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AF 447 Thread No. 6

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AF 447 Thread No. 6

Old 16th Aug 2011, 13:28
  #61 (permalink)  
 
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Unprepared Autopilots

IMHO, at the present level of automation, I don't see enough reasons for an autopilot disconnection. If the solution for UAS is so simple (pitch & power), why the autopilot "refused" to hold the same pitch & power when they lost airspeed indications?

It amases me that a computer "logic" can not perform a partial autopilot disconnect, holding only attitude and power. Forget all the other stuff (navigation, altitude hold, etc...). An autopilot should not "panic" and disconnect just because of UAS. The computer still had enough data to keep the a/c flying, but it wasn't "programed" to do so...

Fill the cockpit with flashing and audio warnings, but give the pilots time to figure out what is the problem.

Autopilot is there to do exactly this: give the pilots time to do the thinking.
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Old 16th Aug 2011, 16:04
  #62 (permalink)  
 
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Originally Posted by Rob21 View Post
IMHO, at the present level of automation, I don't see enough reasons for an autopilot disconnection. If the solution for UAS is so simple (pitch & power), why the autopilot "refused" to hold the same pitch & power when they lost airspeed indications?
Two answers from me, and I'll gladly stand corrected by the 'bus' experts.

- Most of the gains (and some of the logic) in the basic control loops (even in attitude hold) are functions of IAS (or, more usually, Mach).
For a designer it's not easy or obvious to pick a 'default' value to drop back to, when those air data go belly-up (NCD).... otherwise, if you think about it, he wouldn't have introduced those variable gains in the first place.

- The solution for UAS is not simply "maintain pitch and power", and neither are the optimum pitch & power the same values just after take-off or at FL350.
What's more, the actual pitch & power at the moment of the UAS first occurring are not necessarily the ones you want to maintain (depending on the moment in the flight where it occurs).

Finally, the autothrottle did leave the power at the last setting.
Whether it would have been preferable for the autopilot to have reverted to a basic attitude hold is IMHO very much an open question, especially in turbulence.

It amazes me that a computer "logic" can not perform a partial autopilot disconnect, holding only attitude and power..... The computer still had enough data to keep the a/c flying, but it wasn't "programed" to do so...
I tried to explain above why it wasn't "programmed" for that.

Question to all : has anybody already worked out from the report, what the AP (long and lat) and AT modes were at the moment of the disconnect?

Rob's remark above about 'partial disconnect' reminded me of some systems I've seen, where partial input data loss would disengage the affected 'higher' mode, but without disengaging the AP itself, which would revert to ATT HLD and/or HDG HLD.
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Old 16th Aug 2011, 16:41
  #63 (permalink)  
 
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Standby Gains

CJ: I agree with Rob21, and I previously mentioned that the Viper had a "standby gains" function for just this reason - bug in the pitot tube(s), ice, physical damage ( and we had one accident from a huge pelican ripping away the radome and air data sensors).

Granted, we had a much greater speed range and less worry about mach "protection" , but the fixed dynamic pressure ratio value was a bit above normal cruise CAS/mach. It was much lower with gear down, as the stick would have seemed too 'stiff" for the amount of control surface movement we were demanding and the confusers would have applied less movement for the flight condition.

So this seems a very straighforward reversion function and should not completely eliminate the basic attitude control functions of the A/P. Lose the pitot system and the STBY GAINS lite comes on. Hmmmmmm, no big deal and the jet just seems "stiffer", more sluggish for "x" control stick input. The system could even use last known values, but most engineers would prefer a fixed value in non-volatile memory as we did. This implementation would also keep the "mach" protections outta play, but the crew would know this when the warming lite illuminated.

Further, there are probably pressure functions in the control actuators themselves that "limit" them as to rate and amount of movement depending upon actual forces exerted upon the control surfaces.
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Old 17th Aug 2011, 14:13
  #64 (permalink)  
 
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Hello
If you read the graph p111 between 0211:00 and 0212:45
During all this time this is the stall warning the crew does not believe.
We can see Altitude does not vary too much and to quickly (37924 to 36068)
F/O pitch orders up and down.
Stabilizer from -3 to -13
Speed is decreasing and as speed is decreasing, they don't see it and what does the THS do on FBW machine?: It tries to maintain flight path, so as speed is decreasing to maintain flight path the autotrim goes up to the limit, incidence is growing up to maintain flight path.
On a Boeing, even in alternate law, you would have to trim as speed decrease to maintain flight path, it would alert you that something is wrong.
Here, it is like if the pilot is being helped, without being conscious, to install the Airbus in the stall.
No sensation on the joystick, if he does not look sharply at his trim indicator, he does not see, he does not feel that the autotrim is trimming for him to install the stall !!
I think it is not the pitch orders that make the THS pitch up. It is the FBW system and this way does not help....

