AF 447 Thread No. 6
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Hello airtren;
From BEA Final Report into TAROM A310 incident:-
Back to AF447. Semantics can always be an issue. Neutralizing the elevator demand means just that, i.e. if continuous demand is made either NU/ND the THS will move in that direction until such time as the SS is placed in the neutral position. In Alt Law the Alpha protections are not available, and for this reason the elevator demand becomes a THS command as explained. At no time was the SS placed in the neutral position which would have enabled the autotrim function to maintain 1g, so effectively that function was over-ridden by the PF. Hence my reason for saying that 'autotrim' had nothing to do with it.
As an example, go back and have a look at the the initial zoom climb. The initial elevator NU commands were not aided by the THS moving because the allowable 'g' in Alt Law was exceeded ([+1.25/-0.75] where did I get that? Don't know - must have read it somewhere). During the climb the THS moved to maintain the pitch attitude when the SS movements were nominally around the neutral position, but when the 'g' went negative it moved back to 3°NU and only started tracking toward maximum with continued SS NU as the aircraft proceeded to leave the flight envelope.
The red overlaid lines on the Normal Acceleration and Elevator traces are to highlight the similarities, while the THS is also similar but initially with little movement.
As usual, you or others may disagree and I am open to other interpretations.
From BEA Final Report into TAROM A310 incident:-
2.3.2 Analysis of the Stall Protection Logic
Stall protection is organized around three angle of attack thresholds, that for Alphafloor, that for Alpha-trim and that for triggering the stall warning (see 1.16.1.4).
Alpha-floor protection could not play its role as, when angle of attack of 14.5° was reached, the throttle levers were already on maximum thrust.
Alpha-trim protection was triggered at a value for angle of attack of slightly less than 15° in conditions where the flight dynamics were close to the extreme. It should be noted that it also functioned after coming out of the stall by giving the opposite order
to the THS.
The stall warning did not sound and the stick shaker did not operate in the flight phase prior to the stall. When questioned, the aircraft manufacturer indicated that the cause for non-operation of these two warnings was the disturbance of the angle of attack sensors due to the dynamics of the aircraft’s movements, with the speed having dropped below 60 kt before the angle of attack reached 17.5°. The flight crew had, however, been warned of the approach of a stall by buffeting.
Stall protection is organized around three angle of attack thresholds, that for Alphafloor, that for Alpha-trim and that for triggering the stall warning (see 1.16.1.4).
Alpha-floor protection could not play its role as, when angle of attack of 14.5° was reached, the throttle levers were already on maximum thrust.
Alpha-trim protection was triggered at a value for angle of attack of slightly less than 15° in conditions where the flight dynamics were close to the extreme. It should be noted that it also functioned after coming out of the stall by giving the opposite order
to the THS.
The stall warning did not sound and the stick shaker did not operate in the flight phase prior to the stall. When questioned, the aircraft manufacturer indicated that the cause for non-operation of these two warnings was the disturbance of the angle of attack sensors due to the dynamics of the aircraft’s movements, with the speed having dropped below 60 kt before the angle of attack reached 17.5°. The flight crew had, however, been warned of the approach of a stall by buffeting.
As an example, go back and have a look at the the initial zoom climb. The initial elevator NU commands were not aided by the THS moving because the allowable 'g' in Alt Law was exceeded ([+1.25/-0.75] where did I get that? Don't know - must have read it somewhere). During the climb the THS moved to maintain the pitch attitude when the SS movements were nominally around the neutral position, but when the 'g' went negative it moved back to 3°NU and only started tracking toward maximum with continued SS NU as the aircraft proceeded to leave the flight envelope.
The red overlaid lines on the Normal Acceleration and Elevator traces are to highlight the similarities, while the THS is also similar but initially with little movement.
As usual, you or others may disagree and I am open to other interpretations.
Elevators, THS and Trim
mm43
Back to AF447. Semantics can always be an issue. Neutralizing the elevator demand means just that, i.e. if continuous demand is made either NU/ND the THS will move in that direction until such time as the SS is placed in the neutral position. In Alt Law the Alpha protections are not available, and for this reason the elevator demand becomes a THS command as explained. At no time was the SS placed in the neutral position which would have enabled the autotrim function to maintain 1g, so effectively that function was over-ridden by the PF. Hence my reason for saying that 'autotrim' had nothing to do with it.
Back to AF447. Semantics can always be an issue. Neutralizing the elevator demand means just that, i.e. if continuous demand is made either NU/ND the THS will move in that direction until such time as the SS is placed in the neutral position. In Alt Law the Alpha protections are not available, and for this reason the elevator demand becomes a THS command as explained. At no time was the SS placed in the neutral position which would have enabled the autotrim function to maintain 1g, so effectively that function was over-ridden by the PF. Hence my reason for saying that 'autotrim' had nothing to do with it.
First some references out of LTTM (Technical training manual)
GENERAL
The pitch control is achieved by the two elevators and the THS via the computers, and controlled by the pitch side sticks orders or autopilot commands.
