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Trimeresurus
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Those who fly airplanes with FBW flight envelope protections

Sun Nov 29, 2020 10:58 pm

How many times in your career did you actually encounter a situation that you were pushing out of flight envelope and those protections kicked in? What happened afterwards?
 
Flow2706
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Re: Those who fly airplanes with FBW flight envelope protections

Sun Nov 29, 2020 11:18 pm

Got my first job on the A320 in 2012 and was flying it until March this year (until Corona came...). I had an overspeed once while descending into Munich due to wind gradients over the alps, however as the overspeed was minor the autopilot did not disconnect and the high speed protection did not activate. During this event I was still FO - as far as I know the Captain made a tech log entry and he probably filed an ASR as well. After I upgraded to captain I got close to an overspeed again during the cruise but managed to avoid exceeding Mmo by the overspeed prevention procedure (selecting a lower speed, extending speed brakes...). It's quite rare to actually enter those protections in the real aircraft, however its reassuring to know that they are available if they are needed.
 
thepinkmachine
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Re: Those who fly airplanes with FBW flight envelope protections

Sun Nov 29, 2020 11:29 pm

Never... If you get anywhere near the protections, you are waaay out of where you should be
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Starlionblue
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Re: Those who fly airplanes with FBW flight envelope protections

Mon Nov 30, 2020 12:16 am

As Flow2706 says, seeing the protections is very rare. You likely won't in your entire career. And even if you do see protections, it probably won't be anything dramatic like someone blindly letting the speed decay until alpha prot kicks in. It will be events like windshear on final, or mountain waves in cruise.

I've seen overspeed warning on final. Spot of windshear as there was a fair bit of storm activity nearby. We didn't actually go into overspeed protection though.

I've heard of the autopilot very briefly going into alpha protection mode in the cruise due to transient speed decay in areas with mountain wave activity. Nothing serious. Just wait to the speed to get back up, and if it doesn't, descend.
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zeke
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Re: Those who fly airplanes with FBW flight envelope protections

Mon Nov 30, 2020 9:54 am

Trimeresurus wrote:
How many times in your career did you actually encounter a situation that you were pushing out of flight envelope and those protections kicked in? What happened afterwards?


Never during normal flights, see them often enough in the simulator, and they are tested in the air during special validation flights where no passengers are carried.
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CRJockey
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Re: Those who fly airplanes with FBW flight envelope protections

Mon Nov 30, 2020 11:39 am

Trimeresurus wrote:
How many times in your career did you actually encounter a situation that you were pushing out of flight envelope and those protections kicked in? What happened afterwards?


Btw., flight envelope protections don't necessarily correlate with FBW. Stick pusher is arguably envelope protection as well and available on plenty of non-FBW aircraft.
 
Woodreau
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Re: Those who fly airplanes with FBW flight envelope protections

Mon Nov 30, 2020 11:57 am

Coltan 3407 is an example of a flight where the pilot overrode the stick pusher. After receiving the stick shaker. Unfortunately the outcome did not end well for the crew and passengers aboard the plane nor for the people in the building on the ground.
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thepinkmachine
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Re: Those who fly airplanes with FBW flight envelope protections

Mon Nov 30, 2020 12:02 pm

One thing to remember is that stick pushers are there for a reason - if an airplane has one installed, then most likely it has ugly stall characteristics and needed it to meet certification requirements...
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Starlionblue
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Re: Those who fly airplanes with FBW flight envelope protections

Mon Nov 30, 2020 12:49 pm

thepinkmachine wrote:
One thing to remember is that stick pushers are there for a reason - if an airplane has one installed, then most likely it has ugly stall characteristics and needed it to meet certification requirements...


That isn't really the point IMHO. Most swept-wing aircraft have rather unfriendly stall characteristics compared to a straight-winged light prop aircraft. It is a consequence of making the aircraft more efficient aerodynamically.

