Airbus crash/training flight
Seemingly I'll have to elaborate on Airbus protections. The guess that a320 doesn't have independent static pressure line systems for each of its ADIRU's is utterly wrong - they're completely independent, units 1 and 2 using signals from two ADMs each, one for left , one for right static port. ADIRU 3 uses one ADM in duct connecting left and right stby ports. When I wrote that the only protection that pitches nose up is high speed protection, some readers interpreted it as a severe pitch-up, which it is not. It's very gentle (with its limit of 1.75g unlikely to be ever achieved) and it turns off as soon as speed is 349kt. If you hold the stick against the forward stop, it will maintain a couple knots above Vno.
There's absolutely no
in any of the A320 protections. Rapid increase of power called alpha-floor is triggered by FAC calculating that aircraft has reached high AoA. If the aeroplane is near its Vmo, it cannot enter the alpha-floor or, as G-limit is reached at AoA well bellow one needed for A-floor activation.
As for "gimme big red button so I can fly it out myself" brigade, protections are based on comparing data from all three ADIRUS. All three agree - fine. One fails, other two agree - fine. Two agree, third doesn't - still fine as it's outvoted. If one fails, two disagree or all three disagree - protections are off and you're on your own, the FBW has pressed the big red button for you and now your stick commands aileron displacement in roll and you might still have G-command in pitch or you have direct stick-to-elevators-displacement. Now you can stall the aeroplane, roll it on its back, overspeed it, perhaps even over-G it, whatever you choose to do or let the aeroplane do through sheer stick incompetence. As long as things work as designed, there is no way that protection can throw you in extreme attitude believing that it's saving the day. And what if they don't? We'll have to wait for ATSB to have its final say on QF72, the first recorded instance of faulty AoA signal not getting outvoted - in twenty years of FBW Airbi operations.
There's absolutely no
programmed response of a rapid pitchup and power increase
As for "gimme big red button so I can fly it out myself" brigade, protections are based on comparing data from all three ADIRUS. All three agree - fine. One fails, other two agree - fine. Two agree, third doesn't - still fine as it's outvoted. If one fails, two disagree or all three disagree - protections are off and you're on your own, the FBW has pressed the big red button for you and now your stick commands aileron displacement in roll and you might still have G-command in pitch or you have direct stick-to-elevators-displacement. Now you can stall the aeroplane, roll it on its back, overspeed it, perhaps even over-G it, whatever you choose to do or let the aeroplane do through sheer stick incompetence. As long as things work as designed, there is no way that protection can throw you in extreme attitude believing that it's saving the day. And what if they don't? We'll have to wait for ATSB to have its final say on QF72, the first recorded instance of faulty AoA signal not getting outvoted - in twenty years of FBW Airbi operations.
How Do You Get Complete Control?
Clandestino: In the event the voting process goes haywire, is there a way to manually get to the point where the pilot(s) have the full control as you describe when you have all three units disagreeing? 
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Clandestino,
System design very well explained except for the case where two similar but erroneous inputs are sensed by the ADRs (from Pitot/Static system). In such a case, the aircraft doesn't know that it's being fed inaccurate speed information and will try to follow the erroneous signals believing that the voting process is disregarding the "outlier" (quaint Airbus terminology) signal which happens to be the only valid one.
In the sim I have seen pilots become totally confused in level flight at a safe altitude when faced with apparently conflicting information on speed. To be fair to Airbus, they do have that "big red button" - Disconnect the automation and fly the memory pitch/power values. The real problem is in being able to recognise the fact that you have a problem. How I'd react if all that happened as I was turning base after an uneventful(?) 90 minute flight, I'd rather not speculate.
In the Excel case, it seems apparent that whatever happened, it was so unexpected as to take the crew completely by surprise.
Is there any information on the A320 experience levels of the two Excel pilots and were they trained for test flying something as complex as the 320?
System design very well explained except for the case where two similar but erroneous inputs are sensed by the ADRs (from Pitot/Static system). In such a case, the aircraft doesn't know that it's being fed inaccurate speed information and will try to follow the erroneous signals believing that the voting process is disregarding the "outlier" (quaint Airbus terminology) signal which happens to be the only valid one.
