AF447 Thread No. 3
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Hi BOAC
Your latter point is correct to me... they "aren't" (or rather, don't need to).
You do not fundamentally fly the aircraft "differently" in each of the laws. Pull stick back, cows get smaller etc. Yes - Direct Law is a little more "twitchy", but nothing dramatic. Yes - Direct Law needs manual trim, but it tells you that on the AH in Red.
There are "various" flavours of Alternate Law, depending on "how" it got into Altn (or rather, what failed). And they are not fully described in the manuals (nor IMHO do they need to be). If this unique to Airbus? No - I tried reading up the 767 split Control Column / elevator system post the Egyptair accident, and the manuals were again vague - sufficient I would say to fly it, not sufficient to build/mend it, or investigate an accident related to it.
The main difference between the laws is what "protection(s)" are available. In that you never routinely fly to / use those protections, then life goes on as before.
Before over-analysing this accident, we ought to let the BEA analyse it, and see if the stall warnings could have been more helpful. It seems they may have been suppressed at <60K (?) which is pretty much beyond where we expect people to be relying on them, and potentially well beyond certification requirements and controllability?
I am now reeling in a state of shock to find that there are not just 2 'Alternate Law' programmes but at least 5 (Post #1311) and I am wondering how on earth a human is supposed to work out wtf is going on - or perhaps he/she isn't?
You do not fundamentally fly the aircraft "differently" in each of the laws. Pull stick back, cows get smaller etc. Yes - Direct Law is a little more "twitchy", but nothing dramatic. Yes - Direct Law needs manual trim, but it tells you that on the AH in Red.
There are "various" flavours of Alternate Law, depending on "how" it got into Altn (or rather, what failed). And they are not fully described in the manuals (nor IMHO do they need to be). If this unique to Airbus? No - I tried reading up the 767 split Control Column / elevator system post the Egyptair accident, and the manuals were again vague - sufficient I would say to fly it, not sufficient to build/mend it, or investigate an accident related to it.
The main difference between the laws is what "protection(s)" are available. In that you never routinely fly to / use those protections, then life goes on as before.
Before over-analysing this accident, we ought to let the BEA analyse it, and see if the stall warnings could have been more helpful. It seems they may have been suppressed at <60K (?) which is pretty much beyond where we expect people to be relying on them, and potentially well beyond certification requirements and controllability?
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Power at stall examples
"In June 2007 a Boeing 737-300 had an uncommanded and unrecognised autothrottle disconnect during the initial stages of an approach to Belfast Aldergrove Airport. The disconnect occurred with the thrust levers at idle and the aircraft decelerated below its commanded speed of 170 kt. At 112 kt with a 16° nose-up attitude the crew advanced the engines to 96% N1 and a rapid change of pitch to 22° ensued. The aircraft lost some 300 feet before recovering to manoeuvre speed and level flight."
Thomson Fly Pilot notes:
"The operator’s QRH procedure for upset recovery is set out in Appendix B3. The ‘upset recovery’ QRH defines an upset as unintentionally exceeding a pitch angle greater than 25º nose-up. The procedure states:
‘If needed, use pitch trim sparingly.’
The procedure continues:
‘These techniques assume that the aircraft is not stalled. A stall condition can exist at any attitude and may be recognised by continuous stick-shaker activation accompanied by one or more of the following:
Buffeting which could be heavy at times●●
Lack of pitch authority and/or roll control●●
Inability to arrest descent rate●●
If the airplane is stalled, recovery from the stall must be accomplished first by applying and maintaining nose down elevator until stall recovery is complete and stick-shaker activation ceases.’
The upset recovery procedure requires the pilot flying to carry out certain actions including:
25
Apply as much as full nose-down elevator●●
Apply appropriate nose down stabilizer trim●●
Reduce thrust’●●"
MORE DETAIL HERE:
http://www.aaib.gov.uk/cms_resources...%20G-THOF1.pdf
Thomson Fly Pilot notes:
"The operator’s QRH procedure for upset recovery is set out in Appendix B3. The ‘upset recovery’ QRH defines an upset as unintentionally exceeding a pitch angle greater than 25º nose-up. The procedure states:
‘If needed, use pitch trim sparingly.’
