AF 447 Thread No. 11
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I don't see where is the problem?
If you want to say that it is merely a 'mode' of the normal law then fine, do so. But for me it would be truer to say that it is another control law which can only be accessed from normal law. In practice there is no similarity between the two things. In normal law stick movement commands 'g' in alphaprotect it commands AoA; in normal law there is a C* feedback, in alphaprotect there is no such thing.
Last edited by Jetdriver; 9th Nov 2013 at 23:06.
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Chris
I think your assumption of post phase advance needs to be modified. Let's say Valpha prot is 5 degrees (in cruise) and rapid increase in angle of attack causes protection mode to engage at 3 degrees but the rapid pitch up will take it past 5 degrees and when the gust has passed it will pitch down to 5 degrees. Where is the problem? If pitch up was gradual there won't be any phase advance and it would have engaged at 5 degrees and it will resist any more pitch up if possible or will come down to alpha prot when possible. Valpha Max gets adjusted and it is successfull maintained even in windshear. You cannot compare 447 because it was in alternate2. There is another likely misunderstanding about change in AOA mode to Load factor mode. From FCOM below
Thesystem will regain the normal load factor law if the stick is pushed forward ofneutral, but it will re-enter alpha protection if the stick is released with the angle of attack still greater than the value set for alpha protection. Thus to exit alpha protection properly, the pilot should reduce angle attack to a value less than the value set for alpha protection.
These are only mode changes and not pitch ups.
I think your assumption of post phase advance needs to be modified. Let's say Valpha prot is 5 degrees (in cruise) and rapid increase in angle of attack causes protection mode to engage at 3 degrees but the rapid pitch up will take it past 5 degrees and when the gust has passed it will pitch down to 5 degrees. Where is the problem? If pitch up was gradual there won't be any phase advance and it would have engaged at 5 degrees and it will resist any more pitch up if possible or will come down to alpha prot when possible. Valpha Max gets adjusted and it is successfull maintained even in windshear. You cannot compare 447 because it was in alternate2. There is another likely misunderstanding about change in AOA mode to Load factor mode. From FCOM below
Thesystem will regain the normal load factor law if the stick is pushed forward ofneutral, but it will re-enter alpha protection if the stick is released with the angle of attack still greater than the value set for alpha protection. Thus to exit alpha protection properly, the pilot should reduce angle attack to a value less than the value set for alpha protection.
These are only mode changes and not pitch ups.
Last edited by vilas; 9th Nov 2013 at 18:33.
Memory (off-topic)
Quote from Conf_iture, re the A320 Habsheim accident of 1988:
"Sorry Chris but I just can't understand your thinking here as part of the procedure to present the Airbus at high AoA is specifically to inhibit A/THR to prevent Alpha Floor to spoil the demonstration.
How can you suggest the guy was waiting for Alpha-Floor to kick in when his initial intention was to prevent it to interfere in the first place ?"
Salut Confit,
My off-topic reference to Habsheim was merely to illustrate that speed greater than M0.53 is not the only inhibition criterion for Alpha-Floor.
What you say suggests the game plan was even more cavalier than I remembered, and my memory of the tortuous, much-criticised investigation has faded.
That accident was 25 years ago, in our first summer of A320 ops. We fellow A320 pilots were naturally riveted by the excellent camcorder footage of the a/c descending gently into the treetops as the engines spooled up. Much speculation followed, but it was clear to us that the a/c had stabilised safely at Alpha-MAX, but lacked enough thrust to maintain its height.
I assumed the plan had been to stabilize at about Alpha-Prot, maintain height at that speed by increase of manual thrust while passing in front of the crowd, and then go-around. It never occurred to me at the time that the crew would have been reckless enough to attempt to stabilise at Alpha-MAX, as you seem to believe, disabling Alpha-Floor to enable that. I presumed that Alpha-Floor was being retained as a back-up, but that its inhibition below a certain height had been overlooked.
"Sorry Chris but I just can't understand your thinking here as part of the procedure to present the Airbus at high AoA is specifically to inhibit A/THR to prevent Alpha Floor to spoil the demonstration.
How can you suggest the guy was waiting for Alpha-Floor to kick in when his initial intention was to prevent it to interfere in the first place ?"
Salut Confit,
My off-topic reference to Habsheim was merely to illustrate that speed greater than M0.53 is not the only inhibition criterion for Alpha-Floor.