Stick shakers, alpha prot and similar features are, again IMHO, typically there because you can't fly large aircraft by the seat of your pants. For example, you can't "feel" a stall developing in the same way as you can in a light aircraft.
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thepinkmachine
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Re: Those who fly airplanes with FBW flight envelope protections

Mon Nov 30, 2020 1:09 pm

Starlionblue wrote:
That isn't really the point IMHO. Most swept-wing aircraft have rather unfriendly stall characteristics compared to a straight-winged light prop aircraft. It is a consequence of making the aircraft more efficient aerodynamically.

Stick shakers, alpha prot and similar features are, again IMHO, typically there because you can't fly large aircraft by the seat of your pants. For example, you can't "feel" a stall developing in the same way as you can in a light aircraft.


Not exactly - stick shakers are common in all large airplanes, to provide adequate stall warning. Stick pushers, on the other hand, are mostly installed in T-tailed a/c and planes that have tendency to do stuff like wing drop, pitch up, etc.

Jet transports with "conventional" layout (ie. moderately swept wing, underslung engines, conventional tail, like A320/737/767 etc.) actually have inherently benign stall behaviour - they provide adequate warning (buffeting) and don't have tendency for deep stall etc. They normally do not require a stick pusher and don't have one

T-tails with aft-mounted engines (CRJ, EMB etc., but Also ATR, Q400) on the other hand exhibit a tendency to misbehave in stall and therefore need a stick-pusher.

There's a very good video on jet transport stalling, produced jointly by Airbus and Boeing (!) - it's almost 2 hours long, but I highly recommend it to anyone interested in the topic: https://www.youtube.com/watch?v=HVt6LiDbLos
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SheikhDjibouti
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Re: Those who fly airplanes with FBW flight envelope protections

Mon Nov 30, 2020 1:21 pm

Starlionblue wrote:
thepinkmachine wrote:
One thing to remember is that stick pushers are there for a reason - if an airplane has one installed, then most likely it has ugly stall characteristics and needed it to meet certification requirements...

That isn't really the point IMHO. Most swept-wing aircraft have rather unfriendly stall characteristics compared to a straight-winged light prop aircraft. It is a consequence of making the aircraft more efficient aerodynamically.

Stick shakers, alpha prot and similar features are, again IMHO, typically there because you can't fly large aircraft by the seat of your pants. For example, you can't "feel" a stall developing in the same way as you can in a light aircraft.

But, but, but.... there's a well-known poster on this site who has been assuring us for two years now, that a certain aircraft (no, I absolutely refuse to mention it's name :duck: ) has perfectly benign stall characteristics, just like the Cessna 172 he has flown for most of his 120 hrs. There is even a youtube video supporting his argument.

The identity of this aircraft is not relevant; I might as well ask about the A320 instead. Is there a marked difference between the stall when fully laden (just after take-off) as opposed to final approach at the end of a long day? Or are the stall characteristics identical apart from a more sluggish response to increased power input?
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Starlionblue
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Re: Those who fly airplanes with FBW flight envelope protections

Mon Nov 30, 2020 1:53 pm

thepinkmachine wrote:
Starlionblue wrote:
That isn't really the point IMHO. Most swept-wing aircraft have rather unfriendly stall characteristics compared to a straight-winged light prop aircraft. It is a consequence of making the aircraft more efficient aerodynamically.

Stick shakers, alpha prot and similar features are, again IMHO, typically there because you can't fly large aircraft by the seat of your pants. For example, you can't "feel" a stall developing in the same way as you can in a light aircraft.


Not exactly - stick shakers are common in all large airplanes, to provide adequate stall warning. Stick pushers, on the other hand, are mostly installed in T-tailed a/c and planes that have tendency to do stuff like wing drop, pitch up, etc.

Jet transports with "conventional" layout (ie. moderately swept wing, underslung engines, conventional tail, like A320/737/767 etc.) actually have inherently benign stall behaviour - they provide adequate warning (buffeting) and don't have tendency for deep stall etc. They normally do not require a stick pusher and don't have one

T-tails with aft-mounted engines (CRJ, EMB etc., but Also ATR, Q400) on the other hand exhibit a tendency to misbehave in stall and therefore need a stick-pusher.

