's more of an on/off switch in terms of behavior and certification, ie focus on disconnects over complete redundancy.

That's the difference between the two, and that's also why it's taking Boeing so long to get it fixed (obviously they're also being scrutinized to an extreme degree as well, which is certainly not helping). Apologies for the rant - I've wanted to vent this for a while. :lol:
 
WPIAeroGuy
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Re: A320neo Family 'Excessive Pitch' Issue Thread

Thu Oct 03, 2019 12:10 am

estorilm wrote:
WPIAeroGuy wrote:
lightsaber wrote:
I do think there is a bit of talking past each other. Yes, speed has a 2nd order impact on stall (reducing speed reduces the local Reynolds number which shifts stall location a tiny bit).

I think the concern was a sudden loss of lift ehich, since more change AoA is required to acheive the desired lift, one is more likely to experience the scenario. At high speed, controls and habit slow AoA changes reduce to he risk. Heck, the 1.5G limit might be exceeded to take the airframe to stall at speed. ;)

A software upgrade, not a big deal.

Lightsaber


Right. During slow speed flight the airplane will naturally be at a higher AoA , and therefore closer to the critical AoA. If a sudden pitch up maneuver is performed, such as a go around, the aircraft pitch rate can exceed the rate at which it can respond to enevelope protection, which could lead to a low altitude stall. That would most certainly be deadly. I’m glad Airbus caught this, but to say this isn’t a big deal is treating it too lightly.

I wouldn't say it would most certainly be deadly - as others have eluded to, it requires a number of parameters to be met (including, apparently, a high density spaceflex-fitted NEO, probably at a light weight) while performing a go-around-type maneuver.

Even then, the very core design of the flight envelope protections have significant authority to prevent the situation from becoming deadly. It's likely what was detected simply had more to do with HOW the aircraft was SUPPOSED to perform, which no longer fell within the realm of "normal" as far as A32X handling is concerned (ie. how pilots are trained, what they expect a given input to perform, pitch rates, etc). They need to modify the software so that any variation of cabin layout and type (ie NEO) act the same way for continuity, certification requirements, etc.

Commonality within Airbus products has always been a huge selling point, not just with operators but with pilots as well - I'm sure they're highly motivated to get every element of the NEO to act like any other 320-family AC.

A couple other notes, firstly why it "wasn't caught" - I'd imagine they did extensive flight control and software studies / reprogramming during the NEO design/development program, which was fine (the original NEO cabin layout was not part of the issues being reported here from what I understand). However with the introduction of SpaceFlex cabins later on, I'm assuming the same level of aerodynamic and control studies weren't done.

Another note is the fundamental (and physical) design of the aircraft versus the MAX, since many in this thread continue to draw direct comparisons between the two aircraft. From an aerodynamic point of view (as far as I understand it) we are talking about VERY different issues here. The behavior is similar, but the root cause is not. The engines on the NEO are in a nearly-ideal location, both CG and vertically as far as center-of-thrust is concerned (as opposed to the MAX). This issue w/NEO is from a true CG / weight location problem (again, due to layout). Applying TOGA power at slow speeds (regardless of load/CG) on the MAX will result in (as I understand it) a VERY unexpected pitch-up, even with MCAS the plane still does this, it just "has a system to correct it" kinda. Conversely, on the NEO you need to have the right plane in the right cabin configuration at the right weight to encounter this, and even then there are control systems in place to prevent loss of control - the behavior itself is very undesirable though.

As far as fixes are concerned, the two aircraft are on different planets here. The NEO has all the computing power and redundancy it could ever need - it already calculates and protects AoA issues with triple-redundancy on both CEO/NEO. Beyond the flight protection aspect, the very handling and behavior of the plane is FBW, thus if ANY condition during any regime is undesirable, you can tweak the behavior in the core FBW and not rely on a protection in the first place.

When Airbus implements this fix, technically a SpaceFlex high-density NEO can execute a TOGA/missed at light weight and act EXACTLY like a CEO/NEO. THIS is the definition of grandfathering and commonality as far as I'm concerned. Conversely, regardless of whatever MCAS fix is eventually implemented on the MAX, the plane will always exhibit that pitch behavior. They're just concerned about protection afterwards. That's a different definition of "grandfathering" in my book, but oh well. It should work fine when fixed.

Unfortunately the MAX engineers have NONE of this capability; not the sensors, computers (both number and computing power), nor the ability to alter the actual/core flying characteristics in a flexible way - you simply have add-on things to change how it flies, and it's more of an on/off switch in terms of behavior and certification, ie focus on disconnects over complete redundancy.

That's the difference between the two, and that's also why it's taking Boeing so long to get it fixed (obviously they're also being scrutinized to an extreme degree as well, which is certainly not helping). Apologies for the rant - I've wanted to vent this for a while. :lol:



You don’t think a low altitude, low energy stall in an airliner isn’t deadly?

I think you’re really grasping at straws here. Both aircraft could pitch up under very unique conditions because of a combination of aerodynamic factors. On the Max, the control force gradient could lead the pilot to accidentally pull back into a stall because the stick force gradient didn’t linearly increase. In the airbus, a rapid pitch up could cause the airplane to stall because the envelope protection cannot respond fast enough. The situations are far more similar than you think.
-WPIAeroGuy
 
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Re: A320neo Family 'Excessive Pitch' Issue Thread

Thu Oct 03, 2019 3:27 pm

WPIAeroGuy wrote:
estorilm wrote:
WPIAeroGuy wrote:

Right. During slow speed flight the airplane will naturally be at a higher AoA , and therefore closer to the critical AoA. If a sudden pitch up maneuver is performed, such as a go around, the aircraft pitch rate can exceed the rate at which it can respond to enevelope protection, which could lead to a low altitude stall. That would most certainly be deadly. I’m glad Airbus caught this, but to say this isn’t a big deal is treating it too lightly.