What you say suggests the game plan was even more cavalier than I remembered, and my memory of the tortuous, much-criticised investigation has faded.
That accident was 25 years ago, in our first summer of A320 ops. We fellow A320 pilots were naturally riveted by the excellent camcorder footage of the a/c descending gently into the treetops as the engines spooled up. Much speculation followed, but it was clear to us that the a/c had stabilised safely at Alpha-MAX, but lacked enough thrust to maintain its height.
I assumed the plan had been to stabilize at about Alpha-Prot, maintain height at that speed by increase of manual thrust while passing in front of the crowd, and then go-around. It never occurred to me at the time that the crew would have been reckless enough to attempt to stabilise at Alpha-MAX, as you seem to believe, disabling Alpha-Floor to enable that. I presumed that Alpha-Floor was being retained as a back-up, but that its inhibition below a certain height had been overlooked.
Quote from vilas:
Let's say Valpha prot is 5 degrees (in cruise) and rapid increase in angle of attack causes protection mode to engage at 3 degrees but the rapid pitch up will take it past 5 degrees and when the gust has passed it will pitch down to 5 degrees. Where is the problem? If pitch up was gradual there won't be any phase advance and it would have engaged at 5 degrees and it will resist any more pitch up if possible or will come down to alpha prot when possible.
Forgive me, but I'm finding it difficult to be sure which of your figures are AoA, and which are Pitch. My original concern about AoA-mode was that, if engaged by a brief up-gust, it may initiate the entry to a zoom climb with zero stick. This may have happened in the A340 AIRPROX incident, although the overspeed was also a factor in the pitch-up.
We seem to be repeating ourselves?
Let's say Valpha prot is 5 degrees (in cruise) and rapid increase in angle of attack causes protection mode to engage at 3 degrees but the rapid pitch up will take it past 5 degrees and when the gust has passed it will pitch down to 5 degrees. Where is the problem? If pitch up was gradual there won't be any phase advance and it would have engaged at 5 degrees and it will resist any more pitch up if possible or will come down to alpha prot when possible.
Forgive me, but I'm finding it difficult to be sure which of your figures are AoA, and which are Pitch. My original concern about AoA-mode was that, if engaged by a brief up-gust, it may initiate the entry to a zoom climb with zero stick. This may have happened in the A340 AIRPROX incident, although the overspeed was also a factor in the pitch-up.
We seem to be repeating ourselves?
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Laws
If you want to say that it is merely a 'mode' of the normal law then fine, do so.
But for me it would be truer to say that it is another control law which can only be accessed from normal law
But for me it would be truer to say that it is another control law which can only be accessed from normal law
In 'ALTERNATE 1' ALPHA 1 law is replaced by ALPHA 2 law.
Let us see what airbus has to say:
Control laws referred to as 'NORMAL'
- Roll and Yaw
in flight
- Lateral normal law
- Lateral ground law
in flight
- Nz law
- High angle-of-attack protection (ALPHA 1 law) [replaces Nz law]
- High speed protection (VMO 1 law) [modified Nz law)
- Pitch attitude protection [modified Nz law]
- Flare law
- Pitch direct law on ground
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Chris, more than anything, why Habsheim has not a thread on its own ...?
Taking advantage of the electronics it is much easier to stabilize at Alpha-Max, A/THR system being disconnected for the remainder of the flight, than trying to find Alpha-Prot without triggering Alpha-Floor.
Originally Posted by Chris Scott
I assumed the plan had been to stabilize at about Alpha-Prot, maintain height at that speed by increase of manual thrust while passing in front of the crowd, and then go-around. It never occurred to me at the time that the crew would have been reckless enough to attempt to stabilise at Alpha-MAX, as you seem to believe, disabling Alpha-Floor to enable that.
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Chris
It is not that I am averse to consider your view but in absence of any specific document or evidence I am unable to understand it. I am always looking for more information. I found something that may interest you. The change to AOA protection mode disengagement was done through MOI in 2005. With this software change AOA protection is no longer active when alpha is less than alpha prot and side stick has not been deflected since the last autopilot disconnection.
It is not that I am averse to consider your view but in absence of any specific document or evidence I am unable to understand it. I am always looking for more information. I found something that may interest you. The change to AOA protection mode disengagement was done through MOI in 2005. With this software change AOA protection is no longer active when alpha is less than alpha prot and side stick has not been deflected since the last autopilot disconnection.