Max elevator deflection :
30° Nose up
15° Nose down.
Max THS deflection:
14° nose up (THS)
2° nose down.
In AP mode, the Flight Management, Guidance and Envelope Computers
(FMGEC) send the command orders to the FCPCs ; the FCPCs transmit them to the FCSCs
THS General
The aircraft has a Trimmable Horizontal Stabilizer (THS) , which has two elevators, for pitch trim control. The two elevators are attached to the trailing edge of the THS. The THS is attached to the rear fuselage and moves about an axis to permit pitch trim. The hydromechanical operation system of the THS (referredto as THS actuator) is controlled electrically by the Flight Control Primary Computers (FCPC) and mechanically.
Operation/Control and Indicating
There are three control modes for the THS:
autoflight (electrical control)
manual (electrical control)
standby (mechanical control)
In the autoflight mode the command signals fromthe autopilot are sent to the
FCPCs. The FCPCs transmit autotrim signals tothe electric motors which control the THS actuator.
In the manual mode the command signals from the side sticks are sent to the
FCPCs. The FCPCs transmit autotrim signals to the electric motors which control the THS actuator. The computers elaborate command orders to the servocontrols, depending on the different control laws.
In the standby mode the command signals are transmitted mechanically from
the control wheels to the override mechanism. The override mechanism cancels the autotrim signals from the FCPCs. It transmits the mechanical command signals directly to the hydraulic motors of the THS actuator.
ALTERNATE LAW WITHOUT PROTECTION
In this case, the pitch protections are lost except the load factor protection.
This alternate law without protection is activated in the FCPCs after a triple
ADR failure.
DIRECT LAW
In pitch Direct Law, all the pitch protections are lost.
The elevator deflection is proportional to stick deflection.
The autotrim function is lost and only the manual control of the THS is available.
Laws Reconfiguration - General
The reconfiguration of control laws is different in pitch axis and in lateral axis.
Control law reconfigurations are divided into two families :
- ALTERNATE
- DIRECT
In the event of loss of the normal control laws:
When the conditions required for keeping the normal control laws are no longer fulfilled, the control laws are reconfigured. The various degraded law states possible are (in flight or upon flare):
Roll and yaw:
- Yaw alternate law
Pitch:
- Nz law (with limited pitch rate and gains)
- Vc PROT law
- VMO2 law
- Pitch direct law
The laws called ”Alternate” are engaged when the protections related to the
normal laws (ALPHA 1, VM01) are lost.
The laws called ”Direct” are engaged when the Nz law is lost.
Pitch
The aircraft pitch control is achieved from the side sticks and in certain cases, from the pitch trim control wheels, which act on the elevators and on the THS, depending on the different laws.
Nz law
This law, elaborated in the FCPCs, is the normal pitch law engaged in the
flight phase.
Through a pitch action on the side stick, the pilot commands a load factor ;
the Nz law achieves this command, depending on the aircraft feedbacks, so
that:
- The short-term orders are achieved by the elevator servo controls.
- The long-term orders are achieved by the THS actuator (autotrim function).
The gains depend on the Vc, on the flap and slat position and on the CG
location.
In addition, the Nz law permits to achieve:
- A load factor limitation, depending on the flap and slat position.
- A bank angle compensation, for bank angles lower than 33°.
- A deflection limitation of the THS in the nose-up direction in the event of
the activation of the high angle-of-attackprotection, the excessive load
factor and the excessive bank angle exceeding.
The Nz law is such that the aircraft response is quasi independent of the
aircraft speed, weight, and CG location. If both ADIRUs are failed, the Nz
law is kept, but with limited pitch rate and gains. A consolidation of the vertical acceleration and pitch attitude rate is then performed via the two accelerometer units.
TURBULENCE DAMPING FUNCTION
General
The purpose of the Turbulence Damping Function implemented in the Electrical
Flight Control System is to damp the structural modes induced by atmospheric
turbulence.
Architecture
The Turbulence Damping Function consists of two lanes:
Longitudinal lane
The longitudinal Turbulence Damping command is computed by the FCPC1
(FCPC2 as a redundancy) as a function of the Nz accelerometer information.
It is added to the normal law command and transmitted to the associated elevator servo-controls.
Rear lateral lane
The rear lateral Turbulence Damping command is computed by the FCPC1
(FCPC3 as a redundancy) as a function of the informationof a specific Ny
accelerometer located at the rear bulkhead level.
It is added to the normal law command and transmitted to the associated yaw damper.
Specific equipment
The equipment specific to the Turbulence Damping Function are:
- the TURB. DAMP pushbutton switch
- the Ny front accelerometer
- the Ny rear accelerometer.
In the standby mode the command signals are transmitted mechanically from
the control wheels to the override mechanism. The override mechanism cancels the autotrim signals from the FCPCs. It transmits the mechanical command signals directly to the hydraulic motors of the THS actuator.
The pitch control is achieved by the two elevators and the THS via the computers, and controlled by the pitch side sticks orders or autopilot commands.
Max elevator deflection :
30° Nose up
15° Nose down.