What do you think ?
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Old 17th Aug 2011, 14:32
  #65 (permalink)  
 
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For more thoughts on this, you can see Post #2934 on the Rumors AF447 thread:

"Post #2934 on Rumors AF 447 Wreckage Found thread"

and Post# 1862 on this thread :

"Post #1862 on Techlog AF 447 Thrd #6"

Originally Posted by CaptainGef View Post
Hello
If you read the graph p111 between 0211:00 and 0212:45
During all this time this is the stall warning the crew does not believe.
We can see Altitude does not vary too much and to quickly (37924 to 36068)
F/O pitch orders up and down.
Stabilizer from -3 to -13
Speed is decreasing and as speed is decreasing, they don't see it and what does the THS do on FBW machine?: It tries to maintain flight path, so as speed is decreasing to maintain flight path the autotrim goes up to the limit, incidence is growing up to maintain flight path.
On a Boeing, even in alternate law, you would have to trim as speed decrease to maintain flight path, it would alert you that something is wrong.
Here, it is like if the pilot is being helped, without being conscious, to install the Airbus in the stall.
No sensation on the joystick, if he does not look sharply at his trim indicator, he does not see, he does not feel that the autotrim is trimming for him to install the stall !!
I think it is not the pitch orders that make the THS pitch up. It is the FBW system and this way does not help....

What do you think ?
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Old 17th Aug 2011, 14:57
  #66 (permalink)  
 
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So look, at high Mach, and AL, the RTL hobbles the Rudder.

I'll ask (rhetorically) again, if AB thought too much Rudder was a problem, why then did they not also think Pitch might need a looksee? TRIM?

Weary of this "dummy pilot" meme, I'll be brief.

If I am in Court, suing Airbus for this STALL accident, I need do one thing only. Hire a dolly, and roll in an RTLU.

"What is that", says the Jury. Case Closed.

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Old 17th Aug 2011, 15:08
  #67 (permalink)  
 
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Partial autopilot disconnect

CJ's quote: "Finally, the autothrottle did leave the power at the last setting.
Whether it would have been preferable for the autopilot to have reverted to a basic attitude hold is IMHO very much an open question, especially in turbulence."

At the moment of autopilot disconnect, main concern is to fly the a/c.
In Alternate Law, some attitude help would be welcomed, IMO.
Reverting to the last attitude could have given more time for the pilots figure things out.

If autothrottle left the power at the last setting, why not have also an attitude hold at the last setting?

IMO, anything that can give more time for the pilots, is very welcome.
UAS is an emergency situation, and in a very complex FBW system pilots need time to sort things out. Autopilot should give a "hand", basic attitude hold. This will not bring an a/c down as fast as an inadvertent stall.

Just a thought...
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Old 17th Aug 2011, 15:16
  #68 (permalink)  
 
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Hi Rob.

The BUSS system is available. Also available is an Artificial Horizon, independent, and gyro driven.

Air France chose not to fit these to this A330. To some folks, these additional, though optional systems, may also have been a help.

I think in retrospect, those who lost loved ones would have accepted a small hike in the ticket to have had this kit aboard.

Yet we see even this proposal dismissed, and in the name of what?

PRIDE.

#1 If it can happen, it will

#2 If it can be foreseen, and mitigated, it should be.

#3 The rest is autopleasure.
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Old 17th Aug 2011, 15:39
  #69 (permalink)  
 
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Also available is an Artificial Horizon, independent, and gyro driven.

Air France chose not to fit these to this A330.
??????? Can you validate that comment? I've never seen ANY airliner without a standby horizon.....

I know I'm not supposed to feed any grumpy little three fingered bridge minders, but I'm having a hard time watching some of these comments go by. The RTLU hobbled the rudder? What on earth....?
I get the sense that you're prepared to point fingers at anything and everything except the truth.
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Old 17th Aug 2011, 15:53
  #70 (permalink)  
 
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3holelover.

