AF447
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He said: “**** Airbus man. This is the kinda **** we don’t like about it. You know, there’s so many computers we don’t, we don’t know what it ******* does sometimes.”
Thread Starter
vilas... " Anyway it's too late to discuss unreliable speed as Airbus now has mathematically calculated airspeed which they call it digital back up speed. This doesn't require any anemometric input. This supervises the ADR calculations and in case of all ADRs going rogues their speed indications are replaced by the Digital Backup Speed. A350 does it automatically A320 does it through ECAM actions. " Is that BUSS? Back Up Speed Scale? An option on A330, which Air France took a pass on? Still goes to ALT LAW 2 B ?? Begs the question, should duff IAS have trIggered a change to ALT LAW ? Much ado about a condition that needs merely Pitch and Power? ALSO, AoA is the critical instrument? Where was the AoA instrument? Right, not equipped with one...How much money did Air France save on F-GCZP....?
Last edited by Concours77; 27th Mar 2023 at 16:28.
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" Anyway it's too late to discuss unreliable speed as Airbus now has mathematically calculated airspeed which they call it digital back up speed. This doesn't require any anemometric input. This supervises the ADR calculations and in case of all ADRs going rogues their speed indications are replaced by the Digital Backup Speed. A350 does it automatically A320 does it through ECAM actions. "
Is that BUSS? Back up Speed Scale? An option on A330, which Air France took a pass on?
Is that BUSS? Back up Speed Scale? An option on A330, which Air France took a pass on?
Thread Starter
No! Backup speed scale is an older mod. It doesn't calculate speed just shows a green band like TCAS to fly based on AoA. That also came after 447 as a remedy. Digital back up speed is actual speed displayed on speed tape that pilot flies. It is calculated by injecting weight, load factor and AoA in lift equation. It has different indication for pilot to know it's calculated speed.
Last edited by Concours77; 27th Mar 2023 at 16:21.
Thread Starter
Hmmm
punkalouver "Many of us are not fully aware of how we will react under various surprise scenarios. Sudden surprise encounter may be the the important factor."
Holy. S. (Sacre. M.)
Holy. S. (Sacre. M.)
Thread Starter
punkalouver..."A dash-8 pilot flying into Buffalo encounters an artificial stall warning well above the stall speed because of a misconfigured stall warning system."
The Stall Bug had been set for Anti Ice. FO switched off Anti ICE, but neglected to move the Stall Bug associated with the system.Captain had assumed the higher Stall trigger was now set for an actual Stall... Still, why did he pull? He didn't. At least not right away. ColganAir SOP for low level STALLWARN was "Minimize Altitude Loss, Full Power". Which, oddly enough, was Air France's also. Cannot push, and minimize altitude loss... As I recall
The Stall Bug had been set for Anti Ice. FO switched off Anti ICE, but neglected to move the Stall Bug associated with the system.Captain had assumed the higher Stall trigger was now set for an actual Stall... Still, why did he pull? He didn't. At least not right away. ColganAir SOP for low level STALLWARN was "Minimize Altitude Loss, Full Power". Which, oddly enough, was Air France's also. Cannot push, and minimize altitude loss... As I recall
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He pulled instantly and kept 50-100% back pressure on column until he killed everyone 27 seconds later. And the FO put the flaps up unprompted.
You know nothing about what you’re talking about and are an excellent troll.
Here is the digitised FDR/CVR video produced by the NTSB which demonstrates your total ignorance.
You know nothing about what you’re talking about and are an excellent troll.
Here is the digitised FDR/CVR video produced by the NTSB which demonstrates your total ignorance.
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vilas... " Anyway it's too late to discuss unreliable speed as Airbus now has mathematically calculated airspeed which they call it digital back up speed. This doesn't require any anemometric input. This supervises the ADR calculations and in case of all ADRs going rogues their speed indications are replaced by the Digital Backup Speed. A350 does it automatically A320 does it through ECAM actions. " Is that BUSS? Back Up Speed Scale? An option on A330, which Air France took a pass on? Still goes to ALT LAW 2 B ?? Begs the question, should duff IAS have trIggered a change to ALT LAW ? Much ado about a condition that needs merely Pitch and Power? ALSO, AoA is the critical instrument? Where was the AoA instrument? Right, not equipped with one...How much money did Air France save on F-GCZP....?
Last edited by vilas; 28th Mar 2023 at 06:08.
I came across the YouTube video below from a PPRune forum a couple of years ago. The video does a great analysis of startle factor & how we, as humans, are wired. It is well worth the 30 minutes of viewing time in my opinion.
Cheers
VH-MLE
Cheers
VH-MLE
What Air france delayed installing was not the BUSS because it was simply not deviced yet. Actually BUSS was thought of because of AF447. To my knowledge the pitot static equipment which was installed on AF was prone to icing and a better euipment became available which they delayed installing. Stall warning comes fro purely AoA speed has nothing to do with it. But the low speed stability in alternate law which pitches the nose down comes from speed. When speed is not available control laws change to alternate2 which looses the pitch down capability but stall warning remains available since it comes from AoA.
Because the stall warning is inhibited below 80 knots (IIRC) indicated as no one would ever try to fly that slow. That prevents nuisance warnings on the ground when the aoa vane droops due to low/zero airflow.
The only time the back stick was released the speed increased above the inhibition threshold causing the stall warning to restart. The PF’s response was to pull full back stick again which slowed the aircraft back below the threshold causing the stall warning to stop again.
The only time the back stick was released the speed increased above the inhibition threshold causing the stall warning to restart. The PF’s response was to pull full back stick again which slowed the aircraft back below the threshold causing the stall warning to stop again.