The procedure continues:
‘These techniques assume that the aircraft is not stalled. A stall condition can exist at any attitude and may be recognised by continuous stick-shaker activation accompanied by one or more of the following:
Buffeting which could be heavy at times●●
Lack of pitch authority and/or roll control●●
Inability to arrest descent rate●●
If the airplane is stalled, recovery from the stall must be accomplished first by applying and maintaining nose down elevator until stall recovery is complete and stick-shaker activation ceases.’
The upset recovery procedure requires the pilot flying to carry out certain actions including:
25
Apply as much as full nose-down elevator●●
Apply appropriate nose down stabilizer trim●●
Reduce thrust’●●"
MORE DETAIL HERE:
http://www.aaib.gov.uk/cms_resources...%20G-THOF1.pdf
Isn't there an Abnormal Attitude Law as well which was frustrated in this case ?
http://www.pprune.org/tech-log/42692...-airbus-2.html
http://www.pprune.org/tech-log/42692...-airbus-2.html
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Icing, Unikely Or Not?
Bear,
Your quote:
From the Vasquez June 1, 2011 report update:
Just thought it would be good to point this out.
Your quote:
For all we know, she lost a radome into the F/O's Pitot. If one spends enough time with Vasquez' product, ICE is unlikely.
With a flight level temperature of -40 deg C suggested by the proximity sounding (and -36 deg C parcel temperatures) the A330 would be exposed mainly to frozen ice particles and perhaps graupel.
Due to the airspeed sensor problems mentioned at 0210 UTC on the data transcripts, however, this does raise the possibility of icing-induced blockage of the pitot tubes, if not some other electronic or mechanical source of failure.
Tropical storm complexes identical to or stronger than this one have probably been crossed hundreds or thousands of times over the years by other flights without serious incident, including ascents and descents through critical icing zones in tropical showers. My original conclusion from June 2011 is still unchanged: turbulence and possibly icing creating an initial problem that led to a failure cascade.
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Turbine D;
Perhaps you should think twice before adding to the semantic confusion on this and other threads about 'icing'. Icing is the formation of ice due to freezing of liquid water. Transport airplanes, their engines and pitots are approved for flight in icing conditions after demonstrating that capability in extensive tests in natural as well as simulated icing conditions, and by flying with simulated ice shapes. All experts agree that these conditions do not exist at -40 °C. I am grateful to Tim Vasquez' excellent analysis of the meteorological conditions of the accident, but I understand from your middle quote, that he may not be aware of recent research triggered by events in which turbine engines suffered thrust loss flying in clouds of ice particles at altitudes and temperatures similar to the conditions of AF447. A number of publications from the Boeing stable explain the theory developed to explain the mechanism that causes atmospheric ice particles to stick to heated surfaces, such as engine intakes or pitots. Are you aware of these?
Perhaps you should think twice before adding to the semantic confusion on this and other threads about 'icing'. Icing is the formation of ice due to freezing of liquid water. Transport airplanes, their engines and pitots are approved for flight in icing conditions after demonstrating that capability in extensive tests in natural as well as simulated icing conditions, and by flying with simulated ice shapes. All experts agree that these conditions do not exist at -40 °C. I am grateful to Tim Vasquez' excellent analysis of the meteorological conditions of the accident, but I understand from your middle quote, that he may not be aware of recent research triggered by events in which turbine engines suffered thrust loss flying in clouds of ice particles at altitudes and temperatures similar to the conditions of AF447. A number of publications from the Boeing stable explain the theory developed to explain the mechanism that causes atmospheric ice particles to stick to heated surfaces, such as engine intakes or pitots. Are you aware of these?
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Originally Posted by Jazz Hands
Perhaps you're trying to inject your own "spin" with your accusation, for which you appear to provide no evidence.
has not much to do with the BEA note.
Who are you working for Mr Learmount ... ?
Originally Posted by DozyWannabe
And this is not specific to Airbus aircraft CONF. The fact is that when you have pitot/static failure, all bets are off when it comes to warnings/indications and the crew must concentrate extremely hard to work out what's going on.
As long as AoA data are in the STALL range ... keep WARNING !
Originally Posted by alex_brin
"Je ne comprends rien"
BOAC:
Fully agree!
And number 2 is that when airspeed information, something that the flight control system relies on heavily, becomes unreliable, that autotrim of the THS should drop out with the autopilot.
We won't know until we can see the plot of stick motion but it seems to me that the PF didn't know, or forgot, that when he pulled back on the stick, he was trimming into the stall. Do we know that the initial pitch excursion was the result of some action of the flight control system and/or the autopilot, or was it the result of PF action in response to erroneous indications?
