And no, a stab jam is not a "common fault" on the 320 family.
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Volaris A321 loses both ELACS
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Originally posted by ATLcrew View PostAnother alternative was that one was already MEL'd, remember?
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Originally posted by ATLcrew View PostAnother alternative was that one was already MEL'd, remember?
Originally posted by ATLcrew View PostAnd no, a stab jam is not a "common fault" on the 320 family.
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Stab jam (as a common fault) is looking a bit more plausible:
A320, 2008:
Flight control malfunction: the captain was hand flying the turn to base leg for a visual approach to ZZZ runway 7R when we received an amber flight control elac 2 pitch fault ECAM annunciation. Shortly after accomplishing the ECAM SOP for this fault; a second ECAM was displayed for an elac 1 fault followed immediately by a flight control stabilizer jam ECAM and flight control alternate law. All ECAM actions were accomplished with manual pitch trim found to be available. The flight control system degraded to direct law per the flight manual after landing gear extension and the landing was uneventful. Callback conversation with reporter revealed the following information: unfortunately; a power interruption occurred after the aircraft was parked at the gate which erased all the stored maintenance data. Tests revealed that there were disagreements between the ths position sensors but that they were within limits. Maintenance replaced both elac's to return the aircraft to service.
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Originally posted by Evan View PostWhat if I didn't say so? I said that losing both engines is as unlikely and hard to explain as losing both ELAC's. I never said it was as serious. Go back and read the post. It's pretty clear what I meant. Jesus, Gabriel, you were one of the few here that didn't twist my words around.
In any case, it is you who should use more caution when redacting the post. You asked, making ana analogy with the ELAC (and that's not a supposition, you expressly said that you were making the analogy) if it would be wise to dispatch an airplane with one engine. Come on!!!! I keep my position, that is a show-stopper. I cannot keep exchanging ideas with someone who has such idea.
By the way, it is not correct that losing both engines is as unlikely and hard to explain as losing both ELAC's. Loosing bothe engines is much more likely and easy to explain. There are multitude of failure modes that can affect both engines at the same time: Fuel contamination (including ice crystals), birds, volcanic ashes, fuel exhaustion, shutting down the wrong engine. And we have examples (in most cases multiple examples) of all these things happening and leaving the plane without both (and up to 4) engines at the same time. We even have a case of a prop airplane where a blade separated and, in its flight through the fuselage, pulled all the throttle cables (and then cut them) effectively idling all 4 engines and leaving the crew without any control over the engines.
Now to untangle that Gabrielesque post...
No. Wrong.
Once you have lost Normal Law, AoA protections and Alpha Floor...
If you gain enough airspeed to exceed VMO/MMO the nose will come up. This is overrideable with increased stick force. This is true in Alternate law with reduced protections. This is true when you lose both ELAC's.
If you lose enough airspeed to approach stall (5-10 kts above stall warning), the nose will lower. This is overrideable with increased stick force. This is true in Alternate law with reduced protections. This is true when you lose both ELAC's.
Neither the certification authorities nor Airbus are the insane, irresponsible folks you make them out to be. That's what I'm getting at. But that certification was predicated on having certain systems, such as an ELAC, in working order.
It is not the same, ok? The authorities evidently don't agree with me (or at least didn't do it back then, now it would very hard for them to change their previous ruling on the case), but that don't make them "are the insane, irresponsible folks you make them out to be."
We already discussed at length on the Airbus'controls design philosophy and you know that there are several things that I don't agree with, the main of which is the completely lack of visual/tactile feedback regarding "what the plane is doing now" with the controls (does the phrase sound familiar?). And yet, you know, I consider the Airbus planes very safe, have absolutely no problem or concerns when I climb into one, and object those who share my critiques but use these concepts to call the plane a death trap or similar.
UAS is a different animal. Without airspeeds you can't have ANY speed protections...
... and that is far more immediately dangerous. That is why the procedures exist to maintain the airspeed envelope. That is why one of them has the distinction of being a memory item (except at Air France).
