OEB Alpha Prot
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OEB Alpha Prot
Does anyone have more info and supplementary info on this OEB and other incidents. via links?
It appears that the Lufhansa pilots had previous info on this, good for them.
¨When Alpha Prot is activated due to blocked AOA probes, the flight control laws order a continuous nose down pitch rate that, in a worst case scenario, cannot be stopped with backward sidestick inputs, even in the full backward position. If the Mach number increases during a nose down order, the AOA value of the Alpha Prot will continue to decrease. As a result, the flight control laws will continue to order a nose down pitch rate, even if the speed is above minimum selectable speed, known as VLS.¨
This condition, if not corrected, could result in loss of control of the airplane
¨A Lufthansa Airbus A321-200, registration D-AIDP performing flight LH-1829 from Bilbao,SP (Spain) to Munich (Germany) with 109 people on board, was climbing through FL310 out of Bilbao about 15 minutes into the flight at 07:03Z, when the aircraft on autopilot unexpectedly lowered the nose and entered a descent reaching 4000 fpm rate of descent. The flight crew was able to stop the descent at FL270 and continued the flight at FL270, later climbing to FL280, and landed safely in Munich about 110 minutes after the occurrence.¨
It appears that the Lufhansa pilots had previous info on this, good for them.
¨When Alpha Prot is activated due to blocked AOA probes, the flight control laws order a continuous nose down pitch rate that, in a worst case scenario, cannot be stopped with backward sidestick inputs, even in the full backward position. If the Mach number increases during a nose down order, the AOA value of the Alpha Prot will continue to decrease. As a result, the flight control laws will continue to order a nose down pitch rate, even if the speed is above minimum selectable speed, known as VLS.¨
This condition, if not corrected, could result in loss of control of the airplane
¨A Lufthansa Airbus A321-200, registration D-AIDP performing flight LH-1829 from Bilbao,SP (Spain) to Munich (Germany) with 109 people on board, was climbing through FL310 out of Bilbao about 15 minutes into the flight at 07:03Z, when the aircraft on autopilot unexpectedly lowered the nose and entered a descent reaching 4000 fpm rate of descent. The flight crew was able to stop the descent at FL270 and continued the flight at FL270, later climbing to FL280, and landed safely in Munich about 110 minutes after the occurrence.¨
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DEC 2012 ... 2 years earlier :
http://www.pprune.org/tech-log/50207...oa-probes.html
http://www.pprune.org/tech-log/50207...oa-probes.html
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Jimmy Hoffa Rocks
AOA information is used by FAC to calculate the protection speeds like alpha prot and alpha max( actually it is AOA shown as speed). These are high AOA protections basically meant to take care of pilot induced low speed situation. Since the normal operating AOA is much lower at higher Mach/speed, the threshold at which the alpha prot is triggered is also lowered. It is something like from 13 degrees to 5 degrees. When AOA sensors are stuck at low speed(high AOA) as the speed increases alpha prot gets triggered since AOA as received by FAC is above the high speed threshold. In this case the displayed alpha prot and alpha max will also be unduly high and incorrect. Alpha prot condition is a latching condition and will cause nose down elevator as long as speed is below this false Valpha prot. This protection can only be overridden when out of normal law. Hence the switching of two ADRs to get into alternate law. A simple solution can be not have this protection in cruise where its utility is minimal as it should be possible for a professional pilot to recover from stall without ground contact(or is it?)
AOA information is used by FAC to calculate the protection speeds like alpha prot and alpha max( actually it is AOA shown as speed). These are high AOA protections basically meant to take care of pilot induced low speed situation. Since the normal operating AOA is much lower at higher Mach/speed, the threshold at which the alpha prot is triggered is also lowered. It is something like from 13 degrees to 5 degrees. When AOA sensors are stuck at low speed(high AOA) as the speed increases alpha prot gets triggered since AOA as received by FAC is above the high speed threshold. In this case the displayed alpha prot and alpha max will also be unduly high and incorrect. Alpha prot condition is a latching condition and will cause nose down elevator as long as speed is below this false Valpha prot. This protection can only be overridden when out of normal law. Hence the switching of two ADRs to get into alternate law. A simple solution can be not have this protection in cruise where its utility is minimal as it should be possible for a professional pilot to recover from stall without ground contact(or is it?)
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ADR or FAC
Just wanted to add something to the discussion...
Turning two ADRs would force the a/c into alternate law, as would turning the two FACs off.
Considering it is the FACs that determine the speed protections surely it would be more sensible to turn these off rather than the ADRs and leave yourself with only one reference for airspeed info.
With the FACs turned off you would only lose your high and low speed protections which is a better place to be in than losing your actual airspeed? Of course you would lose yaw damping etc. but I would still consider this to be better than losing two air data units.
Please correct me if I am wrong
Cheers.
Turning two ADRs would force the a/c into alternate law, as would turning the two FACs off.
Considering it is the FACs that determine the speed protections surely it would be more sensible to turn these off rather than the ADRs and leave yourself with only one reference for airspeed info.
With the FACs turned off you would only lose your high and low speed protections which is a better place to be in than losing your actual airspeed? Of course you would lose yaw damping etc. but I would still consider this to be better than losing two air data units.
Please correct me if I am wrong
Cheers.
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Magnus456,
I believe the idea was to put in place a procedure as simple as possible, finding 2 ADR switches on a single panel is maybe more practical than looking for specific switches on 2 different panels.
Of course the ideal would be to have a well identified single switch to simply kill the protections ... but is Airbus 'ready' to take that path ... !?
I believe the idea was to put in place a procedure as simple as possible, finding 2 ADR switches on a single panel is maybe more practical than looking for specific switches on 2 different panels.
Of course the ideal would be to have a well identified single switch to simply kill the protections ... but is Airbus 'ready' to take that path ... !?