It seems that a number 1 priority is that AB recognise that their aircraft can stall....
And number 2 is that when airspeed information, something that the flight control system relies on heavily, becomes unreliable, that autotrim of the THS should drop out with the autopilot.
We won't know until we can see the plot of stick motion but it seems to me that the PF didn't know, or forgot, that when he pulled back on the stick, he was trimming into the stall. Do we know that the initial pitch excursion was the result of some action of the flight control system and/or the autopilot, or was it the result of PF action in response to erroneous indications?
Last edited by Smilin_Ed; 5th Jun 2011 at 15:11. Reason: Clarity
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TurbineD
Vasquez:
Quote: "...With a flight level temperature of -40 deg C suggested by the proximity sounding (and -36 deg C parcel temperatures) the A330 would be exposed mainly to frozen ice particles and perhaps graupel..."
and:
"...Quote: Tropical storm complexes identical to or stronger than this one have probably been crossed hundreds or thousands of times over the years by other flights without serious incident, including ascents and descents through critical icing zones in tropical showers. My original conclusion from June 2011 is still unchanged: turbulence and possibly icing creating an initial problem that led to a failure cascade..."
Here, he isolates icing as ascent and descent related.
Here, Vasquez suggests an exposure to frozen "ice particles" and "graupel".
There is no water available, and any ICE related problem would be a "packing" of the Pitot void by micronucleated ice. As Hazelnuts39 points out, a loss of power due to this phenomenon is known, particles sticking to engine parts, (including blades, I think.) Engines have anti icing.
For ICE to plug the Pitot at its orifice, ice particles would have to attach, or enter and pack, or melt and refreeze, to include a plug of the drain, which itself has a proclivity for corroded drain holes.
I believe this is the only way pitots could be plugged in the FL Vasquez is researching. This phenomenon could be eliminated (has been?) by BEA with a simple examination of leading edges of structure, inspecting for the typical abrasion of metal, composite, and painted surfaces caused by solid ice particles impacting at high speed.
That's it for me on ICE, what I think happened is Unusual attitudes caused a discrepancy in airflows into and past the separate Pitot Tubes, and causing sufficient data disruption to fault the AD(IRU). Coupled with a large turbulent flow that may have upset airflow rates, the sequence of events at a/p disconnect (and prior to) was likely the beginning of UAS. If turbulence related, there was a prior input that caused (perhaps) the a/p drop due its own mechanical limits, these limits serving to cause the drop and subsequent upset.
Again, the previous fifteen seconds to a/p drop, and the following 15 seconds seem to me to be the beginning of the accident.
Vasquez:
Quote: "...With a flight level temperature of -40 deg C suggested by the proximity sounding (and -36 deg C parcel temperatures) the A330 would be exposed mainly to frozen ice particles and perhaps graupel..."
and:
"...Quote: Tropical storm complexes identical to or stronger than this one have probably been crossed hundreds or thousands of times over the years by other flights without serious incident, including ascents and descents through critical icing zones in tropical showers. My original conclusion from June 2011 is still unchanged: turbulence and possibly icing creating an initial problem that led to a failure cascade..."
Here, he isolates icing as ascent and descent related.
Here, Vasquez suggests an exposure to frozen "ice particles" and "graupel".
There is no water available, and any ICE related problem would be a "packing" of the Pitot void by micronucleated ice. As Hazelnuts39 points out, a loss of power due to this phenomenon is known, particles sticking to engine parts, (including blades, I think.) Engines have anti icing.
For ICE to plug the Pitot at its orifice, ice particles would have to attach, or enter and pack, or melt and refreeze, to include a plug of the drain, which itself has a proclivity for corroded drain holes.
I believe this is the only way pitots could be plugged in the FL Vasquez is researching. This phenomenon could be eliminated (has been?) by BEA with a simple examination of leading edges of structure, inspecting for the typical abrasion of metal, composite, and painted surfaces caused by solid ice particles impacting at high speed.
That's it for me on ICE, what I think happened is Unusual attitudes caused a discrepancy in airflows into and past the separate Pitot Tubes, and causing sufficient data disruption to fault the AD(IRU). Coupled with a large turbulent flow that may have upset airflow rates, the sequence of events at a/p disconnect (and prior to) was likely the beginning of UAS. If turbulence related, there was a prior input that caused (perhaps) the a/p drop due its own mechanical limits, these limits serving to cause the drop and subsequent upset.