There's a very good video on jet transport stalling, produced jointly by Airbus and Boeing (!) - it's almost 2 hours long, but I highly recommend it to anyone interested in the topic: https://www.youtube.com/watch?v=HVt6LiDbLos


The A320 needs no stick pusher because nose down logic at Alpha Max is built into the flight control system. It isn't a dedicated stick pusher, and the stick won't' move, but the system will still push for you.
Last edited by Starlionblue on Mon Nov 30, 2020 2:23 pm, edited 1 time in total.
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zeke
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Re: Those who fly airplanes with FBW flight envelope protections

Mon Nov 30, 2020 1:54 pm

SheikhDjibouti wrote:
The identity of this aircraft is not relevant; I might as well ask about the A320 instead. Is there a marked difference between the stall when fully laden (just after take-off) as opposed to final approach at the end of a long day? Or are the stall characteristics identical apart from a more sluggish response to increased power input?


I wouldn’t say marked difference, however there is a difference. Reason for that difference is the configuration and CG are normally different between takeoff and landing. The aircraft will stall when the critical angle of attack is exceeded in steady flight, that will occur at different attitudes in takeoff and landing configurations.
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Flow2706
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Re: Those who fly airplanes with FBW flight envelope protections

Mon Nov 30, 2020 2:20 pm

SheikhDjibouti wrote:
But, but, but.... there's a well-known poster on this site who has been assuring us for two years now, that a certain aircraft (no, I absolutely refuse to mention it's name :duck: ) has perfectly benign stall characteristics, just like the Cessna 172 he has flown for most of his 120 hrs. There is even a youtube video supporting his argument.

The identity of this aircraft is not relevant; I might as well ask about the A320 instead. Is there a marked difference between the stall when fully laden (just after take-off) as opposed to final approach at the end of a long day? Or are the stall characteristics identical apart from a more sluggish response to increased power input?

The stall characteristics on the A320 are similar at different weights, but obviously the stall speed will be higher at a higher weight. Also the altitude loss will be greater for the heavier aircraft. Altitude however has a significant impact on the stall behavior. Altitude loss will be a lot greater at typical cruise levels compared to a low altitude stall (2000-3000ft at high altitude vs. around 500ft on the low altitude stall). This is due to the combined effects of the low density of the atmosphere at high altitudes and the lower thrust output of the engines. Unfortunately simulators don't fully replicate the stall behavior of the real aircraft as the data package used by the simulator manufacturer is extracted from data obtained during test flights and test pilots won't enter truly dangerous conditions, so much of the post stall behavior in the sim is based on theoretical calculations/wind tunnel testing. However the simulator is remarkable stable when practicing stalls (compared to some general aviation aircrafts/glider) and its rare to see a significant wing drop in the sim, the most noticeable effect in the sim is the massive rate of descend, however as mentioned above I'm not sure if that representative for the real aircraft.
 
thepinkmachine
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Re: Those who fly airplanes with FBW flight envelope protections

Mon Nov 30, 2020 2:25 pm

SheikhDjibouti wrote:
But, but, but.... there's a well-known poster on this site who has been assuring us for two years now, that a certain aircraft (no, I absolutely refuse to mention it's name :duck: ) has perfectly benign stall characteristics, just like the Cessna 172 he has flown for most of his 120 hrs. There is even a youtube video supporting his argument.

The identity of this aircraft is not relevant; I might as well ask about the A320 instead. Is there a marked difference between the stall when fully laden (just after take-off) as opposed to final approach at the end of a long day? Or are the stall characteristics identical apart from a more sluggish response to increased power input?


It's not easy to answer that one, this is mostly test pilot territory and us, average line bears do not get this kind of info in our manuals and/or training.

All I can say is that generally airplane weight should not affect stall characteristics - other than the speed at which stall occurs increases with weight. Airplane configuration does affect the stall, so does the C.G. position. However, it's the manufacturer's responsibility to ensure adequate stall characteristics throughout the entire stall envelope - be it naturally, or by artificial means.