Max THS deflection:
14° nose up (THS)
2° nose down.
In AP mode, the Flight Management, Guidance and Envelope Computers
(FMGEC) send the command orders to the FCPCs ; the FCPCs transmit them to the FCSCs
THS General
The aircraft has a Trimmable Horizontal Stabilizer (THS) , which has two elevators, for pitch trim control. The two elevators are attached to the trailing edge of the THS. The THS is attached to the rear fuselage and moves about an axis to permit pitch trim. The hydromechanical operation system of the THS (referredto as THS actuator) is controlled electrically by the Flight Control Primary Computers (FCPC) and mechanically.
Operation/Control and Indicating
There are three control modes for the THS:
autoflight (electrical control)
manual (electrical control)
standby (mechanical control)
In the autoflight mode the command signals fromthe autopilot are sent to the
FCPCs. The FCPCs transmit autotrim signals tothe electric motors which control the THS actuator.
In the manual mode the command signals from the side sticks are sent to the
FCPCs. The FCPCs transmit autotrim signals to the electric motors which control the THS actuator. The computers elaborate command orders to the servocontrols, depending on the different control laws.
In the standby mode the command signals are transmitted mechanically from
the control wheels to the override mechanism. The override mechanism cancels the autotrim signals from the FCPCs. It transmits the mechanical command signals directly to the hydraulic motors of the THS actuator.
ALTERNATE LAW WITHOUT PROTECTION
In this case, the pitch protections are lost except the load factor protection.
This alternate law without protection is activated in the FCPCs after a triple
ADR failure.
DIRECT LAW
In pitch Direct Law, all the pitch protections are lost.
The elevator deflection is proportional to stick deflection.
The autotrim function is lost and only the manual control of the THS is available.
Laws Reconfiguration - General
The reconfiguration of control laws is different in pitch axis and in lateral axis.
Control law reconfigurations are divided into two families :
- ALTERNATE
- DIRECT
In the event of loss of the normal control laws:
When the conditions required for keeping the normal control laws are no longer fulfilled, the control laws are reconfigured. The various degraded law states possible are (in flight or upon flare):
Roll and yaw:
- Yaw alternate law
Pitch:
- Nz law (with limited pitch rate and gains)
- Vc PROT law
- VMO2 law
- Pitch direct law
The laws called ”Alternate” are engaged when the protections related to the
normal laws (ALPHA 1, VM01) are lost.
The laws called ”Direct” are engaged when the Nz law is lost.
Pitch
The aircraft pitch control is achieved from the side sticks and in certain cases, from the pitch trim control wheels, which act on the elevators and on the THS, depending on the different laws.
Nz law
This law, elaborated in the FCPCs, is the normal pitch law engaged in the
flight phase.
Through a pitch action on the side stick, the pilot commands a load factor ;
the Nz law achieves this command, depending on the aircraft feedbacks, so
that:
- The short-term orders are achieved by the elevator servo controls.
- The long-term orders are achieved by the THS actuator (autotrim function).
The gains depend on the Vc, on the flap and slat position and on the CG
location.
In addition, the Nz law permits to achieve:
- A load factor limitation, depending on the flap and slat position.
- A bank angle compensation, for bank angles lower than 33°.
- A deflection limitation of the THS in the nose-up direction in the event of
the activation of the high angle-of-attackprotection, the excessive load
factor and the excessive bank angle exceeding.
The Nz law is such that the aircraft response is quasi independent of the
aircraft speed, weight, and CG location. If both ADIRUs are failed, the Nz
law is kept, but with limited pitch rate and gains. A consolidation of the vertical acceleration and pitch attitude rate is then performed via the two accelerometer units.
TURBULENCE DAMPING FUNCTION
General
The purpose of the Turbulence Damping Function implemented in the Electrical
Flight Control System is to damp the structural modes induced by atmospheric
turbulence.
Architecture
The Turbulence Damping Function consists of two lanes:
Longitudinal lane
The longitudinal Turbulence Damping command is computed by the FCPC1
(FCPC2 as a redundancy) as a function of the Nz accelerometer information.
It is added to the normal law command and transmitted to the associated elevator servo-controls.
Rear lateral lane
The rear lateral Turbulence Damping command is computed by the FCPC1
(FCPC3 as a redundancy) as a function of the informationof a specific Ny
accelerometer located at the rear bulkhead level.
It is added to the normal law command and transmitted to the associated yaw damper.
Specific equipment
The equipment specific to the Turbulence Damping Function are:
- the TURB. DAMP pushbutton switch
- the Ny front accelerometer
- the Ny rear accelerometer.
In the standby mode the command signals are transmitted mechanically from
the control wheels to the override mechanism. The override mechanism cancels the autotrim signals from the FCPCs. It transmits the mechanical command signals directly to the hydraulic motors of the THS actuator.