Again, the previous fifteen seconds to a/p drop, and the following 15 seconds seem to me to be the beginning of the accident.
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unrecoverable stall
In the latest issue of Airbus Safety First magazine captain Rosay mentions a couple of times "unrecoverable stall"
An Airbus 330 can get so deep in a stall that you don't have any means to recover from it even if it stalls a a high level?
An Airbus 330 can get so deep in a stall that you don't have any means to recover from it even if it stalls a a high level?
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Glide characteristics
grity ....... every pilot has to build and flow free flow models before he learn to control computers .........
QUESTION: Would you say, then, that anyone with a good model of an Airbus A330-200 with the correct CG etc, could give its HS a 13° nose-up trim and thereby demonstrate its glide characteristics?
Maybe somebody could do this and put a video on U-tube?
I have heard that Rutan's first test of the Spaceship 1 concept was done this way - he threw his model off the top of a building.
It was enough to show the concept was valid.
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CONF iture,
Indeed he suggests (most likely poor editing of the article) the PF initiated the climb before A/P and A/T disconnected. He should have swapped paragraphs 3 and 4 to concur with the BEA note's sequence of events:
Just need to read, this one Air France 447: the facts and what's behind them
has not much to do with the BEA note.
Who are you working for Mr Learmount ... ?
has not much to do with the BEA note.
Who are you working for Mr Learmount ... ?
1. On page 1 the report sets the scene on the flight deck. The captain has gone for a rest, and has been replaced by a supernumerary First Officer. That is standard for long flights.
2. The aircraft is cruising at FL350 (35,000ft) and there are storm clouds in the area, as there always are in the inter-tropical convergence zone. The two copilots are aware of them. The pilot flying (PF) briefs the copilot who has just taken the captain's seat that they are in choppy air but cannot climb above it because the aircraft's weight and the relatively high outside air temperature means that they are about as high as the aircraft can safely go until it has used up more fuel.
3. A few minutes later the PF makes a sidestick control input which raises the nose and causes the aircraft to climb rapidly to 38,000ft. There was no reason to climb, the PF did not announce an intention to do it, and the aircraft was not cleared by ATC to do so. The natural result of climbing without an increase in power is a loss of speed. But we'll deal with that shortly.
4. The problems for the pilots began when the autopilot(AP)/autothrottle (AT) disconnected. The disconnect occurred because there was a temporary disagreement between two independent airspeed sensors (pitot tubes) about what speed the aircraft was flying at. When there is a disagreement between two inputs to the flight control computers, the computers do not adjudicate, they abdicate control to the pilots.
2. The aircraft is cruising at FL350 (35,000ft) and there are storm clouds in the area, as there always are in the inter-tropical convergence zone. The two copilots are aware of them. The pilot flying (PF) briefs the copilot who has just taken the captain's seat that they are in choppy air but cannot climb above it because the aircraft's weight and the relatively high outside air temperature means that they are about as high as the aircraft can safely go until it has used up more fuel.
3. A few minutes later the PF makes a sidestick control input which raises the nose and causes the aircraft to climb rapidly to 38,000ft. There was no reason to climb, the PF did not announce an intention to do it, and the aircraft was not cleared by ATC to do so. The natural result of climbing without an increase in power is a loss of speed. But we'll deal with that shortly.
4. The problems for the pilots began when the autopilot(AP)/autothrottle (AT) disconnected. The disconnect occurred because there was a temporary disagreement between two independent airspeed sensors (pitot tubes) about what speed the aircraft was flying at. When there is a disagreement between two inputs to the flight control computers, the computers do not adjudicate, they abdicate control to the pilots.
BOAC, #1399
question, search terms such as "PGF Airbus accident" and "PJ2", but no
luck. Perhaps there are external links that describe transitions between
laws and the conditions leaning up to them ?.
Something a bit more in depth than "user guide" level would be good. A
control law manual for the 330 perhaps ?...
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Airbus knows, and always has, that their aircraft can stall. Airbus state, and always have, that their aircraft can stall. So where does this "cannot stall" come from, who is saying it ? Are there really actual airbus pilots (as opposed to clueless journalists etc) who believe their a/c cannot stall ? If so, the training is way more broken than even the most extreem comments on this thread have suggested.
And number 2 is that when airspeed information, something that the flight control system relies on heavily, becomes unreliable, that autotrim of the THS should drop out with the autopilot.