The Rudder Travel Limiter 'hobbles" the Rudder. It limits it from unsafe deflection into a too energetic airstream, hopefully preventing damage, or loss of Rudder and or Vertical Stabiliser. The Artificial Horizon is very definitely available as optional equipment, it is fitted on Captain's side, high/left, as I understand it.

BUSS (Back Up Speed System) is also available, and I think provided as basic on the 380.

ISIS is definitely Standby, but driven by the same system that powers the PFDs. If unavailable, a "Steam" AHI is nice.

Do you take seriously the accusation that I am Troll? I thought better of you. I am a pilot, been flying for 40 years, flew commercially, and at one time owned my own air freight concern.

I take flying seriously, I have never had an accident, and I frequently canceled if I thought there was even a chance of anything unseemly. I don't throw tantrums, or poop, and I respect everyone. Making silly accusations is not appropriate, imo.

If something disagrees with me, I may comment on it, I may ignore it, but to personalize it or stoop to childish harping is a waste of time, everyone's.
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Old 17th Aug 2011, 16:10
  #71 (permalink)  
 
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BUSS

Lyman,

It would appear that AB sent a FOT saying that the BUSS system should not be used above F/L 25.0 on 9th. September 2009.
The A/H installations appeared in a photograph on an earlier thread, one for each pilot. ( I do not know how they were powered. I might prefer their own battery(s) !)
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Old 17th Aug 2011, 16:17
  #72 (permalink)  
 
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Lyman, I know what the RTLU does. My "what on earth?" question is, how can you possibly be considering it in any way related to this accident?

I'm sure I've already noted, I'm not a 330/340 guy... I'm an AME, licenced on the 320 family, but the only bigger Bus I have on my licence is the 310... so I'm a little unfamiliar with the 330 panel..... I understand the beast had all the attitude info they needed, and that it was airspeed info only that they were missing for a short time. Am I wrong?
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Old 17th Aug 2011, 16:29
  #73 (permalink)  
 
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3

I don't consider it related to this accident (RTLU). I didn't say it was.

I said that as a consequence of degraded Flight Law, the Rudder Limiter prevents extension beyond certain speed (calculated) limits, to prevent damage.

I compared it to a THS which in Alternate Law, is NOT LIMITED in deflection, and in 447's case, migrated to its NoseUp stop.

The comparison was meant to highlight the decision AB made on the one hand to protect a flight control from damage (Rudder/Vertical Stabiliser), and a disregard for potential Attitude problems caused by an unlimited TRIMMING DEVICE.

There are some well established pilots here who have noted this problem with autotrim.

Not only is this autotrim without designed limits, it works without notification to the cockpit. (Sorry, not correct, the pointer on the manual wheel shows the THS' deflection).

So this sets the stage for some (what I would call boneheaded) design that arguably is responsible in a very demonstrable way for the outcome of 447's flight path.

Did the THS prevent RECOVERY FROM STALL? It does not matter, strictly speaking. The fact that it deflected automatically into a position that caused potential threat suggests a serious flaw in the design of the Aircraft.

Now the argument can be had, (and is) that the PF was ___, ____,_____, and _______, but that is a dodge, intended to distract from the fundamental problem.

As to Attitude, the selfsame lack of design can be isolated and criticised. The Displays were "acting up", and one must admit to some possibility for the various displays to be unreliable, or transient, or gone. So an AH driven independently of the system that was in trouble seems a no brainer, at least to me. One would have to have a good argument against it to say it was not necessary. Clearly, if available, it MIGHT have helped.
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Old 17th Aug 2011, 16:36
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LT and 3hole,

- So far there is still no mention of the primary attitude data or displays going t!ts-up at any time, so discussing the standby horizon is just a sideline... (my firm made them, hence my interest).

- I know there were some photos, but that's the trouble with these forums with hundreds of posts each.... find them!
And not all A330 flight deck instrument fits are identical, so how to confirm you are really looking at the AF447 flight deck?

LT, in 'my' days, the (mechanical) standby horizon ran off the emergency DC bus via its own inverter, and it had its own 'high-speed' gyro, that would keep running on its own inertia for minutes even after electrical power totally disappeared.

I have no idea whether ISIS, or any other standby horizon fitted today, has its own little battery pack (lithium, four AAAs?) to keep the LCD display alive, 'when all else fails'.


Apologies for the O/T.
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Old 17th Aug 2011, 18:08
  #75 (permalink)  
 
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ChristianJ I was perhaps recalling the Hermes 4a, where the emergency standby instruments were from a constantly recharged battery ( 24 volt ? As a pilot I was not entrusted to use a voltmeter !) On checking, my Type Rating has now expired.