Last edited by vilas; 10th Nov 2013 at 04:40.
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Originally Posted by vilas
No way. I think you should read flight controls chapter.
The sidestick was neutral between 01:00:33 and 01:02:06. During this time the pitch attitude increased "on its own" from 4 to 12 degrees, reduced to zero and increased again to 6 degrees.
Last edited by HazelNuts39; 10th Nov 2013 at 08:41.
vilas,
Thanks for the following information (my emphasis):
"The change to AOA protection mode disengagement was done through MOI in 2005. With this software change AOA protection is no longer active when alpha is less than alpha prot and side stick has not been deflected since the last autopilot disconnection."
Must say that the part that I've underlined is news, and doesn't concur with the 2011 FCOM extract posted here by DonH, or the BEA Report into the AF A340 Incident of 2011.
Have you quoted the MOI in 2005 verbatim? If so, in an identical repeat of the A340 AIRPROX of 2001, it would have prevented the engagement of AoA mode (referred to by the AAIB as AoA protection Law). Taken literally, that would represent a radical inhibition of engagement, not an additional means of disengagement.
If, on the other hand, "is no longer active" actually means "will disengage", it would be an additional means (condition, or criterion) for disengagement. But it would not apply if either sidestick had been moved during a period of hand flying. That would seem odd, but perhaps I'm overlooking something.
Thanks for the following information (my emphasis):
"The change to AOA protection mode disengagement was done through MOI in 2005. With this software change AOA protection is no longer active when alpha is less than alpha prot and side stick has not been deflected since the last autopilot disconnection."
Must say that the part that I've underlined is news, and doesn't concur with the 2011 FCOM extract posted here by DonH, or the BEA Report into the AF A340 Incident of 2011.
Have you quoted the MOI in 2005 verbatim? If so, in an identical repeat of the A340 AIRPROX of 2001, it would have prevented the engagement of AoA mode (referred to by the AAIB as AoA protection Law). Taken literally, that would represent a radical inhibition of engagement, not an additional means of disengagement.
If, on the other hand, "is no longer active" actually means "will disengage", it would be an additional means (condition, or criterion) for disengagement. But it would not apply if either sidestick had been moved during a period of hand flying. That would seem odd, but perhaps I'm overlooking something.
Last edited by Chris Scott; 10th Nov 2013 at 11:30. Reason: Last paragraph added.
A340 AIRPROX - pitch-up
Quote from me, commenting on A340 AIRPROX of 2001:
"... although the overspeed was also a factor in the pitch-up."
Reply from HN39:
"Was it ? ...."
I'm rather hoping you can answer that, HN39. After the overspeed of Mach triggered the disengagement of the AP, was the peak Mach of M0.882 corrected by EFCS overspeed protection, involving a pitch-up with neutral sidesticks?
There are obstacles facing many of us when reading the AAIB Bulletin.
(1) After AP disengagement, the precise timings of the increase in speed from M0.855 to M0.882, and the rate of speed decay thereafter, are not included in the narrative.
(2) The absence of a trace of the Mach parameter in their DFDR presentation. Many of us are unable to apply the necessary parameters of SAT and FL to calculate Mach from the CAS trace. So we cannot observe the changes of Pitch alongside Mach. An associated, perhaps minor, difficulty is the unclear annotations on their time scale.
(3) We do not have the overspeed-protection criteria pertaining to the a/c at that time. Was an overspeed of about M0.02 sufficient to trigger it?
On the other hand, did the rise of CAS in itself cause or contribute aerodynamically to the pitch-up? And what effect would such a rise of pitch have on the AoA, and its rate-of-change?
"... although the overspeed was also a factor in the pitch-up."
Reply from HN39:
"Was it ? ...."
I'm rather hoping you can answer that, HN39. After the overspeed of Mach triggered the disengagement of the AP, was the peak Mach of M0.882 corrected by EFCS overspeed protection, involving a pitch-up with neutral sidesticks?
There are obstacles facing many of us when reading the AAIB Bulletin.
(1) After AP disengagement, the precise timings of the increase in speed from M0.855 to M0.882, and the rate of speed decay thereafter, are not included in the narrative.