I am starting to believe that from a user interface point of view, autotrim should either be always on (extension of elevator control, always) or always off. Failure to make the transition from auto to manual trim is becoming a pattern in an lengthening list of accidents and incidents.
We won't know until we can see the plot of stick motion but it seems to me that the PF didn't know, or forgot, that when he pulled back on the stick, he was trimming into the stall. Do we know that the initial pitch excursion was the result of some action of the flight control system and/or the autopilot, or was it the result of PF action in response to erroneous indications?
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Microburst2002
Captain Rosay is a cagey old test pilot. If he says that, he may have seen indications in some of their test data pointing to that conclusion, but I doubt that AB has strayed very far from the immediate area around the stall in their test flying. It is just too risky to do deep stall work. (But see my post in the other AF447 thread http://www.pprune.org/6494757-post1415.html) He has also no doubt seen wind tunnel test results at high AOA.
But to me, the initial description of the AF447 descent seems to indicate that they could have retrimmed the THS and recovered. We will have to see what BEA says about it.
An Airbus 330 can get so deep in a stall that you don't have any means to recover from it even if it stalls a a high level?
But to me, the initial description of the AF447 descent seems to indicate that they could have retrimmed the THS and recovered. We will have to see what BEA says about it.
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HazelNuts 39,
I am sorry if the term "icing" confused the situation, it was a word Tim Vasquez used in his report I quoted from and I didn't change it. I believe icing is when supercooled water encounters a surface and then freezes. In the case of AF447, this was not the case. There was no supercooled water involved to the best of the weather expert's knowledge.
What I was attempting to say was the aircraft passed through a cloud or clouds containing ice crystals which, when coming into contact with wetted heated surfaces, can stick and buildup. I am very aware this phenomenon can and does cause problems with turbofan engines to varying degrees depending on a particular engine design. As Boeing studies have indicated, the ice buildup can both adversely affecting engine airfoil aerodynamics (power loss) and in severe cases, damaged compressor blading (ice shedding) or even cause combustor flame outs (water extinguishes the flame).
From what has been said so far by the BEA, the GE CF6-80E engines were not affected and performed in a normal manner. However, I am not so sure the pitot tubes did, they could have indeed clogged which lead to the erroneous speed sensing and eventually the AP/AT disconnect.
Indeed there is considerable testing done during the initial development and certification testing of new turbofan engines to determine effects of ice ingestion, large and small particles and shedding characteristics. I have seen it done in person on several occasions.
As Boeing points out, it is best to avoid areas of storms where ice crystals are present as the volume tends to be unknown and onboard weather radar may not detect the presence of ice crystals at all.
I stand to be corrected on any of the above.
I am sorry if the term "icing" confused the situation, it was a word Tim Vasquez used in his report I quoted from and I didn't change it. I believe icing is when supercooled water encounters a surface and then freezes. In the case of AF447, this was not the case. There was no supercooled water involved to the best of the weather expert's knowledge.
What I was attempting to say was the aircraft passed through a cloud or clouds containing ice crystals which, when coming into contact with wetted heated surfaces, can stick and buildup. I am very aware this phenomenon can and does cause problems with turbofan engines to varying degrees depending on a particular engine design. As Boeing studies have indicated, the ice buildup can both adversely affecting engine airfoil aerodynamics (power loss) and in severe cases, damaged compressor blading (ice shedding) or even cause combustor flame outs (water extinguishes the flame).
From what has been said so far by the BEA, the GE CF6-80E engines were not affected and performed in a normal manner. However, I am not so sure the pitot tubes did, they could have indeed clogged which lead to the erroneous speed sensing and eventually the AP/AT disconnect.
Indeed there is considerable testing done during the initial development and certification testing of new turbofan engines to determine effects of ice ingestion, large and small particles and shedding characteristics. I have seen it done in person on several occasions.
As Boeing points out, it is best to avoid areas of storms where ice crystals are present as the volume tends to be unknown and onboard weather radar may not detect the presence of ice crystals at all.
I stand to be corrected on any of the above.
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Law reconfiguration.
@Chris:
Think if one will try to flowchart all possible reconfiguration you will end up in spaghetti,
but let’s give it a try and a start, if you need some specific data (sure not knowing them all!) to assist you just PM me.