And I want to make very clear that I am not promoting using this INSTEAD of the procedures (including the memory items). By all means, the procedures are there to be complied with, and that is almost always the correct, required and safest course of action. But not complying with the procedure doesn't explain by itself what the AF pilots did instead of complying with the procedure.
That is why the first order of business when speeds return is to get it back on the automation. I have already agreed with you that UAS is a more dangerous situation on a airplane with automatic pitch trim and thus no out-of-trim 'feel' for speed changes. But UAS is one of those situations technology cannot yet contend with.
It requires disciplined, well-trained pilots to fly safely through it.
What baffles me is that you find the control laws philosophy alarming but not the fact that you can apparently lose both ELAC's in flight to a common fault. But that is because you have the control laws philosophy wrong...
Second, I consider the lose of both ELAC of a seriousness comparable to the loss of autoflight. Comparable, not equal. It is a bit worse because you lose the ailerons (keeping spoilers for roll control) and, more important than that, because, with Airbus flight control philosophy and the change in control law and loss of protections, you leave the pilots flying a different plane, as you said yourself.
I consider that fault serious but not very serious. If it is very serious it is because you don't have pilots (persons who master the art of flying airplanes, as opposed to persons who puch buttons) flying the plane. Then we have a bigger problem because those button pushers sometime find the way to crash the plane even with all the ELACs working.
Did you know that, at least in some types, the whole autopilot is MELlable in certain conditions? (VMC). I was in a 737 flight where the pilots legally took off with no autopilot in working order. How I know? The captain told me that when I went to the cockpit and I asked him why was the FO hand flying.
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Originally posted by 3WE View PostLump 2: Many of us assume (incorrectly) that if they computers go down you get a plane that's very hard to fly.
Lump 3: ATL said (paraphrased) "all you had to do was land the thing, do some paperwork and then hit the coffee shop."
More lump 3: And, in your continued attempt to get me to understand- I keep getting the lumped message that while you lose lots of fancy computer-stabilized flight inputs, you still get something that can be controlled.
I think we agree with Evan there, and maybe we don't want to stall or exceed the big $20 word "Envelope" the thing with the computers off (not that we want to stall it or exceed the "Envelope" with the computers on either)
Briefer bottom line lump: But it sounds to me from your posts and others, that dual ELACS failure is not a NEAR TOTAL AIR DISASTER!!!!!!
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Originally posted by 3WE View PostBlah blah blah...
Yeah, it's nice to have my 172 trimmed for healthy flight so that it "fights me" if I try to stall it, and there's the evil insidious Airbus that will pitch up, but not give me tactile feedback until the stall warning goes off. Shall I place links to ITS going over the top with trashing Airbus and Frenchmen?
So, I'm back to one of my endless, repetitive rants:
Select known, healthy power, attitude and speed settings and (do I have to say this- because it WAS implied) keep monitoring the airspeed and attitude and power (see footnote) to see that the airspeed and attitude stay at those healthy settings ...
...and then you will catch the plane when it starts going to the wrong attitude even though the plane doesn't give tactile feedback (and even though a Cessna would not go to the wrong attitude without tactile feedback)
Footnote: To the best of my knowledge, most aircraft provide gauges (or flat panel readouts) to tell you about the air speed and the attitude and the power settings.
This doesn't mean that you have no option but stall the airplane. You still have the attitude indicator, the power setting instruments, and the memory item that tells you where to put both. You also have your airmanship to know that at 35000 ft you cannot pull 2G and climb 2000 ft at 7000fpm with a pitch angle of 15 degrees, and the stick-and-rudder skills to know how NOT to do that. Finally, if all that fails and you listen the stall warning with that cryptic ambiguous horn shouting STALL STALL STALL in plain English, you may (and many would say "should") think of perhaps lowering the nose a bit instead of "but I've been pulling up all the time".
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Originally posted by Evan View PostThe first officer requested an extended downwind and declared an emergency [note: I think we can assume that they considered this a serious situation].