In layman term the SS commands loadfactor to the FCPC, where this demand is transfered to a n elevator deflection to achieve this demand. SS position does not represent elevator position. As can be seen in the FDR traces the elevators follow the computer demand, in our case the elevators stayed in the full NU position also when SS was not full up That´s because the computers tried to achieve the loadfactor demand. The THS was already full up and the aircraft could not achieve the desired loadfactor with full elevator NU. Later with relaxing of NU command and even with some ND command the reduction of the elevator from full NU was only by 15° to 15° NU, because that was enough to achieve the new corrected loadfactor demand. As the elevators where deflected NU, the trim command to the THS at that time would still have been NU instead of the necessary ND.
Only when the SS input would have been held ND long enough to change the loadfactor demand significantly (dont know if loadfactor protection would come into play) and the elevators would need a ND deflection to achieve this new load factor demand, then the THS trim would start to wind the THS down to neutralize the elevator position.
Why did the THS first not move, and later on continously full up? First the elevator authority was enough to execute the loadfactor demand with little deflection only, with decreasing speed the Computers ordered the elevators to further NU to follow the demand, and then the THS started to compensate for the elevator deflection. But the still decreasing speed and still present loadfactor demand led to a continuos NU command of the elevators and the THS in the following time frame.
To sum it up in my short words, pitch control in Alt2 is the same as in normal law with AP off, except vital protections lost. No change of Autotrim. The mainly NU input of PF ordered a loadfactor, which the computers could not achieve with elevators and autotrimming the THS in the decreasing speed environment. The few moments of reducing NU order or even giving ND order did not bring the elevator into the ND command region, therefore THS stayed all the way NU.
mm43
As an example, go back and have a look at the the initial zoom climb. The initial elevator NU commands were not aided by the THS moving because the allowable 'g' in Alt Law was exceeded ([+1.25/-0.75] where did I get that? Don't know - must have read it somewhere). During the climb the THS moved to maintain the pitch attitude when the SS movements were nominally around the neutral position, but when the 'g' went negative it moved back to 3°NU and only started tracking toward maximum with continued SS NU as the aircraft proceeded to leave the flight envelope.
As an example, go back and have a look at the the initial zoom climb. The initial elevator NU commands were not aided by the THS moving because the allowable 'g' in Alt Law was exceeded ([+1.25/-0.75] where did I get that? Don't know - must have read it somewhere). During the climb the THS moved to maintain the pitch attitude when the SS movements were nominally around the neutral position, but when the 'g' went negative it moved back to 3°NU and only started tracking toward maximum with continued SS NU as the aircraft proceeded to leave the flight envelope.
BEA in its report mentiones the ALT2B law as present, but does not describe in detail, what kind of protections had been lost and which ones still had been active. In my references i couldn´t find what the letter "B" in Alt2B stands for.
Would be interesting to know, how much unloading in term of g would have been accepted by those remaining protections. Because that again would influence elevator position and therefore autotrimming. Also if the turbulance dampening mode was activated and if that one would influence the response to inputs.
IMHO direct law from beginning might have led to an different outcome.
Sorry for the long post.
Last edited by Jetdriver; 20th Aug 2011 at 16:28.
That's the 1mio$ question.
And it effectively applies in this case.
Why did the PF pull half way NU ?
As others already said: In a non FBW aircraft at lower Alt it would have probably shed its feathers or wings (probably both) in much less than 5s after such a pull on the controls. He probably wouldn't have had enough time to sense the feedback and react before being reduced to a lawn dart.
And it effectively applies in this case.
Why did the PF pull half way NU ?
As others already said: In a non FBW aircraft at lower Alt it would have probably shed its feathers or wings (probably both) in much less than 5s after such a pull on the controls. He probably wouldn't have had enough time to sense the feedback and react before being reduced to a lawn dart.
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@ A33Zab. Thank you for your post :
Sorry, I have not been clear enough : at 02:10:06, AP disconnection was unexplained to the crew. (No ECAM message pointing clearly to the cause of this disconnection until 02:12:XX).
Isnt'it reasonable to assume they diagnosed some sort of "computer malfunction" ?
Maybe "users" need better real time information from the system to "understand" what the "smart design" is doing.
IMHO there is room for improvement in the way AP disconnects in those Airbii : AP should not be allowed to quit before a clear ECAM message pointing to the reason for disconnection is displayed.
Once again : "why is such a smart AP/FD system unable to maintain for a few seconds the average pitch of, say, the past 5 or 10", until the proper ECAM alert message is displayed ?"
GerardC :after the, so far unexplained, FBW malfunction
A33Zab : Nothing to explain here, there wasn't a FBW malfunction.
Isnt'it reasonable to assume they diagnosed some sort of "computer malfunction" ?
GerardC : and smarter design are solutions for a better flight safety
A33Zab : but what if a smart design is not understood and not properly used by the user? like AF477.
IMHO there is room for improvement in the way AP disconnects in those Airbii : AP should not be allowed to quit before a clear ECAM message pointing to the reason for disconnection is displayed.
Once again : "why is such a smart AP/FD system unable to maintain for a few seconds the average pitch of, say, the past 5 or 10", until the proper ECAM alert message is displayed ?"
http://www.smartcockpit.com/data/pdf...light_Laws.pdf
the loss of Low speed stability and High speed stability depend on the ADR's.