** When you call any activation of a protection a new ‘law’ then you will find out there are dozens of ‘laws’ more.
** A (like B) documentation isn’t very consistent in making difference between a protection or a ‘law’
In (autoflight or manual flight) and A/C response = commanded --> Normal Law
--------------------------------------------------------------------------------------------------------
If (autoflight or manual flight) and certain A/C protections can’t be fulfilled -->Alternate Law
Possible causes:
High speed and high angle of attack protections enters Alternative law.
ALT1 - If there are faults in the horizontal stabilizer; an elevator; yaw-damper actuation; slat or flap sensor or a single ADR or IR fault.
ALT2 - Dual hydraulic failure(low press), faults in 2 IR or ADR references, with A/P lost except with an ADR DISAGREE; In all spoilers fault; certain ailerons fault or pedal transducers fault.
Indicated by ECAM MSG
F/CTL ALTN LAW
MAX SPEED 305/.82
if auto pitch trim not available à Amber USE MAN PITCH TRIM (first 6 sec flashing) below FMA.
On the PFD specific symbols (=) and formatting of low speed information on the speed scale indicates which protections are available.
When protections are lost, amber crosses (XXX) appear, instead of the green protection symbols (=).
---------------------------------------------------------------------------------------------------------
In manual flight only and if alternate Nz law can’t be kept --> Direct Law
E.g. If all 3 ADR or IR, 3 PRIM failure; 2 Elevator fault.
Indicated by ECAM MSG
F/CTL DIRECT LAW
MAX SPEED 305/.80
MAN PITCH TRIM USE
Amber “USE MAN PITCH TRIM” (first 6 sec flashing) below FMA
-------------------------------------------------------------------------------------------
In case of all electric FCPC/FCSC failure à Mechanical Only
“MAN PITCH TRIM ONLY” below FMA
Pitch: Elevators are hydraulic centered and becomes ‘fixed part’ of THS.
Yaw: à Rudder pedals (supported with yaw damper if available)
************************************************************ *********************
Alternate Law:
. In pitch: Same as in normal law
. In roll: Same as in normal law (ALTN1), or Roll Direct (ALTN2)
. In yaw: Same as in normal law (ALTN1), or degraded (ALTN2)
. Most protections are lost, except :
-- Load factor protection
-- Bank angle protection, if normal roll is still available (ALTN1 only).
At the flight envelope limit, the aircraft is not protected:
. In high speed, natural aircraft static stability is restored with an overspeed warning
. In low speed, the auto pitch trim stops at Vc prot (below VLS), and natural
longitudinal static stability is restored, with a stall warning at 1.03 VS1g.
In certain failure cases, such as the loss of VS1g computation or the loss of two ADRs, the longitudinal static stability cannot be restored at low speed.
In the case of a loss of three ADRs, it cannot be restored at high speed.
VMO/MMO settings are reduced and A FLOOR is inhibited.
If certain values are exceeded abnormal attitude law is triggered.
. Pitch (50 degrees up, 30 degrees down)
. Bank (125 degrees)
. AOA (>30 degrees, < -10 degrees)
. Speed (>440 kt, < 60 kt)
. Mach (0.96, 0.1).
Abnormal attitude law:
. Pitch alternate (adapted Nz Law) with load factor protection (without autotrim)
. Lateral direct law with yaw alternate
After A/C recovery and until landing:
. Pitch Nz Law (with autotrim)
. Lateral direct law with yaw alternate
Think if one will try to flowchart all possible reconfiguration you will end up in spaghetti,
but let’s give it a try and a start, if you need some specific data (sure not knowing them all!) to assist you just PM me.
** When you call any activation of a protection a new ‘law’ then you will find out there are dozens of ‘laws’ more.
** A (like B) documentation isn’t very consistent in making difference between a protection or a ‘law’
In (autoflight or manual flight) and A/C response = commanded --> Normal Law
--------------------------------------------------------------------------------------------------------
If (autoflight or manual flight) and certain A/C protections can’t be fulfilled -->Alternate Law
Possible causes:
High speed and high angle of attack protections enters Alternative law.
ALT1 - If there are faults in the horizontal stabilizer; an elevator; yaw-damper actuation; slat or flap sensor or a single ADR or IR fault.
ALT2 - Dual hydraulic failure(low press), faults in 2 IR or ADR references, with A/P lost except with an ADR DISAGREE; In all spoilers fault; certain ailerons fault or pedal transducers fault.
Indicated by ECAM MSG
F/CTL ALTN LAW
MAX SPEED 305/.82
if auto pitch trim not available à Amber USE MAN PITCH TRIM (first 6 sec flashing) below FMA.