In the sim I have seen pilots become totally confused in level flight at a safe altitude when faced with apparently conflicting information on speed. To be fair to Airbus, they do have that "big red button" - Disconnect the automation and fly the memory pitch/power values. The real problem is in being able to recognise the fact that you have a problem. How I'd react if all that happened as I was turning base after an uneventful(?) 90 minute flight, I'd rather not speculate.
In the Excel case, it seems apparent that whatever happened, it was so unexpected as to take the crew completely by surprise.
Is there any information on the A320 experience levels of the two Excel pilots and were they trained for test flying something as complex as the 320?
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Smilin_Ed...
Attitude from IRS.. so if all 3 ADR data unreliable or suspect, use pitch/power datums in manual flight. Turn off 2 of 3 adrs (1 retains stall warning function). Use datum settings to fly climb/cruise/descent/approach profile to land somewhere.
Attitude from IRS.. so if all 3 ADR data unreliable or suspect, use pitch/power datums in manual flight. Turn off 2 of 3 adrs (1 retains stall warning function). Use datum settings to fly climb/cruise/descent/approach profile to land somewhere.
Chaps, what if we're looking at this the wrong way?
The media (Terrible source, I know
)has reported both a "Surge in power" and also a "Power Surge". We all seem to be assuming they are referring to the same event. But what if they aren't? What if the "Power Surge" is referring to a genuine electrical spike of some kind?
Does anyone have any input as to how the systems on the Airbus (OR Boeing for that matter) tolerate such a power spike, or what happens if they don't tolerate it?
Obviously everything is designed to withstand a lightning strike so something has gone terribly wrong in that case, but it has anyway, hasn't it?
Just a thought...
The media (Terrible source, I know
)has reported both a "Surge in power" and also a "Power Surge". We all seem to be assuming they are referring to the same event. But what if they aren't? What if the "Power Surge" is referring to a genuine electrical spike of some kind?Does anyone have any input as to how the systems on the Airbus (OR Boeing for that matter) tolerate such a power spike, or what happens if they don't tolerate it?
Obviously everything is designed to withstand a lightning strike so something has gone terribly wrong in that case, but it has anyway, hasn't it?
Just a thought...
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NOD and others,thanks for the replies.
in theory then ,if you are flying a dme arc ,and the a/c gives you a sudden unexpected 'stall stall' warning whilst manouvering to stay on the arc (in a turn) what would be the correct recovery ? for each of the the different laws u were flying in ?
give it a couple of seconds to sort itself out ..and see what it does ...or disconnect everything and fly yourself out of it ?
in theory then ,if you are flying a dme arc ,and the a/c gives you a sudden unexpected 'stall stall' warning whilst manouvering to stay on the arc (in a turn) what would be the correct recovery ? for each of the the different laws u were flying in ?
give it a couple of seconds to sort itself out ..and see what it does ...or disconnect everything and fly yourself out of it ?
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camel... Difficult to say... there is a drill, much as any aircraft:
In practice, you will have to assess the Flt Conditions and decide if it could be "real", or whether is is spurious. As with a PPL Stall lesson, there are other symptoms of the stall (attitude, speed, power) that should help you decide. Default is "real" of course, but how long do you push for / maintain full power ?
Woolly answer, sorry
NoD
- Full Power
- Reduce Back Pressure / Attitude
- Roll Wings level
- ....
In practice, you will have to assess the Flt Conditions and decide if it could be "real", or whether is is spurious. As with a PPL Stall lesson, there are other symptoms of the stall (attitude, speed, power) that should help you decide. Default is "real" of course, but how long do you push for / maintain full power ?
Woolly answer, sorry
NoD
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Does anyone have any input as to how the systems on the Airbus (OR Boeing for that matter) tolerate such a power spike, or what happens if they don't tolerate it?
The main generator voltage output is controlled by a regulator contained in the individual generator control units.
A sensing circuit continually measures the generator output voltage and informs the regulator as to how much energy should be applied to the generator field to maintain the proper output.
Excitation faults, generator differential faults, open phase faults, difference current faults, speed faults, synch bus faults will activate appropriate actions to protect associated load circuits.
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No need for Cessna if you have a good FBW design
Cessna 172 Mode
Quote:
Would any Captain want that much responsibility (by pressing said button) on his/her shoulders?