With dual ADR failure Low speed stability is lost, with triple ADR failure High speed stability is lost.
What is not quite clear to me is the question wether and if so how quickly these protections resume once ADR failure has been recovered.
With the speeds being around the 60kts threshold it would be interesting what that means for these speed stability functions.
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Hi GerardC,
I would go further and ask why it could not simply remain in some "ATT"itude where it would maintain pitch and bank as selected by the pilot with no protections. (CWS)
It would have given them more time to comprehend their status without having to struggle to maintain wings level. (I've still not flown in ALT Law at cruise FLs despite 7 years on A320s - and I don't think this crew had either)
why is such a smart AP/FD system unable to maintain for a few seconds the average pitch of, say, the past 5 or 10", until the proper ECAM alert message is displayed ?
It would have given them more time to comprehend their status without having to struggle to maintain wings level. (I've still not flown in ALT Law at cruise FLs despite 7 years on A320s - and I don't think this crew had either)
Last edited by rudderrudderrat; 20th Aug 2011 at 10:09. Reason: CWS
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RetiredF4 & airtren, if I wish to be provocative I can argue that AF447 suggests we have gone as far as we can go on transport aircraft which are not fully automated with no humans involved on the flight deck except as special deluxe SLF seats with all its controls disabled, permanently under computer control. That is an "improvement" in the current direction FBW is moving. {o.o}
At least with AF447, data available on the plane, and some improved computers and algorithms the pilots didn't even need to know there was a loss of airspeed indication from all three pitot tubes. There probably are other sorts of incidents that would benefit from a human pilot or two in the cockpit. But, if a rule can be evolved for the humans to follow, wouldn't a computer follow that rule better?
Humans are for when the rule based flying vanishes. But, the sense I get from descriptions of flight training as have floated through this discussion is that it is very very rule based with a lot of if-then-else-endif involved. That is a computer's playground. And on a computer's playground humans do very badly. While you add a three digit number in your head the computer has added millions or billions of them (depending on whether you are autistic or not.)
With that in mind, I am tempted to hand in my indictment for ABI, the airlines, and the regulators for trying to convert humans into computers following rules rather than having the computers follow the same rules with far better instrument scans for instruments the humans don't have a habit of scanning. Rule based actions are not the best use for humans.
At least with AF447, data available on the plane, and some improved computers and algorithms the pilots didn't even need to know there was a loss of airspeed indication from all three pitot tubes. There probably are other sorts of incidents that would benefit from a human pilot or two in the cockpit. But, if a rule can be evolved for the humans to follow, wouldn't a computer follow that rule better?
Humans are for when the rule based flying vanishes. But, the sense I get from descriptions of flight training as have floated through this discussion is that it is very very rule based with a lot of if-then-else-endif involved. That is a computer's playground. And on a computer's playground humans do very badly. While you add a three digit number in your head the computer has added millions or billions of them (depending on whether you are autistic or not.)
With that in mind, I am tempted to hand in my indictment for ABI, the airlines, and the regulators for trying to convert humans into computers following rules rather than having the computers follow the same rules with far better instrument scans for instruments the humans don't have a habit of scanning. Rule based actions are not the best use for humans.
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Clandestino, you don't seem to get it about communications.
Both pilots, PF and PNF need to start the communications ball rolling, "ATR/AP Disconnect. ALT 2". PF starts to control the plane. States what he is doing. (NU??) The PNF breaks in right there with the correct drill - control roll maintain pitch maintain thrust. If PF does not respond, then he really does need to be hit with a 2 day old dessicated pizza across the face to get his attention. A small inflatable beach ball would probably do.
You cannot have a team if the members never talk to each other so they know what they are doing unless they've worked together so long they KNOW almost instinctively what the other is going to do. SEAL team members may be at that peak of physical and mental condition to achieve this. Mortals like us have bad days. Chatter keeps the other person informed and offers the brain check when something breaks down.
I commented further about the automation above.
Both pilots, PF and PNF need to start the communications ball rolling, "ATR/AP Disconnect. ALT 2". PF starts to control the plane. States what he is doing. (NU??) The PNF breaks in right there with the correct drill - control roll maintain pitch maintain thrust. If PF does not respond, then he really does need to be hit with a 2 day old dessicated pizza across the face to get his attention. A small inflatable beach ball would probably do.
You cannot have a team if the members never talk to each other so they know what they are doing unless they've worked together so long they KNOW almost instinctively what the other is going to do. SEAL team members may be at that peak of physical and mental condition to achieve this. Mortals like us have bad days. Chatter keeps the other person informed and offers the brain check when something breaks down.
I commented further about the automation above.
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Clandestino asked, "Just when did he relax the backpressure? You are acquainted with sidestick traces from 3rd intermediate report, aren't you? A couple of times stick goes forward but quickly gets behind neutral again and stays there before elevators even have the chance to get to neutral."