Precise instruments used to be backed-up by simpler, more reliable, if not quite as precise, earlier generation ones - think of any remote indicating Compass, which would be backed up by something that Captain Cooke would have recognised, subject as that would still have been, to more magnetic deviations and acceleration errors.

I carried a load of Rhodesian Riflemen to Singapore. They had not flown before and asked to see the Flight Deck of the Hermes. The plywood door was enough security, then. They reported back that we :
" had a hundred and twenty twelve clocks, all telling different times..."
which was poetically accurate - but I never counted to see if they were right.
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Old 17th Aug 2011, 18:11
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Lyman said:

I said that as a consequence of degraded Flight Law, the Rudder Limiter prevents extension beyond certain speed (calculated) limits, to prevent damage.
So, probably of not much use then, given this accident was initiated by UAS (so no speeds) and then stalled (also little useful forward speed).....

Again, you refuse to accept the pilots did anything wrong? Right?

You incessant babble is tiring.

I want to ignore you, but you keep changing your username.... why so?
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Old 17th Aug 2011, 18:15
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Lyman,
The THS existing limits need no further limiting, and ought not to be limited any further, since there are imaginable scenarios which could warrant full travel. The rudder, on the other hand, had better be limited, lest air loads exceed structural limitations. Not comparable.

...and when the THS moves, it's not only it's little pointer on the scale that provides indication of it's travel.... there are big white stripes on the large black wheels inboard of each pilot, on the side of the pedestal. When the THS is moving, even peripheral vision will normally draw ones attention to those contrasting white stripes moving by.... Maybe the "whooler" shouldn't have been eliminated, but I'm not at all sure that would have made any difference here.
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Old 17th Aug 2011, 18:53
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I will defer to the certifications, 3holelover. My assumption is that Trim is not considered mandatory for certifying recovery.

That makes it optional. Throw in automatic, and one finds oneself STALLED with a trimset that "may be required in some situations."

Pass. If the a/c can get into a STALL, it should be able to get out the STALL with Elevators. ONLY. In this instance, the THS was NOT trimming the a/c into STALL. IT went all NU after the STALL. Do NOT now say, "BUT THE PILOT", because that is a distraction. It was STALLED, THS at -13, and that was that.

Should we continue to go around the maypole? "But the pilot put it there", YES. We shouldn't have to design a/c as if pilot's will STALL them?

Oh, yes, we should?

I do doubt that the THS is vital for recovery. If I am mistaken, I apologize.

If, and regardless of the pilot's skillset, the a/c is gonna STALL, pumping a TRIM WHEEL to get back to square one seems at the very least counterintuitive, if not demonstrably fatal.
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Old 17th Aug 2011, 19:14
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Should we continue to go around the maypole? "But the pilot put it there", YES. We shouldn't have to design a/c as if pilot's will STALL them?

Oh, yes, we should?
Forgive me Lyman, perhaps I'm thick, but I really do not understand what you're saying here??? Please, if you choose to answer me, make it clear for me, will you? Without your question marks further confusing me as to your point?

Also, re: "I do doubt that the THS is vital for recovery." ....so again, I don't understand why you're going on about it?

If, and regardless of the pilot's skillset, the a/c is gonna STALL, pumping a TRIM WHEEL to get back to square one seems at the very least counterintuitive, if not demonstrably fatal.
Unnecessary. All he had to do was hold a nose down input and the trim would have followed. But counterintuitive? I should think trimming is no such thing to an experienced pilot! It's probably as close to naturally intuitive among pilots as lifting a wing when it falls. You said you were a pilot.... did you not retrim when you changed attitude?
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Old 17th Aug 2011, 19:28
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3hole, a few threads back, I think number 4, a gent who has taught in the A330 simulator related to us how some Unusual Attitude drills and recoveries required use of the trim wheel, manually, to get the pitch under control (in other than normal law, IIRC) in a suitable time frame. He wasn't sure if that was a "simism" or not.

Point?

There were or are some training drills that can be used to accustomize crews to using the trim wheel to control nose pitch in cases where the auto trim is either too slow or not helping redirect the elevators and THS where the pilot needs them. You could call the trim wheels a secondary flight control (Not sure if I am right about that) which means any rated pilot ought to know, like the flaps, when and how to use it.

And practice doing so.
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