AF 447 Thread No. 8
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@rudderrudderrat
Absolutely.
The approximate V/S when the FDs came back online was 1500fps. Even if neither F/O followed the correct procedure - which was to disable them - you'd hope that the PF would ignore them as a matter of course until things were stabilised.
The reason I'm sceptical about the FDs being responsible for the NU inputs is because the inputs continue, and indeed intensify, after the FDs go away again - as well as the fact that he continues to feed in short bursts of ND even after the actual V/S starts falling away dramatically. I have to admit the possibility that the PF did indeed choose to follow them, but I remain to be convinced.
It appears more likely to me that he was chasing the pitch on the artificial horizon as the aircraft entered the buffet at the apogee of the climb and thence into full aerodynamic stall.
Absolutely.
The approximate V/S when the FDs came back online was 1500fps. Even if neither F/O followed the correct procedure - which was to disable them - you'd hope that the PF would ignore them as a matter of course until things were stabilised.
The reason I'm sceptical about the FDs being responsible for the NU inputs is because the inputs continue, and indeed intensify, after the FDs go away again - as well as the fact that he continues to feed in short bursts of ND even after the actual V/S starts falling away dramatically. I have to admit the possibility that the PF did indeed choose to follow them, but I remain to be convinced.
It appears more likely to me that he was chasing the pitch on the artificial horizon as the aircraft entered the buffet at the apogee of the climb and thence into full aerodynamic stall.
Last edited by DozyWannabe; 17th May 2012 at 12:40.
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IMO
I've lost control of the aircraft
Just in time : 2 h 11 min 32 - Maybe, mm43 could add it to his graph.
- The PF was able to maintain 15 degrees of pitch
- The V/S was increasing ... but not any more
- I’m in TOGA eh
- Altitude was under control ... but not any more
- But we’ve got the engines what’s happening (…)?
(…) I don’t have control of the airplane any more now I don’t have control of the airplane at all
I"d like to know what is in (…) ?
Originally Posted by DozyWannabe
as I said earlier, the FD is for navigation - not aviation.
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Are you saying you *would* try to follow the FD bars in an emergency? I'm pretty sure that's not what they are designed for.
And by "navigate" I do mean in three dimensions - you can follow a pre-programmed departure routing with them and you can use them to guide you to waypoints, but there's no way they should be used in emergencies as they're simply a proxy for the autopilot. Which, as was pointed out in the "Children of the Magenta" video, is not capable of flying recoveries or avoidance maneouvres. The FD can tell you where to go, but it can't tell you how to fly (or in other words - "aviate").
And by "navigate" I do mean in three dimensions - you can follow a pre-programmed departure routing with them and you can use them to guide you to waypoints, but there's no way they should be used in emergencies as they're simply a proxy for the autopilot. Which, as was pointed out in the "Children of the Magenta" video, is not capable of flying recoveries or avoidance maneouvres. The FD can tell you where to go, but it can't tell you how to fly (or in other words - "aviate").
Last edited by DozyWannabe; 17th May 2012 at 12:58.
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HDG/VS? Indicating ? Chronic right turn? Chronic Nose Down? What was she doing at a/p loss?
Come left, ascend? wtf? What did PF have at the outset of manual control?
Doze, would you lean toward an inertial problem as well as ADR? Follow Me Flyboy.....
Come left, ascend? wtf? What did PF have at the outset of manual control?
Doze, would you lean toward an inertial problem as well as ADR? Follow Me Flyboy.....
Last edited by Lyman; 17th May 2012 at 13:14.
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Getting bumped by turbulence and having her pitot tubes clogged.
No attitude reached prior to the PF taking the stick was unmanageable, and she didn't actually depart from controlled flight at any point until she hit the stall.
No attitude reached prior to the PF taking the stick was unmanageable, and she didn't actually depart from controlled flight at any point until she hit the stall.
Last edited by DozyWannabe; 17th May 2012 at 13:21.
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No attitude reached prior to the PF taking the stick was unmanageable, and she didn't actually depart from controlled flight at any point until she hit the stall.
You're not wrong.....
You're not wrong.....
Been BZ looking at the Indonesian crash, so not much to contribute here until last two pages ( GASP! world record for posts RE a single crash, ya think?).
Doze has it nailed. Period.