Airbii are a bit different from other airplanes, due to their unique flight control system. In Normal Law they have "hard" envelope protection, which protects them from stalling. However, once in Alternate Law, the autotrim system makes them easier to stall (no protections and neutral speed stability) and makes them harder to recover from stall, as shown in AF447 and XL888T accidents.
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Alias1024
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Re: Those who fly airplanes with FBW flight envelope protections

Mon Nov 30, 2020 4:13 pm

Year and a half on the A320 series and I've yet to see any protections activate in aircraft, only in the simulator.
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VMCA787
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Re: Those who fly airplanes with FBW flight envelope protections

Mon Nov 30, 2020 5:21 pm

thepinkmachine wrote:

Jet transports with "conventional" layout (ie. moderately swept wing, underslung engines, conventional tail, like A320/737/767 etc.) actually have inherently benign stall behaviour - they provide adequate warning (buffeting) and don't have tendency for deep stall etc. They normally do not require a stick pusher and don't have one

T-tails with aft-mounted engines (CRJ, EMB etc., but Also ATR, Q400) on the other hand exhibit a tendency to misbehave in stall and therefore need a stick-pusher.

There's a very good video on jet transport stalling, produced jointly by Airbus and Boeing (!) - it's almost 2 hours long, but I highly recommend it to anyone interested in the topic: https://www.youtube.com/watch?v=HVt6LiDbLos


I don't know if I would characterize the stall behaviour as benign! All swept-wing aircraft suffer from the tendency to enter a deep stall where the horizontal stabilizer is blanked out by the wing sweep and the recovery is very drastic while the stall itself is misleadingly very tame. The problem is if you look at the IVSI during the stall, that is pegged down at over 6000 FPM! Also, the swept-wing aircraft you describe do have stick shakers, with the exception of the 320 family.

Your comments about the T-tail aircraft isn't true for the 727 as there is no stick pusher but a stick shaker.
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thepinkmachine
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Re: Those who fly airplanes with FBW flight envelope protections

Mon Nov 30, 2020 6:48 pm

Deep stall is a phenomenon mostly associated with T-tail/tail-mounted engines. Don’t know about the 727 though - maybe it doesn’t suffer a pitch up during stall, or maybe the certification rules didn’t require a stick pusher back in the day.

I haven’t stalled/spun a jet transport myself, but talked to people who have and they say that eg. the 767 reportedly behaves in a textbook manner. Also, all the available literature confirms what I have written above. Eg. “Handling the Big Jets” by D.P. Davis, or the video I have linked in the previous post.

All the recent stall incidents/accidents of “classic” jet transports (eg. AF447, Turkish in AMS, OZ214, XL888T) didn’t involve an actual “deep stall” and would have been recoverable if there was sufficient altitude and/or appropriate recovery technique applied.

If there were problems with recovery, they were associated with high stabilizer setting, insufficient nose-down input by the crew and/or pitch-up due to high thrust of underslung engine.

Colgan 3407 on the other hand, involved over-riding the Stick Pusher and resulted in a wing drop/spin, rather than just ‘mushing in’ as jet transports tend to...
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VMCA787
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Re: Those who fly airplanes with FBW flight envelope protections

Mon Nov 30, 2020 7:54 pm

AF447 was the classic deep stall and they would have need a good 15,000 to recover due to the long spool up time on the engines at low airspeed. IVSI through the floor, airspeed stable and no wing rock! I would like to speak with someone how who has stalled a 767 or any underwing large transport. I have taken all the 747 series through the approach to stall to calibrate the stick shaker during acceptance flights and it is a terrible thing to sit through. The major issue is the stress put on the engine pylons and sitting in the cockpit you can feel it.

Any swept-wing aircraft will enter a deep stall because of the stall characteristics of the stall starting at the wingtip and working inwards. T-tails are more susceptible to it due to the placement of the stab but if taken far enough any swept-wing aircraft will get into a deep stall.