On the PFD specific symbols (=) and formatting of low speed information on the speed scale indicates which protections are available.
When protections are lost, amber crosses (XXX) appear, instead of the green protection symbols (=).
---------------------------------------------------------------------------------------------------------
In manual flight only and if alternate Nz law can’t be kept --> Direct Law
E.g. If all 3 ADR or IR, 3 PRIM failure; 2 Elevator fault.
Indicated by ECAM MSG
F/CTL DIRECT LAW
MAX SPEED 305/.80
MAN PITCH TRIM USE
Amber “USE MAN PITCH TRIM” (first 6 sec flashing) below FMA
-------------------------------------------------------------------------------------------
In case of all electric FCPC/FCSC failure à Mechanical Only
“MAN PITCH TRIM ONLY” below FMA
Pitch: Elevators are hydraulic centered and becomes ‘fixed part’ of THS.
Yaw: à Rudder pedals (supported with yaw damper if available)
************************************************************ *********************
Alternate Law:
. In pitch: Same as in normal law
. In roll: Same as in normal law (ALTN1), or Roll Direct (ALTN2)
. In yaw: Same as in normal law (ALTN1), or degraded (ALTN2)
. Most protections are lost, except :
-- Load factor protection
-- Bank angle protection, if normal roll is still available (ALTN1 only).
At the flight envelope limit, the aircraft is not protected:
. In high speed, natural aircraft static stability is restored with an overspeed warning
. In low speed, the auto pitch trim stops at Vc prot (below VLS), and natural
longitudinal static stability is restored, with a stall warning at 1.03 VS1g.
In certain failure cases, such as the loss of VS1g computation or the loss of two ADRs, the longitudinal static stability cannot be restored at low speed.
In the case of a loss of three ADRs, it cannot be restored at high speed.
VMO/MMO settings are reduced and A FLOOR is inhibited.
If certain values are exceeded abnormal attitude law is triggered.
. Pitch (50 degrees up, 30 degrees down)
. Bank (125 degrees)
. AOA (>30 degrees, < -10 degrees)
. Speed (>440 kt, < 60 kt)
. Mach (0.96, 0.1).
Abnormal attitude law:
. Pitch alternate (adapted Nz Law) with load factor protection (without autotrim)
. Lateral direct law with yaw alternate
After A/C recovery and until landing:
. Pitch Nz Law (with autotrim)
. Lateral direct law with yaw alternate
Last edited by A33Zab; 6th Jun 2011 at 18:35.
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This thread reminds a little of the story where after paint, a pilot took off and the controls were rigged wrong...turning the yoke left, meant a right turn, and visa versa...he couldn't figure it out, and crashed.
It wouldn't surprise that a pilot trying to get the speed up, pushes on the yoke, but the fly by wire, now with reverse commands pitches up...the pilot keeps pushing forward...and at cruise speed and this condition...a 3k climb would be nothing, it would happen fast...
If the A/S tape was reading wrong as well...low speed meant high speed etc...it would all happen pretty quick..
Maybe lighting from a thunderstorm zapped the computer...
One more reason to use the radar, and have a plane that can actually get up to FL450.
Just a thought.
It wouldn't surprise that a pilot trying to get the speed up, pushes on the yoke, but the fly by wire, now with reverse commands pitches up...the pilot keeps pushing forward...and at cruise speed and this condition...a 3k climb would be nothing, it would happen fast...
If the A/S tape was reading wrong as well...low speed meant high speed etc...it would all happen pretty quick..
Maybe lighting from a thunderstorm zapped the computer...
One more reason to use the radar, and have a plane that can actually get up to FL450.
Just a thought.
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The computers are designed to give the pilots what they ask for in this mode - no more, no less.
I suggest that if the 'finding' is 'pilot error' it may well be quite 'excusable'.
@infrequentflyer - agree 100%
Pilots didn't have to worry too much about the counterweights, levers and so forth that provided artificial feel in the past, why should software laws be any different as long as the training to deal with those changes in laws is correct?
@theficklefinger - Seriously? FBW Airbus models have been struck by lightning more times than you care to shake a stick at, and very few of those even required a computer reset (I think there's a post on this earlier in the thread). The only time controls have been wired up in reverse in an A320 it was due to a maintenance error, and the pilot in the other seat calmly took over control and landed the aircraft safely. Airbus then changed the design of the connectors so it was not possible to wire them up incorrectly in that manner again.