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Triggering of stall warning is from AoA. But below 60kts the system takes it as non computed data and rejects the input to stop the warning.
Thread Starter
I guess my question becomes why would indicated airspeed have any effect on STALLWARN. Was AF447 having AoA sensing issues as well? Much has been made of the change in flight law, seems a serious outcome to have for the cockpit to go sideways due to iced pitots? Roll Direct especially? In turb? sorry if this is a dumb question? thx vilas
No. The aircraft had a temporary issue with the ASI’s that recovered quickly and to any competent pilot an ASI is a convenience item. You can easily fly without any speed indications.
The rest was pilot error. Huge errors.
The rest was pilot error. Huge errors.
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I came across the YouTube video below from a PPRune forum a couple of years ago. The video does a great analysis of startle factor & how we, as humans, are wired. It is well worth the 30 minutes of viewing time in my opinion.
https://youtu.be/BBpqvPujZgM
Cheers
VH-MLE
https://youtu.be/BBpqvPujZgM
Cheers
VH-MLE
Thread Starter
Thank you for your response....!
Last edited by Concours77; 28th Mar 2023 at 17:13.
The computer system is designed with the concept that only 1 subsystem will fail at a time. It determines this by comparing the outputs and using the output that at least 2 of 3 agree (within some tolerance) on. In the case of the ice accumulation, one pitot tube plugged - that left 2 in agreement. Then another pitot tube plugged leaving all 3 in disagreement as the stored pressure would have depleted at different rates due to the moisture bleed port.
That's what triggered the change in control law - the system had 3 different opinions on what the dynamic pressure reading was and there was no winner.
I think the stall came about because when the PIC was handed control he slightly pulled the sidestick back while trying to maintain roll orientation. At that altitude and airspeed the plane was close to stalling and the slight mishandling pushed it to give the warning - the pilot then did what would have been fine if the control law was "normal" and gave it full throttle (causing a hard pitch up) and pulled back, confident that the alpha protection would prevent the stall that was already occurring.
Once the altimeter started unwinding I expect that, even if it was noticed, it would take remembering "how an airplane flies" to convince the pilot to shove the nose down and increase the rate of descent in order to exit the stall and resume normal level flight. I think that at some point the pitot tubes cleared and if they had reset the flight computer it would have recovered hands off because enough valid data would be available. To do that would require knowing that the control law had changed - which the PIC did not appear to know.
That's what triggered the change in control law - the system had 3 different opinions on what the dynamic pressure reading was and there was no winner.
I think the stall came about because when the PIC was handed control he slightly pulled the sidestick back while trying to maintain roll orientation. At that altitude and airspeed the plane was close to stalling and the slight mishandling pushed it to give the warning - the pilot then did what would have been fine if the control law was "normal" and gave it full throttle (causing a hard pitch up) and pulled back, confident that the alpha protection would prevent the stall that was already occurring.
Once the altimeter started unwinding I expect that, even if it was noticed, it would take remembering "how an airplane flies" to convince the pilot to shove the nose down and increase the rate of descent in order to exit the stall and resume normal level flight. I think that at some point the pitot tubes cleared and if they had reset the flight computer it would have recovered hands off because enough valid data would be available. To do that would require knowing that the control law had changed - which the PIC did not appear to know.
Thread Starter
MEgr
"I think the stall came about because when the PIC was handed control he slightly pulled the sidestick back while trying to maintain roll orientation. At that altitude and airspeed the plane was close to stalling and the slight mishandling pushed it to give the warning - the pilot then did what would have been fine if the control law was "normal" and gave it full throttle (causing a hard pitch up) and pulled back, confident that the alpha protection would prevent the stall that was already occurring."
Had the StallWarning been a result of temporary (close to) AOAcrit exceedance, he would have known the AC was in ALTLAW, right? He also would have known ROLLDIRECT was in charge of ailerons, right? The aircraft will NOT Stall in NORMAL LAW. Why would STALLWARN not be sufficient notice to pilots of a change in control action? If the STALLWARN Will sound in NORMAL LAW, would he not expect ALPHAPROT To control AoA?
Thanks for responding, food for thought.
Had the StallWarning been a result of temporary (close to) AOAcrit exceedance, he would have known the AC was in ALTLAW, right? He also would have known ROLLDIRECT was in charge of ailerons, right? The aircraft will NOT Stall in NORMAL LAW. Why would STALLWARN not be sufficient notice to pilots of a change in control action? If the STALLWARN Will sound in NORMAL LAW, would he not expect ALPHAPROT To control AoA?
Thanks for responding, food for thought.
Relying on the protections to prevent a stall has never been an SOP. Flight control protections are the LAST LINE OF DEFENCE, they should never be used to solve a problem because if they fail you’re screwed. That’s why the Airbus stall recovery has ALWAYS been to reduce AOA and accelerate, never “just pull back and let the protections sort it”. It is not a reasonable course of action for an Airbus pilot to gently pull back and let normal law protect you from a stall. The aim is to always fly inside the envelope but have protections if you inadvertently reach the edge, never to go intentionally to the edge and rely on protections to look after you.
There has been an industry wide change in emphasis (all a/c types) in recent years where before a consideration was to minimise height loss whereas now the priority is to aggressively break the stall then recover, as the new emphasis actually results in less height loss.
There has been an industry wide change in emphasis (all a/c types) in recent years where before a consideration was to minimise height loss whereas now the priority is to aggressively break the stall then recover, as the new emphasis actually results in less height loss.