@ Wolf
Our problem in the Viper was we could not command nose down once we exceeded the magic 27 deg AoA limiter by zooming up and having speed decay faster than the FBW system could compensate for. The HS was already at the maximum( leading edge full up to keep AoA under 27 deg), but the pitch moment was such that nose down commands didn't work. So we settled into a fairly comfortable deep stall. The AF jet did the same thing except it wasn't a "deep stall", it was "deeply" stalled.
Back to Doze....
So we saw the AF jet get into the stall the same way we did.
Hold the nose up and at such a steep angle that you run outta those "lifties" before the system can command enough nose down pitch moment. Remember that we flew at a much further aft cee gee than the 'bus. Not having the AoA being used by HAL contributes to the problem, otherwise HAL would have commanded nose down regardless of the SS position/command, just like the Viper. Not so with the 'bus. The PF still had the ability to command nose up when the "protections" should not have allowed an excessive AoA.
I go with some of the other folks here with "light" experience, that the AoA doofer works very well even at low speeds, and I don't recall seeing any speeds below 100 knots or so.
I think the control laws may be under scrutiny by the accident board in this regard, and I would move to use AoA sensors as long as they were not frozen or were way outta agreement with each other. Ours were used/displayed even with WOW, but the speed display quit about 60 knots!!! Hmmmm, same number as the 'bus, and I'll link my LEF failure video so you can see the AoA bracket "cage" as I slowed down on the runway.
If anyone wants to see the video, chime in here.
Doze has it nailed. Period.
@ Wolf
Our problem in the Viper was we could not command nose down once we exceeded the magic 27 deg AoA limiter by zooming up and having speed decay faster than the FBW system could compensate for. The HS was already at the maximum( leading edge full up to keep AoA under 27 deg), but the pitch moment was such that nose down commands didn't work. So we settled into a fairly comfortable deep stall. The AF jet did the same thing except it wasn't a "deep stall", it was "deeply" stalled.
Back to Doze....
So we saw the AF jet get into the stall the same way we did.
Hold the nose up and at such a steep angle that you run outta those "lifties" before the system can command enough nose down pitch moment. Remember that we flew at a much further aft cee gee than the 'bus. Not having the AoA being used by HAL contributes to the problem, otherwise HAL would have commanded nose down regardless of the SS position/command, just like the Viper. Not so with the 'bus. The PF still had the ability to command nose up when the "protections" should not have allowed an excessive AoA.
I go with some of the other folks here with "light" experience, that the AoA doofer works very well even at low speeds, and I don't recall seeing any speeds below 100 knots or so.
I think the control laws may be under scrutiny by the accident board in this regard, and I would move to use AoA sensors as long as they were not frozen or were way outta agreement with each other. Ours were used/displayed even with WOW, but the speed display quit about 60 knots!!! Hmmmm, same number as the 'bus, and I'll link my LEF failure video so you can see the AoA bracket "cage" as I slowed down on the runway.
If anyone wants to see the video, chime in here.
Last edited by gums; 17th May 2012 at 15:16.
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@Dozy:
The other reason is that the FD would have been taking it's information from the selected values, correct? According to the trace, none of the "Selected V/S" values during HN39's excerpt even come close to requiring a 15 degree NU climb.
pitch bar guidance is limited @ +/-22.5° of pitch, 50° FPA, if that limit reflects the +/-6000ft VS limit it would be definitely above 15°.
Once again this is IF!! not VLS protected.
@CONF and Lyman:
I've lost control of the aircraft
If he was following the guidance he would have released the SS and even pointed the nose down between (02:10:55) and (02:11:05) in HN39's graph instead he went back to 15 pitch°
Last edited by A33Zab; 17th May 2012 at 16:22. Reason: Corrected times!
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Originally Posted by DozyWannabe
Are you saying you *would* try to follow the FD bars in an emergency? I'm pretty sure that's not what they are designed for.
If only the PF could have said : "Give me 1000 fpm in descent"
Or the PNF, instead of calling the captain back : "We're high I give you OPEN DES"
I think we are pretty much on target here or we have not been that close before ...
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Thanks for the vote of confidence gums - much appreciated.
Just to clarify - the computer does make use of AoA, otherwise alpha protections wouldn't work. Those protections are *inhibited* in Alternate Law because the systems are not designed to work from a single data value (in this case AoA).