I can assure you the 727 does not pitch up in a stall but exhibits a very definite nose break down through the horizon, thus the need for a stick shaker. The Colgan Air crash was a straight wing aircraft and has completely different stall characteristics than a swept-wing aircraft does. Completely different kettle of fish!!

Just a quick question....you do know what a deep stall is characterized by don't you?????
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thepinkmachine
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Re: Those who fly airplanes with FBW flight envelope protections

Mon Nov 30, 2020 9:33 pm

VMCA787 wrote:
AF447 was the classic deep stall and they would have need a good 15,000 to recover due to the long spool up time on the engines at low airspeed. IVSI through the floor, airspeed stable and no wing rock! I would like to speak with someone how who has stalled a 767 or any underwing large transport. I have taken all the 747 series through the approach to stall to calibrate the stick shaker during acceptance flights and it is a terrible thing to sit through. The major issue is the stress put on the engine pylons and sitting in the cockpit you can feel it.

Any swept-wing aircraft will enter a deep stall because of the stall characteristics of the stall starting at the wingtip and working inwards. T-tails are more susceptible to it due to the placement of the stab but if taken far enough any swept-wing aircraft will get into a deep stall.


I think we are not on the same page regarding the definition of deep stall. The phenomenon I'm talking about (a.k.a. "superstall", or "locked in") is a condition peculiar to swept wing T-tails, where the pitch-up from the swept wing and long forward fuselage completely overpowers the authority of the stabilizer, which is engulfed in the low-energy vortex of the stalled wing. It is irrecoverable and the a/c eventually develops extreme AoA and flat-spins itself into the ground.

AF447 doesn't quite fit that description. It did eventually develop very high AoA and sink-rate in a flat attitude, but the nose was kept high by the stabilizer winding itself all the way up (courtesy of the autotrim) and pilot inputs. Had the crew applied a correct recovery technique, they could have recovered (or at least had enough pitch authority to break the stall).

I can assure you the 727 does not pitch up in a stall but exhibits a very definite nose break down through the horizon, thus the need for a stick shaker. The Colgan Air crash was a straight wing aircraft and has completely different stall characteristics than a swept-wing aircraft does. Completely different kettle of fish!!

Just a quick question....you do know what a deep stall is characterized by don't you?????


I don't know much about the 727, but what you wrote just proves my point - it has adequate natural stall characteristics, so it doesn't need a stick pusher, nor it has one.

Q400 on the other hand has a stick pusher fitted and needs one, as proven by the Colgan crash and what happened when taken beyond the pusher treshold - even if it's a straight wing...
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DH106
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Re: Those who fly airplanes with FBW flight envelope protections

Mon Nov 30, 2020 11:21 pm

AF447 wasn't deep stalled in the generally accepted sense where the wing blankets the tail surfaces. It remained stalled primarily because one of the pilots maintained back pressure on the stick for a large portion of the descent whilst in alternate law (thus without the protections). That situation should have been easily recoverable at any point in the descent (height permitting), merely by applying standard unstalling procedures - forward stick and adding power.
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Acey559
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Re: Those who fly airplanes with FBW flight envelope protections

Fri Dec 04, 2020 1:57 am

The 767 does have a stick pusher. The 757 does not because the slats will automatically deploy, thereby negating the need for one.
 
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Starlionblue
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Re: Those who fly airplanes with FBW flight envelope protections

Fri Dec 04, 2020 2:49 am

DH106 wrote:
AF447 wasn't deep stalled in the generally accepted sense where the wing blankets the tail surfaces. It remained stalled primarily because one of the pilots maintained back pressure on the stick for a large portion of the descent whilst in alternate law (thus without the protections). That situation should have been easily recoverable at any point in the descent (height permitting), merely by applying standard unstalling procedures - forward stick and adding power.


I'll add that you do get some protections in Alternate Law. Relevant to AF447 is Low Speed Stability protection. At low speed, this gives a nose-down signal referenced to indicated airspeed. The pilot can override it with stick input, which is what happened of course.