Page 108 English report shows between 02:12:33 and 02:13:05 the elevator moved from the stop, -30, up to a peak of -15 and from 02:13:35 until 02:14:20 it again staggered towards neutral getting to a peak of -15, again. Those more or less agree with the stick inputs. (The times are approximate given the sizeof the graphs and my laziness.)
(Just providing times for you.)
Page 108 English report shows between 02:12:33 and 02:13:05 the elevator moved from the stop, -30, up to a peak of -15 and from 02:13:35 until 02:14:20 it again staggered towards neutral getting to a peak of -15, again. Those more or less agree with the stick inputs. (The times are approximate given the sizeof the graphs and my laziness.)
(Just providing times for you.)
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GerardC, I am not aware of any place in the BEA version of the FDR timelines where the ECAM messages are shown. Is there one? Or are you using ACARS times for those? Remember the ACARS reports are significantly delayed from what appears in the cockpit.
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@ airtren : You're welcome, Sir.
Please note the THS logic in normal law (from the FCOM):
NB : 2° ND is max position ND of the THS.
So basically, the idea I proposed is already the way Airbus'logic deals with the THS in Normal law. Let's do the same in Alternate law.
I do agree it won't have helped in other cases (i.e. Perpignan D-AXLA), but for the latter, 10" after the stall warning the aircraft go to Direct law for ~25" (then Alt law for the last 25" of flight) ; let's remind that in Direct law, there is no auto-trim (USE MAN PITCH TRIM) = no return to neutral for those 25" either, if we follow your proposed logic, then no help either.
Wrong, think g protection, still active in ALT2 (pitch is not direct, but it is protected)
Also, yaw (rudder) is not direct in ALT2 either, damping & compensation are provided. See the FCOM.
Not under 180kt.
Or are you advocating for a trim free aircraft? I agree with Clandestino on #181.
Wrong. See my previous post. One can see where the THS is.
Yes, I'm aware of that, airspeed was more in the 100kt range.
But the AoA remains unreliable under a (real) airspeed of 60kt. Then isn't having movable pitot probes a better solution than to remove the 60kt limit? Such probes exists, see the Rafale for example (one probe for AoA & pitot).
Please note the THS logic in normal law (from the FCOM):
Automatic pitch trim is frozen in the following cases:
- manual trim order
- radio altitude below 100ft for flare
- load factor lower than 0.5 g
- in high speed protection
When angle of attack protection is active, THS is limited between setting at entry in protection and 2° nose down (i.e. further nose up trim cannot be applied).
Similarly, when the load factor is higher than 1.3 g, or when the bank angle gets outside +/- 33°, the THS is limited between the actual setting and 2° nose down.
- manual trim order
- radio altitude below 100ft for flare
- load factor lower than 0.5 g
- in high speed protection
When angle of attack protection is active, THS is limited between setting at entry in protection and 2° nose down (i.e. further nose up trim cannot be applied).
Similarly, when the load factor is higher than 1.3 g, or when the bank angle gets outside +/- 33°, the THS is limited between the actual setting and 2° nose down.
So basically, the idea I proposed is already the way Airbus'logic deals with the THS in Normal law. Let's do the same in Alternate law.
I do agree it won't have helped in other cases (i.e. Perpignan D-AXLA), but for the latter, 10" after the stall warning the aircraft go to Direct law for ~25" (then Alt law for the last 25" of flight) ; let's remind that in Direct law, there is no auto-trim (USE MAN PITCH TRIM) = no return to neutral for those 25" either, if we follow your proposed logic, then no help either.
Also, yaw (rudder) is not direct in ALT2 either, damping & compensation are provided. See the FCOM.
Or are you advocating for a trim free aircraft? I agree with Clandestino on #181.
But the AoA remains unreliable under a (real) airspeed of 60kt. Then isn't having movable pitot probes a better solution than to remove the 60kt limit? Such probes exists, see the Rafale for example (one probe for AoA & pitot).
Last edited by AlphaZuluRomeo; 20th Aug 2011 at 11:46.
JD-EE
JD-EE
RetiredF4 & airtren, if I wish to be provocative I can argue that AF447 suggests we have gone as far as we can go on transport aircraft which are not fully automated with no humans involved on the flight deck except as special deluxe SLF seats with all its controls disabled, permanently under computer control. That is an "improvement" in the current direction FBW is moving. {o.o}
At least with AF447, data available on the plane, and some improved computers and algorithms the pilots didn't even need to know there was a loss of airspeed indication from all three pitot tubes. There probably are other sorts of incidents that would benefit from a human pilot or two in the cockpit. But, if a rule can be evolved for the humans to follow, wouldn't a computer follow that rule better?
Humans are for when the rule based flying vanishes. But, the sense I get from descriptions of flight training as have floated through this discussion is that it is very very rule based with a lot of if-then-else-endif involved. That is a computer's playground. And on a computer's playground humans do very badly. While you add a three digit number in your head the computer has added millions or billions of them (depending on whether you are autistic or not.)