(2) The absence of a trace of the Mach parameter in their DFDR presentation. Many of us are unable to apply the necessary parameters of SAT and FL to calculate Mach from the CAS trace. So we cannot observe the changes of Pitch alongside Mach. An associated, perhaps minor, difficulty is the unclear annotations on their time scale.
(3) We do not have the overspeed-protection criteria pertaining to the a/c at that time. Was an overspeed of about M0.02 sufficient to trigger it?
On the other hand, did the rise of CAS in itself cause or contribute aerodynamically to the pitch-up? And what effect would such a rise of pitch have on the AoA, and its rate-of-change?
Last edited by Chris Scott; 10th Nov 2013 at 14:48. Reason: Last paragraph added.
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@CONF - I've invited you on several occasions to start your own Habsheim thread in AH&N (the logical place to have it, as the incident is over two decades old) - but you have not as yet done so.
@Chris - I think we do know that Alpha Floor was not a consideration for the pilot of AF296, as he *disabled* A/THR (and thus A. Floor) by holding down the disconnect switches to perform the flypast.
That is interesting HN39, but is it FCS elevator related?
Is the pitch variation because of the frozen trim in 'prot' and a potential for a speed change due to say pilot commanded thrust variation (basic speed stability)....with varying degrees of FCS 'AND' elevator command at times to hold alpha prot during the flight path changes either direction? I'll have to go back and find those traces for N1 and elevator and trim.
Hands off SS, I'm not sure that the FCS will ever command ANU elevator in a 'prot' situation. But I could be wrong. Range and direction of possible neutral SS FCS elevator commands in 'prot' seems to me to be the real question.
From a flight path stable entry to alpha prot with constant thrust, the elevator only goes 'AND' or neutral. Maybe the pitch/FPA variation has more to do with the trim effect during the FPA stable periods 'prot' was exited. But I may be missing something here as to the strange air mass effects.
(edit: I see Chris Scott is asking some of the same type questions.)
Is the pitch variation because of the frozen trim in 'prot' and a potential for a speed change due to say pilot commanded thrust variation (basic speed stability)....with varying degrees of FCS 'AND' elevator command at times to hold alpha prot during the flight path changes either direction? I'll have to go back and find those traces for N1 and elevator and trim.
Hands off SS, I'm not sure that the FCS will ever command ANU elevator in a 'prot' situation. But I could be wrong. Range and direction of possible neutral SS FCS elevator commands in 'prot' seems to me to be the real question.
From a flight path stable entry to alpha prot with constant thrust, the elevator only goes 'AND' or neutral. Maybe the pitch/FPA variation has more to do with the trim effect during the FPA stable periods 'prot' was exited. But I may be missing something here as to the strange air mass effects.
(edit: I see Chris Scott is asking some of the same type questions.)
Last edited by OK465; 10th Nov 2013 at 15:10. Reason: clarified AND & ANU
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I thought the Airprox theory was along the lines of:
We know from AF447 that at cruise level, there was enough kinetic energy at cruise thrust settings to allow the aircraft to climb when the PF pitched the nose up. So in the case of the airprox, an increase in thrust caused by A. Floor would not be necessary to make that aircraft climb.
"What's it doing now"? Simple - it's nose-high and climbing. Best get the nose down and back to our cleared FL, then. No need to worry about laws, modes, or pushing buttons - just do the intuitive thing and the aircraft's systems will comply in a fairly transparent manner.
- Gust triggered overspeed warning, probably engaging high-speed protection
- High speed protection raised the nose - possibly only a degree or so
- Second turbulent gust erroneously triggered either alpha protection or alpha floor
- If it was alpha prot, then the existing thrust settings were sufficient to cause the aircraft to climb as a result of the false overspeed protection
- Or if it was alpha floor, the increase in thrust caused the aircraft to climb in the same manner
We know from AF447 that at cruise level, there was enough kinetic energy at cruise thrust settings to allow the aircraft to climb when the PF pitched the nose up. So in the case of the airprox, an increase in thrust caused by A. Floor would not be necessary to make that aircraft climb.
"What's it doing now"? Simple - it's nose-high and climbing. Best get the nose down and back to our cleared FL, then. No need to worry about laws, modes, or pushing buttons - just do the intuitive thing and the aircraft's systems will comply in a fairly transparent manner.
AF447
Quote:
"Help me AB guys.
Had the pitot heaters not been frozen over the AB laws would not have allowed the AF crew to crash into the ocean. Do I have that correct?"