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Originally posted by Gabriel View PostMaybe it is not pristine, but what is wrong?
But I was explaining the direct law... in that part of the post. I was explaining how the Airbus don't meet the FAR requirement regarding longitudinal stability and what envelope protections they have in place and they used as alternate means of compliance.
Originally posted by GabrielSo, as you can see, the Airbuss don't comply with the FAR's longitudinal stabilty requirements, not in normal law at least.
Originally posted by GabrielWhen the plane looses some systems it reverts to alternate law. In this condition, depending on the kind of failures, the envelope protections are significantly degraded or eliminated alltogether. But the problem, for me unacceptable, is that the plane still lacks longitudinal stability because the basics of the normal law (stick-on-G / stick-on-pitch-rate) remain in place.
Originally posted by GabrielI agree. That's why I later said "When the plane looses some systems it reverts to alternate law. In this condition, depending on the kind of failures, the envelope protections are significantly degraded or eliminated alltogether."
Back to my original point, I think, because the full spectrum of Normal Law protections was required to certify the aircraft without meeting the requirements as written in the FAR's, and scenario in which they are "significantly degraded or eliminated altogether" is a very serious incident. Again, I do not say...
Originally posted by 3WENEAR TOTAL AIR DISASTER!!!!!!
Originally posted by GabrielSecond, I consider the lose of both ELAC of a seriousness comparable to the loss of autoflight. Comparable, not equal.
Originally posted by GabrielI consider that fault serious but not very serious.
Now, all that said, I am learning that there are certain mechanical conditions that might result in both ELAC's tripping offline. That sort of thing might not be preventable from a systems design POV and can only be prevented by vigilant maintenance. Perhaps an AD stressing the need to periodically check the elements that might cause this condition are in order. If this is, in fact, the case.
It would be nice if a finding is eventually reported on this incident, but I'm afraid we will never hear anything more about it.
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Originally posted by Gabriel View PostAgain, not true, unless you use "can't" as "technically perfectly possible and even easy but since this feature was not designed in the system, the system can't".
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Originally posted by Gabriel View PostEvan, if I was one of the few that didn't twist your words, there is a reason for that and I am still the same. I am not twisting your words. I quoted you immediately before my reply. Go and read your post yourself, at least the part that I quoted which trigged my reply.
Losing an engine, while also serious, is to be expected and can usually be easily explained. What about losing two engines, because that is the analogy if you are trying to make one. Did both engines fail by coincidence? Is it wise to dispatch with one engine on the MEL? Or is there a common design vulnerability that could cause both engines to fail?
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Originally posted by Evan View PostNo you weren't. You were explaining in NORMAL law:
And your description of the system behavior under Normal Law is flawed. You've left out key aspects that substitute for traditional speed stability.
Then you were talking about ALTERNATE law:
In most Alternate Law conditions, there is still the artificial speed stability.
Only certain system failure scenarios (i.e. involving loss of ADR's, multiple hydraulic failures or certain slat failures) will result in a loss of all protections. Loss of reliable air data under UAS for instance...
Therefore, in most Alternate Law scenarios I say the problem is serious, not unacceptable.
I've already said that I consider the Airbus planes very safe and fly on them with no concerns (I fear much more the airlines and the pilots than the plane).
Back to my original point, I think, because the full spectrum of Normal Law protections was required to certify the aircraft without meeting the requirements as written in the FAR's, and scenario in which they are "significantly degraded or eliminated altogether" is a very serious incident. Again, I do not say unacceptable. I say "very serious".
In the case of total ELAC failure, serious enough to cause at least two recent incident crews to declare an emergency. Serious enough for every incident to make a diversion or return. Serious enough to look deeply into and prevent if possible in the future.
If "serious enough" is the trigger to revisit the situation and analyze if an improvement is warranted, then by all means I support your "serious enough" diagnostics.
Are you really reading my posts? Loss of both ELAC's results in loss of autoflight. THAT'S WHY IT'S SERIOUS.
That is what reversion laws are intended for: to get the aircraft back on autoflight or on the ground asap. They are not intended for extended manual flight.