Even in Normal Law however, the flight computers cannot *command* the aircraft to change attitude without input from a human pilot or the autopilot (which is a separate and distinct system from the flight computers). Alpha Protection simply maintains pitch attitude slightly below alpha max for the current airspeed. The only positive command that comes out of the protections is when Alpha Floor orders TOGA - and again, autothrust needs to be functional to do this.
@CONF - Obviously anything we have regarding FD behaviour is completely speculative. If rudderrudderrat's right (and I'm inclined to think he is), then the FDs would have been reset to the attitude the aircraft was holding when they returned. Given the significant drop in V/S alone those FDs would not have looked stable for very long. The lack of any indication on the CVR that they thought they were out of the woods, along with the fact that they never tried to re-engage automatics when the FDs came back casts some doubt on the "followed the FD into stall" theory. It's a possibility for sure - but not a certainty.
Just to clarify - the computer does make use of AoA, otherwise alpha protections wouldn't work. Those protections are *inhibited* in Alternate Law because the systems are not designed to work from a single data value (in this case AoA).
Even in Normal Law however, the flight computers cannot *command* the aircraft to change attitude without input from a human pilot or the autopilot (which is a separate and distinct system from the flight computers). Alpha Protection simply maintains pitch attitude slightly below alpha max for the current airspeed. The only positive command that comes out of the protections is when Alpha Floor orders TOGA - and again, autothrust needs to be functional to do this.
@CONF - Obviously anything we have regarding FD behaviour is completely speculative. If rudderrudderrat's right (and I'm inclined to think he is), then the FDs would have been reset to the attitude the aircraft was holding when they returned. Given the significant drop in V/S alone those FDs would not have looked stable for very long. The lack of any indication on the CVR that they thought they were out of the woods, along with the fact that they never tried to re-engage automatics when the FDs came back casts some doubt on the "followed the FD into stall" theory. It's a possibility for sure - but not a certainty.
Last edited by DozyWannabe; 17th May 2012 at 15:29.
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Originally Posted by A33Zab
pitch bar guidance is limited @ +/-22.5° of pitch, 50° FPA
Once again this is IF!! not VLS protected
What would be the command ?
It is IMO a scenario not foreseen on the design board.
At that time it was already in fully developped STALL....
If he was following the guidance he would have released the SS and even pointed the nose down between s55(02:11:05) and s65(02:11:15) in HN39's graph instead he went back to 15 pitch°
@ Doze
J
Fer chrissakes, Doze, the system did not limit the AoA or we wouldn't be here trying to figure out what happened.
I must admit that our primitive FBW system didn't care about attitude - it limited AoA and gee with no regard for aircraft attitude. Different requirements and missions.
We could pull power back in level flight and let the system "trim" up command ( AoA, not pitch). In other words, trimmed for one gee and let HAL do his thing. When we got to 27 deg AoA we were at 1 gee max command and actual parameters. Sucker would then slowly begin to descend at 27 degrees AoA. If we had not entered the deep stall bucket with bad pitch moment, then we could simply push forward on the sidestick and fly out.
On one of our engine failures, the guy ejected and the jet got to the AoA limit and slowly descended until it hit the ground. St and level, as no sidestick roll command and HAL kept roll rate at zero.
One jet actually landed by itself and only suffered a broken main gear. The guilty pilot ( ran outta gas and tried for a deadstick landing until about 300 feet) looked back after landing in the chute and the jet was there with the strobe flashing and the EPU still pumping out poisonous gas, heh heh. They used the jet for maintenance training afterwards.
Our gee command was manually controlled by using our trim switch. So default was 1 gee, but we could trim to 3.5 positive gee or about 2 negative gees.
The 'bus system doesn't work the way ours did and still does.
So I would recommend that once outta primary law that the system uses something like we had.
J
ust to clarify - the computer does make use of AoA, otherwise alpha protections wouldn't work. Those protections are *inhibited* in Alternate Law because the systems are not designed to work from a single data value (in this case AoA).
Even in Normal Law however, the flight computers cannot *command* the aircraft to change attitude without input from a human pilot or the autopilot (which is a separate and distinct system from the flight computers). Alpha Protection simply maintains pitch attitude slightly below alpha max for the current airspeed. The only positive command that comes out of the protections is when Alpha Floor orders TOGA - and again, autothrust needs to be functional to do this.