You also get the aural and visual stall warnings, and Vsw (stall warning speed) is displayed on the speed tape.
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tommy1808
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Re: Those who fly airplanes with FBW flight envelope protections

Fri Dec 04, 2020 6:08 am

Flow2706 wrote:
However the simulator is remarkable stable when practicing stalls (compared to some general aviation aircrafts/glider) and its rare to see a significant wing drop in the sim, the most noticeable effect in the sim is the massive rate of descend, however as mentioned above I'm not sure if that representative for the real aircraft.


Didn´t Air France flight 296 "test" stall behavior to its very conclusion, staying perfectly level all the way into the trees? Didn´t AF447 pretty much all the way down as well?

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Thomas
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Starlionblue
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Re: Those who fly airplanes with FBW flight envelope protections

Fri Dec 04, 2020 7:33 am

tommy1808 wrote:
Flow2706 wrote:
However the simulator is remarkable stable when practicing stalls (compared to some general aviation aircrafts/glider) and its rare to see a significant wing drop in the sim, the most noticeable effect in the sim is the massive rate of descend, however as mentioned above I'm not sure if that representative for the real aircraft.


Didn´t Air France flight 296 "test" stall behavior to its very conclusion, staying perfectly level all the way into the trees? Didn´t AF447 pretty much all the way down as well?

best regards
Thomas


Air France 296 never stalled. It's the other way around. Alpha Protection kept AoA below the stall, which was what allowed it to stay level.

AF447 never spun or anything, but pitch and roll fluctuated significantly, with excursions well outside what you'd normally see in flight. See animation: https://youtu.be/DpZzwcDyaDY
Last edited by Starlionblue on Fri Dec 04, 2020 7:38 am, edited 1 time in total.
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tommy1808
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Re: Those who fly airplanes with FBW flight envelope protections

Fri Dec 04, 2020 7:35 am

Starlionblue wrote:
tommy1808 wrote:
Flow2706 wrote:
However the simulator is remarkable stable when practicing stalls (compared to some general aviation aircrafts/glider) and its rare to see a significant wing drop in the sim, the most noticeable effect in the sim is the massive rate of descend, however as mentioned above I'm not sure if that representative for the real aircraft.


Didn´t Air France flight 296 "test" stall behavior to its very conclusion, staying perfectly level all the way into the trees? Didn´t AF447 pretty much all the way down as well?

best regards
Thomas


Air France 296 never stalled. It's the other way around. Alpha Protection kept AoA below the stall, which was what allowed it to stay level.

AF447 was somewhat level, but pitch and roll fluctuated significantly, with excursions well outside what you'd normally see in flight. See animation: https://youtu.be/DpZzwcDyaDY


Thank you very much.

best regards
Thomas
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T54A
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Re: Those who fly airplanes with FBW flight envelope protections

Fri Dec 04, 2020 7:48 am

Trimeresurus wrote:
How many times in your career did you actually encounter a situation that you were pushing out of flight envelope and those protections kicked in? What happened afterwards?


In 12000hrs of flying A320, A330, A340 and A350, not once have I had a control law downgrade.
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tommy1808
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Re: Those who fly airplanes with FBW flight envelope protections

Fri Dec 04, 2020 8:01 am

T54A wrote:
Trimeresurus wrote:
How many times in your career did you actually encounter a situation that you were pushing out of flight envelope and those protections kicked in? What happened afterwards?


In 12000hrs of flying A320, A330, A340 and A350, not once have I had a control law downgrade.


do you happen to know if there is any "Mean Time between control law downgrades"? figure?

best regards
Thomas
Well, there is prophecy in the bible after all: 2 Timothy 3:1-6
 
T54A
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Re: Those who fly airplanes with FBW flight envelope protections

Fri Dec 04, 2020 9:03 am

tommy1808 wrote:
T54A wrote:
Trimeresurus wrote:
How many times in your career did you actually encounter a situation that you were pushing out of flight envelope and those protections kicked in? What happened afterwards?