Yes he would, provided the "Cessna 172 Mode" is flyable to a reasonable degree.
Quote:
Would any Captain want that much responsibility (by pressing said button) on his/her shoulders?
Yes he would, provided the "Cessna 172 Mode" is flyable to a reasonable degree.
Once you're in control of your bird, and have solved your problem, you could select your Auto-Pilot ON again, and regain your Normal Law capability
(provided required conditions are still met.)Simple, easy and pilot friendly.
Fly Safe
What is known, so far, is that the aeroplane crashed as it was returning from acceptance test flight and that's it. Everything else is uncertain. We don't know if it stalled, whether it pitched up and what was the active control law before the crash.
Stall warning is available in alternate and direct law, when there's no alpha-prot to stop the aeroplane from stalling. However it is possible to get false stall warning in normal law, if AoA probe is damaged. I'm not sure if this FCOM warning can be interpreted as "single (out of three) damaged AoA probe can cause false stall warning", but if it can, it may imply that voting rules are not the same for AoA and speed/attitude. QF72 final report will be very, very interesting reading indeed.
Procedure commonly refered as stall recovery (full power, decrease pitch, wings level) is actually recovery from approach to stall. The significance is that it is initiated as soon as stall warning goes off and therefore before actual stall takes place. If one allows the airliner's wing(s) to stall fully, this procedure does not guarantee recovery, or at least recovery that doesn't include overspeed/overstress/ground contact and its success is largely dependent on all-up weight, centre of gravity and luck.
It is possible to get into direct law with some simple switching but the procedure is strictly unofficial and, as I'm unaware of any occurence of voting process gone haywire, i think it's unnecessary. I stand to be corrected, of course, if some incident/accident report shows otherwise.
We have three indepentent systems, each required to be very reliable. Suddenly two of them simultaneuosly fail in the exactly same manner and their false outputs are diverging from real values with the very similar amplitude over time. I didn't take this scenario into consideration as my opinion is that chances of its occurence are virtually nil.
I beg to differ. One loses every protection in Alt law (EDIT: except G protection, thanks for reminding me). What Airbus euphemistically calls "reduced protections" are really not much of a protection at all.
There is a stall warning and a stall recovery procedure on the A320
Procedure commonly refered as stall recovery (full power, decrease pitch, wings level) is actually recovery from approach to stall. The significance is that it is initiated as soon as stall warning goes off and therefore before actual stall takes place. If one allows the airliner's wing(s) to stall fully, this procedure does not guarantee recovery, or at least recovery that doesn't include overspeed/overstress/ground contact and its success is largely dependent on all-up weight, centre of gravity and luck.
In the event the voting process goes haywire, is there a way to manually get to the point where the pilot(s) have the full control as you describe when you have all three units disagreeing?
System design very well explained except for the case where two similar but erroneous inputs are sensed by the ADRs (from Pitot/Static system).
and you could get your Alternate Law 1 too...(and have real control of your aircraft, without loosing a great deal of protections
Last edited by Clandestino; 30th Jan 2009 at 18:35. Reason: Br@inf*rt
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One loses every protection in Alt law
NoD
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Yes, there are still protections in alternate law. In fact, there is 2 kinds of alternate law.
I will call it an alternate law and alternate law without speed stability (my own description).
Both of them have load factor protections. You loose load factor protection only in direct law.
The "better" alternate law still have low speed stability and high speed stability. The only difference with normal law is, that it is overridable. If high speed protection in normal law kicks in and you push the stick all the way forward and keep it forward, the airplane will pitch up against your input. If you do the same in the alternate law with speed protection, you have to let the stick go, before it will start to pitch up. So you can override it. But in alternate law without speed stability you don't have low and high speed stability. In both cases you have load factor limitation as mentioned above and also yaw damping (unless you lost yaw damping due to ADR failure.
I hope, it makes sense.
I will call it an alternate law and alternate law without speed stability (my own description).
Both of them have load factor protections. You loose load factor protection only in direct law.