Even in Normal Law however, the flight computers cannot *command* the aircraft to change attitude without input from a human pilot or the autopilot (which is a separate and distinct system from the flight computers). Alpha Protection simply maintains pitch attitude slightly below alpha max for the current airspeed. The only positive command that comes out of the protections is when Alpha Floor orders TOGA - and again, autothrust needs to be functional to do this.
Fer chrissakes, Doze, the system did not limit the AoA or we wouldn't be here trying to figure out what happened.
I must admit that our primitive FBW system didn't care about attitude - it limited AoA and gee with no regard for aircraft attitude. Different requirements and missions.
We could pull power back in level flight and let the system "trim" up command ( AoA, not pitch). In other words, trimmed for one gee and let HAL do his thing. When we got to 27 deg AoA we were at 1 gee max command and actual parameters. Sucker would then slowly begin to descend at 27 degrees AoA. If we had not entered the deep stall bucket with bad pitch moment, then we could simply push forward on the sidestick and fly out.
On one of our engine failures, the guy ejected and the jet got to the AoA limit and slowly descended until it hit the ground. St and level, as no sidestick roll command and HAL kept roll rate at zero.
One jet actually landed by itself and only suffered a broken main gear. The guilty pilot ( ran outta gas and tried for a deadstick landing until about 300 feet) looked back after landing in the chute and the jet was there with the strobe flashing and the EPU still pumping out poisonous gas, heh heh. They used the jet for maintenance training afterwards.
Our gee command was manually controlled by using our trim switch. So default was 1 gee, but we could trim to 3.5 positive gee or about 2 negative gees.
The 'bus system doesn't work the way ours did and still does.
So I would recommend that once outta primary law that the system uses something like we had.
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@CONF:
Excuse me, autoflight is complicated and information considering this issue is very fragmented, I am trying to filter and report the relevant bits and pieces related to this specific case not any other mode or CONFIG.
That doesn't mean information is complete.
Altitude is not mentioned considering this limit, but pressure information is an input to FMGEC so could be used in the AP command calculations.
-No, not for me, AP is disengaged and can not be engaged below VLS.
That's a clear statement!,
Such a statement is not made in the FG section.
AP disengagement doesn't prohibit the FG to calculate FD guidance and display.
-The expected guidance would be LEVEL OFF!? ......and handle speed
(Identical as AP/AT command when VLS is encountered in CLB mode)
-Agreed. but there are different views on how such a scenario was initiated and did developped.
-Thx for correction.
The following snippets concerning AP/FD Speed Protection:
(Read the NOTE: section)
What do they mean with -except level off is performed-?
level off as result of this speed protection or level off due to CRZ?
Description of Vmax/Vmin:
Example Speedprotection when AP engaged:
That doesn't mean information is complete.
Whatever the altitude ?
Once again is it sure you'll be VLS protected if you're already 40kt below ?
What would be the command ?
It is IMO a scenario not foreseen on the design board.
What would be the command ?
It is IMO a scenario not foreseen on the design board.
That's a clear statement!,
Such a statement is not made in the FG section.
AP disengagement doesn't prohibit the FG to calculate FD guidance and display.
-The expected guidance would be LEVEL OFF!? ......and handle speed
(Identical as AP/AT command when VLS is encountered in CLB mode)
-Agreed. but there are different views on how such a scenario was initiated and did developped.
-Thx for correction.
The following snippets concerning AP/FD Speed Protection:
(Read the NOTE: section)
What do they mean with -except level off is performed-?
level off as result of this speed protection or level off due to CRZ?
----------------------
Clearing of FD commands
Manual clearance
.....
.....
1// Logic-controlled clearance
a/ Axis-by-axis removal
.......
b/ FD disengage request
The FGE requests the FCU to disengage the FD if:
Clearing of FD commands
Manual clearance
.....
.....
1// Logic-controlled clearance
a/ Axis-by-axis removal
.......
- NCD on the three labels when the FD ENGD condition is lost
- NCD on label 141 (pitch bar) when no longitudinal mode is engaged or when the ROLL OUT mode is active
- ......
b/ FD disengage request
The FGE requests the FCU to disengage the FD if:
- Aircraft speed is not in the flight envelope (VLS, VMO, VFE), and
- The AP is disengaged, and
- The FD is in OPEN CLB/DES or CLB/DES modes
When the FD is disengaged, the A/THR changes to SPEED mode to bring the aircraft speed back in the flight envelope.