In 12000hrs of flying A320, A330, A340 and A350, not once have I had a control law downgrade.


do you happen to know if there is any "Mean Time between control law downgrades"? figure?

best regards
Thomas


I'm sure there is a theoretical figure, but the causes of a flight control law downgrade can be so varied I wouldn't take the number seriously (I mean irrelevant for pilots). For example, a failure of a Flight Control Computer doesn't necessarily lead to a downgrade. Multiple FCC failure would. So the time between multiple FCC failures would be more important than a single failure.

Perhaps Zeke could pull up a figure from somewhere
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zeke
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Re: Those who fly airplanes with FBW flight envelope protections

Fri Dec 04, 2020 1:08 pm

T54A wrote:
I'm sure there is a theoretical figure, but the causes of a flight control law downgrade can be so varied I wouldn't take the number seriously (I mean irrelevant for pilots). For example, a failure of a Flight Control Computer doesn't necessarily lead to a downgrade. Multiple FCC failure would. So the time between multiple FCC failures would be more important than a single failure.

Perhaps Zeke could pull up a figure from somewhere


I dont know the numbers off hand, but to give you an idea under the MEL they can dispatch an aircraft one inoperative, turned off.
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thepinkmachine
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Re: Those who fly airplanes with FBW flight envelope protections

Fri Dec 04, 2020 2:43 pm

FWIW, I have briefly ended up in ALTN LAW on A320 once, but it was self-inflicted.

We had an aileron servo fault one day and I decided to reset an ELAC (A320 primary flight control computer), but Il by mistake I have reset the wrong one... Pooof! We went into ALTN law.

Fortunately, switching the ELAC back ON recovered NORMAL law (though with an unpleasant lateral jolt).

Lesson learned that day - don’t reset stuff in flight, unless absolutely necessary for operation. Even if there’s an ECAM fault and your fingers are itching. Also, don’t try to do stuff from memory, even if you think you’re smart... :)
"Tell my wife I am trawling Atlantis - and I still have my hands on the wheel…"
 
WIederling
Posts: 10043
Joined: Sun Sep 13, 2015 2:15 pm

Re: Those who fly airplanes with FBW flight envelope protections

Fri Dec 04, 2020 6:42 pm

tommy1808 wrote:
Flow2706 wrote:
However the simulator is remarkable stable when practicing stalls (compared to some general aviation aircrafts/glider) and its rare to see a significant wing drop in the sim, the most noticeable effect in the sim is the massive rate of descend, however as mentioned above I'm not sure if that representative for the real aircraft.


Didn´t Air France flight 296 "test" stall behavior to its very conclusion, staying perfectly level all the way into the trees? Didn´t AF447 pretty much all the way down as well?

AF296 never entered a stall.
The types FBW logic kept up its forward speed
countering drag not compensated by thrust with loss of height
Lack of thrust increase let them land into the trees.
Probably the reason why the outcome was rather benign ( for the circumstances.)

AF447 only had a strong stick back input in the last seconds before they pancaked into the ocean.
rest of the time the guy on the stick kept the plane perfectly level :-(
IMU one could make a case that the stall logic misled him because had not understood the constraints
and the resultant inversion of signal.
( forward speed above min for valid -> speed valid, aoa too high -> stall warning.
forward speed below min for valid -> speed invalid, aoa too high -> no stall warning.)
Murphy is an optimist
 
PGNCS
Posts: 2268
Joined: Sun Apr 15, 2007 5:07 am

Re: Those who fly airplanes with FBW flight envelope protections

Wed Dec 09, 2020 1:42 am

Trimeresurus wrote:
How many times in your career did you actually encounter a situation that you were pushing out of flight envelope and those protections kicked in? What happened afterwards?


I got my type rating in the A-320 in 1995 and have flown it the majority of the time since then.

I have never gotten close to an envelope protection, though the most likely one to get seems to be high speed protection in gusty winds or mountain wave, though I am familiar with some Alpha Floor activations, with some particular approaches especially suspect.

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