But the loss of ELAC's means BOTH diminished envelope protections AND a loss of autoflight (itself a form of envelope protection).
And autoflight is NOT itself a form of envelope protection. Figure this:
UAS, AP/AT disconnects, pilots run the memory items and the rest of the procedure, UAS remains for some time and they decide to descend looking for better conditions (warmer air, denser air...). So they idle the engines and follow the required pitch and VS, UAS disappears, they remain in alternate law but they regain autoflight. They engage autoflight and tell autoflight to level off. They forgot the throttle levers in idle....
Now, if I understand the system correctly, nothing (except human airmanship) will prevent the autopilot from keep pitching up while the plane losses hundreds of knots, and nothing will add thrust either. Not, until the LOW SPEED PROTECTION kicks in and lowers the nose. So it was the LOW SPEED PROTECTION that is independent of auto/human flight, not the autoflight, which saves the day.
Now you're just equivocating. It's either serious or it isn't.
Yes, I read your definition of "serious" that came after that. Based on THAT definition, let's call it serious.
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Originally posted by Evan View PostFor the system to overcome this, at least all of the airspeed probes must be of a design that is not vulnerable to the same environment. Two must be working at all times.
GIVEN THE UAS, Airbus could have treated the situation differently.
- The ADRs don't need to disagree at full. They can just agree that they disagree on the speed, and consider this just a speed disagreement and on an ADR disgreement.
- The autoflight and autothrust don't need to give up immediately. At the very least, they can keep the current pitch and thrust (thurst in fact will be kept by the thrust lock feature) while they give the pilots a clear indication of what is happening (a Unerliable Airspeed, take manual control, disconnect AP/AT, keep pitch 5, move throttle off and back to CLB" would be very nice (better than the miryads of ECAM fail messages from which the pilots have to deduce that they have an unreliable airspeed condition) and easy, and the autoflight can wait until pilot action to disangage. A few seconds of that will not hurt, and in any event whatever the current pitch and thrust cannot be worse.
- It would be very easy for the AP/AT to apply the memory items by themselves.
- You could keep the degraded slow speed protection of the standard alternate law using the AoA vanes (if they agree). Yes, stall AoA depends on Match, and Match depends on speed, but you can select a reasonable fixed AoA trigger value that will pitch down slightly faster than required at low Match, and still prevent a stall at high Match.
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Originally posted by Evan View PostHere's my post, verbatim:
The analogy is in what can be expected and explained, not in the level of seriousness. Obviously losing power is a magnitude of seriousness beyond degrading control law and losing autoflight. You don't have to twist my words to fuel the War on Evan here and make me look ridiculous. As always, I'm looking for a dialectic on this forum, not a polemic debate.
I compared that with losing one engine, which is a far more usual situation than losing both ELAC, both of which require land ASAP, and that, in my opinion, losing one engine was more serious than losing both ELAC (meaning that, if both situations happened with equal frequency, I would expect more accidents for the former).
Then you came saying that losing two engines was a better analogy (if you lose both engines chances are that you will land even sooner than ASAP) and asked if it was wise to dispatch a plane with one engine.
But let's put an ending to this, if only for clemency. Evidently you meant something else than what you meant and whether it was because your message was not clear or because I was misinterpreted it is not important.
You know that you and I disagree a lot of times. You know that I respect you, and that (almost) always I reply (to you and everyone) in a constructive way. I simply was startled and didn't know how to react to or answer the "Would you dispatch an airplane with one engine MELed" question. That is beyond my powers. For sure, you can't dispatch my Tomahawk with one engine MELed, for reasons far beyond the fact that the regs don't allow you.
--- Judge what is said by the merits of what is said, not by the credentials of who said it. ---
--- Defend what you say with arguments, not by imposing your credentials ---
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Originally posted by Gabriel View PostBut let's put an ending to this, if only for clemency. Evidently you meant something else than what you meant and whether it was because your message was not clear or because I was misinterpreted it is not important.
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