--------------------------------------------------
NOTE: AP/FD speed protection
The speed protection is applied, according to the mode, in order to protect against Vmin or theta max (=22.5°) when climbing or Vmax when descending with the following load factor limits:
Max pitch attitude limitation is set to theta max =22.5°
The protected modes are OP CLB, OP DES, CLB, DES, ALT*, and V/S-FPA except when a level off has been performed.
The protected modes are OP CLB, OP DES, CLB, DES, ALT*, and V/S-FPA except when a level off has been performed.
Description of Vmax/Vmin:
- 0.3g max versus VMO
- 0.15g max versus VFE or VLE (when landing gear is down).
- Vmax is VMO(MMO)-1kt in clean configuration, VFE/VLE+4kt else
- Vmin is VLS if Vc target >or= VLS +5kt or Vmin is VLS-5kt if Vc target =VLS
With AP engaged, when V/S-FPA target is not held by the AFS because it is excessive, the AP speed protection is activated: a triple click aural indication and a flashing amber box around V/S or FPA mode and target on the FMA are commanded by FMGEC.
Last edited by A33Zab; 17th May 2012 at 19:14.
Beating the dead horse
c'mon, folks.
We know with a large probability/certainty that the jet was flown at a high attitude as the airspeed slowed and that all the "protections" did not keep the jet from exceeding the stall AoA or even the basic limits we see in the manuals.
Basic design problem and pilot problem, IMHO.
Without being a fellow ghost to talk with the PF, we'll never know. And I ain't willing to meet the dude in that great hootch bar in the sky just yet and ask him, "just what the hell what were you thinking?".
Many of the graphs we have seen here should be examined by the accident board, but the focus should be on the basic control laws that the jet employs.
I also have problems with training and exposure to the worst conditions. this thing started with a fairly benign sensor failure, then escalated to a tragedy. Some crew failures, some design deficiencies. It all added up.
Hope to hell that the board recommends some changes to the control laws and reversion sequences.
We know with a large probability/certainty that the jet was flown at a high attitude as the airspeed slowed and that all the "protections" did not keep the jet from exceeding the stall AoA or even the basic limits we see in the manuals.
Basic design problem and pilot problem, IMHO.
Without being a fellow ghost to talk with the PF, we'll never know. And I ain't willing to meet the dude in that great hootch bar in the sky just yet and ask him, "just what the hell what were you thinking?".
Many of the graphs we have seen here should be examined by the accident board, but the focus should be on the basic control laws that the jet employs.
I also have problems with training and exposure to the worst conditions. this thing started with a fairly benign sensor failure, then escalated to a tragedy. Some crew failures, some design deficiencies. It all added up.
Hope to hell that the board recommends some changes to the control laws and reversion sequences.
New pages for the flight manual
O.K., I can't resist. Got the QuickTime video finally, and post it here.
This is not like the AF jet crash. Got the jet back to the ramp. No previous documented failure of the leading edge flap or successful landing. Next one required an ejection. This one was a 100% maintenance failure, as the troops did not insert the "keeper" pin into the drive tube from the hydraulic motor to the flap drive tubes after some work. So the sucker slipped out about the time gear handle went up.
You have to have a QT extension on your browser, or you download the file and then use the QT app to view it with the audio.
Do I have a lotta sympathy for the AF447 crew? Not really. I was faced with the first of its kind and used every trick in the book, not the 30 previous pitot system failures. I also point out the immense help my FBW laws provided. Instead of a huge roll into the bad wing, HAL tried to keep roll at zero roll rate. Turned out that I had about a pound or so authority beyond the laws, so was able to steer left and right. Pitch worked as advertised.
The box with an "x" after tower told me I had traffic was a radar lock I used with the cosmic stuff we had. Finally got a visual, then back to the approach.
I also did not notice how quickly speed went down once speed brakes were extended. They also influenced yaw. Discussed all that later for next troops wit the same problem. Nevertheless, stabilized at 170 knots and cruised in. Biggest surprise was the touch down and speed bleed off. Once mains on the ground was a piece of cake and aero braked to slow down. Normal touch was about 120 knots.
The problem:
The QT video:
http://www.sluf.org/warbirds/lef-landing.m4v
Will edit if not working.
This is not like the AF jet crash. Got the jet back to the ramp. No previous documented failure of the leading edge flap or successful landing. Next one required an ejection. This one was a 100% maintenance failure, as the troops did not insert the "keeper" pin into the drive tube from the hydraulic motor to the flap drive tubes after some work. So the sucker slipped out about the time gear handle went up.