The "better" alternate law still have low speed stability and high speed stability. The only difference with normal law is, that it is overridable. If high speed protection in normal law kicks in and you push the stick all the way forward and keep it forward, the airplane will pitch up against your input. If you do the same in the alternate law with speed protection, you have to let the stick go, before it will start to pitch up. So you can override it. But in alternate law without speed stability you don't have low and high speed stability. In both cases you have load factor limitation as mentioned above and also yaw damping (unless you lost yaw damping due to ADR failure.
I hope, it makes sense.
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The terminology "LAW" is very accurate in this context. Means, the pilot may have have NOT the FULL authority of the aircraft.
Only unauthorized tricks (FACs OFF, Gear Down) bring the aircraft back to basic flying mode if the automatics f*** of., maybe....
Only unauthorized tricks (FACs OFF, Gear Down) bring the aircraft back to basic flying mode if the automatics f*** of., maybe....
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Alt Law 1
Quote:
and you could get your Alternate Law 1 too...(and have real control of your aircraft, without loosing a great deal of protections
Clandestino:
I think you have to check your Manuals again, on this one. Unless your FCOM's are different from mine, ALT1 gives you still a lot of protection but you can override it! And since my idea was to give the option for the pilot to regain complete control of his aircraft while keeping some protection (to prevent a stressing situation to develop into a worse one), I'm reassuming my suggestion as a good one.
PBY: Thanks for clarifying this subject in a manner that non-pilots can understand it. As a matter of fact, there are two ALT LAW levels and I was refering to the very first level, that not only, gives the pilot the required amount of protection a stressfull situation may require and at the same time, gives the pilot full authority to override it.
and you could get your Alternate Law 1 too...(and have real control of your aircraft, without loosing a great deal of protections
I beg to differ. One loses every protection in Alt law (EDIT: except G protection, thanks for reminding me). What Airbus euphemistically calls "reduced protections" are really not much of a protection at all.
I think you have to check your Manuals again, on this one. Unless your FCOM's are different from mine, ALT1 gives you still a lot of protection but you can override it! And since my idea was to give the option for the pilot to regain complete control of his aircraft while keeping some protection (to prevent a stressing situation to develop into a worse one), I'm reassuming my suggestion as a good one.
Yes, there are still protections in alternate law. In fact, there is 2 kinds of alternate law.
I will call it an alternate law and alternate law without speed stability (my own description).
Both of them have load factor protections. You loose load factor protection only in direct law.
The "better" alternate law still have low speed stability and high speed stability. The only difference with normal law is, that it is overridable. If high speed protection in normal law kicks in and you push the stick all the way forward and keep it forward, the airplane will pitch up against your input. If you do the same in the alternate law with speed protection, you have to let the stick go, before it will start to pitch up. So you can override it. But in alternate law without speed stability you don't have low and high speed stability. In both cases you have load factor limitation as mentioned above and also yaw damping (unless you lost yaw damping due to ADR failure.
I hope, it makes sense.
I will call it an alternate law and alternate law without speed stability (my own description).
Both of them have load factor protections. You loose load factor protection only in direct law.
The "better" alternate law still have low speed stability and high speed stability. The only difference with normal law is, that it is overridable. If high speed protection in normal law kicks in and you push the stick all the way forward and keep it forward, the airplane will pitch up against your input. If you do the same in the alternate law with speed protection, you have to let the stick go, before it will start to pitch up. So you can override it. But in alternate law without speed stability you don't have low and high speed stability. In both cases you have load factor limitation as mentioned above and also yaw damping (unless you lost yaw damping due to ADR failure.
I hope, it makes sense.
We're talking semantics here. I never wrote that there are no high and low speed stabilities in alt 1. Just they're not much of a protection compared to high speed protection and alpha protection.
To put things into perspective: while this talk about protections and losses of it scares beejabbers out of interested observes with not much background knowledge of Airbus operations, activating the prot or degradation into alternate law is FDM red event and these get duly reported by our safety bulletin and I cannot recall ever reading about one or other. Ergo, it's not something one would see on a daily or even yearly basis.
To put things into perspective: while this talk about protections and losses of it scares beejabbers out of interested observes with not much background knowledge of Airbus operations, activating the prot or degradation into alternate law is FDM red event and these get duly reported by our safety bulletin and I cannot recall ever reading about one or other. Ergo, it's not something one would see on a daily or even yearly basis.