RetiredF4 & airtren, if I wish to be provocative I can argue that AF447 suggests we have gone as far as we can go on transport aircraft which are not fully automated with no humans involved on the flight deck except as special deluxe SLF seats with all its controls disabled, permanently under computer control. That is an "improvement" in the current direction FBW is moving. {o.o}
At least with AF447, data available on the plane, and some improved computers and algorithms the pilots didn't even need to know there was a loss of airspeed indication from all three pitot tubes. There probably are other sorts of incidents that would benefit from a human pilot or two in the cockpit. But, if a rule can be evolved for the humans to follow, wouldn't a computer follow that rule better?
Humans are for when the rule based flying vanishes. But, the sense I get from descriptions of flight training as have floated through this discussion is that it is very very rule based with a lot of if-then-else-endif involved. That is a computer's playground. And on a computer's playground humans do very badly. While you add a three digit number in your head the computer has added millions or billions of them (depending on whether you are autistic or not.)
There was a time, when pilots used their knowledge (f.e. about aerodynamics, systems, navigation, flightphysiological aspects, weather, ATC, and so on ) to plan and execute the flight. There was a lot of self learned and self aquainted behaviour envolved, sometimes taught as "technique". That was hard work, left a lot room for errors and caused together also some undesired accidents.
New equipment together with automation reduced the workload significantly. To improve safety further, crew reaction to normal and abnormal procedures was developped and streamlined in think tanks from the manufacturer in relation to the new automated systems, and finally we´ve got what we have now and as you describe it.
Unfortunately the knowledge diminished or in some areas got lost in this process as well, as it seemed to be not needed any more. Look at the FCOM or FTCOM, it is a quarter the size of my old F4 Phantom aircraft Dash One. We aditionally had handouts about aerodynamics, navigation, WX, Radar operation, just to name a few. It got replaced by SOP and ECAM and QRH with step by step processes, which can be done by anybody who can read and operate the keyboard of a computer.
There seems to be no longer enough background knowledge available to understand, why those step by step procedures have to be followed and applied and what kind of reactions the application of those procedures will produce in the airframe.
There are for sure pilots out there and especially present in this forum, who still care and try to stay ahead of those procedures and not become the slave of them, but to be the knowlegable executioner of those procedures. They read accident reports, they talk with technicians and engineers, they ask questions and they make up their mind. And when they might find themselves in a similar situation like AF447, they will have learned from the case before the report is out and before the procedures had been changed. They would use manual trim to get the THS down although it is nowhere written in the procedures.
But how many of the pilots are participating here, how many are reading here (or in other similar forums), and how many just go home after their flight and call it a day? What are operaters doing to keep their pilots up to the notch, even improve their knowledge base except order the standard sim sessions? What do the regulators do to control and improve the knowledge after handing out the licence except to manage the renewal of the licence?
Its the system, that is sick and needs treatment badly.
Last edited by RetiredF4; 20th Aug 2011 at 12:05.
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Only if the ADR failure is really transient would the aircraft revert back to Normal law (and associated protections).
I wonder if one can guess that from the FDR traces. Perhaps with the FD availability?
However:
- The speed as NCD (no computed data / under 60kt) was more than transient => see § 1.16.6.1 of the 3rd report.
- The FPV was asked only shorly by the crew (during the end of the 2:11 minute IIRC), that's in the report.
Last edited by AlphaZuluRomeo; 20th Aug 2011 at 12:37.
Originally Posted by HarryMann
Also bear in mind that D. P Davies was writing quite a while ago now... technologically speaking.
Originally Posted by airtren
I was looking for your own words, and your own supporting explanation, as short statements alone are often too brief to be a platform for a discussion, and so can be a book reference
Opinions are debatable, facts shouldn't be so.
Originally Posted by airtren
Unfortunately, I don't have the technical means to share the collection of excellent documentation on theoretical and practical aspects of the workings of the THS and Elevators which I have, for being able to reciprocate.
Originally Posted by mm43
[+1.25/-0.75] where did I get that? Don't know - must have read it somewhere
Originally Posted by rudderrudderrat
I bet they would have felt it.
Originally Posted by JD-EE
Clandestino, you don't seem to get it about communications.
Both pilots, PF and PNF need to start the communications ball rolling, "ATR/AP Disconnect. ALT 2". PF starts to control the plane. States what he is doing.
Both pilots, PF and PNF need to start the communications ball rolling, "ATR/AP Disconnect. ALT 2". PF starts to control the plane. States what he is doing.
Indignant cries of "why can't the autopilot save us when we don't know what we're doing?" remind me of certain young first officer:
Originally Posted by Ernest Kelogg Gann
I can not bear to look at the instruments as Hughen is obliged to do. Their readings are bringing me very close to panic. Where is that rambunctious youth intrigued with the essence of danger? What is happening so very quickly to the young man who thought the present world suffered from oversecurity and produced only mice-hearted men? Captain Hughen, this is all an anachronism. We belong to modern world and should therefore be secure. Please arrange a remedy for this grievous mistake at once.
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Hi Clanddestino,
I disagree. Do you believe that pilots ignore any sense of delta g? Why don't Boeing pilot's pull their wings off?