You have to have a QT extension on your browser, or you download the file and then use the QT app to view it with the audio.
Do I have a lotta sympathy for the AF447 crew? Not really. I was faced with the first of its kind and used every trick in the book, not the 30 previous pitot system failures. I also point out the immense help my FBW laws provided. Instead of a huge roll into the bad wing, HAL tried to keep roll at zero roll rate. Turned out that I had about a pound or so authority beyond the laws, so was able to steer left and right. Pitch worked as advertised.
The box with an "x" after tower told me I had traffic was a radar lock I used with the cosmic stuff we had. Finally got a visual, then back to the approach.
I also did not notice how quickly speed went down once speed brakes were extended. They also influenced yaw. Discussed all that later for next troops wit the same problem. Nevertheless, stabilized at 170 knots and cruised in. Biggest surprise was the touch down and speed bleed off. Once mains on the ground was a piece of cake and aero braked to slow down. Normal touch was about 120 knots.
The problem:
The QT video:
http://www.sluf.org/warbirds/lef-landing.m4v
Will edit if not working.
Last edited by Jetdriver; 19th May 2012 at 11:13.
A33Zab;
From memory!,... they would mean a level off performed by the pilot either in auto flight using the FCU or manual flight using the stick, (autothrust either engaged or not engaged).
As I understand and recall it, a "level-off" is a term that refers to a flight phase change from either the climb or descent phase to a leveling off (no change in altitude), even if the level-off is temporary. If the altitude at which the aircraft is leveled off has been entered in the MCDU PROG page under "CRZ", the FMGC enters the "ALT CRZ" mode for speed and power settings which use the CI and other information entered into the MCDU by the crew either at the start of the flight or during the manoeuvre. "ALT CRZ" is displayed on the PFDs.
If the level-off altitude is different than the altitude entered in the MCDU PROG page under CRZ, the FMGC enters the "ALT" mode and displays "ALT" on the PFD, indicating the difference between the MCDU setting and the captured altitude.
I suspect the meaning of the quoted passage is, the protections afforded in the listed modes don't apply/aren't available when the aircraft is leveled off...which makes sense. (It's interesting to note that ALT* is a protected mode).
What do they mean with -except level off is performed-?
level off as result of this speed protection or level off due to CRZ?
level off as result of this speed protection or level off due to CRZ?
As I understand and recall it, a "level-off" is a term that refers to a flight phase change from either the climb or descent phase to a leveling off (no change in altitude), even if the level-off is temporary. If the altitude at which the aircraft is leveled off has been entered in the MCDU PROG page under "CRZ", the FMGC enters the "ALT CRZ" mode for speed and power settings which use the CI and other information entered into the MCDU by the crew either at the start of the flight or during the manoeuvre. "ALT CRZ" is displayed on the PFDs.
If the level-off altitude is different than the altitude entered in the MCDU PROG page under CRZ, the FMGC enters the "ALT" mode and displays "ALT" on the PFD, indicating the difference between the MCDU setting and the captured altitude.
I suspect the meaning of the quoted passage is, the protections afforded in the listed modes don't apply/aren't available when the aircraft is leveled off...which makes sense. (It's interesting to note that ALT* is a protected mode).
Last edited by PJ2; 17th May 2012 at 21:41.
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Hi PJ2,
I think ALT* became a protected mode after this accident.
ASN Aircraft accident Airbus A330-321 F-WWKH Toulouse-Blagnac Airport (TLS)
It's interesting to note that ALT* is a protected mode.
ASN Aircraft accident Airbus A330-321 F-WWKH Toulouse-Blagnac Airport (TLS)
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The reason Alternate Law exists in the first place is to provide a graceful degradation so that pilots aren't dropped from Normal into Direct, which would be too jarring. It also provides a partial set of "soft" protections in certain circumstances. This makes sense for an airliner - it's not bad design.
One of the crucial factors that Airbus FBW pilots must (and usually do) understand is that the protections cannot be relied upon outside of Normal Law. There were no protections as soon as Alt2 was latched - the pilots should have been aware of this.
You can have computers operating on single data sources in a fighter with a bang seat, because if everything goes to plaid the single human occupant can egress safely in mid-air. This doesn't work for airliners, so the only safe way to apply the technology is to check, cross-check and re-check.