Hi aterpster,
Yes, we've rather shifted off topic... Probably in our efforts to increase our understanding of Airbus FBW, and its evolution, and thereby the mechanisms of FBW and CRM that were involved in AF447. Sometimes the shortest questions are the toughest to provide a short and straight answer! As none of the experts has picked up your question, I'll give it a go.
In your middle sentence, if we replace the clause "...would not have allowed the AF crew to crash into the ocean" with "...would not have allowed the a/c to enter and maintain a stall, even with the sidesticks fully back", the sentence would be correct. As it is, it's plainly wrong.
"Help me AB guys.
Had the pitot heaters not been frozen over the AB laws would not have allowed the AF crew to crash into the ocean. Do I have that correct?"
Hi aterpster,
Yes, we've rather shifted off topic... Probably in our efforts to increase our understanding of Airbus FBW, and its evolution, and thereby the mechanisms of FBW and CRM that were involved in AF447. Sometimes the shortest questions are the toughest to provide a short and straight answer! As none of the experts has picked up your question, I'll give it a go.
In your middle sentence, if we replace the clause "...would not have allowed the AF crew to crash into the ocean" with "...would not have allowed the a/c to enter and maintain a stall, even with the sidesticks fully back", the sentence would be correct. As it is, it's plainly wrong.
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Chris Scott
Why me? I probably know much less of the airplane than you do. My understanding is that activation/deactivation of any protection is recorded by the DFDR by a dedicated discrete parameter changing from OFF to ON, from ZERO to ONE, or whatever, and vice versa. (*) I think it would have been a very strange omission if overspeed protection had been activated and caused the pitch-up and the AAIB report had made no mention of that fact. It says instead: "For 18 seconds after the autopilot disengaged the aircraft remained within 200 feet altitude of FL 360 but once AoA law was invoked at 14:21:50 hrs, the aircraft’s attitude began to pitch nose-up."
Perhaps Owain G is better placed to answer that question. I think that an increase of CAS does not cause a pitch-up. It causes an increase of lift, and hence loadfactor ('gee'), and an AND response of the FCS in Nz law.
(*) A single byte in the data frame can contain up to eight 'discretes', each bit indicating the on/off status of a particular system function.
P.S.
I found a rather interesting description of the phase-advance logic for the A320 in this accident report:
"http://www.rvs.uni-bielefeld.de/publications/compendium/incidents_and_accidents/EC-HKJ.pdf"
The url failed for me, you have to go to PBL's site "rvs.uni-bielefeld.de" and follow the crumb-trail to the report.
Please note that this describes the A320 system and not the A330/340.
Reply from HN39:
"Was it ? ...."
I'm rather hoping you can answer that, HN39. After the overspeed of Mach triggered the disengagement of the AP, was the peak Mach of M0.882 corrected by EFCS overspeed protection, involving a pitch-up with neutral sidesticks?
"Was it ? ...."
I'm rather hoping you can answer that, HN39. After the overspeed of Mach triggered the disengagement of the AP, was the peak Mach of M0.882 corrected by EFCS overspeed protection, involving a pitch-up with neutral sidesticks?
On the other hand, did the rise of CAS in itself cause or contribute aerodynamically to the pitch-up? And what effect would such a rise of pitch have on the AoA, and its rate-of-change?
(*) A single byte in the data frame can contain up to eight 'discretes', each bit indicating the on/off status of a particular system function.
P.S.
I found a rather interesting description of the phase-advance logic for the A320 in this accident report:
"http://www.rvs.uni-bielefeld.de/publications/compendium/incidents_and_accidents/EC-HKJ.pdf"
The url failed for me, you have to go to PBL's site "rvs.uni-bielefeld.de" and follow the crumb-trail to the report.
Please note that this describes the A320 system and not the A330/340.
Last edited by HazelNuts39; 11th Nov 2013 at 07:21. Reason: asterix added
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@aterpster - Chris Scott is correct. I see a little mixing of terminology creeping into the discussion though, so I'm hoping that this crosspost from another thread may help. It is a very simplified description, but I think it's valid:
It is the *protections* that, as Chris says, "...would not have allowed the a/c to enter and maintain a stall, even with the sidesticks fully back". Where flight control laws come into it is that the hard alpha protections only function when the systems are in Normal Law.