Was somebody playing with pressure washer again?
Blocked AoA vanes is extremely rare situation which can nevertheless have severe effect on any FBW Airbus so it makes sense to have single procedure across the fleet, especially for CCQ flyers. True that FACs OFF (by pbs) is one way to degrade minibus into altn but they are not installed on widebodies and 2 ADR OFF will get rid of protections on any FBW Airbus. BTW, there will be two references left, the other being standby.
Originally Posted by Magnus456
Considering it is the FACs that determine the speed protections surely it would be more sensible to turn these off rather than the ADRs and leave yourself with only one reference for airspeed info.
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Considering it is the FACs that determine the speed protections surely it would be more sensible to turn these off rather than the ADRs and leave yourself with only one reference for airspeed info.
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FCOM DSC-22-40-10 When a FAC is disengaged (FAC pushbutton set off) but still valid, the flight envelope function of the FAC remains active.
So I'm not sure if switching FACs off would really solve the problem, as long as the aircraft thinks they provide valid data.
So I'm not sure if switching FACs off would really solve the problem, as long as the aircraft thinks they provide valid data.
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vodmor
You have a valid point. There are twenty two different ways to can get into alternate law. Each may have its own handicap. Switching ADRs may be simpler, less complicated and common to both A320/A330. So that must be the reason AB chose it.
You have a valid point. There are twenty two different ways to can get into alternate law. Each may have its own handicap. Switching ADRs may be simpler, less complicated and common to both A320/A330. So that must be the reason AB chose it.
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As one of the early Bus Pilots in North America I just cant belive that these totally stupid systems have not been removed from Airbus products by now! When we first put crews through training on this aircraft {320s} it became obvious that there were so many problems caused by the totally flawed design concept that we were convinced that Airbus would wake up and fix things, but no, their only reaction was to mumble about "uneducated Canadians" and the merits of everthing French, now the launch customer for whom I worked at the time has given up on them and is disposing of the total Airbus fleet and switching to Boeing, long overdue Im afraid. In the mean time Mr Ziegler and his cohorts push their heads deeper in the sand, combine this with pilots with no real flying background and we will continue to spend time sonar searching the floors of the worlds oceans! {By the way, in case one blames my rant on any anti French bias, I live in French speaking Canada by choice and educated my kids in the French school system}
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clunckdriver
Whether anti French or Airbus you are entitled to your opinion. Only thing is North American opinion is not shared by rest of the world. You can see the order book for yourself. In rest of the world where aviation is expanding Airbus proving quiet popular. Is any airline buying any aircraft in Canada at the moment?
Whether anti French or Airbus you are entitled to your opinion. Only thing is North American opinion is not shared by rest of the world. You can see the order book for yourself. In rest of the world where aviation is expanding Airbus proving quiet popular. Is any airline buying any aircraft in Canada at the moment?
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Villas, these are not just an opinion, they are the result of dealing with a flawed design concept from day one, indeed the reaction of the Airbus staff we were dealing with at the time of the Air India "Alpha Floor" crash was simply, and I quote," The Indians are just not able to manage modern machinery", ignoring the fact that India has a huge aviation history along with turning out some of the worlds very best computer geeks and engineers, if Airbus had simply stated in training and manuals that having one F/D of and one on would inhibit Alpha Floor, {it was neither taught or in the manuals at this time} this crash would simply not have taken place.As for orders in Canada, yes, West Jet, Air Canada and a new Start Up have large orders placed with Boeing, as for the C Series, time will tell, but right now its way over budget and late, no doubt the Canadian taxpayer will pick up the tab again! By the way, I fail to see the conection between order books and design flaws, the "Bean Counters" have little or no concept of anything other than counting the beans, but that a whole other subject!
Last edited by clunckdriver; 21st Feb 2015 at 15:32. Reason: Bean Counters
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clunckdriver
I have gone through the original inquiry report of then Indian Airlines crash and airbus design has nothing to do with it. Brand new machine, unlimited visibility and comfortable morning flight.It is a mirror reflection of SFO B777 crash. In IA crash pilots switched to open descent without realising it and speed kept dropping finally 27 Kts. below Vapp. One pilot switched off his FD without other pilots knowledge. All the time they thought they are in speed mode but no one checked the FMA, there was not a single call about speed by any of them. Finally alpha floor did kick in and also pilots themselves moved to TOGA but they lost their lives because they did it 15 seconds too late. SFO B777 Auto throttle was in thrust hold both experienced pilots never checked their speed and despite much touted moving thrust levers of Boeing they didn't notice that thrust levers were stuck at idle all along, again no call out about speed, speed went 30 kts below Vapp. They also went round but little too late and were lucky to survive. I am sorry but you don't fly approaches like that. Protections are needed for these pilots only. Most pilots won't even experience them in their life time.
I have gone through the original inquiry report of then Indian Airlines crash and airbus design has nothing to do with it. Brand new machine, unlimited visibility and comfortable morning flight.It is a mirror reflection of SFO B777 crash. In IA crash pilots switched to open descent without realising it and speed kept dropping finally 27 Kts. below Vapp. One pilot switched off his FD without other pilots knowledge. All the time they thought they are in speed mode but no one checked the FMA, there was not a single call about speed by any of them. Finally alpha floor did kick in and also pilots themselves moved to TOGA but they lost their lives because they did it 15 seconds too late. SFO B777 Auto throttle was in thrust hold both experienced pilots never checked their speed and despite much touted moving thrust levers of Boeing they didn't notice that thrust levers were stuck at idle all along, again no call out about speed, speed went 30 kts below Vapp. They also went round but little too late and were lucky to survive. I am sorry but you don't fly approaches like that. Protections are needed for these pilots only. Most pilots won't even experience them in their life time.