I wouldn't say it would most certainly be deadly - as others have eluded to, it requires a number of parameters to be met (including, apparently, a high density spaceflex-fitted NEO, probably at a light weight) while performing a go-around-type maneuver.

Even then, the very core design of the flight envelope protections have significant authority to prevent the situation from becoming deadly. It's likely what was detected simply had more to do with HOW the aircraft was SUPPOSED to perform, which no longer fell within the realm of "normal" as far as A32X handling is concerned (ie. how pilots are trained, what they expect a given input to perform, pitch rates, etc). They need to modify the software so that any variation of cabin layout and type (ie NEO) act the same way for continuity, certification requirements, etc.

Commonality within Airbus products has always been a huge selling point, not just with operators but with pilots as well - I'm sure they're highly motivated to get every element of the NEO to act like any other 320-family AC.

A couple other notes, firstly why it "wasn't caught" - I'd imagine they did extensive flight control and software studies / reprogramming during the NEO design/development program, which was fine (the original NEO cabin layout was not part of the issues being reported here from what I understand). However with the introduction of SpaceFlex cabins later on, I'm assuming the same level of aerodynamic and control studies weren't done.

Another note is the fundamental (and physical) design of the aircraft versus the MAX, since many in this thread continue to draw direct comparisons between the two aircraft. From an aerodynamic point of view (as far as I understand it) we are talking about VERY different issues here. The behavior is similar, but the root cause is not. The engines on the NEO are in a nearly-ideal location, both CG and vertically as far as center-of-thrust is concerned (as opposed to the MAX). This issue w/NEO is from a true CG / weight location problem (again, due to layout). Applying TOGA power at slow speeds (regardless of load/CG) on the MAX will result in (as I understand it) a VERY unexpected pitch-up, even with MCAS the plane still does this, it just "has a system to correct it" kinda. Conversely, on the NEO you need to have the right plane in the right cabin configuration at the right weight to encounter this, and even then there are control systems in place to prevent loss of control - the behavior itself is very undesirable though.

As far as fixes are concerned, the two aircraft are on different planets here. The NEO has all the computing power and redundancy it could ever need - it already calculates and protects AoA issues with triple-redundancy on both CEO/NEO. Beyond the flight protection aspect, the very handling and behavior of the plane is FBW, thus if ANY condition during any regime is undesirable, you can tweak the behavior in the core FBW and not rely on a protection in the first place.

When Airbus implements this fix, technically a SpaceFlex high-density NEO can execute a TOGA/missed at light weight and act EXACTLY like a CEO/NEO. THIS is the definition of grandfathering and commonality as far as I'm concerned. Conversely, regardless of whatever MCAS fix is eventually implemented on the MAX, the plane will always exhibit that pitch behavior. They're just concerned about protection afterwards. That's a different definition of "grandfathering" in my book, but oh well. It should work fine when fixed.

Unfortunately the MAX engineers have NONE of this capability; not the sensors, computers (both number and computing power), nor the ability to alter the actual/core flying characteristics in a flexible way - you simply have add-on things to change how it flies, and it's more of an on/off switch in terms of behavior and certification, ie focus on disconnects over complete redundancy.

That's the difference between the two, and that's also why it's taking Boeing so long to get it fixed (obviously they're also being scrutinized to an extreme degree as well, which is certainly not helping). Apologies for the rant - I've wanted to vent this for a while. :lol:



You don’t think a low altitude, low energy stall in an airliner isn’t deadly?

I think you’re really grasping at straws here. Both aircraft could pitch up under very unique conditions because of a combination of aerodynamic factors. On the Max, the control force gradient could lead the pilot to accidentally pull back into a stall because the stick force gradient didn’t linearly increase. In the airbus, a rapid pitch up could cause the airplane to stall because the envelope protection cannot respond fast enough. The situations are far more similar than you think.

Stall? What? First of all the alpha floor caught whatever issue we're talking about here - the plane just behaved in a manner which wasn't expected, and they're fixing it. Second, there are additional stall protections including speed which can't be exceeded without correction by the aircraft automatically.

What Airbus stalled here? Who is grasping at straws? I'm mentioning facts, you're just saying why it can't possibly be true. :?
 
WPIAeroGuy
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Re: A320neo Family 'Excessive Pitch' Issue Thread

Thu Oct 03, 2019 4:11 pm

https://leehamnews.com/2019/07/19/bjorn ... -up-issue/

Suggest you re read this. The whole issue was alpha protection was NOT able to prevent this under certain conditions.
-WPIAeroGuy
 
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Polot
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Re: A320neo Family 'Excessive Pitch' Issue Thread

Thu Oct 03, 2019 5:04 pm

Even if alpha protection was fully working and could technically still prevent a stall, not behaving as you expected is pretty dangerous when you are talking about an aircraft <100 ft above the ground. If it is not behaving as expected it may not have the time/altitude to safely recover the aircraft.
 
VV
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Re: A320neo Family 'Excessive Pitch' Issue Thread

Fri Oct 04, 2019 12:43 pm

Okay.

The thread was supposed to be about an "excessive" pitch.
Now the debate is about stall.

My understanding is that the stall warning is triggered well below the AoA when stall occurs. If my memory serves me well you have the 1.13 Vsr margin plus the maneuver margin

Now you are talking about a risk of stall. What the heck?

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