The existence of those protections was never intended to allow the industry to cut back on training in manual handling and stall recovery.
- FBW is simply a concept whereby the link between the flight controls and flight surfaces is electronic as opposed to mechanical or pure hydraulic
- "Protections" in a FBW system are comparatively basic systems which will in most circumstances keep an aircraft that is already flying within a safe operating envelope
- FCS "laws" are simply a shorthand for system configurations that keep the aircraft handling as close to normally as possible in the event of systems failures
- FBW systems are *not* automation in the usual sense - they will not fly the aircraft for you, and they certainly won't prevent you from messing up an approach and landing!
The existence of those protections was never intended to allow the industry to cut back on training in manual handling and stall recovery.
Back to the future one mo' time
Doze has iterated the basic concept of FBW.
Where application/implementation problems come into play is how much "protection" is included in the software or hard-wired analog systems we had in the early years.
- GAINS: When we had mechanical connections like push rods or cables, you could actually feel the aero pressure on the control surfaces. Then we went to "augmented" systems with hydraulics. And then we went to pure hydraulics in just about all military fighters, but not the heavies. There were still mechanical connections for another 30 years for a few control surfaces.
To keep the plane from exceeding aero/gee limits, we had "gains". The pure hydraulic systems that I flew had springs and pneumatic bellows and bob weights and such. You could "feel" what the jet was doing and adapt. One jet that I flew had "protections" - the VooDoo. AoA and gee were monitored, and unless in a pure reversion mode we had AoA "protection" to keep from the dreaded "pitch up", so I was familiar with such when checking out in the Viper 13 years later.
FBW offered the opportunity to increase the "feel", but basically it simply limited the control surface movement and rates to make the jet "feel" like the old days. Ours was a force/pressure system, but the 'bus and Boeing systems have "movement" of the stick/yoke. Big deal. Most of my ilk never yanked the stick about but used small movements or simple pressure ( the hydraulic valves got lots better, and the A-7 had some electronics that used stick pressure to "augment" actual hydraulic valve commands). So checking out in the Viper was a breeze.
- PROTECTIONS: The Viper had real "protections" for both gee and AoA. We had no "direct control laws" unless the jet went out of control and AoA was above 30 degrees. Even then, we could only control the elevator ( stabilators) directly, and rudder/aileron surfaces remained under control of the computers.
Forget the gee protection. The big one was AoA protection, hence my interest in this discussion of the 'bus 340 uncommanded climb.
We did not have a mach protection for obvious reasons, but we did lose one fellow that tried to see how fast he could go. The motor fried, not the airframe.
- AUTOPILOT/NAV connections: This disturbs me more than the modes/laws of the 'bus and the Boeings.
We did not realize that our autopilot could not command above "x" AoA for a year or more. The GD flight control folks were scared about connections with their super FBW implementaion. So we had very limited otto inputs - heading select and altitude hold. That was all. So no flight management system connects or such.
Later jets had an auto throttle system ( Hornet), and I am not sure of the implementation. Most Nasal radiators and some of us in the SLUF and Viper flew AoA on approach and cross checked the speed to make sure we had the correct configuration.
So I get very concerned when I read about all the "protection" modes and the combinations of the nav system and otto and the FBW computers.
As a full-time SLF dude nowadays, I sometimes wish I could ride the jump seat to see how good the pilots are when Hal or Otto go FUBAR.
Sorry so long a post, but had to get this off my mind.
Where application/implementation problems come into play is how much "protection" is included in the software or hard-wired analog systems we had in the early years.
- GAINS: When we had mechanical connections like push rods or cables, you could actually feel the aero pressure on the control surfaces. Then we went to "augmented" systems with hydraulics. And then we went to pure hydraulics in just about all military fighters, but not the heavies. There were still mechanical connections for another 30 years for a few control surfaces.
To keep the plane from exceeding aero/gee limits, we had "gains". The pure hydraulic systems that I flew had springs and pneumatic bellows and bob weights and such. You could "feel" what the jet was doing and adapt. One jet that I flew had "protections" - the VooDoo. AoA and gee were monitored, and unless in a pure reversion mode we had AoA "protection" to keep from the dreaded "pitch up", so I was familiar with such when checking out in the Viper 13 years later.