Some crew's response to a TCAS RA in the simulator (where there is no change in sensed delta g) can be "over enthusiastic". In normal line flying, pilot pitch rate of change is adjusted according to sensed g.
When faced with an abundance of visual and audio information, the overloaded brain will only process selected bits at any one time. The sensed vertical acceleration would direct attention to pitch. It's part of the human behaviour feed back loop.
edit.
The last two are now done in a simulator which maintains its physical heading, and can only simulate long term horizontal accelerations or very short term vertical (e.g. light turbulence). There is no spatial disorientation in a simulator. What makes you think it is now properly trained?
Instrument rated pilots tend to fly according to instruments, not according to their senses.
Some crew's response to a TCAS RA in the simulator (where there is no change in sensed delta g) can be "over enthusiastic". In normal line flying, pilot pitch rate of change is adjusted according to sensed g.
When faced with an abundance of visual and audio information, the overloaded brain will only process selected bits at any one time. The sensed vertical acceleration would direct attention to pitch. It's part of the human behaviour feed back loop.
edit.
Definition of "properly trained IR pilot" includes, but is not limited to: proper initial IR training, proper type rating training and proper recurrent training.
Last edited by rudderrudderrat; 20th Aug 2011 at 13:57.
From post #201:
Turbulence damping is only available in Normal Law or with the Auto-pilot engaged (and above 200 KIAS).
In ALT 2 with ADR problems the A/P cannot be (re)-engaged, hence no turbulence damping involved here.
Also if the turbulance dampening mode was activated and if that one would influence the response to inputs.
In ALT 2 with ADR problems the A/P cannot be (re)-engaged, hence no turbulence damping involved here.
Thank you for the info, couldn´t find it myself.
Than can we assume that it was active before AP dropped out, as turbulence was expected?
How would that influence the FDR traces before and after AP dropout and would the AC behaviour be more rough thereafter, reflecting in the traces?
Than can we assume that it was active before AP dropped out, as turbulence was expected?
How would that influence the FDR traces before and after AP dropout and would the AC behaviour be more rough thereafter, reflecting in the traces?
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AZR Unprotected as in STALL protection. 'g' limits in AL2? So, yes, the STALL protection is lost, and that is not related to 'g' protection, as we see on the climb to STALL?
-0.75/+1.25 Inhibits the THS. The time spent on either side of these values meant the THS was not trimming. When 'g' returned to ~1, the THS went straight to FULLNU, to chase speeds.
Whether the THS is inhibited by T/Damping? Dunno.
As to the visibility of THS when it is following the Elevators, (on the panel), my question is meant to address the need for the THS at all, here, and only if it is absolutely necessary, should the scan be plumped up with yet another "Where is it?"
-0.75/+1.25 Inhibits the THS. The time spent on either side of these values meant the THS was not trimming. When 'g' returned to ~1, the THS went straight to FULLNU, to chase speeds.
Whether the THS is inhibited by T/Damping? Dunno.
As to the visibility of THS when it is following the Elevators, (on the panel), my question is meant to address the need for the THS at all, here, and only if it is absolutely necessary, should the scan be plumped up with yet another "Where is it?"
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Clandestino,
We don't have to exchange posts, if we can't keep it technical. I apologize in advance, if I got myself, or get in this post, side-tracked into "personal".
I was also looking for your own words, and your own logic, so that it would open up your own understanding, your own thinking, putting the apparent cliche arrogance of "I know better, you know nothing" aside, so we could talk science, ideas casually, as opposed to dismissive references to, or quotations from scripts.
This Forum can be fun, but can get boring if one takes himself too serious...
Discussion with people proposing improvement of the system of which basics they are unaware and unwilling to learn, can be productive only by pure chance. Opinions are debatable, facts shouldn't be so.
No, you would not find that there, as I am not quoting a script.
Did you think about it? Did you tell yourself what is the difference in its effect at deep Stall at high altitude, between an announced THS move to an Optimal Stall Recovery position (as mentioned, tbd, but Neutral as a start) by automation, and a THS moved by means of Manual Trim by the pilot?
We don't have to exchange posts, if we can't keep it technical. I apologize in advance, if I got myself, or get in this post, side-tracked into "personal".
I was also looking for your own words, and your own logic, so that it would open up your own understanding, your own thinking, putting the apparent cliche arrogance of "I know better, you know nothing" aside, so we could talk science, ideas casually, as opposed to dismissive references to, or quotations from scripts.
This Forum can be fun, but can get boring if one takes himself too serious...
Originally Posted by airtren
I was looking for your own words, and your own supporting explanation, as short statements alone are often too brief to be a platform for a discussion, and so can be a book reference.
Did you think about it? Did you tell yourself what is the difference in its effect at deep Stall at high altitude, between an announced THS move to an Optimal Stall Recovery position (as mentioned, tbd, but Neutral as a start) by automation, and a THS moved by means of Manual Trim by the pilot?
Last edited by airtren; 20th Aug 2011 at 17:04.