FBW offered the opportunity to increase the "feel", but basically it simply limited the control surface movement and rates to make the jet "feel" like the old days. Ours was a force/pressure system, but the 'bus and Boeing systems have "movement" of the stick/yoke. Big deal. Most of my ilk never yanked the stick about but used small movements or simple pressure ( the hydraulic valves got lots better, and the A-7 had some electronics that used stick pressure to "augment" actual hydraulic valve commands). So checking out in the Viper was a breeze.
- PROTECTIONS: The Viper had real "protections" for both gee and AoA. We had no "direct control laws" unless the jet went out of control and AoA was above 30 degrees. Even then, we could only control the elevator ( stabilators) directly, and rudder/aileron surfaces remained under control of the computers.
Forget the gee protection. The big one was AoA protection, hence my interest in this discussion of the 'bus 340 uncommanded climb.
We did not have a mach protection for obvious reasons, but we did lose one fellow that tried to see how fast he could go. The motor fried, not the airframe.
- AUTOPILOT/NAV connections: This disturbs me more than the modes/laws of the 'bus and the Boeings.
We did not realize that our autopilot could not command above "x" AoA for a year or more. The GD flight control folks were scared about connections with their super FBW implementaion. So we had very limited otto inputs - heading select and altitude hold. That was all. So no flight management system connects or such.
Later jets had an auto throttle system ( Hornet), and I am not sure of the implementation. Most Nasal radiators and some of us in the SLUF and Viper flew AoA on approach and cross checked the speed to make sure we had the correct configuration.
So I get very concerned when I read about all the "protection" modes and the combinations of the nav system and otto and the FBW computers.
As a full-time SLF dude nowadays, I sometimes wish I could ride the jump seat to see how good the pilots are when Hal or Otto go FUBAR.
Sorry so long a post, but had to get this off my mind.
Re: F-GLZU
FWIW, the way I read the traces shows....
Except for the initial pilot commanded pitch up (FO SS ANU -11) in the first period of alpha prot activation (and maybe the reason for it?), every subsequent entry into alpha prot shows an initial pitch attitude decrease as Mach decays, particularly pronounced at the lowest Mach numbers which is what I would expect.
True, there are minor <1 or so degree pitch variations after those initial pitch downs that I would think could be attributable to 'rough air' and FCS lag. Pitch trend is down or stable.
There are 3 or 4 very minor pitch oscillations (time scale proportioned) in that final long period of apha prot, but in general, with the trim frozen ('prot' occurred at around minimum Mach) in alpha prot, pitch does not trend an increase until calculated Mach number tends to increase continuously from a low of around 0.68 and I would assume there would be a noticeable CAS increase and associated frozen trim pitch up effect to maintain trim speed with this, especially since altitude is still generally decreasing further increasing CAS for the Mach. Possibly even FCS 'AND' elevator commands during this pitch increase. Elevator trace would be nice.
However with the apparent errors (pedantic or not) in the 2 AAIBs, i.e. 'probably alpha floor' with the minimum Mach of 0.67 in the Airprox event and the reference to an 'amber AP OFF' message in this event, I'm beginning to lose my warm fuzzy about the learning value of some of these reports.
Except for the initial pilot commanded pitch up (FO SS ANU -11) in the first period of alpha prot activation (and maybe the reason for it?), every subsequent entry into alpha prot shows an initial pitch attitude decrease as Mach decays, particularly pronounced at the lowest Mach numbers which is what I would expect.
True, there are minor <1 or so degree pitch variations after those initial pitch downs that I would think could be attributable to 'rough air' and FCS lag. Pitch trend is down or stable.
There are 3 or 4 very minor pitch oscillations (time scale proportioned) in that final long period of apha prot, but in general, with the trim frozen ('prot' occurred at around minimum Mach) in alpha prot, pitch does not trend an increase until calculated Mach number tends to increase continuously from a low of around 0.68 and I would assume there would be a noticeable CAS increase and associated frozen trim pitch up effect to maintain trim speed with this, especially since altitude is still generally decreasing further increasing CAS for the Mach. Possibly even FCS 'AND' elevator commands during this pitch increase. Elevator trace would be nice.
However with the apparent errors (pedantic or not) in the 2 AAIBs, i.e. 'probably alpha floor' with the minimum Mach of 0.67 in the Airprox event and the reference to an 'amber AP OFF' message in this event, I'm beginning to lose my warm fuzzy about the learning value of some of these reports.